Diacria major

Abstract

Diacria major (Boas, 1886) (Figs 5 A-B) Description. – A large species (L to 13 mm without caudal spine, W to 11 mm), with a strongly dorsoventrally compressed shell and wide that has the lateral spines pointing in a caudal direction. Ventral side with three longitudinal ribs, dorsal side five. The long slit-like aperture is continuous. The rim of the aperture and other thick parts of the shell are brownish coloured. Remarks. – Van der Spoel (1967) considered this species a form of Diacria trispinosa (Blainville, 1821) but already mentioned that both ‘forms’ often occurred within a single sample and therefore could constitute a higher rank. Diacria trispinosa has the lateral spines perpendicular to the shell axis and is smaller. The caudal spine is usually thrown off and a septum formed (Van der Spoel, 1967: 85). A single larval shell was found, which is relatively long (2.9 mm), slightly curved and ellipsoid in outline. As the shape perfectly matches the growth lines it is interpreted as larval shell, rather than a thrown off caudal spine. Distribution. – Few specimens have been found: offshore Sarawak, in outer shelf silty sand to continental slope planktonic ooze (DD20, DD29, DD15), an adult specimen at Royal Charlotte atoll, a few specimens on the Brunei middle to outer shelf (MES24, 25) and fragments in outer shelf muds in Sabah (DD93). Larval shells / caudal spines are very narrow and have a characteristic corneous colour.

Authors 4

1. Han
2. J. G. M.
3. Raven Aachen

   Naturalis Biodiversity Center

   Affiliation as printed

   Research Associate, Naturalis Biodiversity Center, Leiden, The Netherlands. E-mail: han. raven @ naturalis. nl; https: // orcid. org / 0000 - 0002 - 5305 - 0795

4. David J. Marshall

   Universiti Brunei Darussalam

   Affiliation as printed

   Environmental and Life Sciences, Faculty of Science, Universiti Brunei Darussalam, Brunei Darussalam. https: // orcid. org / 0000 - 0003 - 3771 - 5950 * Corresponding author. E-mail: david. marshall @ ubd. edu. bn