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Sermyla H. & A. Adams, 1854

Diagnostic features

Shell: Relatively small, elongate conical with up to 8 whorls and an evenly rounded last whorl. Main sculptural elements are the widely spaced axial, sometimes pronouncedly opisthocline ribs on the upper part of all whorls, while on the basal part of the last whorl there are prominent spiral grooves. Some forms from near Darwin in NT (Sermyla venustula) have smooth sculptureless shells.  Shell colour  - black to dark brown to pale yellowish horn with reddish brown spots and flecks. Operculum oval and paucispiral.  

Mantle edge with many finger-like papillae.  A brood pouch is located in the neck region of the head foot in females.

Classification

Class Gastropoda

Subclass Caenogastropoda

Order Caenogastropoda

Order Cerithiomorpha

Superfamily Cerithioidea

Family Thiaridae

Genus Sermyla H. & A. Adams, 1854

Type species: Melania tornatella Lea, 1850

Original reference:  H. & A. Adams, 1854. Adams, H. & Adams, A. 1853. The genera of Recent Mollusca; arranged according to their organization. Vol. 1. John Van Voorst, London. 1-256, plates 1-32.

Type locality: Java.

Synonyms: Sermylasma Iredale, 1943

Biology and ecology

Sermyla feed on algae and detritus, and inhabit fresh to brackish waters of rivers and streams. Sermyla females are parthenogenic, and reproduce either ovoviviparously (i.e. releasing juveniles only as free swimming veligers, as is the case for Sermyla riqueti) or euviviparously (i.e. releasing crawling juveniles as more advanced in size and development, seen in Sermyla venustula). This is reflected in the habitats of both species - Sermyla riqueti inhabits more brackish waters and has a wider Indo-Pacific distribution, whereas Sermyla venustula, which is exclusively freshwater and endemic to northern Australia.

Distribution

Widely distributed, occurring in Southeast Asia, the Indo-Malay Archipelago ranging far into the Pacific region, and in northern Australia.

Further reading

Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing.

Brandt, R. A. M. (1974). The non-marine aquatic Mollusca of Thailand. Archiv Für Molluskenkunde 105: 1-423.

Glaubrecht, M., Brinkmann, N. & Pöppe, J. (2009). Diversity and disparity ‘down under’: systematics, biogeography and reproductive modes of the ‘marsupial’ freshwater Thiaridae (Caenogastropoda, Cerithioidea) in Australia. Zoosystematics and Evolution 85: 199-275.

Iredale, T. (1943). A basic list of the fresh water Mollusca of Australia. Australian Zoologist 10: 188-230.

Maaß, N. & Glaubrecht, M. (2012). Comparing the reproductive biology of three “marsupial”, eu-viviparous gastropods (Cerithioidea, Thiaridae) from drainages of Australia’s monsoonal north. Zoosystematics and Evolution 88: 293–315. 

Smith, B. J. (1992). Non-marine Mollusca. Pp. i-xii, 1-408 in W. W. K. Houston. Zoological Catalogue of Australia, 8. Canberra, Australian Government Publishing Service.