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Ataxocerithium serotinum (A. Adams, 1855)

Description: Shell moderately narrow, up to 11 teleoconch whorls, spire straight-sided until penultimate whorl. Protoconch of 2 whorls, first whorl smooth, rest with strong axial folds. Teleoconch whorls convex, either uniformly rounded or angled at lower third. Sculpture variable; axial folds weak or strong, sometimes thickening towards bottom of whorl; spiral cords 5 or 6 per whorl, weak or strong, crossing axials to form beads at intersections. Last whorl with about 5 spirals on base. Last whorl expanded over final one-third of whorl. Aperture nearly circular, outer lip flared, thickened internally; inner lip flared; anterior canal relatively long, tubular and deep. Shell, including protoconch, translucent, uniformly fawn or irregularly marked with light brown, becoming opaque with age, with thin periostracum, usually worn away.

Size: Up to 16 mm in length.

Distribution: Endemic to Australia: Maroochydore, Qld, southwards and around southern Australia, including Tasmania, and northwards in WA to North West Cape.

Habitat: Empty shells from beach washup and down to 100 m. Live specimens from 220 m in association with sponges.

Synonym: Previously recognised synonyms are Ataxocerithium conturbatum Iredale, 1936; Ataxocerithium scruposum Iredale, 1936; Cerithium rhodostoma A. Adams, 1855. 

Remarks: The sculpture of this species is very variable; axial folds may be weak or strong, spirals may be weak or strong, and whorls may be rounded or angled. Fig. 3 shows 3 specimens from the same locality near Woolgoolga showing such variation. Fig. 4 shows the holotype of Ataxocerithium gemmulatum Woolacott, 1957 which has sculpture similar to the specimen on the right in Fig. 3; it may be a further synonym, although the shell is unusually wide and the whorls flatter than usual for A. serotinum

Fig. 1: Off North Head, Sydney, NSW, 20 m, associated with sponges (C.366963)

Fig. 2: Off Kurnell, Botany Bay, NSW 12 m on sponge (C.315643)

Fig. 3: Mullaway Headland, north of Woolgoolga, NSW (C.244565) 

Fig. 4: Gerringong, NSW (C.102801 Holotype of Ataxocerithium gemmulatum)

 

Copyright Des Beechey 2016