Dr. Rob Dillon, Coordinator

Wednesday, June 13, 2018

Invasive Species Updates

Editor’s Note – Although it seems like we touch the subject almost every month, it has actually been almost five years since we rounded up the Pomacea news [1], and even longer for the other invasive gastropod species.  Five recent items of special interest are collected below.

Potamopyrgus in Maryland.  Early last September our good buddy Matt Ashton of the Maryland DNR sent me an email with a couple jpegs attached, including the photo below.  Matt was forwarding the report of a concerned citizen with very good reason to think he had discovered New Zealand Mud Snails in the Gunpowder River at the Prettyboy Dam tailwaters, about 30 km north of Baltimore.  See the 21Sept17 article in The Baltimore Sun from note [2] below for more details.

From Matt Ashton, MD-DNR
The Gunpowder is a lovely little river through most of its course, passing through four state parks on its 90 km journey from headwaters in southern Pennsylvania to mouth at the Chesapeake Bay.  In the late 1980s the Prettyboy Dam tailwaters were stocked with brown and rainbow trout, eggs and fingerlings as well as adults, and both populations have now become self-sustaining [3].  Attention from an avid community of fishermen has quite predictably followed.

This is the second population of Potamopyrgus reported from a US Atlantic drainage.  My readership will probably remember the first report I posted back in November of 2013, from a small tributary of the Susquehanna River in central Pennsylvania, also heavily fished by trout anglers [4].  Spring Creek is perhaps 50 km north of the Gunpowder headwaters.  The implication would be that the little snails were transported from Pennsylvania to Maryland via muddy waders or bait buckets.

From the mouth of the Gunpowder to the heart of our nation’s capital is but another 80 km.  I understand that legislation has been introduced in Congress to build a big, beautiful six-inch wall from the Delaware River to the West Virginia line, with a three-inch guardhouse on the Baltimore/Washington parkway.

And (less surprisingly) in Syracuse.  The Great Lakes populations of Potamopyrgus are much older than the Atlantic populations; New Zealand mud snails were first reported from Lake Ontario as early as 1991 and Lake Erie in 2005.  So, surfing around in the USGS-NAS Nonindigenous Aquatic Species Database [5], I picked up a couple 2016 reports of Potamopyrgus in tributaries of Onondaga Lake, near Syracuse.

The Erie Canal runs from the eastern end of Lake Erie across the width of New York, intersecting Oneida Lake and the tailwaters of several of the Finger Lakes, as well as Onondaga Lake, to meet the Hudson River just north of Albany.  How long will it be until tired, poor Potamopyrgus are tempest-tossed down the Hudson into New York Harbor, to enter Ellis Island through the back door?  Is that one golden, too?

Pomacea progress.  As threatening as an invasion of 5 mm snails down from the north most certainly must be to homeland security, the threat posed by an army of 5 cm snails advancing up from the south is two orders of magnitude worse.  On the plus side, however, we are getting some very good science out of it.

In late 2015 our colleague Ken Hayes and 32 coauthors published a comprehensive review of the biology of the entire family Ampullariidae [6], broader than their systematic paper of 2012 [7] and better-integrated than the big 2006 book edited by Joshi & Sebastian [8].  More than just the economically-important pests and pets, the authors reviewed the entire scientific literature published on all 117 ampullariid species (by their estimate) in all 7 genera worldwide.

But though Ken and his colleagues cast their nets as broadly as possible, what they drew back was almost entirely Pomacea canaliculata.  They concluded with a call for additional research of a comparative nature, including behavioral studies that might reveal patterns that may have played a role in the evolution of the other 116 species.  We most certainly agree.

Fig. 7 of Rama Rao et al. [14]

Maculata/canaliculata hybridization.  Since the first appearance of pest Pomacea in North America, I have continued to be especially curious about reproductive isolation between populations of P. canaliculata and what is now called P. maculata.  So perhaps the most interesting Pomacea news in recent years, from my perspective, was the 2008 discovery that P. maculata has been introduced together with P. canaliculata throughout east and southeast Asia [9].

Apparently published a bit too late to be collected in the nets of Hayes and his 32 colleagues was an excellent 2013 study by Matsukura et al. documenting extensive hybridization between P. canaliculata and P. maculata throughout Japan, Korea, Vietnam and The Philippines [10].  Of the 16 populations sampled, 7 (all Japanese) were apparently pure canaliculata.  The remaining 9 were mixtures, including one population that was primarily maculata with a few hybrids, and one that was primarily hybrid, with a few pure maculata and canaliculata.

Even more interestingly, Matsukura performed a set of no-choice mating experiments between canaliculata and maculata, suggesting that F1 hybrid clutches suffer significant reduction in their hatching rates, from around 80% down to maybe 20% [11].

Pomacea release sex pheromones and demonstrate elaborate courtship behaviors, featuring nuptial gifts [12].  It would be tempting to hypothesize that some sort of prezygotic reproductive isolating mechanisms may have evolved in their native ranges, which have now broken down in Asian rice fields, as lions and tigers mate in zoos.  But in a surprise finish, Matsukura and colleagues also obtained a sample of 17 individual Pomacea from 5 sites in Argentina and discovered evidence of hybridization in ten of them!  Even in the home range.  Fascinating.

If maculata and canaliculata cannot tell each other apart, how can we?  Hayes et al. [7] observed that typical egg masses of P. maculata contain significantly more eggs of a significantly smaller size than P. canaliculata, a result that Matsukura and colleagues confirmed in Japan.  But that’s not terribly helpful with an adult in hand. 

So Hayes et al [7] also suggested a variety of distinguishing shell traits [13], including adult size, ratio of spire height to shell length, shell thickness, umbilicus, shouldering, and lip pigmentation.  But just last month Rama Rao and colleagues [14] published an interesting study of 130 Pomacea sampled from 8 populations in peninsular Malaysia, 5 of which turned out to be canaliculata/maculata mixtures, judging from CO1 sequence. 

Rama Rao and colleagues did not employ nuclear markers, and hence could not identify hybrids [15].  But judging from mtDNA haplotype, they selected 26 canaliculata and 26 maculata and performed an extensive series of shell morphological and morphometric analyses, including simple linear measures and ratios as well as the geometric analysis shown in the figure above.  They did discover a statistically-significant difference between the two groups in ratios of shell height to shell width and aperture height, but of such a fine nature as to be practically useless.  The bottom line is that the Pomacea of Malaysia seem to comprise one single heap of big slimy snails, darn near indivisible.

And meanwhile, in South Carolina.  Our colleague Elizabeth Gooding and six coauthors (including yours truly) have just published a statewide survey [16] for Pomacea at the highest latitudes of its current US range [17].  The Socastee/Myrtle Beach area [18] is on the northern tip of USDA cold-hardiness zone 8b, with average annual extreme minimums around 15 to 20 degrees F, or -9 to -6 degrees C.  We report both copulation and egg laying year-round, even in coldest months of winter [19].

I understand that legislation has been introduced in Washington to build a big, beautiful wall on the North Carolina line from Cape Hatteras to Tennessee, 50 feet tall by back-of-the-envelope calculation [20], Pedro himself manning the I-95 guardhouse just two mucus trails and one gigantic traffic jam North of the Border.


