Clenchiella minutissima ( Wattebled, 1884 )

Ponder, Winston F., Fukuda, Hiroshi & Hallan, Anders, 2014, A review of the family Clenchiellidae (Mollusca: Caenogastropoda: Truncatelloidea), Zootaxa 3872 (2), pp. 101-153 : 126-130

Clenchiella minutissima ( Wattebled, 1884)

Figures 2–4 , 14 , 15 , 33

Valvata minutissima Wattebled, 1884: 131 , pl. VI, fig. 8. Clenchiella papuensis Benthem Jutting, 1963: 438 –439, fig. 6a–c. Clenchiella sp.; Wilke et al., 2013: 725.

Clenchiellid n. gen. n. sp.; Criscione & Ponder, 2013: 1077. Clenchiella minutissima (Wattebled) ; Golding, 2014: 4.

Types and type localities. Valvata minutissima . Holotype: “L’arroyo [stream] de Long-Xuyen”, Conchinchine ( Vietnam) (Long-Xuyen is in An Giang Province, Mekong Delta region of southwestern Vietnam) (MNHNP, no number).

Clenchiella papuensis . Holotype: Robinson River Plantations near Cloudy Bay, E. of Port Moresby, Papua New Guinea (NHML, registration number not known). Paratypes “numerous”, 6 examined.

Material examined. Type material of V. minutissima and Cl. papuensis .

Singapore: Mandai River, mangroves behind estuary, 1° 25' 59”N, 103° 46' 01”E, 6 Sep. 1979. Coll. W.F. Ponder & D. Murphy (AMS C.463397, 20 spms). Same locality, mangroves near river mouth. 6 Sep. 1979. Coll. W.F. Ponder & D. Murphy (AMS C.462967, 7 spms).

Thailand: Thonburi, Klong Bang, O., 13° 45' 32.4" N, 100° 29' 13.1994" E, 29 Oct. 1966. Coll. R. Brandt & P. Temcharoe (AMS C.460379, 3 spms). Thonburi Province, Thonburi Town. Bang Phlad District. Coll. ‘S.M.R. Team’ 8 Feb. 1967 (Museum of Zoology, University of Michigan, 318936 4-6-268, 7 spms).

Australia, Western Australia: Port Hedland, Four Mile Creek, on leaf litter from pools at back of dense mangrove forest beside road, 20° 19' 18.66"S, 118° 38' 44.18"E, 0 2 Jul. 2012. Coll: R. Golding & M. Hill (AMS C.476007, 20+ spms).

Northern Territory: Darwin, East Point, Ludmilla Creek, on deep muddy sand, upper edge of mangroves, 12° 25' S, 130° 50' E, 14 Jun. 1976. Coll. W.F. Ponder (AMS C.412278, 3 spms); East Arm Boat Ramp, Elizabeth R., in pools near road amongst mangroves, 12° 32' 16" S, 130° 58' 38" E, 22 Mar. 2005. Coll. W.F. Ponder (AMS, C.463248, 15 spms); Darwin, mouth of Rapid Ck, 12° 22' 43" S, 130° 51' 37" E, 19 Mar. 2005 Coll. W.F. Ponder, V. Kessner & H. Fukuda (AMS C.452018, 4 spms); Rapid Creek, dead mangrove leaves in pools, 12° 23' 2" S, 130° 51' 56" E, 14 Aug. 2010. Coll. F. Criscione (AMS C.475884, 10 spms); Arnhem Land, Liverpool River mouth, 12° 5' S, 134° 12' E, 5 Jun. 1976. Coll. W.F. Ponder (AMS C.463108, 4 spms).

