Helicarionidae Bourguignat, 1877

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 : 20-21

Family Helicarionidae Bourguignat, 1877

Remarks. The combination of characters given in the description is unique for this family but, nevertheless, the only unifying character for Helicarionidae as currently recognised is the absence of a stimulator. None of the Australian species show even the slightest vestige of a stimulator on the male or female side. Solem (1966) believed that this group primitively lacked the stimulator but Hausdorf (1998) argued for the homology of the stimulators of all Limacoidea s. l., suggesting that the stimulator has been lost in all Helicarionidae . If this has occurred, the lack of any vestigial traces of this structure may indicate that the loss was homologous and occurred once in the ancestral helicarionid. As the stimulator has apparently been lost multiple times in other groups, including members of Urocyclidae ( Van Mol 1970a; van Goethem 1977; Hausdorf 1998; Schileyko 2002b) and Ariophantidae ( Hausdorf 1998; Schileyko 2002b, 2003a), this convergent loss makes it difficult to determine the status of the three families when their classification relies so heavily on this one structure.

The description of Helicarionidae given below contrasts with that given by Schileyko (2002b), who made extensive changes to the classification of Limacoidea s. l., especially in the definitions of Helicarionidae and Ariophantidae . The key characters he used to distinguish the two groups included the epiphallic flagellum (axial filament absent and cryptae rare in Helicarionidae , axial filament and cryptae both present in Ariophantidae ); the attachment of the penis retractor muscle (to the penis or epiphallus but never the epiphallic caecum in Helicarionidae , to the epiphallic caecum in Ariophantidae ); and the stimulator (where present, penial or atrial in Helicarionidae , vaginal in Ariophantidae ). In the current study, it is demonstrated that the flagellum is absent in a few Helicarionidae , but where it is present, it always has an axial filament (including in the type genus, Helicarion ). Internal cryptae in the flagellum are not seen in every species but are present in members of Helicarion and several other genera. The penis retractor muscle attaches to the tip or the middle or the epiphallic caecum in many cases (e.g., Nitor ), but in some taxa attaches to the junction of the epiphallus and the caecum (e.g., Westracystis ) or if the caecum is absent, to the epiphallus (e.g., Helicarion ). The attachment site can vary within a genus (e.g., Stanisicarion ), although this is uncommon. None of the helicarionid taxa examined here had a stimulator, so Schileyko’s third character cannot be assessed. However, the distinction he makes between Helicarionidae and Ariophantidae cannot be supported based on the material examined here.

Based on morphological data, the monophyly of Helicarionidae cannot be confirmed. A phylogenetic analysis using mitochondrial DNA ( Hyman et al. 2007) showed Helicarionidae (as defined in the current study) to be monophyletic in most analyses, with posterior probabilities of 81–96% in Bayesian analyses. However, sometimes Sheldonia poeppigii ( Pfeiffer, 1846) (Urocyclidae) diverged from within Helicarionidae . Few representatives of the closely related Ariophantidae and Urocyclidae were included, so the relationship and boundaries among the three families could not be rigorously tested.

Four helicarionids from Mauritius and two from Madagascar were examined in the current study. Two of the Mascarene species were previously included in the subfamily Ereptinae , which was created by Thiele (1929 –1931) for nine genera from the Mascarene Islands and one from the Nicobar Islands. Baker (1941a) synonymised Ereptinae with Helicarionidae , but both taxa were was recognised by Zilch (1959). Schileyko (2002b) treated Ereptinae as a subfamily of Ariophantidae and added the Madagascan genera Kalidos Gude, 1911 , Methvenia Robson, 1914 and (tentatively) Bathia Robson, 1914 . Schileyko (2002b) defined Ereptinae based on the presence of a rather long flagellum and the absence of an epiphallic caecum and a stimulator. However, all but one of the Mascarene and Madagascan species examined in the current study had an epiphallic caecum, the exception being Caldwellia angularis ( Férussac, 1821) . All species also had a long, slender flagellum but no stimulator. Erepta odontina and Ctenophila caldwelli (Benson, 1859) were united by the presence of very small mantle lobes, radial ribs on the teleoconch and a small diverticulum at the apex of the penis. They also lacked mantle laps and minor venation on the roof of the mantle cavity. The two species of Caldwellia H. Adams, 1873 shared some of these characters [absent mantle laps, very small mantle lobes, distinct shell sculpture, diverticulum at the apex of the penis in Caldwellia imperfecta (Deshayes, 1863) , little minor venation on the roof of the mantle cavity], but they also shared a very distinctive and unusual radula (see Figures 30B , 31A–F ) not found in any other species. In addition, both species had a shell with an angulate or keeled periphery and a relatively high spire, in contrast to the rounded whorl profile and flattened shell of E. odontina and C. caldwelli . Schileyko (2002b) placed Caldwellia in Trochozonitini ( Trochozonitinae , Ariophantidae ) based on the shape of the shell, the long flagellum, the presence of an epiphallic caecum, the attachment of the penial retractor muscle to the base of the caecum or the epiphallus and the presence of a thin penial sheath. Before this placement can be confirmed, the radulae of typical species of Trochozonitinae need to be examined.

