Trochomorphidae

Hyman, Isabel T. & Ponder, Winston F., 2010, A morphological phylogenetic analysis and generic revision of Australian Helicarionidae (Gastropoda: Pulmonata: Stylommatophora), and an assessment of the relationships of the family 2462, Zootaxa 2462 (1), pp. 1-148 : 116-117

Family Trochomorphidae

Remarks. Hausdorf (1998) gave the following synapomorphies for this group: stimulator absent and penial sheath absent (the latter given with a question mark). None of the species included in the current study had a stimulator, but penial sheaths were observed in all but Trochomorpha rubens . However, in all species the penial sheath was closed at the distal end, not open as in Helicarionidae . Schileyko’s (2002a) concept of Trochomorphidae was based on a well-developed, solid, trochiform to lenticular shell with the last whorl angulated or carinated, an undivided sole of the foot and aspects of the reproductive system.

Trochomorpha rubens and Videna planorbis and are typical trochomorphids. They share a number of characters, including a thick, strongly keeled, trochiform shell and a reproductive system with the bursa copulatrix at the junction of the penis and free oviduct, no epiphallic caecum or flagellum and a penial sheath absent ( T. rubens ) or if present ( V. planorbis ), fused to the epiphallus at the distal end. Spermatophores were not found in either species. However, soft spermatophores have been recorded from two species of Videna and possibly from one species of Trochomorpha ( Baker 1941a) , so it is possible that spermatophores were not found in T. rubens and V. planorbis simply because they are fragile and break down quickly in the spermatheca. In addition, these species share a distinctive radula, in which the central tooth has no ectocones and the mesocone is triangular and longer than the tooth base. The lateral and marginal teeth have no endocones and very small ectocones. Finally, the caudal apparatus of both species is clearly Muratov’s (1999) zonitid type rather than his helicarionid type.

Some of the above characters are shared by Orpiella concavum and Dendrotrochus eva eva . The latter taxon shares the trochiform shell with a strong keel, while O. concavum has a rounded whorl profile. Both species have a similar reproductive system to T. rubens and V. planorbis , and both have a soft-walled spermatophore. Neither species shares the distinctive radula type seen in T. rubens and V. planorbis ; in addition, neither appears to have a zonitid caudal apparatus (see Figure 35 ). Muratov (1999) includes both Orpiella and Dendrotrochus in Trochomorphidae on the basis of their zonitid caudal apparatus and soft-walled spermatophore. He figures the caudal apparatuses of V. gouldiana (Pilsbry, 1901) , T. xiphias (Pfeiffer, 1856) , T. swainsoni ( Pfeiffer, 1846) and D. cleryi (Recluz, 1851) ; all appear to be the zonitid type and all are very similar, in contrast with the caudal apparatus of D. eva eva figured in the current study ( Figure 35F ).

Based on these characters, Orpiella and Dendrotrochus cannot be placed unequivocally in Trochomorphidae . The absence of a hard spermatophore indicates that these genera are not members of Helicarionoidea . Hausdorf (1998) placed Orpiella and Dendrotrochus in Chronidae (Gastrodontoidea) , a family defined by the presence of a flagellum and distinct minor venation on the roof of the mantle cavity (lung). However, neither of these characters is present in O. concavum or D. eva eva . Schileyko (2002b) placed Dendrotrochus in Trochomorphidae and Orpiella in Helicarionini (Helicarioninae, Helicarionidae ). Hyman et al. (2007) showed that O. concavum grouped with Videna planorbis (Trochomorphidae) in a phylogenetic analysis based on the mitochondrial gene COI.

Overall, Orpiella and Dendrotrochus appear to have strongest similarities to Trochomorphidae and are therefore we tentatively place them there.

Based on our analysis, the key characters of Trochomorphidae are:

Shell not reduced, usually trochiform, with keeled or angulate periphery. Genital system oviparous; bursa copulatrix inserted at junction of penis and free oviduct; stimulator absent; epiphallic retractor caecum and flagellum absent; small lime-sac present in some taxa. Spermatophore absent or if present, soft-walled.

Description. Shell present, not reduced. Shell shape usually trochiform; whorl profile with keeled or angulate periphery. Shell sculpture variable. Mantle laps absent; mantle lobes absent or very small. Sole of foot tripartite or undivided; caudal apparatus formed from curled up sole ( Muratov’s 1999 helicarionid type) or with sole longer than foot ( Muratov’s 1999 zonitid type). Kidney unilobed; mantle with no visible minor blood vessels. Genital system oviparous. Bursa copulatrix inserted on vagina or at junction of penis and free oviduct. Stimulator absent. Penial sheath absent or present; if present, closed at distal end. Epiphallic retractor caecum absent; epiphallic flagellum absent; small lime-sac present in some taxa. Spermatophore long softwalled tube closed at both ends (only observed in Dendrotrochus and Orpiella ). Radula relatively long and narrow. Central tooth with no ectocones and triangular mesocone or with small ectocones and lanceolate mesocone. Lateral and marginal tooth fields distinguishable; tooth rows straight.

Figures

FIGURE 35. External morphology of caudal regions. A. Kalidos balstoni, AM C205303. B. Macrochlamys petrosa, AM C205303. C. Everettia sp., BMNH 20020188. D. Greenwoodoconcha nux, AM C433375. E. Videna planorbis, FMNH 160957. F. Dendrotrochus eva eva, FMNH 160957. Scale bars 1 mm (D), 2 mm (E–F), 5 mm (A–C).