"Dendrolimax" vangoethemi Rowson

Rowson, B, Warren, B. H. & Ngereza, C. F., 2010, Terrestrial molluscs of Pemba Island, Zanzibar, Tanzania, and its status as an " oceanic " island, ZooKeys 70, pp. 1-39 : 8-11

2. "Dendrolimax" vangoethemi Rowson sp. n. Figs 11 –1264– 75

Type material

(all from TANZANIA: Zanzibar: Pemba Island). Holotype (NMW.Z.2009.013.00211): slug 30.0 mm long in 80% ethanol, on understorey foliage during day, Ngezi FR (Locality 2 in Fig. 1 and Table 1), 8 February 2009, leg. B. Rowson, B. H. Warren, C. F. Ngereza & local collectors.

Paratype 1 (NMW.Z.2009.013.00212): slug 37.5 mm long in 80% ethanol; other data as holotype. Paratype 2 (NMW.Z.2009.013.00213): slug 31.0 mm long in 80% ethanol; other data as holotype. Paratype 3 (NMW.Z.2009.013.00214): slug 25.0 mm long in 80% ethanol; other data as holotype. Paratype 4 (IRSNB.IG.31599/MT2317): slug 18.0 mm long in 80% ethanol; other data as holotype. Paratype 5 (NMT): slug 19.0 mm long in 80% ethanol, on understorey foliage during day, Ngezi FR (Locality 6 in Fig. 1 and Table 1), 8 February 2009, leg. B. Rowson, B. H. Warren, C. F. Ngereza & local collectors. Paratype 6 (NMW.Z.2009.013.00215): slug 18.5 mm long in 80% ethanol; leaf litter during day, Ras Kiuyu FR (Locality 7 in Fig. 1 and Table 1), leg. B. Rowson, B. H. Warren, C. F. Ngereza & local collectors.

Diagnosis:

Medium-sized slug (to at least 55mm in life) with strong keel prolonged into long caudal appendage, with mantle completely covering shell. Pale to colourless, with dorsum covered in pustules. Viscera not extending far into tail, shell mineralised, jaw with no or weak projection. Radula unique in having up to 280 tiny, tricuspid teeth per half-row. Genitalia broadly similar to other Dendrolimax .

Description:

Note: points of agreement with an unnamed East Usambara species as discussed by Verdcourt and Polhill (1961) (see below) are marked with “*”.

External features: Medium-sized slug (extended length to at least 55mm in life, or 37.5mm in 80% ethanol)*. Tail strongly keeled* and hollowed out behind mantle*; keel prolonged into long straight caudal appendage* above small caudal pore*. Viscera extending little more than half-way into tail*. Body bell-shaped in cross-section when extended, but able to flatten body considerably. Sole not narrow, evenly tripartite*. Peripodial grooves clear, from tail to genital orifice and head. Mantle fully attached posteriorly, free anteriorly, not grooved, subangulate rather than rounded behind, completely covering shell, lacking a dorsal pore or slit*. Pneumostome in posterior third of mantle*. Genital orifice far forward, near right lower tentacle. No head wart or similar structure detected. Integumental tubercles barely detectable on mantle, tail or cephalopodium; instead, whole dorsum rather densely and regularly covered in hemispherical (rather than prickly) pustules*. Dorsum largely colourless and translucent*, with green, grey or pink tinge*, acquiring a green cast when on foliage; keel white; sole colourless. Diffuse, slate-grey pigment on caudal appendage, bordering keel* and/or in obscure blotches or bands on mantle in some specimens*, absent in others; remains on preservation. Pustules conspicuously white*, remaining so on preservation. Ommatophore retractors grey-ochre on preservation.

Jaw and radula: Jaw solid, semi-lunate, lacking median projection (holotype), or projection very weak (paratype). Radula of holotype broad (3.65 mm wide × 2.20 mm long), of 155 rows (over 50 angular rows per mm length). Teeth extremely small* and extremely numerous*, to nearly 450 in each half-row*, with a central tooth. All teeth (including central tooth) tricuspid*, with very little change across the row, perhaps becoming more s-shaped laterally. Ectocones larger (or at least projecting further) than mesocones in all teeth except central tooth. This is unlike any radula figured in van Goethem (1977) where mesocones are always the largest cusps, and the maximum number of teeth per half-row is around 280, and only in radulae over 5.00 mm wide. The radula form may suggest a microphagous, rather than phytophagous diet.

Shell and pallial complex: Shell unguiform, bilaterally symmetrical, to at least 4.10 mm long, infilled, mineralised and white* (i.e. not fragile as in other Dendrolimax ). Pallial area well vascularised.

