Pseudomohnia kurilana (Dall, 1913) Strong & Sirenko & McLean, 2021

Strong, Ellen E., Sirenko, Boris I. & McLean, James H., 2021, The only species of Mohnia Friele, 1879 (Caenogastropoda, Buccinoidea, Buccinidae) in the North Pacific represents an unrecognized new genus of Newtoniellidae (Triphoroidea), ZooKeys 1055, pp. 69-87 : 69

publication ID	https://dx.doi.org/10.3897/zookeys.1055.68911
publication LSID	lsid:zoobank.org:pub:EDAA550D-C7AB-4C4D-8CA9-1D988F4F3940
persistent identifier	https://treatment.plazi.org/id/A2AE0E17-F79C-5A6F-AA99-F4D0BBB2C333
treatment provided by	ZooKeys by Pensoft
scientific name	Pseudomohnia kurilana (Dall, 1913)
status	comb. nov.

Treatment

Pseudomohnia kurilana (Dall, 1913) View in CoL comb. nov.

Figs 1A, B View Figure 1 , 3A, B, E View Figure 3 , 4 View Figure 4 , 5A View Figure 5

Mohnia kurilana Dall, 1913: 503; Dall 1925: 21, pl. 34, fig. 1; Kosuge 1972, pl. 12, fig. 2 (Fig. 1A View Figure 1 )

Mohnia kurilana : Golikov and Sirenko 1998: 112, fig. 7E; Kantor and Sysoev 2006: 187, pl. 93, figs J, J’ (Fig. 1B View Figure 1 )

Type material.

Lectotype. Kuril Islands • 13.40 mm in length; off Simushir Island; 46°42'N, 151°45'E; 229 fm [~ 419 m]; 24 June 1906; USFC steamer Albatross stn 4803; USNM 205224, here designated (Figs 1A View Figure 1 , 3A, B, E View Figure 3 , 4 View Figure 4 , 5A View Figure 5 ).

Other material.

Kuril Islands • 1 spm; near Iturup Island; 44°47.7'N, 148°55.5'E; 660 m; 27 July 1984; R/ V Odyssey; B Sirenko leg.; ZIN 57494 View Materials GoogleMaps / 1 (Fig. 1B View Figure 1 ); • 2 spms; Krusenstern Strait ; 48°35.6'N, 153°54.8'E; 210 m; 9 October 1987; R/ V Tikhookeanskiy; V Lukin leg.; ZIN 62774 View Materials GoogleMaps /2.

Description.

Shell. Shell broadly turreted, spire angle ca. 42°, ~ 14 mm in adult shell length, consisting of approximately six, thin, convex whorls, separated by deeply impressed suture (Fig. 1A, B View Figure 1 ); growth indeterminate. Shell whitish, with thick, velvety periostracum. Larval shell non-planktotrophic, ~ 2.75 low, convex whorls, with smooth, blunt nucleus; well-defined opisthocyrt riblets and spiral threads producing cancellate sculpture on subsequent whorls. Inferred transition to teleoconch marked by change in orientation of axial sculpture and slight expansion in whorl diameter (Fig. 3A, B View Figure 3 ). Teleoconch with six to eight distinct, flattened, regular, spiral cords, separated by broader grooves, and which extend onto base. Spiral ornament crossed by variably developed, well separated, weakly prosocline axial threads and growth increments; axial threads becoming obsolete on body whorl. Aperture broad, outer lip thin, sharp. Axis slightly gyrate, pervious; columellar plait lacking. Anterior canal short, slightly recurved.

Operculum [Lectotype]. Operculum thin, corneous, honey in color, thinning toward edges; paucispiral, nucleus eccentric, occupying ca. 31% of operculum length (Fig. 3E View Figure 3 ).

Radula [Lectotype]. Radula taenioglossate (Fig. 4A View Figure 4 ). Rachidian small, concave, narrow, tapering slightly to chevron-shaped base (Fig. 4B, C View Figure 4 ). Cutting edge flaring slightly, bearing single, prominent, blunt cusp and smaller irregular denticle at outer edge on each side. Radular membrane diagonally creased between rachidian and lateral teeth of each row. Lateral teeth robust, broad, with smooth inner edge of shaft curving posteriorly; cutting edge with prominent, dagger-like, pointed cusp, occasionally with small, rounded accessory denticle at inner base, and with small, blunt inner cusp (Fig. 4A, B View Figure 4 ). Marginal teeth long, slender, with cylindrical shafts and slight constriction below claw-like tips; cutting edges of inner and outer marginal teeth bearing unequal numbers of short, curving, smoothly conical cusps, with three to four cusps on inner marginal teeth, and two to three on outer marginal teeth (Fig. 4D, E View Figure 4 ).