The two Madagascan species examined share some similarities with the Mascarene species. Both Kalidos balstoni and Madagascan species MA1 have shells with rounded whorl profiles and distinct but fine radial ribs on the teleoconch (very faint in MA1). Kalidos balstoni has no mantle laps and small mantle lobes; MA1 has moderately long mantle laps as well as small mantle lobes. Neither species has an apical diverticulum on the penis and distinct minor venation on the roof of the mantle cavity is present in MA1.

The characters outlined above do not conclusively group the six Madagascan and Mascarene species. Erepta Albers, 1850 and Ctenophila Ancey, 1882 appear to be very similar and it is possible that the two genera should be synonymised ( Baker 1941a). Without a closer study of more members of the subfamily, it is not possible to determine whether or not Ereptinae is a valid group. In the current study all six species are tentatively included in Helicarionidae .

Families Nitoridae ( Iredale 1937c) , Gudeoconchidae ( Iredale 1944) and Epiglyptidae ( Iredale 1944) are synonymised with Helicarionidae by Smith (1992), Hausdorf (1998) and Schileyko (2002b) and in the current study as they have no significant distinguishing features.

Based on our study and analysis we define Helicarionidae , rather unsatisfactorily, as follows:

Shell complete or reduced. Stimulator absent. Fibres of the penial nerve may or may not run through the cerebral ganglion ( Hausdorf 1998). Epiphallic retractor caecum and flagellum absent or present; lime-sac present in few taxa.

Within this grouping we informally recognise several subgroups within the Australian taxa, as listed below. These are in no way intended to be recognised as phylogenetically distinct groups but rather as convenient groupings of morphologically similar taxa to facilitate discussion. Non-Australian taxa not dealt with in conjunction with the Australian taxa are listed in geographical groupings following the descriptions of the Australian taxa.

Description. Shell present, complete or reduced, ranging in diameter from ~ 5 mm [ Echonitor albumenoidea ( Cox, 1868) ] to 35 mm ( Gudeoconcha sophiae magnifica Iredale, 1944 ). Shell shape and sculpture variable. Mantle laps absent and mantle lobes present ( Caldwellia , Ctenophila , Erepta ) or mantle laps and lobes both present (most taxa), ranging in size and degree of fusion. Sole of foot tripartite; caudal apparatus present, formed from curled up sole; caudal horn very small to large; caudal foss diamond-shaped to vertical slit. Kidney unilobed; minor venation on roof of mantle cavity absent or present; pigmentation absent or present; mantle gland absent. Genital system oviparous; oviduct glandular. Bursa copulatrix variable in length; inserted on vagina or, if vagina absent, at junction of free oviduct and penis. Stimulator absent. Epiphallus enters penis through simple pore, fleshy lips or verge; interior of penis with no sculpture, or with pustules, ridges, longitudinal pilasters or circular pilasters. Penial sheath present, sometimes not covering entire penis; open at distal end. Epiphallic retractor caecum absent or present; epiphallic flagellum absent or present. Spermatophore as for superfamily. Radula narrow or wide; central tooth with small ectocones (except in Levidens : ectocones absent); central tooth mesocone lanceolate (except in Parmellops and Echonitor : small and rounded). Lateral and marginal fields distinguishable and tooth rows straight (except in Caldwellia ).

Figures

FIGURE 30. Whole radulae. A. Peloparion iridis, QMMO51026. B. Caldwellia imperfecta, AM C205300. C. Coneuplecta pampini, AM C438751. D. Cystopelta astra, AM C354840. E. Parmellops sp., AM C393245. Scale bars 0.5 mm (A–C), 1 mm (D–E).

FIGURE 31. Radulae. A–C. Caldwellia imperfecta, AM C205300. D–F. Caldwellia angularis, AM C205299. G–I. Ctenophila caldwelli, AM C205301. J–L. Erepta odontina, AM C205302. M–O. Kalidos balstoni, AM C205303. P–R. Madagascan species MA1, AM C205304. Scale bars 10 mm (A–C), 20 mm (D–L, P–R), 50 mm (M–O).