[1] My earlier Pomacea reviews include:
[2] Invasive New Zealand mud snails found in Gunpowder River. The Baltimore Sun 21Sept17.

[3] The situation is actually a bit more complicated.  The first 7.2 miles below the dam are managed as a wild trout stream, catch-and release.  Anglers in the next 4.2 miles can keep two trout/day.  And the next 6.1 miles are stocked in the spring and fall with ordinary hatchery-reared trout, creel limit five trout/day.  See MD-DNR-fisheries.

[4] For more about the discovery of New Zealand Mud Snails in central Pennsylvania:
  • Potamopyrgus in US Atlantic Drainages [19Nov13]
[5] For my reviews of state and national invasive species online databases, see:
  • To Only Know Invasives [16Oct15]
  • To Only Know Invasives in My General Vicinity [9Nov15]
[6] Hayes KA, Burks RL, Castro-Vazquez A, Darby PC, Heras H, Martín PR, et al. (2015) Insights from an integrated view of the biology of apple snails (Caenogastropoda: Ampullariidae). Malacologia 58(1–2):245–302.

[7] Hayes KA, Cowie RH, Thiengo SC, Strong EE (2012) Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda). Zool J Linn Soc. 166(4): 723–753.

[8] Joshi RC, Sebastian LS. (2006) Global advances in ecology and management of golden apple snails: Philippine Rice Research Institute (PhilRice), 600 pp.

[9] Hayes, K. A. et al. (2008) Out of South America: multiple origins of non-native apple snails in Asia.  Diversity and Distributions 14: 701-712.
Matsukura, K. et al. (2008) Genetic divergence of the genus Pomacea (Gastropoda: Ampullariidae) distributed in Japan, and a simple molecular method to distinguish between P. canaliculata and P. maculata.  Appl. Entomol. Zool. 43:535-540.

[10] Matsukura, K et al.  (2013) Genetic exchange between two freshwater apple snails, Pomacea canaliculata and Pomacea maculata invading East and Southeast Asia.  Biol. Invasions 15: 2039-2048.

[11] The hatchability experiment was not as neat as one might hope, and the results a bit ambiguous.  See the paper itself [10] for details.

[12] Burela S, Martin PR. 2009.  Sequential pathways in the mating behavior of the apple snail Pomacea canaliculata (Caenogastropoda: Ampullariidae).  Malacologia 51: 157 – 164.
Burela S, Martín PR. 2011. Evolution and functional significance of lengthy copulations in a promiscuous apple snail, Pomacea canaliculata (Caenogastropoda: Ampullariidae).  Journal of Molluscan Studies 77: 54–64.
Takeichi M, Hirai Y, Yusa Y. 2007. A water-born sex pheromone and trail following in the apple snail, Pomacea canaliculata.  Journal of Molluscan Studies 73: 275–278.

[13] There are also anatomical differences between canaliculata and maculata, most notably a difference in penial sheath.  A study of anatomical hybrids would be most salutary.

[14] Rama Rao S, Liew T-S, Yow Y-Y, Ratnayeke S (2018) Cryptic diversity: Two morphologically similar species of invasive apple snail in Peninsular Malaysia. PLoS ONE 13(5): e0196582.

[15] Back in the allozyme days, I could have solved that problem with one afternoon in the laboratory and $30 for reagents.  It does frustrate me that science often seems to lose good old technology in its restless quest for the new.

[16] This is the same survey of which I made passing mention in my essays of November and December of 2015.  Although we did not discover any Pomacea on Hilton Head Island, we do formally report invasive populations of Bellamya, Biomphalaria, Melanoides and Pyrgophorus in our 2018 paper [17].  To refresh your memory:
  • The Many Invasions of Hilton Head [16Dec15]
[17] Gooding, E. L., A. E. Fowler, D. Knott, R. T. Dillon, T. Brown, M. R. Kendrick, & P. R. Kingsley-Smith (2018) Life history and phenological characteristics of the invasive island apple snail, Pomacea maculata (Perry, 1810) in stormwater retention ponds in coastal South Carolina, USA.  Journal of Shellfish Research 37: 229 - 238. [PDF]

[18] Yes, the introduction of Pomacea we first reported from the Myrtle Beach area in 2008 may even be spreading.  I understand that the initial site of discovery around that trailer park in Socastee was treated with copper sulfate, but the snails seem to have jumped a couple km SE into ditches and stormwater retention ponds around a sprawl of strip malls and big-box retailers.  For ancient history, see:
  • Pomacea spreads to South Carolina [15May08]
  • Two dispatches from the Pomacea front [14Aug08
[19] Although no juveniles seem to hatch in the South Carolina winter.  One presumes that egg masses laid in the winter will hatch in the spring.

[20] If a 6-inch wall is sufficient to stop a 5 mm gastropod coming south between Baltimore and Washington, then to stop a 5 cm gastropod advancing north from the Carolinas we need 100 x 6 inches = 600 inches = 50 feet.

Thursday, May 10, 2018

Dichotomous Dichotomous Keys

Last month [1] we reviewed the Gastropoda chapter contributed by Christopher Rogers to the new Fourth Edition of Thorp & Covich’s Keys to Nearctic Fauna [2].  The bottom line was, “Buy this book.”  And among the several lines of support I offered for this recommendation was a somewhat enigmatic observation to the effect that the new fourth-edition dichotomous key complements, but is in many cases strikingly different from, the old third-edition key.  What did I mean by that?

In two words, Christopher’s new key is evolutionary, whereas the old one was ecological.  Christopher has divided the North American freshwater gastropods phylogenetically, designing his dichotomous key to branch as a phylogenetic tree might branch.  The older key divided the fauna functionally, according to morphological adaptation.

Broad/flat vs. Narrow/filiform, if you're curious...

 So, couplet #1 of the old Third Edition was a choice between “shell coiled” and “shell an uncoiled cone.”  The former choice took the user onward into the body of the key, while the latter choice immediately took the user aside to seven limpet genera.  Those seven limpet genera are assorted into three families: the Ancylidae with four, the Acroloxidae with one, and the Lymnaeidae with two.  This is an ecological distinction – the limpet shape demonstrating superior strength against predation, and superior performance against hydrodynamic drag, given a solid substrate upon which its bearer can graze.

That patelliform shape has, of course, evolved many, many times independently in many, many different gastropod lineages, both freshwater and marine [3].  And it has apparently evolved (at least) three times separately in the freshwater gastropods – in the Acroloxoidea, in the Lymnoidea, and in the ancylid taxa of the Planorboidea.

So Christopher elected to open his new Fourth Edition gastropod key with operculum present/absent as his couplet #1. This is the easiest character by which to distinguish pulmonates from prosobranchs, the primary phylogenetic division in the freshwater gastropod fauna.  All the freshwater limpets are pulmonates, missing an operculum, hence all go together to his couplet #7.  Then at Christopher’s couplet #7, the user finds: 
7(1) Shell not patelliform, or if patelliform, then spire sinistral (apex centered or to right of midline) and blunt, with adult patelliform shell larger than 7 mm … go to #8.
7’ Shell patelliform with spire dextral (apex to left of midline), acute; adult shell less than 7 mm in length … Acroloxidae.
So I understand what Christopher is trying to do here, and I appreciate his effort.  He is beginning to sort the pulmonate families using evolutionary distinctions.  But I’m just not sure it works.

