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Ennucula obliqua (Lamarck, 1819)

Description: Shell large for family. Shape equivalve, inequilateral with umbones situated well behind midline, moderately inflated; anterior end broadly rounded; posterior end narrowly rounded to almost pointed; umbones rounded and hardly projecting. Hinge taxodont, with up to 19 strong teeth on anterior side and 6-10 on posterior side. Chrondrophore prominent, oblique, directed anteriorly. Interior nacreous silvery, ventral margin not crenulate. Exterior with microscopic, concentric growth striae; large specimens sometimes with coarse growth ridges. Periostracum glossy, completely smooth, dark brown, thin dorsally, sometimes thick towards ventral margin. Exterior shell colour fawn or white.

Size: Up to 15 mm in length.

Distribution: Port Stephens, NSW, southwards to Eyre Peninsula, SA, including Tas.

Habitat: In NSW, live specimens have been dredged shallowly in harbours such as Sydney, Broken Bay and Port Stephens, and also offshore in 33-100 m. Empty shells are common in dredged material used for land reclamation.

Comparison: This is by far the largest species of the family in NSW, reaching a length of 15 mm. The next largest species, Nucula beachportensis, has a maximum length of 6.2 mm.

Synonymy: A list of synonyms was given by Lamprell & Healy (1998, sp. 12). This included Nucula simplex A. Adams, 1856 which was renamed Ennucula astricta Iredale, 1931, which itself becomes a synonym of E. obliqua (Lamarck, 1819). WoRMS (2020) also gives as synonyms Nucula antipodum Hanley, 1860, Nucula consobrina A. Adams & Angas, 1864, Nucula obliqua subdilecta Iredale, 1929 and Ennucula duritas Iredale, 1931.

Fig. 1: Off Crookhaven, NSW, in 55-64 m (C.331340)

Fig. 2: East of Twofold Bay, NSW, in 294-304 m (C.331318). Hinge detail.


Copyright Des Beechey 2022