Wallaconchis melanesiensis Goulding & Dayrat

Goulding, Tricia C., Khalil, Munawar, Tan, Shau Hwai & Dayrat, Benoit, 2018, Integrative taxonomy of a new and highly-diverse genus of onchidiid slugs from the Coral Triangle (Gastropoda, Pulmonata, Onchidiidae), ZooKeys 763, pp. 1-111: 1

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Wallaconchis melanesiensis Goulding & Dayrat

sp. n.

Wallaconchis melanesiensis Goulding & Dayrat  sp. n. Figs 59, 60, 61, 62, 63, 64, 65

Type locality.

Papua New Guinea, Madang, SW Hargun Island, 05°01.60'S, 145°47.90'E, st PM24, night tide.

Type material.

Holotype, 13/10 mm [5417], designated here (IM-2013-13761).

Additional material examined.

Indonesia, Lombok, Seriwe Bay, 08°51.70'S, 116°32.87'E, 1 specimen 27/14 mm [2963], st 147, small beach of coral rubble and rocks (UMIZ 00070); Sulawesi, Tamperong, 01°41.51'N, 125°00.80'E, 1 specimen 8/7 mm [2202], st 85, sand and small rocks outside a mangrove (UMIZ 00066); Sulawesi, Bahoi, 01°43.36'N, 125°01.23'E, 1 specimen 26/17 mm [2215], st 88, sand and small rocks outside a mangrove (UMIZ 00067); Ambon, Haruku Island, 03°36.52'S, 128°25.07'E, 3 specimens 31/25 mm [2735], 31/25 mm [2732], and 13/8 mm [2733], st 127, rocky Sonneratia  mangrove with coral rubble (UMIZ 00068); Halmahera, Sofifi, 00°45.40'N, 127°35.47'E, 1 specimen 15/8 mm [5065], st 204, muddy, rocky intertidal (UMIZ 00065); Halmahera, Foli, 01°14.66'N, 128°10.61'E, 4 specimens 27/17 mm [5133], 25/19 mm [5131], 23/18 mm [5132], and 22/13 mm [5026], st 217, large rocks with algae high in intertidal of beach (UMIZ 00069). Papua New Guinea, Madang, SW Hargun Island, 05°01.60'S, 145°47.90'E, 1 specimen 17/14 mm [5421], st PM24, night tide (IM-2013-14039); Madang, SW Hargun Island, 05°01.60'S, 145°47.90'E, 1 specimen 7/6 mm [5446], st PM24, night tide (IM-2013-14046); New Ireland, Kavieng, 02°41.00'S, 150°57.00'E, 1 specimen 19/18 mm [6089], st KM05, mixed hard platform and seagrass bed at outlet of rivulet (IM-2013-53524); New Ireland, Kavieng, 02°41.00'S, 150°57.00'E, 1 specimen 20/15 mm [6090], st KM05, mixed hard platform and seagrass bed at outlet of rivulet (IM-2013-53522). Vanuatu, Santo Rose Point, 15°34.90'S, 167°02.40'E, 1 specimen 14/13 mm [5483], st VM02, intertidal, coral sand (IM-2013-62405); Santo Rose Point, 15°34.90'S, 167°02.40'E, 1 specimen 14/12 mm [5484], st VM02, intertidal, coral sand (IM-2013-62406).


Indonesia: Ambon, Halmahera, and Sulawesi. Papua New Guinea: Madang and Kavieng. Vanuatu.


(Fig. 59, Table 3). Wallaconchis melanesiensis  is found in the rocky intertidal, on rocks or large pieces of coral rubble generally covered by a thin mat of algae.


Wallaconchis melanesiensis  is named after the region of Melanesia, as it is the only Wallaconchis  species found in Papua New Guinea and Vanuatu.


(Table 5). Externally, Wallaconchis melanesiensis  cannot be distinguished from grey or black specimens of other Wallaconchis  species. Internally, the combination of a narrow penis, an apple-shaped spermatheca, and a free oviduct (not attached to the body wall by fibers) distinguishes W. melanesiensis  from all Wallaconchis  species except W. comendadori  , from which it differs by a shorter penis and a less convoluted deferent duct (in the anterior copulatory apparatus).

Color and morphology of live animals

(Fig. 60). The dorsal notum is generally grey, but may be blackish red. The ocular tentacles are dark grey. The hyponotum is light grey. The foot is yellow-orange.