Anatomy [Lectotype]. Foot elongate oval. Propodium large, triangular, presumably with deep, propodial groove (Fig. 5A View Figure 5 ), but depth could not be determined. Shallow furrow (= epipodial skirt) continuous with opercular lobe, evident along sides of foot sole, becoming obsolete in deep groove where propodium joins neck below snout. Foot sole divided longitudinally by deep medial cleft that deepens posteriorly before shallowing again along posterior quarter of sole. The presence and/or disposition of any glands could not be determined, although the epithelium in a broad swath on either side of the cleft is opaquely white and glandular in appearance.

Head with broad, muscular snout and long, tapering cephalic tentacles. Eyes conspicuous, on prominent ocular peduncles at outer bases of tentacles. Mantle edge smooth, with short siphon at left. Columellar muscle long, extending roughly one whorl to the level of mid-stomach. Mantle cavity one-half whorl in length. Mantle roof partially adhering to head and neck, not well preserved. Details of osphradium not readily observable. Ctenidium long, extending from siphon to base of mantle cavity. Hypobranchial gland well developed at left of rectum, releasing abundant mucus upon rehydration. Rectum broad, filled with sponge spicules, terminating in non-papillate anus well back from mantle edge. Pallial gonoduct presenting thin, non-glandular, open furrow below rectum. Penis lacking. Pericardial complex behind rear of mantle cavity compressed owing to retraction; details not observable. Bordered just behind by intestine.

Proboscis acrembolic, short. Jaws large, robust, dorsally flanking mouth. Buccal mass large with large odontophore occupying posterior two-thirds of buccal cavity behind jaws when retracted. Odontophore flattened, elongate, projecting upward from ventral posterior buccal mass, with flattened anterior end projecting against buccal roof behind jaws. Long, narrow, glandular subradular organ projecting between jaws from antero-ventral surface of odontophore. Moderately long radular ribbon emerging mid-ventrally near posterior end, embedded within acinous salivary glands posteriorly enclosing posterior buccal mass, and extending alongside anterior esophagus. Rather narrow mid-esophagus forming mid-esophageal gland with broad, glandular septae almost completely occluding lumen.

Stomach extending to ~ 1.5 whorls back from mantle edge, forming elongate chamber ~ 0.5 whorl in length, lying along left side of whorl ventrally surrounded by digestive gland. Stomach chamber broader posteriorly, narrowing anteriorly, filled with sponge spicules (Fig. 4F View Figure 4 ). Posterior esophagus entering stomach at left, near posterior quarter. Anterior end of stomach lying just behind reno-pericardial complex, large intestine curving right across body whorl, then turning anteriorly at base of mantle cavity on right side of body to form rectum. Digestive gland extending to anterior curve of intestine behind mantle cavity. Gonad dorsally overlying digestive gland at right of stomach.

Distribution and ecology.

Known only from the Kuril Islands (Fig. 2 View Figure 2 ) in 210-660 m, feeding on sponges.

Remarks.

The original description stated that the type material was dredged by the U.S. Bureau of Fisheries steamer Albatross in 229 fathoms (~ 419 m) off the Kuril Islands. The original, handwritten accession ledger at the USNM indicates that it was collected off Simushir Island at station 4803, which was sampled on 24 June 1906, 46°42'N, 151°45'E.

Only limited morphological observations were possible given the size and condition of the dried soft parts but agree well with those obtained for Pseudomohnia sp. (see below). Although undeveloped, the pallial gonoduct appears to lack accessory sperm storage pouches ( Fretter 1951; Houston 1985) and hence the dissected individual is inferred to be male. Details of the nervous system were not observable.

Analysis of the gut contents revealed the common occurrence of large (297 × 14 µm mean length × width) along with skinnier oxeas (248 × 6 µm) (Fig. 4F View Figure 4 ) which point toward a halichondriid sponge as the principal diet ( Demospongiae, Suberitida , Halichondriidae ) (K Ruetzler, pers. comm.).