Mareleptopoma pellucens, Renard & Bouchet, 2003

Renard, Jacques Le & Bouchet, Philippe, 2003, New species and genera of the family Pickworthiidae (Mollusca, Caenogastropoda), Zoosystema 25 (4), pp. 569-591 : 578-580

Mareleptopoma pellucens n. sp. ( Fig. 6 )

TYPE MATERIAL. — Holotype (dd) AMS 135347 ; 11 paratypes AMS 135347 and 135349; 1 paratype each MNHN and MZB 31019.

TYPE LOCALITY.— Bathurst, Rottnest I., Western Australia.

ETYMOLOGY. — From the Latin pellucens , meaning translucent, alluding to the particular transparency of the shells of this species.

MATERIAL EXAMINED.— A total of 28 specimens (5 lots).

Western Australia. Bathurst, Rottnest I., 1977, leg. Hewitt, 14 dd (holo- and paratypes). — HMAS Moresby , off Rottnest I., 31°38’S, 115°13.6’E, 62 m, sand and coral, 1981, 2 dd ( AMS 331822 ; identification uncertain). — HMAS Moresby, off Rottnest I., 31°43.1’S, 115°12.5’E, 98-124 m, broken shell and coral, 1981, 2 dd ( AMS 331823 , 331819 ; identification uncertain). — HMAS Moresby, Direction Bank, off Rottnest I., 31°36.7’S, 115°11.9’E, 72 m, 1980 ,

8 dd ( AMS 331817 ; identification uncertain). — HMAS Moresby, Direction Bank, off Rottnest I., 31°42’S, 115°13.6’E, 105-120 m, 1980, 2 dd ( AMS 331821 , 331824 ; identification uncertain). DISTRIBUTION. — Western Australia .

DESCRIPTION

Holotype ( Fig. 6A, B, C ). Shell very small, rissoiform, consisting of five translucent uncoloured whorls. Protoconch ( Fig. 6C ) smooth, consisting of 1.5 whorls, with nucleus slightly immersed. Transition indistinct between protoconch and teleoconch. Sculpture initially consisting of two rounded spiral cords, slightly nodulose where they intersect rounded oblique axial ribs. Adapical cord situated very close to suture, separated from it by narrow abrupt sutural ramp. Abapical cord situat- ed at lower third of whorl, separated from suture by flat deep channel. Body whorl occupying 63% of total height; base with two additional spiral cords, equal in strength and sculpture to others. Columellar area with narrow, deep umbilicus, separated from base by rounded cord merging with apertural rim. Peristome prosocline, surrounding 3/4 of aperture, depressed at center. Aperture with distinctly raised margin.

Dimensions

H = 1.1 mm, D = 0.74 mm.

REMARKS

Mareleptopoma pellucens n. sp. is easily distinguished from other species by its glassy shell and rounded sculpture, difficult to observe because of the transparency of the shell. Some specimens (e.g., paratype Fig. 6D ) have a shallower suture, axial sculpture restricted to the first teleoconch whorl, and a simply sculptured body whorl with five smooth spiral facets. It most closely resembles M. drivasi n. sp.: the protoconch of both species is non-planktotrophic, but that of M. pellucens n. sp. has a unique appearance due to its immersed nucleus. M. pellucens n. sp. is also more slender; its sculpture is smoother, without sharp tubercles. The transparency of the shell and the shape of the protoconch give this species a pyramidellid appearance, but the obvious relationship with M. drivasi n. sp. has led us to include the present species in Mareleptopoma , although with some hesitation; M. pellucens n. sp. shows the most distant characters when compared with M. karpatensis , the type species of Mareleptopoma , to which it seems to be linked by a continuum of species with intermediate morphologies.

Several lots from Rottnest Island listed above have corroded shells and look subfossil; due to this bad preservation, these are only tentatively referred to M. pellucens n. sp. This is so far the only Pickworthiidae known from Western Australia.

Figures

FIG. 6. — Mareleptopoma pellucens n. sp., Rottnest I., Western Australia (AMS 135347); A-C, holotype, H = 1.1 mm; A, B, apertural and side views; C, protoconch; D, paratype, H = 0.75 mm. Scale bar: C, 100 µm.