First, as a practical matter, users cannot determine if the spire is sinistral or dextral for 99.999% of all the limpets in the creek – they’re blunt and smooth.  So, users must read over that text to “apex centered or to the right of midline” vs. “apex to left of midline.”  And second, being finely evolutionary, both Acroloxus and the lymnaeid limpets (Lanx and Fisherola) demonstrate shell apexes to the left of midline, at least when young [4].

Now I understand if Christopher does not want to engineer his dichotomous key to the entire freshwater gastropod fauna of North America around an accommodation for juvenile-Lanx-collectors.  So I’ll let it go.  Let’s suppose we have under our scope some non-patelliform pulmonate, like Physa or Helisoma.  And we have dodged through couplet #7 to arrive at couplet #8, undiscouraged.  Here we read: 
8(7) Tentacles narrow, filiform …. 9
8’ Tentacles broad, flat, triangular; haemoglobin absent; coiled shell always dextral, patelliform shell with apex central or sinestral [sic]; never planospiral … Lymnaeidae
For heaven sake!  Now Christopher seems to expect us to have a living animal under our scope, or at least a very well-preserved one, to distinguish narrow tentacles from broad tentacles?  Narrow compared to what?  There’s no tentacle figure.  Haemoglobin, are you serious?  Must I medevac this little speck of coiled brown nothing to England and set up an IV?  Typed and cross-matched, stat?

In the Third Edition key, after I had observed that my Physa was coiled and been directed to couplet #8, I was next asked if the shell was planospiral or “with raised spire.”  If planospiral go to Planorbidae, otherwise go on to couplet #20.  Simple.

I am not going to criticize every couplet in Christopher’s entire 20-page key.  It’s a tremendous effort, and I don’t want to diminish his contribution.  I will simply observe that the evolutionary approach taken in the Fourth Edition is not as user-friendly as the ecological approach taken in the third.

So, here’s the bottom line for this month’s essay.  Don’t throw away your old Third Edition of Thorp & Covich.  Open it up on the lab bench next to your new Fourth Edition and use both simultaneously.  The two works side by side are a dichotomous perspective on the wonderful diversity that marks the North American freshwater gastropod fauna.


[1] REVIEW: Thorp & Covich Fourth Edition [12Apr18]

[2] Thorp, J. H., and D. C. Rogers (2016) Keys to Nearctic Fauna.  Thorp and Covich’s Freshwater Invertebrates, Fourth Edition.  Volume II.

[3] Actually, the “hypothetical ancestral mollusk,” from which all sevenish of the molluscan classes diverged back in the Precambrian, is generally modelled with a limpet-like (or plate-like) shell similar to that borne by the present-day Monoplacophora.

[4] Basch, P. (1963) A review of the recent freshwater limpet snails of North America. Bull. Mus. Comp. Zool. Harvard 129: 399-461.

Thursday, April 12, 2018

REVIEW: Thorp & Covich Fourth Edition

Thorp, J. H., and D. C. Rogers (2016) Keys to Nearctic Fauna.  Thorp and Covich’s Freshwater Invertebrates, Fourth Edition.  Volume II.

“What a marvelous contribution!  I never thought I would live to see the day.”

Both these sentiments oscillated through my mind in rapid succession as I flipped through the pages of Christopher Rogers’ “Class Gastropoda” key in the new edition of Thorp & Covich displayed on the auction table in Raleigh [1] last June.  The taxonomy is complete, thorough, well-researched and modern.  Just three genera of living pleurocerids, check.  Hubendick’s single, broadly-inclusive genus of lymnaeids, check.  Just two genera of physids, check!  Bellamya yes, Planorbella no.  Onward as the pages turned.  What a marvelous contribution!  I never thought I would live to see the day.

This was not the first time such thoughts had flickered through my mind, however.  It had happened twice before.

I imagine that most of my readership will be familiar with the Thorp & Covich tradition.  The first edition of Ecology and Classification of North American Freshwater Invertebrates, as the collaboration was originally called, was published in 1991, with a second edition in 2001 and a third in 2010.  Over this 20-year span Thorp & Covich has become the primary bench reference for biologists working with the (non-insect) freshwater macrobenthic fauna of the United States [2].

Ken Brown was the solo author of the Gastropoda chapter through its first two editions, Chuck Lydeard joining him in 2010 [3].  Ken has an excellent background in freshwater gastropod ecology, which together with anatomy, physiology and (later) gene trees comprised the first 70% of the chapter.  The remaining 30% was allocated to a dichotomous key following the taxonomy of Burch [4] rather closely [5], but I am not criticizing.  That’s all there was.

So the first time that “marvelous-contribution-but-it’ll-never-happen” thought flickered through my brain was in March of 2011, when I opened an email from Jim Thorp.  Jim intimated to me that, even though his third edition was only a single year off the press, he and Christopher were already making plans for a major revision.  He projected that his fourth edition would expand into a series of volumes, the first of which would be dedicated to more ecological themes, the second of which would present dichotomous keys to the Nearctic fauna, the third to the Palaearctic, and so forth [6].  The fourth-edition keys would be much larger and more detailed than those of the third edition, extended down to the species level wherever possible.  And he wanted me to lead the Nearctic Gastropoda team.

I was flattered, of course.  But the series of negotiations into which we entered did not ultimately yield fruit.  I am a big fan of review and synthesis, and I greatly appreciate the value of reference works like Thorp & Covich for biologists in the field today.  But I climb onto the shoulders of giants with a pair of binoculars looking up, not down.  An historian I am not.

So for example, of the roughly 150 nominal species of pleurocerid snails Calvin Goodrich recognized in North American fresh waters [7], forwarded to the present day by Burch, I should estimate that no more than about 30 – 40 are biologically valid.  How am I to construct a dichotomous key to such a biota, I asked Jim, if most of the taxa to be keyed are not legitimately distinguishable?  Could I synonymize?

Jim (quite understandably) demurred.  Christopher suggested that, in cases such as the Pleuroceridae, I simply key down to the lowest firm taxon and drop it, with some language to the effect that “This genus is in need of revision and therefore identifications are left at genus level.”  Well, I thought to myself, all the North American freshwater gastropod genera are in need of revision.  Most have never had a vision in the first place.  Ultimately, I found it impossible to rationalize the expenditure of my own time and effort unless I could move the ball forward [8].

So Volume 1 of the Fourth Edition appeared in 2015, our good friend Mark Pyron’s name appearing above that of Ken Brown as author of Chapter 18, “Introduction to Mollusca and the Class Gastropoda.”  I was pleased to see that the Pyron & Brown contribution extended to 41 pages, up from the 30 pages of the 1991 original.  And sure enough, those 41 pages were focused entirely upon ecology and evolution, no dichotomous key anywhere in evidence.

And the second time that “marvelous-contribution-but-it’ll-never-happen” thought flickered through my brain was later that same year, when Christopher emailed me to request that I review the dichotomous key he himself had prepared for Volume 2.  His draft looked excellent – I really didn’t have a whole lot of suggestions to offer.  In retrospect, I think that from among the entire 3 x 10^8 population of the United States of America, I might have been the worst possible choice to review a freshwater gastropod key.  Because I understood what Christopher was trying to say, and I often skipped ahead, knowing where he was trying to go.

