Clenchiella bicingulata, Ponder, Winston F., Fukuda, Hiroshi & Hallan, Anders, 2014

Ponder, Winston F., Fukuda, Hiroshi & Hallan, Anders, 2014, A review of the family Clenchiellidae (Mollusca: Caenogastropoda: Truncatelloidea), Zootaxa 3872 (2), pp. 101-153 : 115-119

Clenchiella bicingulata n. sp.

Figures 1 , 3–9 , 14

? Clenchiella microscopica ; Brandt, 1974: 69 (in part), pl. 6, fig. 86 [not of Nevill, 1877]. Clenchiella cf. microscopica ; Swennen et al., 2001: 114, fig. 320 [not of Nevill, 1877].

Etymology. bi -: two, cingulus: girdle (Latin).

Types and type locality. Holotype: Sembawang Estuary, opposite Admiralty Road, Singapore. In pools in mangroves, 1°27' N, 103°49'01" E, 5 Sep. 1979. Coll. W.F. Ponder and W.F. Ponder Jr (AMS, C.462959). Paratypes: same locality (AMS, C.460375, 20+ spms; AMS, C.463396, 20+ spms).

Material examined. Type material: Mandai River, in mangroves behind estuary, 1° 26' N, 103° 46' E, 6 Sep. 1979. Coll. W.F. Ponder, W.F. Ponder Jr and D. Murphy (AMS C.269814, 6 spms).

Sembawang Estuary, opposite Admiralty Road, on ground amongst mangroves, in back of estuary, 1° 27' N, 103° 49' E, 9 Sep. 1979. Coll. W.F. Ponder and W.F. Ponder Jr (AMS C.460374, 9 spms); Same locality, opposite pools and creeks in back of estuary, 1° 27' N, 103° 49' E, 9 Sep. 1979. Coll. W.F. Ponder and W.F. Ponder Jr (AMS C.460376, 1 spm).

Distribution. Known from mangroves in Singapore and possibly Thailand ( Brandt 1974), suggesting that it may be more widespread in southeast Asia.

Description. Shell. Small (up to 2.2 mm in maximum diameter; Table 3), spire flat ( Figs 1 D–F and 3A–C). Protoconch not elevated above spire, about 1.5 whorls, surface slightly worn in available specimens but protoconch I appears to have about 4 widely spaced spiral threads and terminated by narrow, indistinct varix; protoconch II about 0.7 whorl, apparently smooth, terminated by weak varix. Teleoconch of about 2.0–2.2 whorls, rounded except for angulations from two prominent carinae, one mid-dorsal, one mid-basal; whole surface with distinct spiral sculpture: on inner dorsal part of shell spirals weak to subobsolete, with linear interspaces; on outer side of dorsal carina spiral lirae have interspaces 2–3 times their width while on periphery lirae slightly weaker, with narrow interspaces; about 4–8 lirae on outer side of dorsal carina and about 9–11 spiral threads on inner side at end of penultimate whorl; irregularly spaced commarginal growth lines cross spirals. Periphery evenly convex, spiral lirae weaker and closer together in middle part of peripheral area, similar in strength and spacing on lower peripheral area and base as on outer dorsal surface. Base evenly convex except for mid-basal carina, umbilicus wide (more than half width of base), basal spiral sculpture continuous within. Sutures moderately impressed. Aperture near circular, with simple, slightly thickened peristome, external varix well developed, narrow, slightly behind edge of aperture. Periostracum light reddish brown, shell white.

Operculum. Horny, near circular, of 4–5 slowly increasing whorls ( Fig. 4 A, B). Interior with narrow, raised edge to muscle attachment area close to slightly thickened, ridge-like columellar edge and small raised nipple-like projection in middle.

Head-foot. Living animal (Mandai, Singapore) very similar to Cl. victoriae , with black pigment on snout except for median line which may not be as densely pigmented, and black band on distal half of each pale yellow tentacle little posterior to tip. Head and neck grey to black. Foot cleft anteriorly and expanded laterally as pointed extensions; evenly tapering posteriorly. Anterior edge of foot with black pigment; grey pigment laterally along dorsal sides of foot. Opercular lobe thin, inconspicuous. Sole translucent white except for scattered denser mucous gland cells and grey pigment showing through. Long, stationary cilia on distal ends of tentacles.

Ctenidium . About 30 filaments.

Radula . Typical of family. Cusp formulae 4–5+1+4–5, 4+1+4, 16–18, approx. 15, median cusps of central and lateral teeth long (about twice as long as adjacent cusps), narrowly triangular, pointed; other cusps on all teeth slender, pointed ( Fig. 5 A, B).

Gut. Anterior oesophagus with two very strong folds; rectum with one tight loop ( Fig. 6 ).

Penis. Moderately long, wide distally and proximally ( Figs 7 A, B and 8A); distal portion with three glandular lobes visible dorsally: on right edge two equally-sized large, round lobes, one of which is continuous ventrally with distal lobe on left; in addition, on left edge one small swelling very close to tip. Tip narrow, blunt, with no distinct papilla. Penial duct slightly undulating.

Oviduct. Albumen gland about as long as capsule gland ( Fig. 7 E, F). Coiled oviduct wide, with single large coil. Seminal receptacles short, about equal in size. Ventral channel very short, straight. Bursa large, lying on left side of oviduct gland, about 2/3 behind posterior wall of mantle cavity; posterior part wide, narrows anteriorly to open to strongly curved bursal duct angled posteriorly at about 45˚ on left side of capsule gland. Genital opening simple, on ventral edge of meeting point of ventral channel and bursal duct.