Queensland: Magnetic Is, Ned Lee Creek, under wood in pools in middle of mangroves, 19° 10' 5" S, 146° 48' 47" E, 22 Sep. 1980. Coll. W.F. Ponder & Ian Loch (AMS C.412277, 3 spms); Magnetic Island, Cockle Bay, Ned Lee Creek, pools in middle mangroves with leaf litter, rocks and sticks, 19° 9' 59" S, 146° 49' 4" E. 24 Sep. 2011. Coll. R. Golding & S.A. Clark (AMS C.470868, 1 spm); Port Douglas, 16° 29' S, 145° 27' 33" E, 1960 Coll. B. Page. (AMS C.462958, 1 spm); Townsville, N side of Ross River, 1 km from mouth, mainly under leaves in mangroves, 19° 17' S, 146° 48' 53" E, 31 May 1977. Coll. I. Loch & P.H. Colman (AMS C.412276, 2 spms); Brisbane River, Breakfast Creek, 27° 26' 00" S, 153° 03' 00" E, 1862. Coll. J. Brazier (AMS C.63868, 2 spms); Brisbane, Nudgee Beach, pool in upper mangroves near road, below stormwater outlet; leaf litter; also sand flat in front of mangroves, 27° 20' 38" S, 153° 5' 57" E, 12 Oct. 2011. Coll. R. Golding & S.A. Clark (AMS C.470975,>20 spms); Ningi Creek, stormwater drainage gutter leading to mangrove forest; leaf litter in water and damp litter, 27° 3' 18" S, 153° 4' 24" E, 12 Oct. 2011 Coll. R. Golding & S.A. Clark (AMS C.470966, 10 spms); Tin Can Bay, corner of Toolara and Trevally Streets, pool of brackish water near stormwater outlet and damp leaf litter, 25° 55' 19" S, 153° 30" E, 11 Oct. 2011 Coll. R. Golding & S.A. Clark (AMS C.470959, 20+ spms); Turkey Beach, near water treatment plant, sparse, small-leaved mangroves (multi-stemmed) with small pools and moist leaf litter on surface of mud, 24° 5' 17" S, 151° 38' 50" E, 10 Oct. 2011. Coll. R. Golding & S.A. Clark (AMS C.470947, 1 spm); Sarina Beach, pools in mangrove forest with leaf litter and roots, 21° 23' 30" S, 149° 18' 42" E, 9 Oct. 2011. Coll. R. Golding & S.A. Clark (AMS C.470933, 20+ spms); Sarina Beach, N end behind Coral Point, seepage in mangroves, 21° 22' 30" S, 149° 19' E, 29 May 1977. Coll. I. Loch & P. H. Colman (AMS 413700, 7 spms); Tin Can Bay, mouth of Crab Creek, sandy mud in upper mangroves with damp leaf litter from small-leaved, multistemmed mangroves, 25° 55' 52" S, 153° 49" E, 11 Oct. 2011 Coll. R. Golding & S.A. Clark (AMS C.470954, 14 spms); Bowen, Magazine Creek, flat area with mangroves and many pools containing roots and litter; also partially buried logs; area between canals, 20° 54" S, 148° 15' 40" E, 5 Oct. 2011. Coll. R. Golding & S.A. Clark (AMS C.470910, 20+ spms); Hervey Bay, River Heads, muddy path through mangrove forest, 25° 24' 3" S, 152° 54' 54" E, 20 Sep. 2011. Coll. R. Golding & S.A. Clark (AMS C.470846, 1 spm); Hervey Bay, Point Vernon, Gatakers Bay, dead green filamentous algal mat in clearing in beach mangroves, 25° 15' S, 152° 49' E), 23 Oct. 1976. Coll. I. Loch (AMS C.41367, 3 spms); Hervey Bay, Pulgul Creek, 0.5 km S of Urangan Boat Anchorage, under leaves & timber & in reeds at back of mangroves, 25° 18' 36" S, 152° 55' E, 24 Oct. 1976. Coll. I. Loch & B. Duckworth (AMS C.413699, 6 spms); Boyne Is, S of Gladstone, on dead leaves, among mangroves, 23° 55' 47" S, 151° 21' E, 22 May 1992. Coll. G.A. Clark (AMS C.378421, 5 spms); Cape Gloucester, S end Dingo Beach, under stones in seepage in mangroves, 20° 5' S, 148° 30' 30" E, 30 May 1977. Coll. I. Loch, P. H. Colman & R. Creese (AMS C.413698, 2 spms); Three Mile Creek, Palarenda, Townsville, in creek on leaves and roots, 19° 12' 36" S, 146° 46' 30" E, 23 Feb. 1997. Coll. W. F. Ponder & J. Leroi (AMS C.410968, 3 spms); Lucinda, at outer edge of mangroves, near pier, 18° 32' S, 146° 18' 23" E, 27 Sep. 1980. Coll. W.F. Ponder (AMS C.425065, 2 spms); Central Lakes, Townsville, along edges, under palm frond and amongst mussels, 19° 16' S, 146° 49' E, May 1992. Coll. G.A. Clark (AMS C.463391, 20 spms); Moreton Bay, Wellington Point, mangroves, 27° 28' S, 153° 14' E, 1978 (AMS C.412279, 2 spms); Pine River, under bark on log in mud, Sep. 1975. Coll. J. McNalty (AMS C.187053 [SEM]).

