Euchelus alabastrum (Reeve, 1858)

Herbert, D. G., 2012, A revision of the Chilodontidae (Gastropoda: Vetigastropoda: Seguenzioidea) of southern Africa and the south-western Indian Ocean, African Invertebrates 53 (2), pp. 381-381 : 425-426

Euchelus alabastrum (Reeve, 1858)

Fig. 21

Trochus (Euchele) alabastrum: Reeve 1858 in 1857–58: 209, pl. 38, figs 1a, b; Pilsbry 1890 in 1889–90: 448. Type loc.: Island of Diego Garcia .

Euchelus alabastrum: Pilsbry 1890: 344 .

not Trochus alabastrum: Beck ms Philippi 1847 in 1846–55: pl. 15, fig. 14; idem 1849 in 1846–55: 9 [= Margarita alabastrum: Beck ms Lovén, 1846 = Calliostoma occidentale (Mighels & C.B. Adams, 1842) ].

There is no type material for this species in the NHMUK and although Reeve mentioned additional material in the Cuming collection, no specimens identified under this name could be found in the NHMUK general collection. Nonetheless, two specimens labelled ‘ triangulata var.’ (without locality), from the Cuming collection, bear considerable resemblance to Reeve’s original figure of Trochus alabastrum ( Fig. 21A ). The larger of the two is here figured for comparison ( Fig. 21B ). Like alabastrum it is chalky-white with small spots (now much faded and pale purple-brown rather than black) on the spiral keels.

This material represents pale, particularly strongly keeled individuals of the quadricarinatus form of the highly variable Euchelus asper ( Gmelin, 1791) . Although it can not be considered type material for T. alabastrum , its resemblance to the description and original figure of the latter strongly suggests that it may have been the Cumingian material referred to by Reeve. There can be little doubt that it is conspecific therewith. I therefore propose that Trochus alabastrum Reeve, 1958 be considered a synonym of Euchelus asper ( Gmelin, 1791) and that it represents the form quadricarinatus (Holten, 1802) (cited figure reproduced in Fig. 21C ) of that species. Monodonta tricarinata Lamarck, 1822 is already established as another synonym (Fischer 1878 in 1875–80). This form of the species is evidently widespread in the Indo-West Pacific, occurring as far east as Japan (Sasaki 2000). It was also recorded from Durban by Sowerby (1897), but it seems more probable that this was a misidentified or mislocalised specimen. Fresher material from Thailand is illustrated for comparison ( Fig. 21D ) and an additional figure was provided by Poppe and Tagaro (2008: pl. 43:8). The extent of variation within E. asper is considerable and requires further study in order to evaluate its significance and to determine if it is genetically, environmentally or sexually determined.

The original Trochus alabastrum material described by Reeve (1858) came from the collection of Sir David Barclay, which was sold at auction in 1891 ( Dance 1986). Some types from this collection were subsequently purchased by the NHMUK from G.B. Sowerby (3 rd), but the whereabouts of others is not known (J. Pickering pers. comm., Feb. 2011).

Figures

Fig. 21. Euchelus alabastrum (Reeve, 1858): (A) original figure of Trochus (Euchele) alabastrum given by Reeve (1858), diameter 5/8 poll. [=15.9 mm]; (B) Euchelus ‘triangulata var.’ subadult, diameter 15.5 mm, Cuming coll’n (NHMUK); (C) original Chemnitz figure Trochus quadricarinatus cited by Holten (1802), dimensions not given; (D) Euchelus asper form quadricarinatus (Holten, 1802), Pattani, Gulf of Thailand, diameter 17.0 mm (NMSA L5162).