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MURCHISONELLIDAE


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Murchisonella declivita (Laseron, 1951)

Description: Shell minute, elongate and narrow, spire straight-sided, up to 8 whorls. Protoconch of 1 whorl. Teleoconch whorls uniformly rounded or angled at top quarter; upper quarter of whorls smooth with shelf below, sculptured below shelf with 5-14 fine spiral grooves, crossed by dense axial growth lines. Aperture with inner lip reflected, expanded anteriorly, sinus at suture. Old shells opaque white.

Size: Up to 2.3 mm in length.

Distribution: Holotype from Gunnamatta Bay, Port Hacking, NSW, which is the only specimen known from Australia. Peñas & Rolán (2013, p. 45) reported it from Philippines, New Caledonia, Fiji, Solomon Islands and Japan.

Habitat: The holotype was sorted from shell sand. Peñas & Rolán (2013) reported it mainly from shallow waters, down to 30 m, but also from dredgings down to 600 m. Uncommon.

Comparison: This species is smaller and not as elongate as. M. anabathron. The shelf separating the smooth upper quarter of whorls from the part below is very distinct (but hardly visible in the immature, worn holotype).

Remarks: The holotype of this species (Fig. 1) is a specimen of only 5 whorls. Peñas & Rolán (2013) figured more mature specimens, up to 8 whorls, one of which is reproduced in Fig. 2.  This shows a greater resemblance to the other NSW species of the genus, Murchisonella anabathron, than the immature holotype.of M. declivita. 

Fig. 1: Gunnamatta Bay, Port Hacking, NSW (C.105373) HOLOTYPE of Pandorella declivita. Photo Australian Museum

Fig. 2: Aesé Island, Vanuatu. Figure reproduced from Peñas & Rolán (2013, Pl. 16, Fig. 2)

 

Copyright Des Beechey 2017