Distribution. Based on current records, this is the most widespread of all clenchiellid species (see Figure 14 ). It is known to occur in tropical northwestern, northern and eastern Australia, Singapore, Papua New Guinea, Vietnam and Thailand.

Description. Shell. Minute (up to 1.9 mm in maximum diameter; Table 3), spire flat ( Fig. 2 ). Protoconch not elevated above spire, about 1.6 whorls, protoconch I of about 2/3 whorl, with three widely spaced weak spiral threads on first half whorl, remainder smooth, no varix at termination; protoconch II smooth except for indistinct growth lines, terminated by weak varix. Teleoconch of about 1.8 convex whorls, surface usually sculptured with distinct, spiral lirae with interspaces up to twice their width, about 10 at end of penultimate whorl, innermost spirals become subobsolete on last whorl, rest becoming weak to subobsolete on last third of last whorl; finer, close-spaced weak, irregularly-spaced commarginal growth lines intersect spirals. Periphery evenly convex, spiral lirae weaker on peripheral area. Base evenly convex, umbilicus wide (more than half width of base), spiral sculpture continuous within in penultimate whorl, although very weak to absent in some, subobsolete to obsolete on inner part of umbilicus in first half of last whorl; spirals generally subobsolete to obsolete over all of base in last half of last whorl, although quite strong in some. Sutures impressed. Aperture near circular, with simple, slightly thickened peristome, external varix well developed. Colour variable, periostracum generally bright reddish brown to dark red, amber in some specimens, sometimes lighter toward varix.

Operculum. Horny, near circular, of approximately 8 slowly increasing whorls ( Fig. 4 E–F). Interior with narrow, raised edge to muscle attachment area close to thickened, ridge-like columellar edge. Small slightly to moderately raised third to half-spiral projection in middle part.

Head-foot. Similar to Clenchiella iriomotensis ( Fig. 15 A–C).

Ctenidium . About 20 filaments.

Radula . Typical of family. Cusp formulae 4+1+4, 2–3+1+3–4, 20–22, 21–24. Median cusps of central and lateral teeth long (about 1.5 times as long as adjacent cusps), narrowly triangular, pointed; other cusps on all teeth slender, pointed ( Fig. 5 C, D).

Gut. Anterior oesophagus with two folds; rectum with two tight loops ( Fig. 15 D).

Penis. Small, rather short, wide distally and narrow proximally; on distal portion four large (5 in some, see remarks), distinct, round swellings, two on right edge, another on middle part ( Fig. 15 E–G). Tapering papilla arising from central part of penis, with pointed tip. Penial duct slightly undulating.

Oviduct. Albumen gland about as long as capsule gland ( Fig. 15 I, J). Coiled oviduct narrow, with single large coil. Seminal receptacles moderate in length, about equal in size. Ventral channel long, distinctly curved. Bursa large, lying on left side of oviduct gland, about half behind posterior wall of mantle cavity; posterior part wide, narrows anteriorly 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. Similar to Cl. bicingulata .