Nervous system. Pleural-supraoesophageal connective extremely long. Suboesophageal ganglion longer and wider than left pleural ganglion ( Fig. 9 ).

Remarks. This species is somewhat similar to Cl. victoriae but the shell differs in being smaller, more depressed, the basal keel being weaker, as well as the spiral sculpture being less pronounced on the dorsal surface. In addition, the main penial lobe is extended ventrally so that it gives the appearance of a third lobe when viewed dorsally. The coiled oviduct appears to be wider in Cl. bicingulata than in the other clenchiellids studied here.

Brandt (1974) recorded Clenchiella microscopica from Thailand and Swennen et al. (2001) recorded and figured Cl. cf. microscopica . We have examined only one lot from Brandt’s collections, and that lot is not conspecific with the species he illustrated but appears to be Clenchiella minutissima (see below). The shell of the specimen he illustrated resembles Cl. bicingulata , as does the figure of Cl. cf. microscopica given by Swennen et al. (2001), and we have tentatively identified these as such pending a more detailed comparison. Brandt noted that the penis in the specimens he examined was short and blunt and had “one large, but low glandular lobe”, features that do not agree with Cl. bicingulata or Cl. minutissima . In addition, his description of the animal does not mention the distinctive black bands on the tentacles characteristic of species of Clenchiella , although he mentioned “a few darker pigment spots, particularly on the rostrum” (p. 69). His radular description agrees reasonably well with Cl. bicingulata but differs in having a smaller number of cusps on the lateral and inner marginal teeth. Further, his description differs from the radula of Cl. minutissima in having fewer cusps on both marginal teeth. Thus it is clear that two species were included in Brandt’s concept of microscopica . However, his description of the animal appears to be based on another, probably as yet unnamed taxon.

Figures

FIGURE 1. Holotypes of species of Clenchiella with distinct keels (from left towards right: dorsal, lateral and ventral view respectively). A – C, Clenchiella victoriae (USNM 488534; shell diameter 2.1 mm); D – F, Clenchiella bicingulata n. sp. (AMS C. 462959; shell diameter 1.97 mm); G – I, Clenchiella varicosa n. sp. (AMS C. 460738; shell diameter 1.96 mm); J – L, Clenchiella iriomotensis n. sp. (AMS C. 445413; shell diameter 1.94 mm).

FIGURE 3. Shell details of keeled Clenchiella spp. A – C, dorsal, lateral and ventral view of Clenchiella bicingulata (AMS C. 460375); D – F, dorsal, lateral and ventral view of Clenchiella varicosa (AMS C. 462993; specimens from Taiwan); G, protoconch, Clenchiella varicosa (Taiwan); H-L, Clenchiella iriomotensis (AMS C. 445413); H, I, protoconch, J – L, dorsal, lateral and ventral views of shell; J, L, juveniles, K, adult.

FIGURE 4. External and internal view (left to right) of opercula. A, B, Clenchiella bicingulata (AMS C. 460375); C, D, Clenchiella iriomotensis (AMS C. 445413); E, F, Clenchiella minutissima (AMS C. 452018). Scale bars: 200 µm.

FIGURE 5. Radulae of Clenchiella bicingulata (AMS C. 460375) and Clenchiella minutissima (AMS C. 452018). Clenchiella bicingulata: A, central, lateral and marginal teeth; B, central and lateral teeth. Clenchiella minutissima: C, central, lateral and marginal teeth; D, central and lateral teeth.

FIGURE 6. Mantle cavity and stomach of Clenchiella bicingulata (AMS C. 460375). A, B, internal (A) and external (B) views of roof of mantle cavity; C, stomach, showing digestive gland stippled. Scale bars: 500 µm. Abbreviations: ac, anterior chamber; ct, ctenidium; fp, faecal pellet; hg, hypobranchial gland; in, intestine; o, oesophagus; od, pallial oviduct; os, osphradium; pc, posterior chamber; r, rectum; ss, style sac.

FIGURE 7. Reproductive anatomy of Clenchiella bicingulata (AMS C. 460375). A, penis, ventral view; B, penis, dorsal view; C, testis; D, ovary; E, female reproductive system shown from anterior (left) to posterior (right); F, female reproductive system shown from posterior (left) to anterior (right). Scale bars: 200 µm. Abbreviations: ag, albumen gland; bc, bursa copulatrix; cb, cut base of penis; cg, capsule gland; co, coiled oviduct; pd, penial duct; pl, penial lobe; ppw, position of posterior wall of mantle cavity; sr, seminal receptacle; sv, seminal vesicle.

FIGURE 8. Penes of A, Clenchiella bicingulata (AMS C. 460375) and B, Clenchiella varicosa (AMS C. 462993). Scale bars: 100 µm.

FIGURE 9. Nervous system of Clenchiella bicingulata (AMS C. 460375). A, dorsal view; B, left lateral view; C, dorsal view of pedal ganglia; D, right lateral view. Scale bars: 200 µm. Abbreviations: bm, buccal mass; cc, cerebral commissure; cg, cerebral ganglion; lpg, left pleural ganglion; mtg, metapodial ganglion; oes, oesophagus; pg, pedal ganglion; prg, propodial ganglion; rpg, right pleural ganglion; sg, salivary gland; sog, suboesophageal ganglion; spo, supraoesophageal ganglion; stc, statocyst.

FIGURE 14. Type localities of Clenchiella victoriae, Cl. bicingulata, Cl. varicosa, Cl. iriomotensis, and all recorded localities of Cl. minutissima (type locality Vietnam).