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Pyrgophorus platyrachis Thompson, 1968

Diagnostic features

Shell elongate-conical with 5-6 whorls usually with raised spiral threads around periphery, frequently the uppermost thread has conical or triangular spines. Spire straight-sided. Suture deeply impressed. Color brown or olive. Peristome complete around aperture. Sexually dimorphic in size; length of female shell 3-5 mm. males about half as large as females. Male Pyrgophorus have a distinctive penis fringed with numerous papillae: 3-7 papillae along right margin and a projection with 1-4 papillae near end on left side (Hershler & Thompson 1992).

Classification

Pyrgophorus platyrachis Thompson, 1968

Common name: Serrate Crownsnail

Class Gastropoda

Subclass Caenogastropoda

Order Littorinimorpha 

Superfamily Truncatelloidea

Family Cochliopidae

Genus Pyrgophorus Ancey, 1888 (Type species: Paludina parvula Guilding, 1828; St Vincent, Lesser Antilles, Caribbean)

Original name: Pyrgophorus platyrachis Thompson, 1968. Thompson, F. G. (1968). The Aquatic Snails of the Family Hydrobiidae of Peninsular Florida. University of Florida Press: Gainesville, Florida. 1-268 pp.


Type locality: Florida, USA.

Biology and ecology

Pyrgophorus platyrachis is most commonly found in fresh water, including man-made structures such as canals, also lakes, streams, rivers, swamps etc. and has been collected in brackish marshes. It most commonly occurs in streams and canals with a slight current and a soft, silty bottom but some populations may be found in mangrove swamps. Individuals are generally found on plants but may also be found on any submerged object on the bottom (Thompson, 1968).

Pyrgophorus feeds on algae and biofilm. Pyrgophorus species are ovoviviparous brooders, females holding eggs until hatching in a brood pouch in the pallial oviduct. The embryos are clearly visible through clean shells.

Distribution

Native to Florida, USA; recently introduced to Singapore.

Notes

This species resembles Potamopyrgus antipodarum but differs in that the spines and sculptural ornamentation of the shell is composed of calcium carbonate (shell) and not proteinaceous material (periostracum) as in Potamopyrgus. Also Pyrgophorus has low (often indistinct) multiple spiral cords around the shell. Potamopyrgus only develops a single spiral thread or row of spines on the whorl shoulder of some individuals under certain environmental conditions. Anatomically Pyrgophorus differs in having a number of short finger-like glandular papillae on the penis of males; Potamopyrgus has a simple penis.

Although Pyrgophorus is not yet recorded from Australia, given that it is established in freshwater in Singapore, and because of its close resemblance to Potamopyrgus, we include it here as a species to watch.

Further reading

Hershler, R. & F. G. Thompson (1992).  A review of the aquatic gastropod subfamily Cochliopinae (Prosobranchia: Hydrobiidae). Malacological Review Supplement 5: 1 - 140. 

Liu, Hsiu-Ping, R. Hershler & F. G. Thompson (2001). Phylogenetic relationships of the Cochliopinae (Rissooidea: Hydrobiidae): an enigmatic group of aquatic gastropods. Molecular Phylogenetics and Evolution 21: 17-25.

Nava, M., Severeyn, H. & Machado, N. (2011). Distribución y taxonomía de Pyrgophorus platyrachis (Caenogastropoda: Hydrobiidae), en el Sistema de Maracaibo, Venezuela [Distribution and taxonomy of Pyrgophorus platyrachis (Caenogastropoda: Hydrobiidae) in the Sistema de Maracaibo, Venezuela]. Revista de Biologia Tropical 59: 1165-1172.

Ng, T.H.; Liew, J.H., Song,  J.Z.E. and Yeo, D.C.J.  (2016) First record of the cryptic invader Pyrgophorus platyrachis Thompson, 1968 (Gastropoda: Truncatelloidea: Cochliopidae) outside the Americas. BioInvasions Records Volume 5, Issue 2: 75–80.

Ng, T.H., Tan, S.K., Wong, W.H., Meier, R., Chan, S-Y., Tan, H.H. and Yeo, D.C.J. 2016. Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLOS One. DOI:10.1371/journal.pone.0161130.

Rosenberg, G., Moretzsohn, F. & García, E. F. (2009). Gastropoda (Mollusca) of the Gulf of Mexico. Pp.  in D. L. Felder & Camp, D. K. Gulf of Mexico origin, waters, and biota: Volume 1, Biodiversity. Corpus Christi, Texas, Texas A&M University Press.

Thompson, F. G. (1968). The aquatic snails of the family Hydrobiidae of peninsular Florida. Gainsville, Florida, University of Florida Press.

Thompson, F. G. (1999). An identification manual for the freshwater snails of Florida. Walkerana 10(23): 1-96.