Bathylepeta linseae, Schwabe, Enrico, 2006

Schwabe, Enrico, 2006, A new species of Bathylepeta Moskalev, 1977 (Mollusca: Gastropoda) from the Weddell Sea, Antarctica, Zootaxa 1297, pp. 37-45 : 39-43

Bathylepeta linseae new species

Figures 1–2 , Table 1

Type material. Holotype: ( ZSM Moll 20050785), leg.: K. Linse, J. Bohn & E. Schwabe, German Research Vessel “Polarstern”, ANDEEP III­Expedition, March 6 2005.

Type locality. Antarctica , Weddell Sea, Weddell Abyssal Plain, St. PS 67/102–11 (65°34.34’S 36°31.18’W to 65°35.51’S 36°28.83’W), 4805– 4797 m.

Etymology. The species is named in honour of Dr. Katrin Linse (British Antarctic Survey) for her long time work on Antarctic molluscs and kindly coordinated work on board during the relevant cruise.

Diagnosis. Shell large, elevation nearly of half of shell length, postcentral apex. Head moderately large compared to the foot. Genital papilla anteriorly at right side. Radula, rachidian tooth comprised of fused pair of lateral teeth, marginal teeth with smooth edges, basal plates not overlapping.

Description. External morphology. Shell ( Fig. 1 A) size of holotype: 26 mm long, 22.7 mm wide, 11.7 mm high, not arched, height/length ratio 0.45, width/length ratio 0.87 ( Table 1 ). Anterior slope straight, posterior slope slightly convex. Aperture broad oval, with posterior widening from midpoint of shell onwards. Shell margin smooth, very thin, sharply edged. Protoconch and teleoconch strongly eroded. Apex (broken during examination) slightly posteriorly directed, situated immediately behind the center. Shell microsculpture smooth; with about 50, randomly arranged, faint off­white radial streaks shining through otherwise translucent blue­grey surface. Interspace of streaks narrower in anterior half. Whole shell with fine concentric growth lines.

Soft parts generally cream white, lacking pigmentations. Head about of half of foot length ( Fig. 1 B). In relation to head mouth very large, rounded, anteriorly with large horseshoe­shaped jaw plate showing small beak in center ( Fig. 1 D). Tentacles rather long, eyeless; oral lappets present on both sides of snout ( Figs 1 B, D). Foot fleshy, oval, separated from head by deep furrow. Mantle edge thick, undulated, broad, with darker inner fold ( Fig. 1 B). Mantle cavity shallow around foot, slightly depressed in cephalic region. Gills absent; anus and genital papilla immediately anteriorly of head, on right side ( Figs 1 B, C).

Internal anatomy. Gross anatomy is given for externally visible organs only. Shell muscle horseshoes­shaped, even thickness, occupying posterior two thirds of body.

Digestive System—Mouth anteriorly with pair of single plates (each approx. 1.3 mm wide), forming jaw plate, centrally with small beak ( Fig. 2 A). Oral cavity nearly completely occupied by pair of elongate oval pharyngeal glands. Odontophore consists of pair of radula cartilages, well­developed, elongate oval, about 3.6 mm long ( Fig. 1 E).

Radula ( Figs 1 E–F; 2B–F) docoglossate, formula 2­2­0­ 2 ­2 x 32. Radular ribbon 12.4 mm long. Central element ( Figs 1 F; 2B, C) consisting of fused first pair of lateral teeth sharply pointed, slightly curved and about 365 µm in length, rachidian tooth missing, base up to 140 µm wide. Second pair of lateral teeth sharply pointed, triangular in outline, about 100 x 60 µm ( Fig. 2 C). Basal plates underneath each lateral tooth not overlapping, rectangular, 390 x 295 µm. Two pairs marginal teeth, interpreted as functional uncini ( Lindberg 1998: 644); similar in form and size. Each tooth slender, parallel sided, strongly curved, with sharply pointed slightly inward directed tip, edges smooth ( Fig. 2 E); 240 µm in long 47 µm wide.

