Omalonyx geayi Tillier, 1980

Arruda, Janine O., Barker, Gary M. & Thomé, José W., 2016, Revaluation of the taxonomic characters and distribution of Omalonyx geayi (Gastropoda, Succineidae), Iheringia, Série Zoologia (e 2016019) 106, pp. 1-6 : 4-6

Omalonyx geayi Tillier, 1980

Omalonyx geayi TILLIER, 1980:87 , figs 69-71; Pl. 5, FIg. 6 ; 1981:135, figs 11, 12 (anatomy and dIstrIbutIon).

Omalonyx unguis : HERMANN & DUNDEE 1967:1-5 (in part) [some specimens erroneously determined; not Omalonyx unguis (d’Orbigny, 1835) ].

Omalonyx matheroni : TILLIER, 1981:129 (in part) [synonym list; not Omalonyx matheronii (Potiez & Michaud, 1835) ].

Type material. Holotype and four paratypes, MNHN unnumbered (examined). Type locality. Kaw swamp, French Guiana.

Diagnosis. Reproductive system ( Fig. 7 ) with phallus complex about 23 mm in length. Phallus slender, about four times length of epiphallus; internally with longitudinal wrinkled folds or longitudinally elongate papillae in the proximal one fourth, followed by an extensive zone of elliptical or polygonal shaped papillae, and distally with discoid papillae; often the entry to the atrium is characterized by lozenge - or rectangular - shaped papillae organized in longitudinal folds. Phallus sheath thick, muscular, to approxImately one fifth length of the phallus from Its dIstal extremity, thereafter extending over phallus and epiphallus as a thin, transparent veil. Epiphallus and phallus of the same width. The epiphallus outer wall smooth, with a visible epiphallial sphincter. Free oviduct with longitudinal folds lining the lumen, readily discernable externally.

Shell ( Fig. 8 ) reduced, not capable of housing the animal, sited mid-dorsally and partially covered by mantle; about 13 mm in height, 8 mm width, comprising a nearly obsolete spire (~0.5 whorl) atop of a rapidly expanding, weakly convex body whorl; aperture oval, comprising ~0.96 shell height and entire shell width. Shell relatively larger than in other species.

Distribution. Omalonyx geayi had only been previously recorded from the type locality in the Kaw swamp, French Guiana ( TILLIER, 1980, 1981). Based on the examIned materIal, the specIes Is now recorded for the first time in Suriname, Ecuador, Brazil and Bolivia. In Suriname this species is recorded for Paramaribo, in Ecuador for Limoncocha (Sucumbios), in Brazil for states of Amazonas and Alagoas, and in Bolivia for Department of Santa Cruz. We predict that the species occurs widely in northern and central South America, from latitude 5°N to 18°S.

Remarks. In O. geayi the phallus and epiphallus are very sImIlar In wIdth and often It Is dIfficult to dIstInguIsh their limits without opening the phallus. According to TILLIER (1981), the phallus in O. geayi is 30-36 mm when extended. However, In the figure 71 of TILLIER (1980), in which the epiphallus and phallus can be easily distinguished, the extended phallus length is depicted at approximately 19 mm. This latter estimate is similar to the phallus lengths measured here for specimens from Suriname, Bolivia and Brazil (Amazonas and Alagoas), which were between 17- 19 mm.

We illustrate dorsal, ventral, lateral and protoconch views ( Fig. 8 ) of the shell from an O. geayi paratype and this is the same shell depicted the dorsal view by TILLIER (1980, Pl. 5, Fig. 6 ). Although Omalonyx shells are not considered very informative in taxonomy, the shell of O. geayi is larger, relatIvely wIder, more flattened and ovoId than those of O. matheronii and O. convexus .

The ovariotestis and hermaphrodite duct described by TILLIER (1980) as diagnostic characters for Omalonyx geayi were based on parasitized specimens. Despite this systematic misinterpretation, O. geayi is a valid species based on the characters of the male genItalIa and shell. The first record of parasitism in Omalonyx was made by LUTZ (1921), who reported a natural infection by a species of Leuchlocoridium Carus, 1835 ( Trematoda, Leuchlocoriidae). TRAVASSOS (1928) subsequently used specimens of Omalonyx from Mato Grosso, Brazil as experimental host for this trematode which develops in the slug’s visceral cavity, but does not infest host organs. MONTRESOR et al. (2008) described an experimental infection of Omalonyx sp. by Angiostrongylus costaricensis Morera & Céspedes, 1971 (Nematoda, Protostrongylidae ), and MOZZER et al. (2011) by Angiostrongylus vasorum (Baillet, 1866) . Although these experiments prove the susceptibility of Omalonyx to parasitism by A. costaricensis and A. vasorum , no natural infections have been recorded. Many other parasites utilize land snails as hosts, but studies of the life cycle in South America are presently limited, but include Eurytrema coelomaticum (Giard & Billet, 1892) ( Trematoda, Dicrocoeliidae ) and Hasstilesia tricolor (Stiles & Hassall, 1894) ( Trematoda, Brachylaemidae ) ( ROBINSON, 1953; ROWAN, 1955; PASCHOAL & AMATO, 1995, 1996, 2001). Unfortunately, our Omalonyx material was preserved in alcohol and not suitable for determination of the family or specIfic IdentIty of the parasItes InfectIng the gonad and hermaphrodite duct. No spermatozoids were observed within the parasitized ovariotestes from the Carauari and

Trinidad specimens ( Figs 1-4 ). This absence of male gamete development could indicate parasitic castration. This pathology is well documented for many Gastropoda species (e.g. WILSON & DENILSON 1980; PASCHOAL & AMATO, 1996; JORDAENS et al., 2007; VOUTILAINEN et al., 2009; AVERBUJ & CREMONTE, 2010).

Figures

Figs 1-6. Histological micrographs of the ovariotestes of Omalonyx. Figs 1-2, parasitised ovariotestis tissues from Carauari (MCP 9183). Figs 3-4, parasitised ovariotestis tissues from Trinidad (USDA 100453). Fig. 5, healthy ovariotestis tissues from Carauari (MCP 9183). Fig. 6, healthy ovariotestis tissues from Santa Maria (MCP 8831). Asterisks indicate spermatozoids, and arrows parasites. Haematoxylin-eosin stain.

Fig. 7. Reproductive system of Omalonyx geayi Tillier, 1980 (Paramaribo, UF 463461), with phallus and vagina opened to show ornamentation of the Internal wall (ag, albumen gland; dd, defferent duct; ep, epIphallus; es, epIphallIc sphIncter; fo, free ovIduct; gg, gametolItIc gland (bursa copulatrix); hd, hermaphrodite duct; ov, ovariotestis; ph, phallus; po, pallial oviduct; pr, prostatic gland; ps, phallus sheath; rm, retractor muscle; sv, seminal vesicles; va, vagina). Scale bar: 1 mm.

Fig. 8. Shell of Omalonyx geayi Tillier, 1980 paratype (MNHN unnumbered) in dorsal, ventral, lateral and protoconch views.Height =13 mm (TILLIER, 1980).