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Agatha angusta (Laseron, 1951)

Description: Shell large for family, elongate and slender, up to 9 whorls, last whorl almost half of shell length. Whorls increasing in diameter rapidly over first four whorls, then increasing more slowly, with 9th whorl inflated. Protoconch coiled (Type B) of about 2 whorls, set on teleoconch with axis inclined at about 110 to teleoconch. Teleoconch whorls straight-sided, suture moderately indented. Whorls without spiral or axial sculpture. Aperture more than twice as long as wide, unusually wide and not pointed anteriorly; very strong plait on columella. Shell glossy, white.

Size: Up to 10 mm in length.

Distribution: Endemic to Australia: Southport, Qld, southwards to Twofold Bay, NSW.

Habitat: Empty shells are known from beach washup and down to 15 m.

Comparison: The four species of Agatha can be distinguished by shell and spire shape:

A. australis has the broadest shell of the group with the spire convex in outline. 

A. petterdi is fairly wide but not so wide as A. australis. The spire is convex in outline with the whorls weakly rounded but less so than A. australis.

A. manifesta is the largest of the group. The spire is straight-sided and the whorls almost straight-sided. 

A. angusta is the most slender of the group. The whorls increase in diameter rapidly over the first 4 whorls, making the spire at first convex and then straight-sided. The aperture is abruptly truncated

Fig. 1: Shellharbour, NSW (C.105301 HOLOTYPE).

 

Copyright Des Beechey 2016