Wallaconchis graniferum (Semper, 1880) Semper, 1880

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

Wallaconchis graniferum (Semper, 1880) comb. n. Figs 43, 44, 45, 46, 47, 48, 49

Onchidium graniferum Semper, 1880: pl. 19, fig. 13, pl. 23, fig. 3; Semper 1882, 273-274, pl. 21, fig. 10; Hoffmann 1928: 80-81 (as Oncidium graniferum ).

Paraoncidium reevesii : Britton 1984: 184-185, fig. 4 [non Onchidium reevesii J. E. Gray, 1850].

Onchidella sp.: Sun et al. 2014: fig. 4 [non Onchidella J. E. Gray, 1850].

Type locality.

Bohol (Philippines).

Type material.

Three syntypes (ZMB 39032), between 22/14 mm and 11 mm, according to Semper (no width was provided by Semper for the smaller specimen). The syntypes were destroyed prior to the present study, and it is only through Semper’s description that it could be ascertained that there were originally three syntypes. Only small pieces of dorsal notum and of one digestive system (stomach, intestine, and digestive glands) now remain.

Additional material examined.

Indonesia, Timor, Oesapa, 10°08.73'S, 123°38.10'E, 1 specimen 30/19 mm [5902], st 250, sandy part of mangrove with Sonneratia and Avicennia trees (UMIZ 00073). Philippines, Luzon, Lian, Batangas, 13°59.76'N, 120°37.43'E, 1 specimen 46/27 mm [3163], st 181, sandy, open Avicennia forest (PNM 041227); Bohol, Loay, 09°36.23'N, 123°59.72'E, 6 specimens 28/17 mm [3636], 26/18 mm [3638], 26/15 mm [3635], 18/12 mm [5760], 16/13 mm [5762] and 16/11 mm [5761], st 198, mostly sand, and a few Avicennia (PNM 041228).

Distribution.

Indonesia: Timor. Philippines: Bohol (type locality) and Luzon. China. All records are new except for the type locality.

Habitat

(Fig. 43, Table 3). In Bohol, Wallaconchis graniferum was found on a sandy beach with a few Avicennia trees; the sand was finely grained, mixed with many broken shells, and sculpted into round pellets by sand bubbler crabs. In Luzon, it was found on fine sand in a coastal mangrove forest, near the roots of an Avicennia tree. In Timor, one animal was found in a sandy area of a Sonneratia and Avicennia mangrove.

Diagnosis

(Table 5). Wallaconchis graniferum cannot be distinguished externally from other Wallaconchis species. Brown specimens cannot be distinguished from any other species, and brightly-colored specimens cannot be distinguished from W. nangkauriense and W. ater . The peculiar pattern of penial hooks of W. graniferum (two proximal regions of hooks separated from a distal region of hooks by a gap without hooks) has not been observed in any other onchidiid genus.

Color and morphology of live animals

(Fig. 44). The dorsal color is variable and may be brown, yellow or orange but additional color variants may exist. The ocular tentacles are white, beige, yellow-orange, or orange-brown. The hyponotum is white or beige-orange. The foot is orange or yellowish white.

External morphology.

Approximately three to twelve papillae bear dorsal eyes, with three or four eyes per papilla. There is a retractable papilla with eyes in the center of the dorsal notum, which may be slightly raised above the dorsal surface.

Digestive system

(Fig. 45, Table 4). Examples of radular formulae are presented in Table 4. The length of the rachidian teeth is approximately 25-30 µm, significantly smaller than that of the lateral teeth. The length of the hook of the lateral teeth gradually increases, from 40 to 60 µm, from the inner teeth 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. 46). In the posterior (hermaphroditic) part of the reproductive system, the oviduct is larger than the deferent duct and is especially wide distally. The spermatheca is spherical and joins the distal end of the oviduct through a short duct. In the specimen from Luzon, the spermatheca was larger than in the specimens from Bohol.

Copulatory apparatus

(Figs 47-49). The penis bears hooks in three distinct regions, two proximal regions being separated from one distal region by a gap with no hooks (Fig. 47A). When the penis is partially evaginated, only the hooks near the base can be observed (Figs 47C, 48D, E). In large individuals, the penis may reach approximately 8 mm in length when fully evaginated (Fig. 48 A–C). In the first, most proximal region (at the base of the penis), the hooks are small, between 50 and 90 μm long, and clustered on one side of the penis. Following these hooks, a second region bears slender hooks, closely packed together, which vary in size. They may be longer on one side of the penis (between 90 and 170 μm, Figs 48B, 49C) than on the other side (between 40 and 50 μm). Then the penis is smooth (with no hooks) (Figs 48B, 49A, C). Finally, distally, at the tip of the penis, a fourth region bears hooks between 60 and 100 μm long (Figs 48C, 49). When it is evaginated, the penis is enclosed within the penial vestibule, which may be spherical or pear-shaped depending on the orientation of the penis inside (Fig. 47B). When it is not evaginated, the penis is within the penial sheath, and the hooks are hidden within the penis (Fig. 49 A–C). All specimens examined were sexually mature. The deferent duct is narrow and convoluted. The retractor muscle is long (equal to at least one third of the length of the body cavity) and inserts posteriorly by the rectum.

Remarks.