Regarding the problematic groups, I was gratified to see that Christopher had taken the approach he had first advocated during our 2011 negotiations.  Here’s a verbatim quote from his section entitled Limitations: 
“Particularly vexing is the strange confusion in the taxonomic literature, with many taxa accepted or rejected without explanation, and good quantitative taxonomic revisions ignored without explicit justifications.  Because of this issue, the keys are taxonomically conservative, often terminating with species groups rather than species.”
 So Christopher judged such terminations to be necessary for 13 “species groups” in the Nearctic freshwater gastropod fauna all told: the hydrobioid genera Amnicola, Lyogyrus, Clappia and Fluminicola, the hydrobioid families Cochliopidae and Hydrobiidae (ss), assorted prosobranch genera Valvata, Campeloma, Pleurocera/Lithasia, and Leptoxis, and the planorbid genera Helisoma, Carinifex, and Menetus.  Fine.  It’s hard to know which of those thirteen groups is the biggest mess.

The rest of the freshwater gastropods of North America Christopher did, very bravely, key all the way down to the species level.  Among the pulmonates he recognized 10 species of Lymnaea, 9 species of Physa, and 24 species of (non-Helisoma, non-Carinifex, non-Menetus) planorbids [9].  All good estimates – probably pretty close.  From among the entire 3 x 10^8 population of the United States of America, I may well appreciate the effort that Christopher must have put into this contribution the most.

So buy this volume.  Actually, you should back up and buy Volume 1 if you haven’t already, as well as Volume 2.  Do it for three reasons.  First, the gastropod taxonomy is correct, complete, and current.  Second, the new fourth-edition keys complement, but in many cases are strikingly different from, the old third-edition keys.  We’ll develop that theme next time.  And finally, assuage my guilt.  In retrospect, I may have been more a hindrance than a help to Christopher as he labored over this marvelous contribution.  I never thought I would live to see the day.


[1] SFS Raleigh  [4Apr17]

[2] Pennak held that position when I was coming up through the ranks, and is still an excellent reference.  Nothing in the essay above is intended to take anything away from Doug Smith’s (2001) Fourth Edition of “Pennak’s Freshwater Invertebrates of the United States” at all.

[3] Alan Covich and Ken Brown asked me to help with the 2010 edition.  I was flattered, but ultimately declined, for reasons similar to the ones I gave Jim Thorp in 2011.  I can be a difficult person to deal with.

[4] This is a difficult work to cite.  J. B. Burch's North American Freshwater Snails was published in three different ways.  It was initially commissioned as an identification manual by the US EPA and published by the agency in 1982.  It was also serially published in the journal Walkerana (1980, 1982, 1988) and finally as stand-alone volume in 1989 (Malacological Publications, Hamburg, MI). 

[5] The hydrobioid subfamilies were raised to the full family level in the third (2010) edition.

[6] Twelve volumes are now on the drawing board, according to a more recent communication I enjoyed with Jim.  Volume III is now Neotropical Hexapoda, and Volume IV is the Palaearctic Fauna, which was slightly delayed.  But both are currently in press. 

[7] The Legacy of Calvin Goodrich [23Jan07]

[8] My exact words to Jim and Christopher were, “It’s the fourth quarter of my career.  I won’t take a knee on the ten-yard line.”

[9] Ancylid limpets integrated with the Planorbidae.  OK, fine.

Friday, March 16, 2018

Psst, Buddy! Wanna buy an Apple Snail?

Editor’s Note –This is the sixth (and final) installment in my series on the general topic of freshwater snails in the aquarium hobby.  Previous posts have been “What’s Out There?” [9Oct17], “Loved to Death?” [6Nov17], “Pet Shop Malacology,” [21Dec17], “Snails by Mail” [24Jan18], and “Freshwater Gastropods and Social Media” [14Feb18].  It might help you to read (at least) my previous (February) post on this subject before going on to the essay below.

First let us clarify the situation as pertaining to law.  In addition to their broader body of regulations regarding the movement of gastropods generally, the Feds have a set of explicit restrictions regarding the importation and movement of ampullariids [1].  Quoting the USDA-APHIS verbatim: 
“aquatic snails in the family Ampullaridae (e.g., Pomacea canaliculata, channeled apple snail), with one exception, may not be imported or moved interstate except for research purposes into an APHIS inspected containment facility. One species complex in the family Ampullaridae, Pomacea bridgesii (diffusa) may move interstate without a permit because these snails are not known to be agricultural pests but are primarily algae feeders. An import permit is required for aquatic snails in order to verify species and examine shipments for contaminants that are agricultural pests.” [2] 
Note that it is not illegal to own, buy, sell, trade, breed or propagate invasive apple snails of the maculata/insularum/canaliculata type, conventionally abbreviated IAS.  Naturalized populations of IAS are already widespread in certain regions of the United States.  I, living in South Carolina for example, could easily gather Pomacea maculata from any number of local retention ponds in my area and enjoy them in my home aquarium.  I cannot, however, ship them to my friends in North Carolina, nor carry them in a cooler up I-95.  Nor can my Tarheel buddies come down here and fetch any.

So in last month’s [14Feb18] essay I shared my impressions from 30 days of monitoring the conversation on a Facebook group called, “Snails, Snails, Snails.”  I tallied eight mentions of IAS during that month, including four separate appeals for purchase, and concluded: “Without a doubt, significant pent-up demand exists within the community of aquarium hobbyists for large, invasive apple snails.”

"Last round of Peruvian Apple Snails"

I didn’t mention it at the time, but I am mentioning it now, because I think it is especially significant.  Among the eight mentions of IAS I logged during my 30 days of observation on Snails, Snails, Snails was one offer to sell.  A pet supply store in South Dakota named “Woofs & Waves” posted the photo above, simply captioned, “Last round of Peruvian Apple Snails for the season.”

This post generated 10 comments, plus about 25 associated replies.  Comments included, (1) Cooooool!! and (2) Oh I wish I could get those, and (3) I want one so bad!  He’d do great in my 110! and (4) what does he charge for those?  Where is he located?

The reply to the previous query was, “$9.99, Sioux Falls.”  Then this discussion followed: “I am sure they wold ship if you asked nicely” and “Pretty sure they can’t cuz those are illegal in many places” and “Yeah, South Dakota is pretty lax on wildlife stuff unless you’re poaching.”

I think that independent aquarium stores may be the primary agents for the introduction and spread of invasive apple snails around the USA.  The survey I posted in December [21Dec17] satisfied me that the big-box pet stores don’t sell them, and the desultory survey of major online retailers I published in January [24Jan18], including Amazon and Ebay, didn’t turn up any.  Are Mom-and-Pop independents, which in the patois of social media are called “LPS” (local pet stores), the well from which North American populations of invasive apple snails spring?

