Serrata stylaster Boyer 2008, comb. nov.
Creators: name: Boyer, Franck
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neogastropoda
Marginellidae
Serrata
Serrata stylaster

description: <i>Serrata stylaster</i> (Boyer, 2001) comb. nov. Fig. 40 <i>Dentimargo stylaster</i> Boyer, 2001: 159-160. TYPE MATERIAL. — Holotype (dd) MNHN 20748 and 2 paratypes (dd) MNHN 20749-20750. TYPE LOCALITY. — Banc Stylaster, guyots nord de la Ride de Norfolk, 23°38’S, 167°43’E, 430-452 m [SMIB 8: stn DW 167]. MATERIAL EXAMINED. — <b>Norfolk Ridge</b>. SMIB 8: stn DW 167, 23°38’S, 167°43’E, 430-452 m, 2 dd (holotype, Fig. 40, 1 paratype MNHN 20749); stn DW 169, 23°37’S, 167°42’E, 447-450 m, 1 dd (paratype MNHN 20750). DISTRIBUTION. — Stylaster Bank, northern Norfolk Ridge, shells in 447-450 m. DESCRIPTION. — Shell ovate biconical, solid, opaque. Protoconch paucispiral, wide, bulging, smooth. Spire tall, subconical, inflated, apex blunt, whorls weakly convex to flat. Aperture widening moderately over lower part, very oblique, narrowed anteriorly. Base tapering. Outer lip thin over lower part, thicker and reflected over upper part, slightly oblique, slightly sinuous. Shoulder slightly sloping, rounded, lower part of outer edge oblique, nearly straight, weakly convex in the centre, outer margin moderately thickened, rounded, not stepped, inner edge not reflected, weakly concave, bearing 10 faint unequal denticles, 2 strongest ones are the first one, situated deep within the aperture along the siphonal canal, and the penultimate one, on the posterior part of the inner labrum. Four thin columellar plaits, anterior one very thin, fragile, very oblique, second and third ones thin, oblique, fourth one shorter, less oblique. Colour porcellaneous white, spire pale golden, sutural zone chalk white. Dimensions: 4.70 x 2.35 mm. Radula unknown. REMARKS. — <i>Serrata stylaster</i> was described in the genus <i>Dentimargo</i>, referring to its biconical outline and the shape of its denticulate outer lip. Boyer (2001) noted, however, that the species has a distinctive subovate outline by comparison with Recent species referred to <i>Dentimargo</i>, and he also recorded its affinity with <i>Longinella tollere</i> Laseron, 1957 from Queensland. The latter was said by Coovert (1999: 35) to be a radulate species with “ <i>Volvarina</i> - type ” comb-like plates, whereas the genus <i>Dentimargo</i> was said to lack a radula (Coovert &amp; Coovert 1995), despite very few species having been checked from this perspective. This situation led Boyer (2001) to a discussion about the possible occurrence of several lineages of radulate and nonradulate species descending from an early stock of radulate <i>Volvarina-Dentimargo</i>. Boyer (2001) suggested that until the issue could be clarified, his new species should be provisionally allocated to the genus <i>Dentimargo</i>, as <i>D. stylaster</i>. The more recent discovery of a <i>Volvarina</i> -like radula (comb-like pattern with few cusps) in a typical <i>Dentimargo</i> species off Yucatan (Boyer 2005) proved that the genus <i>Dentimargo</i> cannot be characterized by the lack of a radula, and the thesis of a common <i>Volvarina-Dentimargo</i> clade was reinforced. However, this leads to the need to examine more closely the possible discrimination among <i>Dentimargo</i>, <i>Volvarina</i> and <i>Serrata</i> on the basis of shell features. The range of morphological variation in <i>Serrata</i>, as recorded in this study, demonstrates that <i>D. stylaster</i> belongs in this genus. Very disparate shell morphologies are currently accepted in the genus <i>Dentimargo</i>, which contains biconical plain or weakly decorated shells with a smooth or denticulate outer lip. However, when present, the denticles in <i>Dentimargo</i> are more prominent on the upper part of the lip, and in most species the largest one, very sharp and produced, is uppermost, contrary to the situation in <i>Serrata</i> where the denticles are relatively subequal in denticulate species. In <i>Dentimargo</i> species with a smooth labrum, the central part of the inner lip is never distinctly reflected and the anterior part is not excavated. However, some non-denticulate or regularly denticulate species currently attributed to <i>Dentimargo</i> may not be distinguishable from <i>Volvarina</i> or <i>Serrata</i> on the simple basis of shell morphology. <i>Dentimargo stylaster</i> is transferred to the genus <i>Serrata</i> on the basis of its sinuous labrum, which is much narrowed anteriorly with a sharp edge, reflected over its upper half, and distinctly excavated over its lower half, with regularly distributed, indistinct denticles, among which the most prominent penultimate upper one is not much more pronounced than its neighbours. This labrum pattern matches very well the most common pattern found in <i>Serrata</i> and is not found in <i>Dentimargo</i>. <i>Serrata stylaster</i> seems to be a rare endemic species from Stylaster Bank, on the northern Norfolk Ridge, with no close relatives known to me in New Caledonian waters.
description: Published as part of <i>Boyer, Franck, 2008, The genus Serrata Jousseaume, 1875 (Caenogastropoda: Marginellidae) in New Caledonia, pp. 389-436 in Mémoires du Muséum national d'Histoire naturelle 196</i> on pages 421-422
description: {"references": ["BOYER F. 2001. - Especes nouvelles de Marginellidae du niveau bathyal de Malacologia Mostra Mondiale (Cupra Marittima, Italy) 35: 12 - 17.", "LASERON C. F. 1957. - A new Classification of the Australian Marginellidae PONDER W. F. 1970. - Some aspects of the morphology of four species of (Mollusca), with a review of species from the Solanderian and Dampierian the Neogastropod family Marginellidae with a discussion on the evolution zoogeographical provinces. Australian Journal of Marine and Freshwater of the toxoglossan poison gland. Journal of the Malacological Society of Research 8 (3): 274 - 311. Australia 2 (1): 55 - 81.", "BOUCHET P. (eds), Tropical Deep-Sea Benthos 25. Memoires du Museum COOVERT G. A. &amp; COOVERT H. K. 1995. - Revision of the supraspecific", "BOYER F. 2005. - The discovery of a radula in a Dentimargo species and its Records of the South Australian Museum 9 (2): 197 - 224, pls 17 - 20."]}