Remarks. This species differs from the other species of Clenchiella in having the dorsal and ventral keels extremely weak to absent, with most specimens appearing to be uniformly spirally striate. In a few specimens the spiral threads are also very weak to absent (e.g., in one lot from Nudgee Beach, near Brisbane AMS C.470975, which is genetically identical to spirally ribbed specimens). Comparison of shells from Darwin, Port Hedland, Queensland and Thailand with the type specimen of V. minutissima from Vietnam shows that they are virtually indistinguishable, indicating that this taxon has a broad distribution in the Indo-West Pacific region. Furthermore, Cl. minutissima is very similar to one of two new taxa introduced from Papua New Guinea by Benthem Jutting (1963), Cl. papuensis , and we treat them as synonyms. Benthem Jutting (1963: 439) noted that “it was not impossible” that Cl. papuensis may be Valvata microscopica . However, a “co-type” of V. microscopica figured in Annandale & Kemp (1916) shows that it has a narrower umbilicus and lacks a varix, and we therefore regard it as a separate taxon (see below). Brandt (1974: 69) synonymised Cl. papuensis and Cl. microscopica with V. minutissima and recorded Cl. microscopica from several locations in Thailand and Burma. However, his figure does not resemble any of these taxa, having a dorsal and ventral keel somewhat similar to that seen in Cl. bicingulata . Specimens from Brandt in the USNM and AM collections are similar to V. minutissima and we have been unable to examine any of his specimens that resemble his figured keeled specimen.

Cl. minutissima differs from the other congeners in having a flat spire, wide umbilicus, fine spiral striae, and lacks the strong mid-dorsal and mid-ventral spiral cords characteristic of the other species of Clenchiella . It is possible that more than one species is contained within our current concept of this species, but this cannot be further resolved until comparative anatomical or molecular studies are carried out on specimens from other parts of its supposed range.

In lacking distinct dorsal and ventral keels, the shell of this species is superficially similar to that of some species of Coliracemata n. gen. (see below). However, like other species of Clenchiella , the head-foot has distinct black pigment, including the near distal band on each cephalic tentacle, the shell has a prominent apertural varix, and the smooth penial glands are also typical of Clenchiella , although this species has 4–5 (see below) rather than the usual 2–3.

Specimens from Magnetic Island, Queensland are attributed to this species and are indistinguishable in shell characters. The pigmentation of the living animal is similar and the penis has smooth penial glandular lobes, but five instead of four. We know little of the potential variation in this character so this difference may or may not be significant. Another clenchiellid, a species of Coliracemata n. gen., occurs in the Townsville area and is similar in shell characters (see below).

Partially uncoiled shells were observed in some specimens from Tin Can Bay and Bowen, Queensland (AMS C.470954 and C.470910 respectively), in which the whorls are not in contact with the preceding whorls. The specimens are otherwise identical with typical Cl. minutissima .

Figures

FIGURE 2. Type specimens of Clenchiella minutissima (from left towards right: dorsal, lateral and ventral view respectively). A – C, holotype of Clenchiella papuensis, synonymised with Clenchiella minutissima herein (NHML, registration number not known; shell diameter 1.69 mm); D – F, syntype of Clenchiella minutissima (MNHNP; shell diameter 1.70 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 14. Type localities of Clenchiella victoriae, Cl. bicingulata, Cl. varicosa, Cl. iriomotensis, and all recorded localities of Cl. minutissima (type locality Vietnam).

FIGURE 15. Head-foot, digestive, and reproductive characters of Clenchiella minutissima (AMS C. 452018). A, head-foot, lateral view; B, head, dorsal view; C, tapering posterior end of foot, dorsal view; D, external view of intestine and rectum; E, head with penis, dorsal view, F, G, penis; H, ovary; I, female reproductive system shown from anterior (left) to posterior (right); J, 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; db, distal pigment band on cephalic tentacle; fa, female aperture; int, intestine; pd, penial duct; pl, penial lobe; ppw, position of posterior wall of mantle cavity; sr, seminal receptacle.

FIGURE 33. Maximum Likelihood phylogeny of the Clenchiellidae based on the partial COI mitochondrial gene. Bootstrap support of> 80 % is indicated by branch nodes. The identifiers ‘ a, b’ by the branch of Clenchiella varicosa n. sp. indicate that identical sequences from the same locality were obtained.