Following this hunch, last week I made a field trip across town to the only independent aquarium store in the Charleston Area, a really handsome shop with great stock and a knowledgeable staff called, “Tideline Aquatics.”  And in addition to the usual assortment of mystery snails and nerites and rabbit snails [4], I found offered for sale a small batch of “jumbo gold mystery snails,” maybe six or eight head in the lot, crammed timidly into the corner of an aquarium on the bottom rack, behind the filter.  These are clearly not our benign little friend Pomacea diffusa/bridgesii.  These are invasive apple snails.  Click for larger:

NOT Pomacea diffusa
And more than just any random IAS, my local pet store is apparently stocking golden-form apple snails, of a kind widely introduced throughout Asia and the Pacific Islands.  We don’t host any golden morphs at all in the populations of Pomacea maculata naturalized here in South Carolina.  I’ll bet dollars-to-donuts that the stock of “Jumbo gold mystery snails” for sale a few miles from my house originated from Asia, probably from dealers not unlike the ones surveyed by Ting Hui Ng and her colleagues in 2016 [5].  See figure #14 in the Ng et al. plate I shared with you all back in October [9Oct17].

And here we also reprise a theme I developed in December [21Dec17] – the mysterious origins of aquarium stocks worldwide which, like any other commodity I suppose, it behooves suppliers to protect.  And the plasticity of the names attached to such stocks.  Common use and legal precedent has developed such that “apple snails” are bad and “mystery snails” are good.  So the “jumbo mystery snail” has been born, to mysteriously arrive at an independent aquarium-stock retailer near you.

And so we have now come full circle, which means that it is time to sum up.  I am charmed, genuinely charmed, by the widespread interest and heartfelt love often demonstrated by aquarium hobbyists toward our mutual friends, the freshwater gastropods.  And I think such interests should be encouraged, if for no other reason than they might blossom.  I cannot see how harvest of wildstock freshwater gastropod populations for the aquarium trade could endanger such populations, at any imaginable harvest rates.  I can see, however, a problem with the spread of invasive species.

Here a tiny and obscure freedom, escaping the notice of our founding fathers, is associated both with a tiny societal benefit, and a tiny hazard.  I can’t think of any solution to the tiny hazard, beyond what we’re already doing.  Let’s just leave that freedom alone, shall we?


[1] And I should immediately stipulate that some states have their own regulations more restrictive than the Feds.  Our good buddy Joshua Vlach from the Oregon Department of Agriculture informs me that Oregon has a five-page list of invertebrates that are ALLOWED to cross its state lines, and all others are prohibited [3].   The bottom line is the same for IAS, however.  Go home!

[2] US Department of Agriculture, Animal and Plant Health Inspection Service.  Plant Health / Import into the US / Permits / Regulated Organisms and Soil Permits / Snails Slugs.  [html]

[3] This reminds me of a scene from one of the Peanuts videos, where Violet and Lucy tell Charlie Brown, “There were two lists, Charlie Brown.  There was a list to invite, and a list NOT to invite.  And you were on the WRONG LIST!”

[4] The shells of the “Rabbit Snails” were completely encrusted with calcification.  Absolutely unidentifiable.  The ugliest gastropods I have ever seen in captivity.

[5] Ng Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130.  https://doi.org/10.1371/journal.pone.0161130

Wednesday, February 14, 2018

Freshwater Gastropods and Social Media

Editor’s Note –This is the fifth installment of my series on the general topic of freshwater snails in the aquarium hobby.  Previous posts have been “What’s Out There?” [9Oct17], “Loved to Death?” [6Nov17], “Pet Shop Malacology,” [21Dec17] and “Snails by Mail” [24Jan18].  But don’t worry.  Full appreciation of Essay #5 is not contingent upon familiarity with Essays #1 – 4.

I am not social, in any medium.  I don’t even text, much less twitter or tweet or insta-chat or whatever it is that the kids are doing these days.  I understand that social media can be effective tools for communicating on a large scale.  I did join Facebook about ten years ago, in order to “like” a political group of which I was serving as an officer [1].  I regretted it at the time, and regret it now.

In any case, about once a week I gather up my courage and log onto Facebook.  And watch in horror as great garbled masses of disconnected conversations and news and opinions and jokes and photos and videos from family and friends and professional colleagues and high school classmates and Sacred Harp Singing Societies are disgorged simultaneously onto my desk in one gigantic, hideous, stupefying dose.

So several months ago, a Facebook friend called my attention to a group called “Snails, Snails, Snails.”  Heart racing with a mixture of curiosity and dread, I clicked over to the homepage for the group, and what to my wondering eyes should appear, but an internet forum for “lovers, keepers, breeders, and sales of freshwater and saltwater snails and slugs,” boasting 5,442 members!

"Gary doesn't smell so good."
It was a closed group.  So I submitted my CV, top five recent publications, and three letters of reference, and was, after some period of deliberation, duly admitted to membership.  And have subsequently been charmed.

What an engaging assortment of odd-lot humanity!  Mostly young, apparently from a wide variety of backgrounds, hailing from all over the world, unified by the love, yes love often and freely confessed, of gastropods.  Most of the members seem to be freshwater aquarium hobbyists.  Posts about marine gastropods are occasional, as are photos of pet land snails, and even peripheral aquarium fauna, like shrimp.  But I would estimate that, of the perhaps 15 – 20 posts per day, at least 80% have to do with somebody’s freshwater aquarium pet.

Fascinated by the social interactions as they unfolded before me, I resolved to log onto Snails, Snails, Snails every day for 30 days, beginning 25Aug17, and monitor all activity.

I recorded 16 different freshwater gastropod categories receiving mention during my month of observation, totaling 375 mentions.  Of that total, 230 mentions (61%) were of Pomacea diffusa/bridgesii, almost universally referred to as “mystery snails,” apparently the most popular gastropod pet in the home aquarium by far.  Indeed, at some point during the month my attention was called to a pair of independently-operating FB groups dedicated exclusively to P. diffusa, “Mystery Snail and Aquatic Lovers” with 3,166 members and “Mystery Snail Addiction” with 1,818 members [2]. 

The discussion seems to focus on husbandry – food, water quality, life history in culture – not too much different from chatter about aquarium fish, I don’t suppose.  One probably reads more of the “How do I tell if Gary is dead” sorts of questions.  One also reads a surprising number of posts sharing “the cute thing I saw Lightning do,” probably very similar to typical social media interactions about cats and dogs.

The next-most-popular category of freshwater snails in social media seems to be the nerites of all species, with 33 mentions on Snails, Snails, Snails for the month.  This is unsurprising, given the results of the survey of big-box pet retailers I reported in December [3].  The remainder of the species with double-digit mentions during my 30 days of monitoring were “Ramshorns” (24), Melanoides tuberculata (19), Physa (17), Assassin snails (14), and “Rabbit Snails” (Tylomelania, all species) with 10 mentions [4].

I tallied eight mentions of “apple snails” during my month of observation, by which I was able to unambiguously confirm that the author was referring to large, invasive Pomacea maculata/insularum/canaliculata types.  I also caught two mentions of the invasive “Columbian Rams Horn” Marisa.

One young lady in Houston shared an article from the Houston Chronicle entitled, “Harvey Floodwaters bring weird pink things to the Houston landscape [5].”  There were 11 comments and replies, most of the “LOL” sort.  But other comments included "I'll take them 😄" and "I wish I could find some of these here," and "So jealous!  I'm in Illinois and haven't been able to get my hands on a pair."

