Halgerda abyssicola, 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 : 479-482

Halgerda abyssicola n. sp.

( Figs 1D ; 5-7 )

HOLOTYPE. — Vanuatu. MUSORSTOM 8 , stn CP1084, 15°50.9’S, 167°17’E, 207-280 m, 5.X.1994, 1 sp., 17 mm ( MNHN).

PARATYPE. — Banc Nova. Coral Sea, MUSORSTOM 5, stn DW304, 22°10’S, 159°26’E, 385-420 m, 12.X.1986, 1 sp., 26 mm ( MNHN).

ETYMOLOGY. — The specific name is taken from the latinised form of the Greek abyssos meaning the deep sea and the Latin cola meaning dweller. This species was found at depths between 207- 420 m.

DISTRIBUTION. — This species is found in the Coral Sea, east to Vanuatu (present study) at depths from 207 to 420 m.

DESCRIPTION

External morphology

Transparencies of living animals and preserved specimens were studied. The animals have a firm, smooth body. The body profile is high and the dorsum has ridges arranged in a reticulate pattern ( Figs 1D ; 5 ). 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 both the living animals and in the preserved state. There are dark lines that outline both sides of each ridge. The ridges and tubercles are pale yellow-white. There is thick, dark pigment in lines perpendicular to the mantle edge, and there are dark spots along the mantle margin. There are the same dark spots on the underside of the body and on the foot.

The rhinophores are tapered towards the tips. The rhinophore base is white with a thick, dark line extending down the length on the posterior side of the stalk. There are 43-45 rhinophoral lamellae.

The bipinnate gill is sparsely pinnate. There are two anterior and two posterior gill branches. Each of the two posterior branches is divided into three secondary branches and each has a dark stripe on the anterior side. The anal papilla is long and has dark pigment on the tip.

Radular morphology

The buccal mass is not pigmented. The radular sac is elongate and protrudes from the buccal mass. The labial cuticle is smooth and devoid of any jaw rodlets. The radula ( Fig. 6 ) of the holotype (MNHN MUSORSTOM 8 CP1084) has a formula of 35 × 57.0.57 and the paratype (MNHN MUSORSTOM 5 DW304) has a formula of 39 × 37.0.37. The three outer teeth ( Fig. 6A ) are much smaller than the inner and middle lateral teeth and only the outermost tooth has very small, blunt denticles. The second and third teeth have no denticles. The 10 or so inner lateral teeth ( Fig. 6B ) are much 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. 6C ) are hamate with extremely long, pointed hooks. They have a flattened base that overlaps the adjacent tooth.

Reproductive system

The reproductive system ( Fig. 7 ) is triaulic. The ampulla is thick, long and lies 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 of the animal examined appeared to be not fully mature owing to its small size. 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 long, thick, convoluted duct, that loops three times, then enters the large, wide penial bulb. The short uterine duct emerges from the female gland mass and joins the spherical receptaculum seminis near its base. The duct connecting the receptaculum and the bursa is long and coiled. The round receptaculum seminis is much smaller than the thin-walled spherical bursa copulatrix. The prostate does not cover the bursa copulatrix, but wraps around it as is common in other species of Halgerda . The vaginal duct that emerges from the base of the bursa copulatrix is long. At its exit is the top of a large, bulbous vagina. The common genital atrium is wide and large.

DISCUSSION

The external morphology of Halgerda abyssicola has some external similarity to H. okinawa (Carlson & Hoff 2000) . These similarities include body profile and coloration, presence of tubercles, and rhinophoral coloration. Due to these external similarities, a comparison is made between these two species.

Both species have a smooth, firm, high body profile with ridges and depressions as typical for the genus. Both have tubercles at the junctions of the ridges, but H. abyssicola has lower, less pronounced tubercles. Both have smooth rhinophoral and gill sheaths. The rhinophores of both species are long, with a slight posterior angle. The highly pinnate gill of H. okinawa is divided into four main branches whereas the gill of H. abyssicola is sparsely pinnate and is divided into three main branches.

The external coloration of the two species is similar in that both have a translucent white body, and the upper part of the tubercles is yellow. Halgerda okinawa has dark pigmentation lining the tubercles and along the ridges, whereas H. abyssicola has dark pigmentation lining the ridges only. The other dark pigmentation on H. abyssicola appears as thick streaks that begin below the dorsal ridges and run perpendicular to the mantle edge. Dark spots can be seen on both animals, with those of H. abyssicola along the mantle edge only and those of H. okinawa all over the dorsum.

The rhinophore coloration of both species is similar. The base is translucent and the club is yellow. There is a dark line on the posterior side of the rhinophores of both species, but the line is much thicker on Halgerda abyssicola .

The gill coloration is very different between the two species. Halgerda okinawa has a bright to pale yellow gill with dark spots scattered over all branches. Halgerda abyssicola has a translucent white gill with a dark stripe on the anterior side.

The radula of both species is similar in that the three outer teeth are reduced and not denticulate. The outermost tooth of Halgerda abyssicola can have very small, blunt denticles.

There are also some similarities between the reproductive systems of the two species. The reproductive systems are similar in that the bursa copulatrix is large and enfolded by a glandular prostate that does not cover the bursa. The differences between the reproductive morphologies are as follows: the vas deferens differs between the species, with that of Halgerda okinawa being thin and having one fold before it reaches the large penial sheath. The vas deferens of H. abyssicola is quite thick, long and coiled several times before reaching the large penial sheath. The vaginal duct also differs between the two species. Halgerda okinawa has a vaginal duct that widens only slightly at the distal end, whereas the duct of H. abyssicola is long, tubular and widens considerably into the vagina. Both the vagina and the penial sheath of H. abyssicola are bulbous and the same size.

The external and reproductive morphology of Halgerda abyssicola distinguishes it as a new species.

Figures

FIG. 1. — Photos of new Halgerda species from the deep sea; A, Halgerda fibra n. sp., living animal, dorsal view (MNHN BATHUS 3); B, Halgerda fibra n. sp., preserved animal, ventral view (MNHN BATHUS 3); C, Halgerda fibra n. sp., living animal, dorsal view (MNHN CHALCAL 2 CP20); D, Halgerda abyssicola n. sp., living animal, dorsal view (MNHN MUSORSTOM 8 CP1132). Scale bar: A, B, 5 mm; C, 2 mm; D, 3 mm.

FIG. 5. — Halgerda abyssicola n. sp., preserved animal, (MNHN MUSORSTOM 8 CP1132); A, dorsal view; B, ventral view. Scale bar: 4 mm.

FIG. 6. — Electron micrographs of H. abyssicola n. sp. (MNHN MUSORSTOM 8 CP1084), radular morphology; A, outer lateral teeth; B, inner lateral teeth; C, middle lateral teeth; D, middle lateral teeth. Scale bars: A, 75 µm; B, 150 µm; C, 75 µm; D, 100 µm.

FIG. 7. — Drawing of H. abyssicola n. sp., reproductive morphology. Abbreviations: am, ampulla; bc, bursa copulatrix; ej, ejaculatory duct; fgm, female gland mass; ga, genital atrium; p, penis; pr, prostate; rs, receptaculum seminis; v, vagina. Scale: 7.5 ×.