Melayonchis Dayrat and Goulding, 2017

Dayrat, Benoît, Goulding, Tricia C., Apte, Deepak, Bhave, Vishal & Ngô Xuân, Qu ảng, 2017, A new genus and four new species of onchidiid slugs from South-East Asia (Mollusca: Gastropoda: Pulmonata: Onchidiidae), Journal of Natural History (J. Nat. Hist.) 51 (31 - 32), pp. 1851-1897 : 1860-1861

Melayonchis Dayrat and Goulding gen. nov.

Type species

Melayonchis eloisae , designated here.

Etymology

Combination of Melayu and Onchis . Melayu is the Malay word for Malays. It is selected here because the core of the known distribution of the new genus described here mostly corresponds to the historical Malay world – that is, Peninsular Malaysia (including Singapore) and coastal Borneo. Onchis is one of the names used for onchidiid slugs.

Diagnosis

Body not flattened. No marginal glands in the notum. No dorsal gills. Dorsal eyes present on notum. Fully retractable, central papilla (with three dorsal eyes) present. Short eye tentacles. Male opening below the right ocular tentacle, slightly to its left. Pneumostome median. Intestine of types II and III (and intermediary between types II and III). Rectal gland present. Accessory penial gland and hollow spine present or absent. Penis with no hooks.

Remarks

A new generic name is needed because no existing name could apply to the clade described here. We provide here a few remarks on the status of the generic names that are potentially valid in Onchidiidae ( Dayrat 2009) . Our remarks are based on the examination of all the type specimens available, especially those of all the type species, as well as the careful analysis of all the original descriptions (especially when no type specimens were available). More details will be provided in our revisions of the corresponding genera. However, here we do not comment on the generic names that refer to Onchidella J.E. Gray, 1850 and Hoffmannola Strand, 1932 , which are not represented in the tropical Indo-West Pacific ( Dayrat 2009; Dayrat et al. 2011b; Avila-Poveda et al. 2014). Several generic names apply to a clade including all the onchidiid slugs with dorsal gills – that is, Peronia Fleming, 1822 ; Eudrastus Gistel, 1848 ; Lessonina Starobogatov, 1976 ; Onchis d’ Audebard de Férussac, 1821 ; Paraperonia Labbé, 1934 ; Quoyella Starobogatov, 1976 ; and Scaphis Labbé, 1934 . The generic name Labella Starobogatov, 1976 is a junior synonym of Onchidium Buchannan, 1800 which applies to a different clade including the type species Onchidium typhae Buchannan, 1800 , and is characterised by large conical papillae on the dorsal notum ( Dayrat et al. 2016). The generic name Paraoncidium Labbé, 1934 is a junior synonym of Onchidina Semper, 1885 which applies to a species with no dorsal eyes (Dayrat and Goulding submitted). Peronina von Plate, 1893 applies to its type species Peronina alta von Plate, 1893 , characterised by a pneumostome distinctly and unusually located on the margin of the notum (a feature that is present in the type material of Peronina alta ). Platevindex Baker, 1938 applies to a clade including species with a distinctly flattened body and narrow foot, such as the type species Platevindex coriaceum ( Semper 1885) . Finally, Semperoncis Starobogatov, 1976 applies to species that are adapted to terrestrial life in the Philippines ( Dayrat 2010a). As no other generic name exists for the taxon described here, a new name is needed.

Distinctive diagnostic features

No external diagnostic feature seems to unambiguously distinguish Melayonchis from all other genera (which is not surprising because many onchidiid species from different genera look very similar externally). Internally, however, the lateral radular teeth of Melayonchis are characterised by a protuberance on their inner lateral margin (see arrows in Figures 6 , 13 , 18 , 24 and 25 ) which is a distinctive feature that has not been observed in any other species so far (e.g. Dayrat 2010a, 2010b; Dayrat et al. 2011 b, 2016).

Figures

Figure 6. Radula, Melayonchis eloisae. (a) Innermost lateral and lateral teeth, Malaysia (USMMC 00007, #1). (b) Lateral teeth, Brunei Darussalam (BDMNH, #1). (c) Rachidian tooth, Malaysia (USMMC 00007, #1). (d) Outermost lateral teeth, Malaysia (USMMC 00007, #1). (e) Lateral teeth, detail, Brunei Darussalam (BDMNH, #1). The arrows indicate the lateral protuberance which is characteristic of the teeth in Melayonchis. Scale bars: a = 40 mm; b = 30 μm; c = 10 μm; d = 20 μm; e = 5 μm.

Figure 13. Radula, Melayonchis siongkiati. (a) Rachidian and innermost lateral teeth, Malaysia (USMMC 00016,#2). (b) Rachidian and innermost lateral teeth, same as (a). (c) Outermost lateral teeth,same as (a). (d) Lateral teeth, same as (a). (e) Rachidian and innermost lateral teeth, Brunei Darussalam, station 30 (BDMNH, #1). (f) Lateral teeth, inferior view, same as (e). The arrows indicate the lateral protuberance which is characteristic of the teeth in Melayonchis. Scale bars: a, d = 40 μm; b, c, e = 20 μm; f = 4 μm.

Figure 18. Radula, Melayonchis annae, Singapore (ZRC.MOL.6503, #2). (a) Median region of left half rows. (b) Rachidian and innermost lateral teeth. (c) Lateral teeth, inferior view. (d) Outermost lateral teeth. (e) Lateral teeth. The arrows indicate the lateral protuberance which is characteristic of the teeth in Melayonchis. Scale bars: a = 100 μm; b, d, e = 20 μm; c = 4 μm.

Figure 24. Radula, Melayonchis aileenae, Malaysia (USMMC 00019, #2). (a) Median region of left half rows. (b) Rachidian and innermost teeth. (c) Rachidian and innermost teeth. (d) Outermost lateral teeth. (e) Lateral teeth. The arrows indicate the lateral protuberance which is characteristic of the teeth in Melayonchis. Scale bars: a = 40 μm; b, e = 10 μm; c, d = 5 μm.

Figure 25. Radula, Melayonchis aileenae, Malaysia. (a) Innermost lateral and lateral teeth (USMMC 00019, #1). (b) Rachidian tooth (USMMC 00019, #1). (c) Lateral teeth, inferior view (USMMC 00019, #1). (d) Outermost lateral teeth (USMMC 00021). The arrows indicate the lateral protuberance which is characteristic of the teeth in Melayonchis. Sclae bars: a, d = 20 μm; b, c = 5 μm.