Species L W H WL HL AL Source Iothia 4.9 3.2 1.78* 0.65 0.36 0.12* Dell (1990)

coppingeri n = 1

5.3 4.3 2.5 0.81 0.47 0.14* Smith (1881) holotype Ventrally lying intestine forms three large clockwise arranged loops ( Fig. 1 D). From loop to loop, diameter decreasing. After third loop, intestine bypassing dorsal lying midgut gland ( Fig. 1 C) on right side, before anteriorly bending towards anus, situated anterior of head in so­called nuchal cavity.

Gonad ventrally situated on left side, partly covered by intestine. Genital papilla 2.3 mm long, with slightly curved tip to right of anus ( Fig. 1 B).

Ecological notes. By using data from Sediment Profile Imaging Systems (SPIS), Multi and Large Box corers, and Acoustic Streamer the investigated area is interpreted as a 50 m deep and about 2.5 km wide channel on the sea floor. Its sediment is a greyish brown mud, consisting of angular quartz, lithic and mineral grains. The sediment also contains minor amounts (10%) of diatoms and centrics and radiolarian fragments. Video sequences obtained from SPIS shows a weak bottom current, and a bioturbated seabed with some scattered manganese­coated clasts, and possibly some sponges. A Conductivity­ Temperature­Depth data logger measured at 4731.6 m the following parameter: pressure 483.3 bar, temperature ­0.5°C, salinity 34.64, oxygen­content 5.48 ml/liter.

Figures

FIGURE 1. Shell and softpart morphology of Bathylepeta linseae n. sp., holotype ZSM Moll 20050785. A. Dorsal view of the shell, anterior at the right side. B. Ventral view of the intact animal. C. Dorsal view of the visceral organs, after removing shell and mantle mainly showing the midgut gland and the intestine. D. Ventral view after removing the foot, showing the intestine and gonad. E. Odontophore with centrally lying radula ribbon. F. Close­up of figure 5. Scale bars: A = 10 mm; B = 5 mm; C, D = 2 mm; E = 1 mm; F = 500 µm. an — anus, ant — anterior, cpt — cephalic tentacle, flt — fused first pair of lateral teeth, ft — foot, g — gonad, gp — genital papilla, h — head, i — intestine, j — jaw (dorsal jaw plate), mg — midgut gland, mn — mantle, mo — mouth, orl — oral lappet, rc — radula cartilage, sma — shell mid­axis, smu — shell muscle.

FIGURE 2. Radula characteristics of Bathylepeta linseae n. sp., holotype ZSM Moll 20050785. A. Isolated jaw plate, anterior part is below. B. Two radula segments in side view. C. Anterior part of radula seen from frontal. D. Posterior view of a radula segment. E. Close­up of the marginal teeth with their smooth edges. F. Posterior part of a basal plate of the radula, showing the non overlapping condition. Scale bars: A = 500 µm; B – D, F = 100 µm; E = 20 µm. b — beak, bp — basal plate, flt — fused first pair of lateral teeth, lt — second pair of lateral teeth, mt — marginal teeth, rs — radula segment.

Tables

TABLE 1. Shell morphometric characters of the Antarctic lepetid species including the data of Bathylepeta laevis Moskalev, 1977 from off Chile. Values marked with an asterisk are generated from illustrations of the relevant sources. L—length in mm; W—width in mm; H—hight in mm; WL—width / length ratio; HL—height / length ratio; AL—ratio of distance between apex and anterior shell margin to length (value higher than 0.5 reflect a posterior position); n—number of specimens; mean value in brackets; standard deviation in square brackets. † Thiele in its original description obviously confused the anterior / posterior orientation

Propilidium 4.2 pelseneeri	2.9	1.9	0.69	0.45	0.64*	pers. obs. on holotype †
5.8	4.2	2.9	0.72	0.5	0.59	ZSM n = 1
Propilidium 1.7 sp.	1.3	0.7	0.76	0.41	­	Pelseneer (1903) n = 1