Halgerda orstomi, Fahey & Gosliner, 2000

Fahey, Shireen J. & Gosliner, Terrence M., 2000, New records of Halgerda Bergh, 1880 (Opisthobranchia, Nudibranchia) from the deep western Pacific Ocean, with descriptions of four new species, Zoosystema 22 (3), pp. 471-498 : 485-490

Halgerda orstomi n. sp.

( Figs 11-13 )

HOLOTYPE. — Vanuatu. MUSORSTOM 8 , stn CP1140, 15°48’S, 167°09’E, 235-251 m, 11.X.1994, 1 sp., 13 mm ( MNHN).

PARATYPES. — Vanuatu. MUSORSTOM 8, stn CP1132, 15°38’S, 167°03’E, 160-182 m, 11.X.1994, 2 sp., 14 mm, 20 mm ( MNHN). — Stn CP1133, 15°39’S, 167°03’E, 174-210 m, 11.X.1994, 1 sp., 11 mm ( MNHN).

ETYMOLOGY. — The specific name, a patronym, refers to the Institut de Recherche pour le Développement, the acronym of which (now IRD, then ORSTOM) is combined with the Muséum national d’Histoire naturelle, Paris, in the MUSORSTOM expeditions.

OTHER MATERIAL EXAMINED. — Philippines. MUSORSTOM 3, stn CP134, 12°01’N, 121°57’E, 92-95 m, 5.VI.1985, 1 sp., 22 mm (MNHN).

Nouvelle-Calédonie. MUSORSTOM 4, stn DW204, 22°37’S, 167°06’E, 120 m, 27.IX.1985, 1 sp., 20 mm ( MNHN).

DISTRIBUTION. — This species is presently recorded from Vanuatu and the Philippines, at depths from 92 to 251 m.

DESCRIPTION

External morphology

The preserved animals studied have a firm, smooth body. The body profile is high and the dorsum has low ridges arranged in a reticulate pattern ( Fig. 11 ). There are pronounced tubercles at the ridge junctions. The gill and rhinophoral pockets are smooth. The ground color of the dorsum and foot is white with a gray tinge in preservation. The tubercles have retained dark pigmentation in a ring near the apex. The holotype has a single dark spot in the depressions between the ridges. The paratype has dark lines of pigmentation. On both the mantle and foot margins of both animals are a series of dark lines that lie perpendicular to the edge. The rhinophores are long and tapered towards the tips. The rhinophoral base is gray-white with a spot of dark pigmentation on the posterior side. Dark pigmentation circles the length of the stalk. The club is dark with a white apex.

The bipinnate gill is moderately pinnate. Each of the four main gill branches is divided into three secondary branches. The base color is gray-white. Each branch has a streak of brown pigmentation the length of the anterior side. The posterior side is covered with dark spots. The anal papilla is long, white at the apex and has some dark pigment near the base.

Buccal armature

The buccal mass is not pigmented; however, there are small dark spots at the buccal opening. The labial cuticle is smooth and devoid of any jaw rodlets. The radular sac is elongate and curves downward, behind the posterior end of the buccal mass. The radula of the holotype ( MNHN MUSORSTOM 8 CP1140) has a formula of 43 × 47.0.47. The three to four outer-most teeth ( Fig. 12A, B ) are much smaller than the inner and middle lateral teeth and have short, finely divided denticles. The 20 or so inner lateral teeth ( Fig. 12C ) are smaller and have shorter hooks than the middle lateral teeth and the rows are arranged in a V-shaped pattern. The middle lateral teeth ( Fig. 12D ) are hamate with long, pointed hooks. They are flattened at mid-point and overlap the adjacent tooth.

