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Description

Chlanidota (Paranotoficula) anomala n. sp.

 

(Fig. 1-3, 16)

 

 

Description. Shell (Figs. 1A-C) small (23.7 mm), thick, solid, broadly ovate in outline, with a short, conical spire. Protoconch unknown, early whorls eroded. Teleoconch of 4+ evenly rounded, convex whorls. Suture adpressed, weakly abutting. Axial sculpture limited to fine, weakly recurved, prosocline growth striae. Spiral sculpture absent. Aperture high, broadly rounded anteriorly, tapering posteriorly beneath suture, deflected from the coiling axis by 16°. Outer lip moderately thin, evenly rounded.

 

Columella short, ⅓ aperture length, concave, with strong siphonal fold. Callus of thin transparent glaze overlying the parietal region, siphonal fasciole. Siphonal notch broad, axial, slightly dorsally recurved, with straight columellar and rounded apertural margins that form the borders of the fasciole. Shell colour whitish tan, with translucent whitish outer shell layer overlaying a caramel-colored inner layer that is evident on eroded early whorls and along margin of outer lip. Aperture with whitish glaze. Periostracum indiscernible due to abrasion. Operculum absent.

 

 

External anatomy (Fig. 2, A-B). The upper part of the digestive gland was damaged during the extraction of the body from the shell. The remaining soft tissues comprise approximately 1½ whorls. Mantle cavity spans < ⅓ whorl, kidney ¼ whorl. Mantle edge thick, does not cover head and base of penis. Columellar muscle short, broad, attached to shell at rear of mantle cavity. Foot large, broadly oval (length/width ~ 1.3). Body base color pinkish-yellow, dorsal surfaces of the head, tentacles, siphon, and anterior part of the foot mottled with dark greyish black. Head large, with broad, tapering tentacles, black eyes. Siphon long, free, muscular. Operculum and opercular disk absent.

 

 

Mantle cavity. (Fig. 2, C). Mantle edge smooth, thickened. Mantle cavity short, length about ½ of width. Siphon long (~ 0.4 of aperture length, AL), muscular, extending substantially beyond mantle edge. Osphradium greenish, bipectinate, with broad axis, spanning about 0.6 of mantle cavity length. Ctenidium large, wide, spanning about 3/4 mantle cavity length. Hypobranchial gland formed of numerous distinct closely spaced oblique folds.

 

 

Alimentary system. (Fig. 3). Proboscis smooth, unpigmented, of moderate length when retracted (~ 0.7 AL). Holotype specimen preserved with proboscis slightly protruded through rhynchostome. Proboscis sheath very thin-walled, translucent in anterior half, becoming muscular and of same thickness as proboscis wall. Mouth opening forming triangular slit.

 

Buccal mass muscular, large, protruding beyond rear end of retracted proboscis (Fig. 3, A — bm). Odontophoral cartilages paired, fused anteriorly, spanning nearly entire length of buccal mass. Radular ribbon long (8.2 mm; 0.44 AL), slightly longer than odontophoral cartilages, wide (~ 580 μm; 0.031 AL), triserial (Fig. 1, D-F), consisting of 67 rows of teeth; posteriormost 5 rows nascent. Rachidian teeth with 3 equal, recurved, closely spaced cusps on posterior portion of broad, anteriorly deeply arched basal plate. Lateral teeth with 3 cusps. Outer cusp stoutest, nearly twice as long as inner cusp. Intermediate cusp shortest, nearly half the length of inner cusp, immediately adjacent to it. Salivary glands small, compact, ascinous, separate, dark-pink, dorsal to nerve ring, right salivary gland totally (Fig. 3, B— rsg) covering valve of Leiblein. Salivary ducts thin, passing loosely along both sides of esophagus. Valve of Leiblein well defined, large, pyriform (Fig. 3, A — vL). Gland of Leiblein long, narrowly tubular, highly coiled, opens with slight constriction to mid-esophagus close to the nerve ring. Esophagus not wide, muscular, of similar diameter along most of its length, widening before opening into the stomach. Posterior part of esophagus (Fig. 3, D-F —poe) lined with epithelium somewhat darker than that of the stomach, forming very tall, distinct folds. Transition of posterior esophagus into stomach marked by change in epithelium color and arrangement of folds. Stomach U-shaped, without caecum (Fig. 3, D-E). Folds of stomach epithelium rather low (accentuated on drawing). Posterior duct of digestive gland (Fig. 3, F — pdg) lying immediately at esophagus opening, small, situated in shallow groove (lg), bordered by low longitudinal folds. This groove continuing to larger anterior duct (Fig. 3, F –adg), then becoming obsolete. Both ducts lying in shallow depressions, visible on outer surface of stomach, adjacent to digestive gland (Fig. 3, E). Stomach subdivided into ventral (longitudinal groove, Fig. 3, F — lg) and dorsal channels. Dorsal channel lined with minute mostly longitudinally oriented folds. A medium-sized subtriangular cuticularized shield (Fig. 3, F — cs), present along the right side of anterior duct of digestive gland, slightly above stomach floor. A transverse groove (Fig. 3, F — tg) lined with orange epithelium arranged in sharp, low folds leads from the dorsal channel toward the anterior duct of the digestive gland. Transverse groove bordered anteriorly by tall, thick transverse fold (Fig. A2, F — tf) directing flow of food particles towards ventral channel. Anterior to this fold is a style sac lined with numerous, low, narrow folds (Fig. 3 F — ss).

 

Typhlosoles low, bordering shallow intestinal groove (Fig. 3, F — ig), lined with very low epithelium. Intestinal groove visible through stomach walls as a dark band (Fig. 3, E — ig). Rectum thin walled, terminating with small, well-defined anal papilla. Stomach and rectum filled with sand grains.

 

 

Male reproductive system. Seminal vesicle large, of small, numerous loops. Penis short, occupying entire mantle cavity length, slightly dorsoventrally compressed, with smooth walls (Fig. 2, D-E). Penis with long (about ⅓ of the total penis length) papilla, expanded at midlength, surrounded by deep circular fold around its base.

 

 

Female reproductive system. Unknown.

 

 

Type locality. Elephant Island, South Shetland Islands, Antarctica, 60°53’S, 55°32’W, 120-178 m (R/V Polarstern, Sta. 42/079).

 

 

Type material. Holotype, USNM 1010542, from the type locality.

 

 

Distribution. (Fig. 4). The species is known only from the type locality.

 

 

Etymology. anomala from Greek anomalos, irregular, abnormal, reflecting the abnormal absence of operculum and significant differences in shell sculpture from the typical representatives of Chlanidota.

 

 

Remarks. Although the genus Chlanidota has a circum-Antarctic distribution at depths ranging from 3 to 1559 m, the subgenus Pfeferria is endemic to the waters surrounding South Georgia Island (Harasewych & Kantor, 1999). Chlanidota (Paranotoficula) anomala is presently known only from the South Shetland Islands, where it co-occurs with Chlanidota (Chlanidota) signeyana Powell, 1951, at comparable depths. It may be readily distinguished from C. signeyana on the basis of its thicker shell, shorter spire, absence of spiral sculpture, and an aperture that tapers posteriorly. Chlanidota (Paranotoficula) anomala differs from all species of Chlanidota sensu stricto and Chlanidota (Pfefferia) in lacking an operculum, and in having separate salivary glands, a gland of Leiblein that is long and tubular, and a complex stomach morphology with a subtriangular cuticularized shield.”

 

 

(Kantor & Harasewych, 2008: 18-23)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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