Pseudotricula Ponder, 1992

Ponder, W. F., Clark, S. A., Eberhard, S. & Studdert, J. B., 2005, A radiation of hydrobiid snails in the caves and streams at Precipitous Bluff southwest Tasmania, Australia (Mollusca: Caenogastropoda: Rissooidea: Hydrobiidae s. l.),, Zootaxa 1074 (1), pp. 1-66 : 9-11

Genus Pseudotricula Ponder, 1992

Type species: Pseudotricula eberhardi Ponder, 1992 (original designation).

Description

Shell. Moderate to large in size (adults 1.7 to 4.4 mm SL), conical. Protoconch of about 1.5 whorls, typically sculptured with small, close pustules with some coalesced into weak, irregular radial ridges; separation of protoconch from teleoconch distinct, with varix­like border. Teleoconch with spire much longer to slightly shorter than length of aperture. Aperture ovate, slightly angled and typically channelled posteriorly, inner lip attached to parietal wall or partially to completely detached, although never markedly so; usually lower part raised well above base. Outer lip usually prosocline, with terminal growth, typically markedly expanded and flared, simple in some species; weak external varix present in one species ( P. elongata n. sp.). Periphery rounded, base simple, imperforate in both adults and juveniles. Usually semi­opaque to opaque, white, sometimes yellowish or brownish; with a thin pale yellowish periostracum.

Operculum. Ovate, paucispiral, flat, columellar edge slightly convex, outer edge strongly convex; outer surface simple, paucispiral, nucleus markedly eccentric; inner surface with weak ridges (probably representing reduced pegs) or (more often) white smear only.

Radula. Central teeth large, cutting edge broad, indented mid dorsally, with 4–5 cusps on either side of narrow sharp median cusp; narrow, thin lateral projections emerge at about 45º from mid laterally; base with short, rounded basal tongue not extending beyond lateral projections; two small to moderate basal cusps emerge from ventral face of tooth on either side of basal projection, innermost largest. Lateral teeth with short cutting edge, about 3–6 small cusps on inner side of narrow median cusp and 4–7 small cusps on outer side; neck prominent, near vertical; lateral flange about twice as long to slightly less than twice as long as cutting edge; prominent U­shaped projection on base below cutting edge; inner edge short, inner side of base excavated. Inner marginal teeth with 15–33 tiny cusps on rather wide cutting edge (ratio of cutting edge to shaft on inner marginal teeth about ¼; sides approximately parallel, outer edge thickened. Outer marginal teeth narrow, thickened on inner edge, distal end with 14–32 minute cusps; ratio of cutting edge to shaft about ¼.

Head­foot. Simple, unpigmented, with long cephalic tentacles, unpigmented eyes present in weak bulges at outer bases of tentacles; snout of moderate length, tapering, weakly bilobed distally. Foot short, rounded posteriorly.

Non­genital anatomy. Pallial cavity elongate, osphradium large and oval, towards posterior end of ctenidium; ctenidium with small ctenidial filaments and long efferent vein (ctenidium occupies only anterior ½ of pallial cavity). Hypobranchial gland variably developed. Kidney and pericardium usually about ½ in pallial roof; renal gland orientated longitudinally. Stomach with anterior and posterior chambers about equal or posterior smaller; style sac moderately long; no posterior caecum. Rectum with long S­shaped coil; overlying but not indenting pallial oviduct.

Male reproductive system. Prostate gland about ½ within pallial cavity; compressed to oval in section, with very thin ventral wall; pallial vas deferens opens at about ⅓–½ length of pallial portion. Penis located on right side of head well behind base of right tentacle; lacking glands but has an inconspicuous to moderately developed swelling in the distal portion just behind a papilla­like distal end; distal portion long and tapering; medial part simple and parallel sided; basal part wide to moderate.

Female reproductive system. Ovary simple sac; coiled oviduct smooth, firm, not embedded in connective tissue, initially inverted U­shaped, usually straight distal to seminal receptacle (one species with bend), usually reaching posterior end of bursa (sometimes a little more or less) then sharply bent to run anteriorly; Seminal receptacle ovoid to pyriform, with short duct, opening to oviduct, located opposite middle to ventral part of left side of bursa copulatrix. Bursa copulatrix rather large, ovoid to pyriform, posterior to albumen gland except for small overlap on right side, either just behind posterior pallial wall or extending in front of it; bursal duct arises from anterior or ventroanterior wall, simple to undulating, joins oviduct dorsally at posterior pallial wall or in front of it as far anterior as junction of albumen and capsule glands. Common duct straight. Albumen gland ½ or more within pallial roof, shorter to longer than capsule gland. Capsule gland compressed­oval in section, divided into three glandular zones, short anterior and posterior translucent white zones and long yellowish to orange middle zone; anterior end blunt to steeply tapering; genital opening short, terminal to slightly anterior of capsule gland. Ventral channel extended into weakly to moderately developed vestibule anteriorly. No brood pouch.

Distribution and habitat

Species of Pseudotricula are restricted to stream and seep habitats in the Precipitous Bluff caves.

Remarks

The relationships of this genus with Nanocochlea Ponder and Clark, 1993 are now well established, with molecular data ( Perez et al. 2005) showing they are sister taxa. Anatomically the two genera are also very similar. They share the same type of ctenidium which only occupies the anterior half of the pallial cavity and with the filaments reduced in size and narrower than the normal broadly­triangular type. Other common features include the long, S­shaped rectal coil, unpigmented eyes, stomach morphology and genital anatomy. It could be argued that the fauna from Precipitous Bluff described herein shows a transition between the type species of Nanocochlea and Pseudotricula , both of which lie at the extremes of what perhaps could be regarded as a single genus. The main differences between Nanocochlea and Pseudotricula are shell characters. The shell in typical Pseudotricula is broadly conical in shape, rather than elongate conic to pupiform, with a relatively large aperture that typically bears an expanded, prosocline outer lip. Other differences are detailed below under Nanocochlea .

The shell differences between the type species of Nanocochlea and Pseudotricula are considerable and their close relationship was not fully realised at the time of their description. Anatomically the two genera are very similar and this similarity is reflected in their sister­group relationship ( Perez et al. 2005). The paper describing Pseudotricula is listed as “in press” in Ponder et al. (1993), but it was actually published shortly before in 1992.

The species of Pseudotricula are rather uniform in anatomy, radular and opercular morphology, the latter differing only in the presence or absence of a peg on the inner surface. However, the species that we recognise here are readily discriminated on shell morphology (see below).

The penial swelling was not noted in the original description of P. eberhardi because it is very weakly developed in that species (confirmed by re­examination). It is, however, present in the other species of Pseudotricula and an identical structure is also seen in several species of Nanocochlea .