Retusa trunca, 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 : 737-740

Retusa trunca n. sp.

Figs 75E, F, 76

TYPE MATERIAL. — Holotype MNHN 20423 and 8 paratypes MNHN 20424-20426, 4 paratypes LACM 3005 .

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FIG. 75. Shell morphology of species of Retusa Brown,1827 . A, Retusa lenis n. sp., holotype MNHN 20419 (2 mm),ventral view, New Caledonia, BATHUS 1 stn DW 688; B, same shell, posterior view. C, Retusa abyssicola n. sp., holotype MNHN 20405 (3 mm), ventral view, New Caledonia, BIOCAL stn KG 85; D, same shell, posterior view. E, Retusa trunca n. sp., holotype MNHN 20423 (5 mm), ventral view, New Caledonia,BIOCAL stn KG 03; F, same shell, posterior view. G, Retusa sp. 1 , (4.5 mm), ventral view, Fiji, BORDAU 1 stn DW 1459; H, same shell, posterior view.

TYPE LOCALITY . — Loyalty Ridge, 20°35’S, 166°53’E, 735 m [BIOCAL: stn KG 06 ] .

MATERIAL EXAMINED. — Norfolk Ridge. BIOCAL: stn DW 70 , Wallis and Futuna. MUSORSTOM 7: stn DW 560 , Banc Tusca- 23°25’S, 167°53’E, 965 m, 1 dd, paratype ( MNHN 20425 ). rora, 11°47’S, 178°20’W, 697-702 m, 1 dd; stn DW 594 , Banc Loyalty Ridge. BIOCAL: stn KG 06, 20°35’S, 166°53’E, 735 m, 7 Field, 12°31’S, 174°20’W, 495-505 m, 1 dd .

dd, holotype ( MNHN 20423 ; Figs 75E, F) and paratypes ( MNHN Tonga. BORDAU 2 : stn DW 1543 , SW of Tongatapu, 21°16’S, 20424) . — BIOGEOCAL: stn DW 307 , 20°35’S, 166°55’E, 470- 175°18’W, 427-436 m, 11 dd (4 paratypes LACM 3005 ) .

480 m, 1 dd, paratype (MNHN 20426).

DISTRIBUTION. — Specimens collected only from New Caledonia, Tonga and the Wallis and Futuna region (Fig. 76),

in 436- 965 m.

DESCRIPTION. — Shell morphology. Length 5 mm, width 3 mm (holotype). Shell solid, oval to elongate, with nearly parallel sides (Fig. 75E). Only 1 whorl visible, forming nearly the entire shell, except for a visible portion of the spire. Protoconch partially visible. Apex flat, truncate, slightly depressed in some specimens (Fig. 75F). In other specimens the spire rises slightly above the body whorl. The aperture lip does not rise from the right side of the shell. Anterior end of the shell rounded. Aperture as long as the shell, wider anteriorly and narrowing gradually at about 1/4 of its length. Columellar margin slightly thickened. Columella with an inconspicuous fold. Umbilicus closed. Sculpture of a number of strong, simple spiral lines, only present near the anterior end of the shell, and densely arranged growth lines. On the posterior end of the spire there is a distinctive pattern of curved and well-marked growth lines. Colour uniformly whitish to pale brown.

Anatomy. Unknown. All shells collected lacked soft parts.

REMARKS. — Retusa trunca is clearly distinguishable from other Indo-Pacific species of the genus by the truncate apex and the presence of numerous spiral lines near the anterior end of the shell. Other species with a truncate shell are Retusa waughiana Hedley, 1899 and Retusa minima Yamakawa, 1911 , both illustrated by Hori (2000c), but they are distinguishable from R. trunca by having concave sides and the shell wider near the anterior end. Also, the sculpture of R. waughiana has stronger spiral grooves all over the shell, whereas in R. trunca they are concentrated near the anterior end only and are less marked. In R. minima the spiral grooves are only present on the posterior end of the shell and the growth lines are much more conspicuous than in R. trunca .

This species is placed in Retusa , based on the shell morphology, pending availability of complete specimens.

ETYMOLOGY. — From the Latin truncus (maimed, cut off), in reference to the flat shape of the apex of this species.