Without a doubt, significant pent-up demand exists within the community of aquarium hobbyists for large, invasive apple snails.  I counted four separate appeals to purchase such animals during my 30 days of observation, generally of the form, “Does anyone have a LARGE (like, baseball sized) apple snail that they would sell? I LOVE snails and I can't find any that large near me.” 

It is impossible to know, of course, to what extent such requests are satisfied through one-on-one “messaging.”  Typical public replies to such solicitations included “You’d have to find locally. So you should post your location. Shipping adults is dangerous.” or “For channeleds you'd have to find a local seller. I believe it's illegal to ship them over state lines.”  Here’s one (especially revealing) reply: “Haha thank you! Yes our aquarium shop gets lucky once in a great moon and they have a personal tank with one literally apple size so I am always checking in.”

I never saw any misgivings expressed by any member of the Snails, Snails, Snails FB Group about the potential for large apple snails to become invasive pests.  Significant qualms were not uncommonly expressed, however, about the potential for large apple snails to destroy valuable aquarium plants.  One member asked, “How do you stop apple snails from eating your expensive plants?”  After several commiserations, condolences, and expressions of despair, the Group Administrator posted this meme, which I do not understand:

Finally.  I leave you on this Valentine’s Day with one woman’s heart-wrenching testimonial to the love she bore for her gastropod friends.  She posted: 
“My son was in a horrific car accident on Tuesday and almost lost his life. He is home now and doing well but, while i was away i had my kids feeding my snails for me. It did not turn out so well. I lost a banjo catfish, a betta, and all but two of my big apple snails. I am praying these two guys will recover but idk.”
Yes, you read that correctly.  Her son was in an automobile accident, and she is praying for her snails.


[1] The South Carolinians for Science Education. [SCSE]  Like us on Facebook!

[2]  The list goes on and on, actually.  A simple search for “snails” within Facebook will also return groups called “Land Snails” (742 members), “Tree and Land Snails” (925 members), “Snail Enthusiasts: USA” (1,400 members) and even (I wish I was kidding) “Giant African Land Snails” with 5,800 members.

[3] Pet Shop Malacology [21Dec17]

[4] Others mentioned included Bellayma (6), “Pagoda snails” (5), Thiara scabra (3), “Devil’s Spike” (1), Lymnaea peregra (1), Gyraulus parvus (1), and New Zealand Mud Snails (1).

[5] Houston Chronicle (7Sept17).  Harvey Floodwaters bring weird pink things to the Houston landscape. [html]

Wednesday, January 24, 2018

Snails by Mail

Last month we surveyed the elements of the freshwater gastropod fauna widely available to hobbyists in the Big Box retail outlets that seem so dominant on the landscape of aquarium supply today [1].  We found two categories of snails reliably offered for sale, strikingly different in their biology but ironically similar in their provenance – the “mystery snails” (Pomacea bridgesii/diffusa) and the nerites.  But, as my readership has already doubtless inferred from my essay of 9Oct17 [2], ampullariids and neritids do not the entire market comprise.  What else might be available online?

Assassin Snail - Aquatic Arts
If one simply enters “freshwater snails” on the subject line of a google search, the first 50 hits include four major retail suppliers – Amazon, eBay, aquaticarts.com, and liveaquaria.com.  Most of the stock available for purchase from these sources are (once again) nerites or mystery snails in their various color varieties.  But below I have compiled a brief review of the remainder, sorted into seven pigeonholes.  The first four taxa or groups of taxa appear to be widely available for purchase online, the next two categories seem to be occasionally available, and the last category is what I would call a “wastebasket.”

Ramshorns – These easy-to-culture snails seem to have remained a perennial favorite of aquarium hobbyists for many years, at least since I was a kid.  All the stocks with which I have any personal experience are North American Helisoma trivolvis, but Ng and colleagues [3] identified Singapore ramshorns as Oriental Indoplanorbis exustus.  I wish I knew more about the relationship between these two taxa.  Most of the offerings for sale online today are “red ramshorns,” which are actually albinos, their absence of body pigmentation allowing that red hemoglobin so characteristic of planorbids to show through.  Stocks with wild pigmentation are marketed as either “brown” or “black.”  There is also a “leopard” variant for sale that has patchy pigmentation on its mantle, and a “blue” that (I think) demonstrates some sort of mutation in shell pigmentation.  I wish I knew more about that, too.

Assassin Snails – Approximately thirty nominal species of the nassariid genus Clea (or Anentome) burrow in the soft bottoms of broad, coastal rivers from southern China and Southeast Asia into The Philippines.  What fascinating creatures!  The group is one of only two neogastropod genera to have successfully invaded fresh waters [4].  As their name implies, assassin snails are predatory – hunting other freshwater snails and sucking them out of their shells.  The little tigers widely marketed to the aquarium hobby today are universally identified as Clea helena, but the excellent recent study by Ellen Strong and colleagues [5] suggests that commercial stocks may represent as many as four species, none of which seems to match topotypic Anentome helena from Java.

Rabbit Snails – Several species of the pachychilid genus Tylomelania are not uncommonly offered for purchase online, variously marketed as “giant” or “orange” or “golden” rabbit snails.  It may be recalled from my October essay that Ng and colleagues [3] identified four Tylomelania species in the Singapore aquarium trade, all of which are apparently endemic to Lake Pozo on the Indonesian Island of Sulawesi.  Some conservation concern has been expressed, but see the follow-up essay I published on this subject in November [6].

Japanese Trapdoor Snails – Yes, our old familiar Bellamya japonica (or maybe B. chinensis?) often seems to be marketed to the indoor aquarium hobby, generally labelled as "Viviparus malleattus.”  The biology of these large oriental viviparids will be well known to my FWGNA readership, but see my species pages [japonica] and [chinensis] for a refresher.
Rabbit Snail - Aquatic Arts

Pagoda Snails – Several nominal species of the pachychilid genus Brotia bearing heavy, strikingly spiny or tuberculate shells are harvested from the rivers of Thailand and occasionally available from online retailers as “Pagoda snails.”  We touched on these back in October as well.

Chopsticks, Spikes, or Long nosed Snails – Occasionally the discriminating freshwater gastropod connoisseur will find thiarids of the genus Stenomelania offered for sale online.  Again, Ng and colleagues [3] identified four Stenomelania species marketed in the Singapore pet trade, although raising no conservation concerns.  The Discover Life website lists 36 nominal species in the genus, ranging throughout Southeast Asia, Australia, and Oceania.  The most common specific nomina mentioned in the pet trade are Stenomelania torulosa and S. plicaria, both distributed widely from India through Indonesia to China.

The Wastebasket – Although (almost) universally reviled, stocks of the “Malaysian Trumpet Snail” (Melanoides tuberculata) are available for purchase on Amazon and eBay.  This invasive thiarid, apparently native to low latitudes throughout the Old World (in various clones), has been widely introduced into the New.  See my FWGNA species page [tuberculata] for more.  And (if you can believe it) hobbyists with a thirst for the small, brown, and mundane can also purchase Physa acuta stocks from Amazon.  I get the impression that both the Physa and the Melanoides are primarily marketed as prey for Assassin snails.  The Physa listing on Amazon advertises, “great natural food for your puffer.”

