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Nucula praetenta Iredale, 1924

Description: Shell relatively small for family, thick. Shape equivalve, inequilateral with umbones behind midline, slightly inflated; anterior end broadly rounded; posterior end subtruncate. Hinge taxodont, with strong teeth, with up to 9 anterior and 6 posterior teeth. Chondrophore small, oblique. Interior nacreous silvery, smooth, with crenulations all round ventral margin. Exterior with weak concentric sculpture and radial ribs towards margin. Periostracum thin, smooth, pale yellowish brown. Exterior shell colour white.

Size: Up to 4.8 mm in length.

Distribution: Known only from 2 lots. Type lot from 750 m off Sydney, from Challenger station 164B. Another lot was collected in 1976 from off Wollongong, NSW, in 1200 m.

Habitat: Deep water; known from 750 and 1200 m depth.

Synonymy: Nucula umbonata E.A. Smith, 1891 (which is an invalid name because it is a junior homonym of both Nucula umbonata Seguenza, 1876 and of Nucula umbonata Hall, 1885, so replaced by Nucula praetenta Iredale, 1924).

Comparison: This species is like Nucula pusilla in shape, hinge structure and marginal denticles internally, but is separated specifically because of its deep water habitat (i.e. Nucula pusilla occurs from 0-164 m, whereas N. praetenta occurs from 750-1200 m).

Remarks: This species was first named Nucula umbonata E.A. Smith 1891, but that name was preoccupied and Iredale (1924) replaced it with Nucula praetenta.

Fig. 1: Off Wollongong, NSW, in 1200 m (C.449137).


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