Onchidium graniferum must be transferred to Wallaconchis because the diagnostic combination of characters of Wallaconchis is found in Semper’s original description and in what remains of the syntypes. Semper (1882: 274) wrote that there is no accessory penial gland and no rectal gland in O. graniferum , which is fortunate here because the copulatory organs of the syntypes are all missing. Semper did not describe the intestinal loops type but the one digestive system that remains in the type material is clearly of type I. Semper’s description of the male opening below the right tentacle also is consistent with the fact that O. graniferum belongs to Wallaconchis .

The only issue in Semper’s description (1882: 274, our translation from German) of O. graniferum is that he wrote that the retractor muscle of the penis inserted "somewhat behind the center of the animal," or slightly posterior to the center of the body cavity. In all Wallaconchis species, the retractor muscle inserts at the posterior end of the body cavity, near the rectum. More precisely, that type of insertion is found in all mature animals. In small animals (which may or may not be fully mature), the retractor muscle occasionally inserts near the heart, approximately at mid-length of the body cavity. One of the syntypes that Semper examined was only 11 mm long and would likely be immature. If Semper observed the insertion of the retractor muscle in this immature specimen, it could explain why his description of the retractor muscle differs from the insertion observed here.

The publication dates of various sections of the volume on Landmollusken by Carl Semper in the Reisen im Archipel der Philippinen series were clarified by Johnson (1969). The species name Onchidium graniferum was first published by Semper in 1880 (pl. 19, fig. 13 & pl. 23, fig. 3) with two illustrations of the external anatomy and the radula and no written description. Because Onchidium graniferum was published before 1931, ICZN (1999) Article 12.2.7 applies, and Semper’s figures are regarded as an indication accompanying the new name Onchidium graniferum . The text of the description and the illustration of the radula (pl. 21, fig. 10) were published in 1882. No other existing names were found to apply to the species described here.

The copulatory organs of the syntypes were all destroyed prior to the present study (likely by Semper himself), but Semper (1882: 274, translated from German) described the penis of O. graniferum as a "cartilaginous tube" with only a "tooth-bearing portion" and "cartilage teeth of very different sizes." Semper (1882: 274, our translation from German) also indicated a specific order in which penial hooks (which he called teeth) of different sizes are organized, which is in agreement with the arrangement of hooks described here: "The foremost ones are very irregular and broad; they are on average 80 μm long. Then a section with teeth three times as long, of 180 μm, then again another with small ones; but in the last part great ones are found. The large teeth are very tightly pressed." Semper illustrated these penial hooks of different sizes individually, but not the hooks together in situ, so the exact arrangement of the penial hooks that he observed cannot be known with certainty. Semper also did not indicate whether the penis was evaginated or not, but it can be assumed that his “foremost” hooks are at the base (i.e., proximal on the penis when evaginated). So, overall, Semper’s description of the arrangement of penial hooks of different sizes is consistent with the pattern of penial hooks observed here from the proximal base of the penis to its evaginated tip. Semper’s illustrations of a thick penial sheath and the shapes of the penial hooks are also consistent with the species described here. Finally, Semper described the penis as slightly shorter than the retractor muscle. The retractor muscle was found to be shorter than the penis in the species described here, but this trait varies within Wallaconchis species and is not useful for identification.

Britton (1984: fig. 4D) illustrated the penial anatomy of an onchidiid species from Hong Kong which matches the penial anatomy of the species described here perfectly. Britton misidentified that species as Paraoncidium reevesii (J. E. Gray, 1850) because the valid name Onchidium reevesii J. E. Gray, 1850 actually applies to a species with both an accessory penial gland and a rectal gland, both of which Britton noted were absent from his Hong Kong specimens ( Dayrat et al. 2016). Britton’s description (1984: 184) of the intestinal loops of type II is unlikely given the distinctive penial anatomy he illustrated (known only in this onchidiid species). Britton either made an error characterizing the intestinal loops, or the specimens he examined were a mix of multiple species with different intestinal types. Britton’s record of Paraoncidium reevesii is thought to be a misidentification for Wallaconchis graniferum . Finally, the presence of Wallaconchis graniferum in China is also known thanks to a few DNA sequences found in GenBank, misidentified as Onchidella sp. ( Sun et al. 2014) and that are part of the species described here (Fig. 1).

Labbé (1934) identified a specimen from the Philippines as Paraoncidium graniferum for which he mentioned intestinal loops of type I, no rectal gland, and no accessory penial gland, which together, if correct, indicate that he examined a Wallaconchis species. Labbé’s description (1934: 228) of the penis as "curled, with teeth anteriorly" suggests that he probably examined W. graniferum , but the description of the hooks is not detailed enough to be sure that he did not examine W. uncinus or another species. At any rate, this species is found in the Philippines and Labbé’s record would not improve our knowledge of their geographic distribution.

Finally, Hoffmann (1928: 80-81, our translation from German) commented that Semper’s description was inconsistent: "the cartilage of the penis is approximately 3 mm long and has only the tooth-bearing portion" but in "his illustration, which is made in natural size, the penis is 7 mm long." However, contrary to Hoffmann’s claim, Semper’s description is not inconsistent. Indeed, it is the entire penial sheath which is 7 mm long in Semper’s illustration and not the penis itself.