Melayonchis annae Dayrat, 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 : 1878-1885

publication ID	https://doi.org/ 10.1080/00222933.2017.1347297
publication LSID	lsid:zoobank.org:pub:671922DB-C6C1-44A5-B2CD-A3A3127CB668
DOI	https://doi.org/10.5281/zenodo.5191656
persistent identifier	https://treatment.plazi.org/id/2E2FDB0D-CC99-4619-AADF-4DB5F9381183
taxon LSID	lsid:zoobank.org:act:2E2FDB0D-CC99-4619-AADF-4DB5F9381183
treatment provided by	Felipe
scientific name	Melayonchis annae Dayrat
status	sp. nov.

Treatment

Melayonchis annae Dayrat View in CoL sp. nov.

( Figures 16–19 View Figure 16 View Figure 17 View Figure 18 View Figure 19 )

Type locality

Singapore, Lim Chu Kang , 01°26.785 ʹ N, 103° 42.531 ʹ E, 5 April 2010 [station 9, mangrove East of the jetty; open forest with medium trees and medium mud, ending on sunexposed mudflat outside the mangrove with soft mud] GoogleMaps .

Type material

Holotype, designated here: one specimen 32/20 [DNA 1010] mm, in formalin and 70% alcohol, with a piece in 95% alcohol, leg. B. Dayrat and S.K. Tan ( ZRC.MOL.6502).

Additional material examined

Singapore, Mandai, 01°26.237 N, 103° 45.730 E, 2 April 2010, 13 specimens (33/22 [#1] to 18/ 14 mm [#2]; 18/15 [DNA 1008] and 22/15 [DNA 1009] mm), leg. B. Dayrat and S.K. Tan [station 6, following the river from the railroad towards sea, open mangrove forest with tall trees and soft mud, ending on sun-exposed mudflat outside the mangrove with very soft mud, heavily polluted with trash] ( ZRC.MOL.6503); Brunei Darussalam, Mentiri, Jalan Batu Marang, 04°59.131 ʹ N, 115°01.820 ʹ E, 29 July 2011, 16 specimens (32/19 [#1] to 10/7 [#2] mm; 26/15 [DNA 1046] and 20/12 [DNA 1045] mm), leg. B. Dayrat, T. Goulding and S. Calloway [station 34, old mangrove with tall Rhizophora trees with high roots and Thalassina mounds, but specimens collected on cemented walls at the margin of the mangrove] ( BDMNH).

Distribution

Singapore (type locality) and Brunei Darussalam .

Etymology

Melayonchis annae is dedicated to Anna Dayrat, for the time that her father (the first author) has to spend away from her, exploring mangroves and missing her.

Habitat ( Figure 16a View Figure 16 )

Melayonchis annae is found in the high intertidal. In Singapore, it was found quite high on tree trunks. In Brunei Darussalam, it was found on rocks and cemented walls at the margin of an old Rhizophora forest. So far, it has not been found directly on mud, or on muddy dead logs.

Abundance

Melayonchis annae is a rare species. We found it only at three of the dozens of mangrove sites that we visited in the region. However, in two of three sites, we found a reasonable number of specimens (more than 10) without difficulty (animals which live high on trunks and on rocks just outside mangroves are not cryptic).

Colour and morphology of live animals ( Figure 16b–g View Figure 16 )

Live animals are not covered dorsally with a thin layer of muddy mucus and the colour of their dorsal notum can readily be seen. The dorsal notum is irregularly mottled with cream, light brown, and dark brown areas. The colour of the hyponotum varies between cream to light grey. Because it is lightly coloured, its margin is not marked by a significantly lighter ring. The foot is cream ( Figure 16e View Figure 16 ). The brown ocular tentacles are short and extend for only a few millimetres beyond the notum margin when the animal crawls undisturbed. The head is small and remains covered by the dorsal notum as the animal crawls.

The body is not flattened. The dorsal notum is elongated, oval. The dorsal notum is not particularly thick. Its surface, when the animal is undisturbed, is not smooth. Dorsal gills are absent. Large papillae are absent but small conical papillae are present. From eight to 12 of those papillae bear a black ‘dorsal eye’ which, when the animal is undisturbed, seems to form a slight bump. A slightly larger, central papilla bears three black ‘dorsal eyes’. In addition, the notum is finely granular throughout. When the animal is disturbed (typically, if one touches its dorsum), all papillae tend to retract but the dorsal notum remains finely granular. It may also excrete an oily mucus when disturbed, but not as frequently as M. siongkiati , and in a much smaller amount. When disturbed, animals do not coil up into a sphere. Crawling individuals can measure up to 33 mm, but most of them measure about 20 to 25 mm on average. Preserved specimens no longer display the distinctive colour traits of live animals. The ventral colour, in particular, is homogeneously whitish or creamish.

Visceral cavity and pallial complex

The kidney and the lung are slightly asymmetrical, the right part being slightly longer than the left part.

Digestive system ( Figures 17a View Figure 17 , 18 View Figure 18 )

Examples of radular formulae are ( Figure 18 View Figure 18 ): 95 × (280–1–280) in BDMNH station 34 #1 (32 mm long), 65 × (185–1–185) in BDMNH station 34 #2 (10 mm long), 100 × (290–1– 290) in ZRC.MOL.6503 #1 (33 mm long), and 90 × (260–1–260) in ZRC.MOL.6503 #2 (18 mm long). The length of the rachidian teeth is about 25 µm, significantly less than that of the lateral teeth. Along a half row, all the lateral teeth do not have exactly the same length and shape. The length of the hook of the lateral teeth gradually increases (from innermost to outermost) from about 40 to 50 µm, excluding the first few (about 5) innermost and outermost lateral teeth which are significantly smaller than the rest of the lateral teeth. Finally, the tip of the hook of the lateral teeth is round throughout the entire half row. The pattern of its loops is of type II ( Figure 17a View Figure 17 ).

Reproductive system ( Figures 17b, c View Figure 17 , 19 View Figure 19 )

There is a small, oval, slightly bent receptaculum seminalis (caecum) along the hermaphroditic duct. The oval spermatheca (for the storage of exosperm) is large and connects to the oviduct through a very short duct ( Figure 17b View Figure 17 ).

The male anterior organs consist of the penial complex (penis, penial sheath, vestibule, deferent duct, retractor muscle; Figure 17c View Figure 17 ). There is no penial accessory gland. The penial sheath is very short (about 1 mm in length) and straight. The penial sheath protects a penis which consists of a short, slightly conical papilla of about 0.4 mm long ( Figure 19 View Figure 19 ). There are no penial hooks. The vestibule is both longer and larger than the penial sheath. The insertion of the retractor muscle marks the separation between the penial sheath and the deferent duct. The retractor muscle is longer than the penial sheath but inserts in the anterior part of the visceral cavity. The deferent duct is highly convoluted with many loops, even though the deferent duct is significantly less convoluted in immature specimens.

Distinctive field diagnostic features

A table at the end of the introduction summarises the most important features that can help distinguish and identify Melayonchis species ( Table 3). In the field, individuals of M. annae remain difficult to identify because their dorsal colour is highly variable. However, other features differ sufficiently from the other species of Melayonchis , such as the ventral colour (white to light grey). It secretes much less oily mucus than M. siongkiati . Also, unlike M. eloisae , animals do not coil up into a sphere. Finally, the habitat of M. annae seems more specific (on the dry bark of mangrove trees as well as on rocks outside mangroves) than that of the other species described here.