Reproductive system

The reproductive system ( Fig. 13 ) is triaulic. The ampulla is an angular tube, moderately elongate and lies flat against the female gland mass. The ampulla narrows into the postampullary duct, which bifurcates into the vas deferens and oviduct. The short oviduct enters the female gland mass. The female gland mass is about the same size as the prostate gland. The short vas deferens separates from the ampulla and widens into the glandular prostate. The prostate consists of two distinct glandular types and they are well-differentiated as in most other members of Halgerda . The muscular portion of the vas deferens leaves the distal prostate in a moderately long, convoluted duct, that loops once, then enters the wide penial bulb. The relatively short uterine duct emerges from the female gland mass and joins the pyriform receptaculum seminis midway along its length. The duct connecting the receptaculum and the bursa is very long and coiled. The pyriform receptaculum seminis is much smaller than the thin-walled bursa copulatrix. The prostate completely covers the bursa copulatrix. The vaginal duct that emerges from the base of the bursa copulatrix is long and thick. At its exit at the top of the very large, bulbous vagina is a large sphincter. The common genital atrium is wide, large and has dark pigmentation on the interior that can be seen through the wall of the atrium.

DISCUSSION

The external markings on the dorsum of Halgerda orstomi are unique among other members of the genus. Due to some internal morphological similarities with Halgerda formosa Bergh, 1880 , a comparison is made between these two species. First, in comparing the external morphology of these species, the following similarities and contrasts are noted.

Both Halgerda orstomi and H. formosa (Bergh 1880; Fahey & Gosliner 1999a) have distinct ridges. Halgerda orstomi has pronounced tubercles with dark pigmentation at the ridge junctures, but H. formosa has low, indistinct ridges. Both Halgerda orstomi and H. formosa have dark spots in the depressions between the ridges, and dark perpendicular lines along the mantle edge. However, the spots on the dorsal surface of Halgerda orstomi are more numerous and of a more consistent size than those of H. formosa . The lines of dark pigmentation in the ridge depressions of the paratype are uniform in thickness. The dark marginal lines are also more numerous and evenly spaced on H. orstomi and are also present on the foot margin. There are no lines on the foot of Halgerda formosa , but there are some dark spots remaining in preservation. The pigmentation on the rhinophores also differs between the two species. Halgerda orstomi has a single dark spot on the posterior side of the base, and dark pigmentation circling the club but not on the apex. Halgerda formosa has dark patches on the posterior side of the stalk and dark pigmentation on the club that extends to the apex. The gills also differ between the two species. Halgerda orstomi and H. formosa have four main branches that each divides into three secondary branches. Each branch of the gill of both species has a streak of dark pigmentation the length of the anterior side. The gill of Halgerda orstomi has dark spots covering the posterior side and Halgerda formosa has dark pigmentation circling the tips of the the exterior. The genital atrium of H. formosa does not have dark pigmentation.

Although there are some similarities between the two species, it is evident that Halgerda orstomi is a new species with distinct characteristics particular to it.

The known geographical and bathymetrical ranges of these species differs markedly. Halgerda formosa has been found in the Indian Ocean, from South Africa to Western Australia at depths above 60 m. Halgerda orstomi has been found in the western Pacific Ocean at depths exceeding 160 m.

Halgerda brunneomaculata Carlson & Hoff,

Figures

FIG. 11. — Halgerda orstomi n. sp., preserved specimen (MNHN MUSORSTOM 8 CP1140); A, dorsal view; B, ventral view. Scale bar: 2.5 mm.

FIG. 12. — Electron micrographs of H. orstomi n. sp. (MNHN MUSORSTOM 8 CP1140), radular morphology; A, outer lateral teeth; B, outer lateral teeth; C, inner lateral; D, middle lateral teeth. Scale bars: A, C, 30 µm; B, 20 µm; D, 43 µm.

FIG. 13. — Drawing of H. orstomi n. sp. reproductive morphology. Abbreviations: am, ampulla; bc, bursa copulatrix; ej, ejaculatory duct; fgm, female gland mass; gap, genital atrium pigment; p, penis; pr, prostate; rs, receptaculum seminis; v, vagina; vs, vaginal sphincter. Scale: 20 ×.