Botelloides bassianus
A small marine snail endemic to Australian waters.
Botelloides bassianus is a marine gastropod mollusk belonging to the family Trochidae, commonly known as top snails. This sea snail species is endemic to Australian waters, with a range that includes New South Wales, South Australia, Tasmania, Victoria, and Western Australia.
Two subspecies are recognized. The first, *Botelloides bassianus bassianus*, was described by Hedley in 1911 and has synonyms including *Rissoa (Onoba) glomerosa* and *Rissoa (Onoba) bassiana*. The second, *Botelloides bassianus borda*, was named by Cotton in 1944 and is also known as *Botelloides borda*.
The shell is solid, oblong, and subcylindrical, rounded at both ends. It reaches a height of 4.5 mm and a diameter of 2 mm. In terms of coloration, the upper part of each whorl is dull white, while the lower portion is slate-purple; the anterior extremity is again dull white, and a dark band on the middle third of the body whorl fades before reaching the aperture. The apex is brown. The five whorls increase rapidly in size and are wound obliquely, with the last two-thirds of the shell accounting for most of the total length. Sculpture is minimal on earlier whorls, but later whorls bear fine incised spiral grooves—about thirty on the last whorl, eighteen on the penultimate, and twelve on the antepenultimate. Occasional growth striae cross the shell obliquely. The aperture is pyriform, the columella is excavate, and the outer lip is grooved inside and bevelled to a sharp edge. The subspecies *Botelloides bassianus borda* differs in having a more cylindrical shell and rather flattened whorl sides.
Quick Facts
- Taxon
- Botelloides bassianus
Facts from the source article.
Lore & Background
The shell of Botelloides bassianus is solid, oblong, and subcylindrical, rounded at each extremity. Its coloration includes a dull white upper part of each whorl, a slate-purple lower part, and a brown apex. The dark band on the median third of the body whorl fades before reaching the aperture. The five whorls increase rapidly in size and are wound obliquely, with the last two-thirds of the total length comprising the final whorls.
Sculpture consists of fine incised spiral grooves on later whorls: the last whorl has about thirty grooves, the penultimate eighteen, and the antepenultimate twelve. Occasional growth striae cross the shell obliquely. The aperture is pyriform, the columella excavate, and the outer lip grooved within and bevelled to a sharp edge. The subspecies Botelloides bassianus borda differs by its cylindrical shell and rather flattened whorl sides.
Reader's Guide
Botelloides bassianus is notable as a species of marine gastropod mollusk within the family Trochidae, documented through taxonomic work by Hedley, Cotton, and others. The species includes two recognized subspecies: Botelloides bassianus bassianus and Botelloides bassianus borda, each with distinct shell morphology. The species is endemic to Australia, with a distribution spanning New South Wales, South Australia, Tasmania, Victoria, and Western Australia. Its shell dimensions—height 4.5 mm and diameter 2 mm—and detailed sculptural features, such as the number of spiral grooves per whorl, provide key diagnostic traits. The species has been referenced in works by Cotton (1944), Ponder (1985), Hickman & McLean (1990), and Wilson (1993), contributing to the systematic understanding of trochacean gastropods. Its presence in multiple Australian states underscores its ecological range within the region.
Did You Know?
- The shell height of Botelloides bassianus attains 4.5 mm and its diameter 2 mm.
- The species has two subspecies: Botelloides bassianus bassianus and Botelloides bassianus borda.
- The last whorl bears about thirty fine incised spiral grooves.
- This marine snail is endemic to Australia, found off New South Wales, South Australia, Tasmania, Victoria, and Western Australia.
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