What I did not find for sale online last week, thank heaven, was any ampullariid stock other than Pomacea bridgesii/diffusa. I remember in years past being able to purchase, at least occasionally through mail order or mom-and-pop aquarium stores, Pomacea insularum/maculata (“Golden Apple Snails”), Pomacea paludosa (“Florida Apple Snails”) and Marisa cornuarietis (“Giant Ramshorns.”)  But I was unable to find, at least upon superficial search, any listing for any such invasive ampullariids through the major online retail outlets today.

So to conclude.  Should we be concerned that any of the freshwater gastropod groups listed above might escape to become pests here in North America, other than the ones already introduced and spreading?  We have reviewed the criteria for invasiveness on quite a few occasions in the past [7], ultimately settling on two ecological qualities which I have called “weedy” and “different.”  So the ramshorns, trapdoors, and wastebaskets are already here.  And the rabbits, pagodas, and chopsticks are not all that ecologically different from North American pleurocerids, in many cases, nor do their life histories seem especially weedy.  That leaves the Assassin snails.

Could an introduction of Clea succeed here in North America?  Some concern has already been expressed [8].  All the range maps I have seen for the genus seem to suggest that their natural distribution is entirely tropical – apparently ranging from the equator to around 20 degrees N latitude.  So our own Key West floats in the Caribbean at latitude 24.5 degrees N, perhaps still a bit too temperate to raise concerns about the threat of gastropod assassination here in the USA.  But you all down in Mexico and Central America might best be on the lookout.


[1] Pet Shop Malacology [21Dec17]

[2] What’s Out There?  [9Oct17]

[3] Ng Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130. https://doi.org/10.1371/journal.pone.0161130

[4] The only other neogastropod group to invade fresh waters is the marginellid genus Rivomarginella.

[5] Strong EE, Galindo LA, Kantor YI. (2017) Quid est Clea helena? Evidence for a previously unrecognized radiation of assassin snails (Gastropoda: Buccinoidea: Nassariidae) PeerJ 5:e3638 https://doi.org/10.7717/peerj.3638

[6] Loved to Death?  [6Nov17]

[7] For the biology of freshwater gastropod invasions, see:
  • Invaders Great and Small [19Sept08]
  • Community Consequences of Bellamya Invasion [18Dec09]
  • The Most Improbable Invasion [11Oct12]
  • The Many Invasions of Hilton Head [16Dec15
[8] Mienis HK. 2011. Will the uncontrolled sale of the snail-eating gastropod Anentome helena in aquarium shops in Israel result in another disaster for Israel’s native freshwater mollusc fauna? Ellipsaria 13(3):10-11.

Bogan AE, Hanneman EH. 2013. A carnivorous aquatic gastropod in the pet trade in North America: the next threat to freshwater gastropods. Ellipsaria 15(2):18-19

Thursday, December 21, 2017

Pet Shop Malacology

Back in the early 1960s, the very first aquarium shop to open its doors in Waynesboro, Virginia, was an aquatic wonderland called “Fin Fair.”  Sometimes, especially in the winter, I prevailed over my father to drive me to their store on West Main Street just so I could stroll among the dozens of tanks filled with glistening little jewels of nature.  Of course, I wanted my own aquarium.  I kept a series of aquaria through my childhood, as I grew up, and the things in them didn’t.

from Brookana Ashley Patton
And of course, any proper aquarium must have snails to scavenge the uneaten food, am I right?  In the 1960s and 1970s, in my personal experience, almost all I ever saw for sale were “ramshorns,” apparently Helisoma trivolvis.  No fancy colors, either.  Just plain, brown, “ramshorns.”

So you may be able to imagine, knowing me as you all do, the impression made by the first “mystery snail” I ever saw [1].  They were Pomacea paludosa, almost certainly wild-collected down in Florida, and they were huge!  The pet shop owner explained to me that they laid eggs out of water, the mystery being that nobody ever saw them do it.  I bought three mystery snails with my hard-earned allowance money, and I don’t think they lasted two weeks [2].

But a couple years later, the Dillons went on a family vacation down to Florida, and among our many adventures, booked passage on a glass bottom boat out of Silver Springs.  I remember the experience being very much like sailing across the top of Fin Fair.  And almost immediately, my eyes were attracted down through the schools of catfish and bream to the bottom of the springs where, to my fascination, lay small piles of mystery snail shells.  My father boosted me over the back fence on the way out to the parking lot, and I was able to snatch a couple empty shells from the marshy margins of the springs.  Watch for gators, he said.  Great father.

It is difficult for me to place myself at age 12 here in Charleston, 2017.  But one thing is certain.  The Charleston area today is blanketed by big-box pet stores - PetSmart (5 outlets) and PetCo (4 outlets).  And the eyes of any kid walking into the well-stocked aquarium departments of any of these giant retail outlets will fall on two types of freshwater gastropods, both spectacular in their own way: modern-day mystery snails [1] and nerites.

The mystery snail of the modern aquarium hobby is Pomacea diffusa, ne bridgesii [3].  They are big enough and active enough to have a personality, and charmingly diverse in coloration, as witnessed by the lovely photo montage above.  I surveyed several of the local big-box retailers, and found Black, Ivory, Blue, and Gold varieties, which for some reason PetCo calls “Gold Inca.”

The inheritance of color polymorphism in P. diffusa is a fascinating topic, to which we may return in a future post.  I cannot find anything published about it in the scientific literature, but somebody, somewhere, really seems to know what he is doing. If any member of my vast readership has any good information on the striking color polymorphisms manifest in commercial P. diffusa stocks, especially where these things are ultimately coming from, please contact me at your earliest convenience [4].

Wild Pomacea populations range through the lower latitudes of the New World, specializing on floating macrobenthic vegetation [5].  They are especially large-bodied as freshwater gastropods go, with even larger mouths with specialized lips to manipulate leafy greens, and even larger teeth.  Their shells are bulbous and surprisingly light, adapted to enfold an air bubble, making their bearers positively buoyant.  The reproductive adaptations of Pomacea are weird and wonderful – climbing up out of the water to lay huge clutches of huge eggs, typically on emergent vegetation.

Now here’s a riddle.  Among the prosobranch fauna of warm freshwaters, what is the opposite of Pomacea?  How about an unspecialized grazer of benthic periphyton with an especially heavy shell adapted to high-energy environments in the Old World?  Laying tiny eggs that go down?  How about the nerites?

Zebra nerite "N. natalensis" from Wikipedia
Nerites are the best known group of freshwater gastropods about which nothing is known [6, 12].  Although much smaller than the mystery snails, the nerites marketed to the aquarium hobby are even more eye-catchingly colorful.  All the big-box stores sell a nice variety.  Our hypothetical twelve-year-old-boy would find “tiger nerites” and “zebra nerites” in the local PetCo, and “black nerites” and “mixed nerites” at the PetSmart.

