Cylichnium mucronatum, Valdés, 2008

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 703-704

Cylichnium mucronatum n. sp.

Figs 55C, D, F, 56D-F, 57B, 58

TYPE MATERIAL. — Holotype MNHN 20363 and 4 paratypes MNHN 20364-20366, 1 paratype LACM 2997 .

TYPE LOCALITY. — Makassar , Indonesia, 02°03’S, 118°45’E, 1710-1730 m [CORINDON: stn CH 286] .

MATERIAL EXAMINED. — Indonesia. CORINDON: stn CH 286, Fiji. MUSORSTOM 10: stn CP 1354, SE of Viti Levu , 17°43’S, Makassar, 02°03’S, 118°45’E, 1710-1730 m, 1 dd, holotype ( MNHN 178°55’E, 959-963 m, 2 dd, paratypes ( MNHN 20365 ). — BOR- 20363; Figs 55C, D). DAU 1: stn CP 1400, 16°28’S, 179°50’E, 1004-1012 m, 1 dd, para- Coral Sea. CORAIL 2: stn DW 172 , Mellish Reef, 18°26’S, type ( LACM 2997 ), 1 lv, dissected, paratype ( MNHN 20366 ; Figs 155°12’E, 1100 m, 1 dd, paratype ( MNHN 20364 ; Fig. 55F). 56D-F, 57B); stn CP 1407, 16°40’S, 179°39’E, 499-527 m, 1 dd .

DISTRIBUTION. — Known from several localities in the Coral Sea, Fiji and Indonesia (Fig. 58), in 527-1710 m, live in 1004-1012 m .

DESCRIPTION. — Shell morphology. Length 34 mm, width 14 mm (holotype). Shell elongate in adult specimens, with convex sides (Fig. 55C). Only 1 whorl visible, forming nearly the entire shell (Fig. 55D). Apex pointed, forming an elongate cone. Anterior end of the shell rounded. Aperture as long as the shell, wider anteriorly and constricted posteriorly, ending in a long, narrow canal. Columellar side thickened. Columella twisted near the anterior end of the shell. Juvenile shells shorter, with the aperture about 4/5 of the shell length and a pointed apex (Fig. 55F). Sculpture of fine, irregular spiral lines, crossed by thin axial lines. Colour uniform dark brown.

Anatomy. The digestive system contains 3 smooth and oval gizzard plates, all of them similar in size and shape (Fig. 56F). One of the ends of the gizzard plates is extended into a short protuberance. The radular formula is 35 x 7.0. 7 in a paratype from Fiji (BORDAU 1 stn CP 1400). The lateral teeth are hamate and smooth, with no denticles (Fig. 56D). All teeth are similar in shape and size.

FIG. 57. Reproductive anatomy of species of Cylichnium Dall, 1908 . A, Cylichnium ancillarioides (Schepman, 1913) , Vanuatu, MUSORSTOM 8 stn CP 1055, scale bar = 1 mm. B, Cylichnium mucronatum n. sp., paratype MNHN 20366, Fiji, BORDAU 1 stn CP 1400,scale bar = 1 mm. Abbreviations: ag, albumen gland; am, ampulla; bc, bursa copulatrix; esg, external seminal groove; fco, female copulatory organ; mg, mucous gland; pn, penial sac; pr, prostate; sr, seminal receptacle; v, vagina.

The reproductive system is monaulic (Fig. 57B). The ampulla is long and convoluted. It narrows abruptly into the post-ampullary duct. The large, oval seminal receptacle enters the post-ampullary duct, which continues distally to the common general atrium. Also entering the common atrium are the female glands and the bursa copulatrix. From the gonopore an open seminal groove runs anteriorly to the protrusible cephalic penis and the prostate. At the vaginal opening there is a complex female copulatory organ (Fig. 56E).

REMARKS. — Cylichnium mucronatum is clearly distinguishable from other species of the genus in having a long pointed apex. The other tropical Indo-Pacific species, C. ancillarioides (Schepman, 1913) , has a more rounded apex. Anatomically, these two species differ in the morphology of the reproductive system. In C. mucronatum the prostate is much shorter than in C. ancillarioides but the ampulla is larger and more complex. Additionally, the gizzard plates of C. mucronatum have a pointed extension that is absent in C. ancillarioides , and the radula of C. mucronatum contains a smaller number of teeth per row and more rows than in a specimen of C. ancillarioides of similar size.

This species is assigned to the genus Cylichnium based on the radular morphology with several, simple hamate teeth and the reproductive system with a complex female copulatory organ next to the vaginal opening.

ETYMOLOGY. — From the Latin mucronatus (pointed), in reference to the pointed apex.