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Scutellastra chapmani (Tenison-Woods, 1876)

Description: Shell low, regularly or irregularly star shaped, with eight strong radial ribs and finer secondary radial ribbing over the whole surface. Major ribs coloured cream or white, with one or several of the central riblets on each rib reddish-brown; irregularly marked with reddish-brown between the major ribs. Interior white, sometimes with external brown colouration irregularly showing through.

Size: Up to 38 mm in length.

Distribution: Endemic to Australia: Yamba, NSW, to Dongara, WA, including Tasmania.

Habitat: Lives at very low tide level and below on exposed rocky shores, among algae on the upper surface of rock platforms and boulders, and is often encrusted with algae. Common subtidally, but rare above low tide level. It appears to feed exclusively on coralline algae.

Comparison: Recognised by its irregular star shape, with the ribs extending well beyond the shell margin..

Synonymy: Synonyms include Acmaea alba Tenison-Woods, 1877, Acmaea saccharina perplexa Pilsbry, 1891, Patella octoradiata Hutton, 1873.

Remarks: The radial sculpture varies considerably in this species. Shells taken from exposed positions are relatively flat with strong ribs (see Fig. 1), while those from sheltered environments are taller with weaker ribs and the star shape is less pronounced (See Fig. 2).

Fig. 1  Angourie Point, NSW (C.349684)

Fig. 2 a. Beachport, SA (C.087592) b. Northern Tasmania (C.017666) c. Angourie Point, NSW (C.084603)

Fig. 3  Live animal. Long Reef, Collaroy, NSW (DLB5067)