Both the tigers and the zebras are labelled as “Nerita natalensis” in my local PetCo, but I am just not sure.  I can google around the internet like the best college freshman, and I did (in fact) find a variety of Wikipedia and hobbyist-type references to Neritina (or Nerita) natalensis, depicting the tiger-striped snail sold by PetCo, listing the native habitat as the freshwater-tidal and brackish mangrove-type habitats of East Africa.  The problem is that I pulled my trusty copy of D. S. Brown [7] off the shelf, and the PetCo nerites don’t really match Brown’s figures of Neritina natalensis.  They do match the figures labelled “Vittina coromandeliana” and “Vittina turrita” in the paper by Ting Hui Ng we reviewed back in October [8], both of which are elements of the Oriental / Pacific Islands fauna, not Africa.

Oh, good!  Ng and colleagues got CO1 sequences for their Singapore samples of Neritina (Vittina).  That should help us out here, right?  Nope, sequence data are worse than useless in this situation [9].  The individual Vittina turrita sequenced by Ng didn’t match anything in GenBank.  The V. coromandeliana sequence did match a GenBank sequence labelled as turrita, as did the sequence of a third nerite from the Singapore pet shops, which Ng identified as V. waigiensis.  Quoting Ng directly: 
“Two individuals identified by morphology as Vittina coromandeliana and Vittina waigiensis were 99–100% matched to two separate submissions on GenBank that were identified as Vittina turrita. Neither study included photographs of the species, nor could the sequenced individuals be located; because the two GenBank sequences for Vittina turrita were separated by a 4.5% uncorrected pairwise distance, we retained our morphology-based identifications.” 
So that brings up Neritina (Vittina) waigiensis, which may be what is lying sullen at the bottom of the tank labelled “mixed nerites” in my local PetSmart.  That’s the impression I got from my google search, anyway.  Almost all neritid populations demonstrate striking shell color polymorphism, but the snails that pet stores tend to call the “red nerite” and the internet usually identifies as Neritina waigiensis beat anything I have ever seen.  The combinations mix a delicious-looking strawberry-red color with brilliant gold and black zig-zags.  In fact, it seems possible to me that the nerites separated out as zebras and tigers in the big-box pet stores are almost within the range of color polymorphism of waigiensis.  I don’t know.
Neritna (Vittina) waigiensis
Van Bentham Jutting [10] gave the range of Neritina (Vittina) waigiensis as “especially in the eastern part of the Malay Archipelago, also in the Philippines.”  I can’t discover anything about its habitat or life history.  The species appears in both freshwater and marine references.  Most of the Oriental / Pacific Island neritids live in rapidly-flowing streams that empty directly into the sea, their eggs hatching into planktonic larvae swept down to develop into marine juveniles, migrating back into fresh water [11].  Other tropical neritid species inhabit tidal, mangrove-type environments, laying eggs that hatch into crawling juveniles, like normal freshwater prosobranchs.  The various popular aquarium nerite species seem to manifest both types of life cycles, as may be judged on YouTube, if you’d like to conduct your own cutting-edge research in freshwater neritid biology.

So we’ll close this month’s essay with one more general observation on the oppositeness of the mystery snails and the nerites, and a final point of ironic similarity.  Pomacea diffusa stocks are all (I feel sure) captive-bred.  But the nerites must be gathered from the wild – I cannot imagine an aquarist completing the life cycle of a neritid in culture.

From Chris Lukhaup
What this means is that whoever is gathering these strikingly colorful tropical nerites, whatever they are, does not want us to know where he is finding them – this is their “trade secret,” in a sense.  In fact, it will actually be to the perceived advantage of the sellers to mislead the buyers about all aspects of their malacological commodity – especially range and habitat, probably even identity.  I wouldn’t be surprised if, at some point in the supply chain between the hunter/gatherer source and your neighborhood Big-box aquarium supply outlet, the East African name “Nerita natalensis” is written in grease pencil on aquaria full oriental nerites fraudulently, in a deliberate effort to mislead.

And the ironic similarity is this.  For all their tremendous popularity in the worldwide aquarium hobby, the colorful varieties of mystery snails are every bit as genetically mysterious as the colorful varieties of nerites are ecologically mysterious.  Both categories of information seem to be jealously-guarded trade secrets.  Such are the challenges of Pet shop malacology, 2017.


[1] Common names make no sense, and there’s no sense in trying to make sense out of them.  Sometime between the 1970s and the 2000s, the name “mystery snail” was transferred to viviparids like Bellamya (Cipangopaludina), the mystery being that nobody ever saw them lay eggs.  And the various Pomacea became known as “Apple Snails.”  So that is the convention followed in both the Perera & Walls (1996) “Apple Snails in the Aquarium,” and the Turgeon et al. (1998) “Common and Scientific Names of Mollusks.”   But I think the bad press suffered by the larger, invasive, pest species of Apple snails, variously identified as Pomacea canaliculata/insularum/maculata, prompted the aquarium trade to move back to writing “mystery snail” on tanks of Pomacea bridgesii/diffusa.  Only the pest Pomacea species are still called “apple snails” by the aquarium hobby.

[2] I didn’t know what to feed them.

[3] Rawlings, T.A., K. A. Hayes, R. H. Cowie, and T. M. Collins (2007)  The identity, distribution, and impacts of non-native apple snails in the continental United States.  BMC Evolutionary Biology 7: 97.

[4] I have seen the (2004) paper by our good friend Yoichi Yusa on the inheritance of body color polymorphism in Pomacea canaliculata.  The situation in P. diffusa is obviously more complicated.

[5] Hayes, K. A. et al. (2015)  Insights from an integrated view of the biology of apple snails (Caenogastropoda: Ampullariidae)  Malacologia 58: 245 – 302.

[6] Well, European Theodoxus is fairly well studied.  There’s lots of general biology in Fretter & Graham’s (1962) “British Prosobranch Molluscs.”  And see my book pp 85 – 86 for diet & habitat.

[7] Brown, D. S. (1994) Freshwater Snails of Africa and their Medical Importance.  London: Taylor & Francis.

[8] Ng, Ting Hui, Tan SK, Wong WH, Meier R, Chan S-Y, Tan HH, Yeo DCJ (2016) Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLoS ONE 11(8): e0161130.  Review:
  • What’s Out There? [9Oct17]
 [9] Here’s another vivid demonstration of a point we have made repeatedly on this blog.  Sequence data are a dependent variable, not an independent.  They cannot be used to elucidate the systematics or evolution of an unknown study group.  Only if we have a previous hypothesis about the evolution of a group, from good, hard science, can sequence data be interpreted.  See:
[10] van Benthem Jutting WSS. Systematic studies on the non-marine Mollusca of the Indo-Australian archipelago: V. Critical revision of the Javanese freshwater gastropods. Treubia 1956; 23: 259–477.

[11] Alison Haynes published several papers on the neritid fauna of the Pacific Islands in the 1980s, which although not especially helpful to identify the Malaysian/Philippine species of immediate interest in this essay, are useful for the biology of the family.  See:

Haynes, A. (1988)  Notes on the stream neritids (Gastropoda: Prosobranchia) of Oceania.  Micronesica 21: 93 – 102.  I’ve also heard that her (2001) book is good, but don’t have access to a copy.

[12] Several weeks subsequent to the post of this blog, my attention was called to the 2016 publication of an expensive, two-volume set entitled "Neritidae of the World" by Thomas Eichhorst.  I understand the work is excellent, but have not seen a copy.