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Acanthochitona pilsbryi (Sykes, 1896)

Description: Animal ovatel, narrowly elongate, girdle broad. Median valves with jugal area well defined, nearly rectangular, with fine longitudinal grooves; lateral and pleural areas not differentiated, with strong nodules, aligned or randomly placed. Girdle with small tufts of coarse spicules, one beside each median valve and 4 in front of anterior valve; rest of girdle naked. Fringe of spicules around foot. Colour reddish fawn to brown, occasionally black.

Size: Up to 10 mm in length.

Distribution: Endemic to Australia: NSW southwards to SA, including Tas.

Habitat: Under stones around the low tide level, in muddy or silty situations.

Comparison: This species has a naked girdle apart from the prominent tufts beside each valve junction. The tufts consist of spicules which are relatively thick and short, in contrast to the long and fine spicules of the tufts of A. kimberi. Among the NSW species of the genus, only this species and A. kimberi have naked girdles.

Synonymy: Acanthochiton pilsbryi maughaneanus Ashby, 1919, from Sydney Harbour, is a previously recognised synonym based on having "pustules less raised and rounded".

Remarks: The girdle tufts of this species are often weak and sometimes missing, as in Fig. 1.

Fig. 1: Composite drawing by Michael Shea of Australian Museum specimens.

Fig. 2: Sydney Harbour (C.011938). This is a dried specimen with the girdle greatly shrunken and the sutural tufts missing.


Copyright Des Beechey 2019