External morphology.

Between eight and ten papillae bear dorsal eyes (three or four per papilla). There is a retractable papilla with eyes in the center of the dorsal notum, which is not raised above the other papillae.

Digestive system

(Figs 61-62, Table 4). Examples of radular formulae are presented in Table 4. The length of the rachidian teeth is approximately 20 µm, significantly smaller than that of the lateral teeth. The length of the hook of the lateral teeth gradually increases (from 30 to 50 µm) from the inner to the outer teeth (excluding the innermost and outermost lateral teeth which are significantly smaller). The intestinal loops are of type I.

Reproductive system

(Fig. 63). The oviduct is narrow (approximately the same width as the deferent duct). The spermatheca is apple-shaped, with two lobes, and joins the oviduct through a short duct.

Copulatory apparatus

(Figs 64-65). The penis (from 0.5 to 1 mm long) is extremely narrow (approximately 20-30 µm) and smooth with no hooks (Fig. 65). The penial sheath is narrow proximally and widens distally into a vestibule (of which the shape varies) (Fig. 64). The penis is within the proximal region of the vestibule, i.e., near the end of the penial sheath (Fig. 64A). The deferent duct is highly convoluted. The length of the penial sheath is approximately two thirds of the body cavity. The deferent duct is thicker than the penial sheath (excluding the vestibule). The retractor muscle is narrow and inserts at the posterior end of the body cavity, near the rectum.


Wallaconchis melanesiensis  is the only Wallaconchis  species found in New Ireland (Papua New Guinea), which is the type locality of Onchidium granulosum  Lesson, 1826. Lesson’s (1826: pl. 14, fig. 2) illustration of the dorsal notum and his written description of small, dorsal tubercles ( Lesson 1830) are similar to the granular dorsal notum of Wallaconchis  . Hoffmann (1928:86) considered Onchidium granulosum  to be part of the genus Oncis (Platevindex)  and Oncis lata  to be a synonym of O. granulosum  . However, Onchidium granulosum  does not belong to Platevindex  because the foot originally illustrated by Lesson (1826: pl. 14, fig. 2B) is much wider than the very narrow foot of Platevindex  species. However, while the width of the foot indicates it does not belong to Platevindex  , there is not enough information to confirm it is a Wallaconchis  species. Because Lesson did not describe or illustrate the internal anatomy and because the type material is lost, Onchidium granulosum  is regarded here as a nomen dubium.

The application of Onchidium cinereum  Quoy & Gaimard, 1832 (with a type locality in Tonga) has remained confusing. The original description is short and uninformative. The type material was not located. At this stage, it cannot be determined whether Onchidium cinereum  applies to a species of Peronia  , Wallaconchis  , or another genus. Therefore, Onchidium cinereum  is regarded here as a nomen dubium. Semper re-described O. cinereum  based on Tonga specimens from the collections of the Museum Godeffroy (not part of the type series), and these specimens are part of a Wallaconchis  species (based on the anatomical characters mentioned). The specimens that Semper examined indicate that a Wallaconchis  species lives in Tonga, which could be W. comendadori  , W. melanesiensis  , or even a distinct species, but this could not be tested here because we did not have access to Tonga material. Finally, note that Hoffmann (1928) and Labbé (1934) commented on O. cinereum  based on Semper’s re-description, not based on the original descriptiotion or new material.

Intra-specific genetic divergence is higher in W. melanesiensis  than in other Wallaconchis  species. Specimens from Vanuatu are 3.8% to 5.6% genetically divergent from the other specimens (from Indonesia and Papua New Guinea). High genetic divergences are even observed between specimens from the same locality (e.g., 3.4% within Vanuatu and Halmahera, and 4.4% within Kavieng, Papua New Guinea). The genetic divergence between the individuals from Vanuatu and those from Papua New Guinea and Indonesia could simply be an artifact of the geographic isolation of Vanuatu. Also, intra-specific divergences up to 5.5% were observed within other onchidiid species ( Dayrat et al. 2016). The presence of a distinct species in Vanuatu cannot be excluded but would result in splitting W. melanesiensis  into three or more species, as the specimens from Papua New Guinea and Indonesia are not reciprocally monophyletic with respect to Vanuatu individuals; therefore, specimens from Vanuatu are not currently considered to be a distinct species.