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Plotia scabra (O. F. Müller, 1774)

Diagnostic features

Shells highly polymorphic. Relatively small with pronouncedly stair-like whorls and subsuturally angulated last whorl; spire mostly elongated, often decollated. With distinct axial ribs that apically often run out in short spines. Spiral sculpture of low cords which cross the axials on the lower half of the shell. Aperture oval, slightly narrowing at the upper margin, with the basal lip slightly flaring. Overall brown to black colour, with red to brown dots or flames. The operculum is oval and paucispiral.

Anatomy largely as for the rest of the Thiaridae: pigmented head foot with long, broad bilobed snout, and long, thin tentacles with eyes at their base, a mantle edge with many finger-like papillae. The radula is taenioglossate with loss of the basal extension on the central tooth of the radula. The ctenidium is long with long filaments. Salivery glands are anterior to the nerve ring. Hyperbranchial gland weak.  The stomach contains a short style sac, a crystalline style and a gastric shield. The female pallial gonoduct is closed along its entire length. A brood pouch is located in the neck region of the head foot in females.

Classification

Plotia scabra (O. F. Müller, 1774)

Class Gastropoda

Subclass Caenogastropoda

Order Cerithiomorpha

Superfamily Cerithioidea

Family Thiaridae

Genus Plotia Röding, 1798 (Type species: Buccinum scabrum O. F. Müller, 1774; India).

Original name: Buccinum scabrum O.F.Müller, 1774. Müller, O.F. 1774 Vermivm Terrestrium et Fluviatilium, seu Animalium Infusorium, Helminthicorum, et Testaceorum, non marinorum Succincta Historia. Havniae& Lipsiae: Heineck& Faber Vol. 2 xxvi  214pp.

Type locality: “In paludosis littoris Coromandel Tranquebari Danorum maxime vulgarae; centena & ultra benevoleutia D.Spengler” ie, India: Tranquebar Coromandel coast.

Synonyms: Helix aspera Gmelin, 1791; Melania spinulosa Lamarck, 1822; Melania doreyana Lesson, 1831; Melania spinescens Lesson, 1831; Melanium granum von dem Busch, 1842; Melania scabrella Mousson, 1848; Melania acanthica Lea, 1850; Melania denticulata Lea, 1850; Melania pagoda Lea, 1850; Melania datura Dohrn, 1858; Melania elegans Reeve, 1859; Melania pugilis Reeve, 1859; Melania rugosa Brot, 1860; Melania snellemanni Schepman, 1880; Melania bockii Brot, 1881; Melania savinieri Morlet, 1884; Melania subcancellata Boettger, 1890; Melania pinguicola Martens in Weber, 1897; Melania varia Bullen, 1904; Melania intrepida Fulton, 1914; Melania sykesi Degner, 1928.

Biology and ecology

On and in sediment, rocks and on water weeds in estuarine and freshwater rivers and streams. A detritus and algal feeder. Plotia females are parthenogenic and reproduce by releasing at a fairly advanced stage of hatching as crawling juveniles and carry a varying number of embryos in the brood pouch (up to 29 shelled juveniles in different developmental stages).

Additional information on the biology and ecology of members of this family can be found in Fauna of Australia, vol. 5B, p. 727-729.

Distribution

Monsoonal Northern Territory and tropical north east Queensland.

Extralimitally from India and the Indian Ocean islands through SE Asia, the Philippines, New Guinea and south west Pacific.

Notes

Shells are highly polymorphic. This species has a large, elongate shell with rounded whorls and strong axial and spiral sculpture. It is usually a light brown colour with dark brown flames and speckles. Thought to be invasive in some countries.

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.