Genitalia: Right ommatophore retractor passes between penis and vagina. No atrial diverticulum or stimulator*. Long flagellum present in place of calc sac*. Epiphallus long, stiff, not spiralling around penis*. Penial retractor short, attaching well below flagellum, perhaps obtaining from diaphragm. Penis with basal sheath, contiguous with penis wall apically, internally with longitudinal pilasters and a basal papilla; similar to that of several Dendrolimax (see van Goethem 1977). Bursa copulatrix duct arising low on vagina, bound to it by sheath-like circular muscle fibres. Bursa copulatrix long, weakly clavate, reaching upper part of spermoviduct*. Vagina and free oviduct with a clear, thick-walled sheath*. Hermaphroditic duct extremely short*, barely perceptible between spermoviduct and large yellow ovotestis, which lies near rear of mantle. Albumen gland small, hook-shaped*. No spermatophores were recovered from the Pemba material which may not be fully adult.

Remarks:

This distinctive species was found only in FRs. At Ngezi, the slugs were found on the underside of large understorey leaves, up to 2m above ground. The body was held flattened with one optic tentacle protruding (Fig. 12). At Ras Kiuyu FR the species was found in litter. It appears to be undescribed although it (or a similar species) may occur in the East Usambara Mts. Beyond that its affinities are less certain.

Van Goethem (1977) thoroughly revised the known urocyclid slugs of Africa and Madagascar and provided keys to internal characters. The Pemba species keys readily out to Dendrolimacini (sole genus Dendrolimax Heynemann, 1868). The only East African record of the mainly Central-West African Dendrolimax is an unnamed and incompletely described species collected by Verdcourt (1960) from Thika Gorge, Kenya, who indicated a swollen lower oviduct not present in the Pemba species. Moreover the Pemba species differs from all other Dendrolimax in the radula, body form, and shell, although the genitalia are similar. It shows much clearer similarities to a taxon referred to as "Genus et species nov." by Verdcourt and Polhill (1961, p. 32-33, fig. 42) from Sigi in the East Usambara Mts. (1961). They said, "This mollusc does not belong to the family Urocyclidae judging by [the] radula but to an isolated subfamily of the Helicarionidae near to the Durgellinae". Van Goethem (1977) could not obtain material of this taxon for his revision but considered it a urocyclid. He treated it as "Species E", incertae sedis after Dendrolimacini and Upembellini along with a "Species D" from Grand Comore to which he noted a similarity in the genitalia, but not the radula. Neither Verdcourt and Polhill (1961) nor van Goethem (1977) were certain whether the specimens of "Species E" or "Species D" were adult. This is an important consideration since slugs may change in appearance as they grow. However, neither Verdcourt and Polhill, van Goethem with his experience of growth series of many taxa, nor other slug workers (e.g. Forcart 1967) could attribute these forms to any known species or genus. Verdcourt and Polhill (1961) noted that there was no absolute criterion, e.g. concerning the size of the albumen gland, for recognising adulthood in urocyclid slugs. Since 1977 there has been little further work on the group in East Africa. The Pemba species, which will probably prove to include also the East Usambara species, is here described provisionally in Dendrolimax . Consideration was given to erecting a new genus but owing to a lack of unique features in the genitalia, and the large number of available genus-group names, is avoided until more data are available.

Although this species is fully limacised, there are also similarities in the body form and genitalia to numerous Afrotropical semi-slug genera, among them Verrucarion van Mol, 1970 of West and central Africa ( van Mol 1970) and Malagarion Tillier, 1979 of Madagascar. The resemblance to the latter extends to the radula and white pustules (see Tillier 1979, Emberton 1994). Van Mol (1970) treated all African genera in Urocyclidae: Urocyclinae or Gymnarioninae. Tillier (1979) considered Malagarion to belong, with the Mascarene Colparion Laidlaw, 1938 in Helicarionidae: Ariophantinae and not Urocyclinae(/idae). He noted that the radula, but not genitalia, of Malagarion was similar to the Asian Durgellini (founded on the Burmese semi-slug Durgella Blanford, 1863). Verdcourt and Polhill (1961) had also noted a radula similarity between their East Usambara species and the Durgellinae, although this was not discussed by van Goethem (1977). Certainly the radula would be unique in Urocyclinae sensu van Goethem (1977), and resembles Malagarion in the size and number of teeth, and the large ectocones (at least on the more marginal teeth of Malagarion ). The monophyly of these major groups is questionable while the systematics of trop ical Limacoidea is still far from resolved (e.g. Tillier 1979, Hausdorf 1998, Schileyko 2002), but it remains possible that this species is related to one of them rather than other Dendrolimax .

Distribution:

Pemba island; probably also East Usambara Mts.

Etymology:

vangoethemi, a noun in the generative case, for Dr. J. L. van Goethem of IRSNB, in recognition of his thorough and highly accessible monograph on Afrotropical urocyclid slugs.