Trapania japonica Rudman 1987
Creators: name: Smirnoff, Dimitri S.
name: Donohoo, Samantha A.
name: Gosliner, Terrence M.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Nudibranchia
Goniodorididae
Trapania
Trapania japonica

description: TRAPANIA JAPONICA (BABA, 1935)
(FIGS 2A, 3, 4A)
Drepania japonica Baba, 1935: 336–338, fig. 4.
Trapania japonica (Baba, 1935) Rudman, 1987: 197– 201, figs 3C, 7A, 8, 9; Baba, 1990: 8–9, figs 1–3; Rudman & Darvell, 1990; Nakano, 2004: 93, top photograph; Gosliner et al., 2018: 63, middle-right photograph.
Trapania norakhalafae Khalaf & Khalaf, 2017:7–30.
Material examined: CASIZ 182896 A, two specimens, one sequenced, Mabini, Batangas Province, Luzon Island, Philippines, May 2010, collected by Peri Paleracio. CASIZ 222116, one specimen, dissected, Mabini, Batangas, Philippines, May 2017, collected by Peri Paleracio.
Geographical distribution: Widespread in the IndoPacific: known from Japan (Baba, 1935, 1990; Nakano, 2004), Australia (Rudman, 1987), Hong Kong (Rudman & Darvell, 1990), the United Arab Emirates (Khalaf-Prinz & Khalaf, 2017) and the Philippines (present study).
External morphology: Living animal 3–5 mm in length (Fig. 2A). The body is opaque white, randomly covered in at least eight medium and small circles of dark-to-light brown pigment. Extra-rhinophoral and extra-branchial appendages are pointed with bright yellow from tip to the base, which is opaque white. Rhinophores, six to eight lamellae and a pointed tip. Rhinophores are uniformly wide along their length and the same colour as the brown circles. Oral tentacles are typically elongate and completely coloured the same brown as the rest of the body. The anterior margins of the foot, which extend laterally as elongate appendages, are opaque white adorned halfway down its length with a circle similar to the body. The gill plume branches are pigmented brown interspersed with areas of opaque white.
Buccal mass: The buccal mass is muscular with a moderately developed buccal pump on the dorsal surface. Inside the anterior portion of the mass is a pair of weakly developed jaws. The jaws contain weakly developed triangular elements and have less cuticularization compared to other Trapania (Fig. 3A). The radular formula of one specimen (CASIZ 222116) is 28–30 × 1.0.1. The older teeth are much smaller than the newer ones and the radula widens towards the more newly developed teeth. The morphology of the individual teeth is atypical of Trapania. The teeth (Fig. 3B) bear numerous denticles on either side of the primary large cusp, which is pointed and slightly curved. Externally to the large cusp lie seven to nine evenly small denticles that resemble the teeth of a hair comb. Internally to the large cusp lie five to six small triangularly shaped denticles, diminishing in size toward the medial line. The older teeth have fewer denticles than the more recently developed ones. The interior denticles are larger than those found external to the large cusp in the middle of the width of the tooth.
Reproductive system: The mature reproductive system is triaulic (Fig. 4A). The narrow pre-ampullary duct enters the posterior end of the elongated cylindrical ampulla. The ampulla terminates where the post-ampullary duct divides into the oviduct and vas deferens.The short oviduct enters the female gland mass. The vas deferens is initially narrow, widening into a glandular prostatic portion as it loops over itself. This gradually transitions into the narrower, muscular ejaculatory portion that is continuous with the wide, straight, elongate penial sac. The penial sac terminates at the gonopore adjacent to the vagina. The vagina is moderately long and uniformly narrow throughout its length and joins the large, spherical bursa copulatrix and short, narrow receptaculum duct. The receptaculum duct is extremely short and connects with pyriform receptaculum seminis near the division of the short uterine duct, which enters the female gland mass. The female gland mass is composed of the large mucous gland and the smaller albumen and membrane glands.
Remarks: Our molecular phylogeny, the 16S ABGD analysis and the bPTP analysis support Trapania japonica as a distinct species and reveal that it is part of a clade composed of T. scurra, T. palmula, T. tatsulok and T. kahel. The external anatomy and radula have been previously described (Baba, 1935; Rudman, 1987), but not the reproductive system. Rudman noted the unique nature of the radular teeth, with a single, large denticle near the middle of the tooth. Khalaf (2017) described T. norakhalafae from specimens noting the similarity of this species to Trapania sp. 13 in Gosliner et al. (2015). Khalaf also noted the similarity of T. norakhalafae to T. japonica, but did not elaborate on this. His description did not include any internal anatomy and described only the living animal and its coloration. Subsequently, Gosliner et al. (2018) concluded that the specimen they had previously identified as T. sp. 13 was indeed T. japonica and noted that T. norakhalafae was likely a synonym. In this study, we confirm that the specimens identified as this species by Gosliner et al. (2018), have radular morphology consistent with T. japonica. No aspects of the external morphology of T. norakhalafae are inconsistent with those described for T. japonica and we can find no basis for the separation of T. norakhalafae as a distinct species. Therefore, we consider T. norakhalafae to be a junior synonym of T. japonica.
description: Published as part of Smirnoff, Dimitri S., Donohoo, Samantha A. & Gosliner, Terrence M., 2022, Extra-branchial processes manifest extra diversity: systematics of the genus Trapania (Nudibranchia: Goniodorididae) and nine new species descriptions, pp. 270-313 in Zoological Journal of the Linnean Society 196 on pages 279-281, DOI: 10.1093/zoolinnean/zlac009, http://zenodo.org/record/7037746