Baseodiscus curtus, (HUBRECHT, 1879)

Kajihara, Hiroshi, Abukawa, Shushi & Chernyshev, Alexei V., 2022, Exploring the basal topology of the heteronemertean tree of life: establishment of a new family, along with turbotaxonomy of Valenciniidae (Nemertea: Pilidiophora: Heteronemertea), Zoological Journal of the Linnean Society 196, pp. 503-548 : 534-535

BASEODISCUS CF. CURTUS ( HUBRECHT, 1879)

( FIG. 3F )

? Polia curta Hubrecht, 1879: 209 (Naples, Italy).

? Eupolia curta: Bürger, 1892: 151 (Naples, Italy); 1895a: 601, pl. 4, fig. 17 (Naples, Italy); (figs 3–5, 7, 9 supposedly depict the same species, but their identity needs to be further scrutinized).

? Baseodiscus curtus: Bürger, 1904: 82 ; Timofeev, 1911: 39 (Villefranche-sur-Mer, France); Corrêa, 1956: 199–201, pl. 2, figs 6–9, 11 (Naples, Italy).

Eupolia curta: Takakura, 1898: 185 , fig.7 (Misaki, Japan).

Baseodiscus curtus: Iwata, 1952: 141–142 , fig. 14 (Fukue, Japan); Kajihara, 2017: 243, fig. 16.2a.

? Eupolia curta: Joubin, 1904: 327 ( Djibouti) .

? Taeniosoma curtum: Verrill, 1900: 597–598 , pl. LXX, fig. 3, text-fig. 10a, b ( Bermuda).

? Baseodiscus delineatus var. curtus: Coe, 1940: 261 (in part).

Material examined: Two specimens, ICHUM 6328 , 6329 , 12 November 2003, subtidal, ~ 2 m depth, among shells of the cultured oyster Magallana gigas ( Thunberg, 1793) , Hiroshima Bay (c. 34°23′N, 132°10′E), Japan, collected by H. Kajihara.

Sequences: From ICHUM 6328 : LC178663 , 16S (507 bp) ; LC190943 , COI (615 bp). From ICHUM 6329 : LC178591 , 18S (1798 bp) ; LC178620 , 28S (2097 bp) ; LC178664 , 16S (507 bp) ; LC190944 , COI (658 bp) .

Description: Body up to 17 cm long, 4 mm wide; background body colour cream white; dorsally mottled with narrow, longitudinal, broken, reddish brown stripes; ventrally without markings ( Fig. 3F ).

Distribution: Baseodiscus cf. curtus in the sense of this study has been reported from Japan ( Takakura, 1898; Iwata, 1952; Kajihara, 2017; present study). Baseodiscus curtus s.s. has been reported from Italy ( Hubrecht, 1879; Bürger, 1892, 1895a; Corrêa, 1956) and the Mediterranean coast of France ( Timofeev, 1911).

Remarks: Considering the geographic distance between Italy and Japan, application of the name curtus to our material from Japan needs confirmation with barcode sequences from topotypes from Naples. If our specimens are actually B. curtus , then the species is different from B. delineatus , as Crandall et al. (2002: 3) noted, although Gibson (1995: 479) synonymized these two species.

Hubrecht (1879: 209) established Polia curta , which was supposedly ‘Distinguished from the foregoing (= Polia delineata = Baseodiscus delineatus ) by its greater width in comparison to its length. The brown stripes are much more closely set on the back, 12–15 being counted in a transverse line on the back. The belly remains white; only in the largest examples it becomes striped too, the region of the mouth and undersurface of the head always excepted. In young examples the stripes are yet stellate pigment specks, whereas at the same age they are stripes already in Polia delineata .’

Under the name Eupolia curta, Bürger (1892, 1895a ) referred to four different forms from Naples, as follows: (1) small, 0.5–2.0 cm long, light yellow ground colour, speckled with dark brown dots in anterior part of body, probably only dorsally ( Bürger, 1895a, pl. 4, fig. 3); (2) the most common type, co-occurring with B. delineatus , 5–6 cm long, 2.5 mm wide, yellow grey in ground colour, dorsally marked with brown, reticular longitudinal stripes; a larger specimen was 10 cm long, 4 mm wide, with longitudinal stripes also present on ventral surface of body ( Bürger, 1895a, pl. 4, fig. 7); (3) bulky, broad form, 15 cm long, 8–9 mm wide, vermilion red in background body colour, with fine, yellow reticular pattern both dorsally and ventrally [not obvious in Bürger’s (1895a, pl. 4, figs 5, 5a) illustration], head light yellow on dorsal margins, deep yellow ventrally, with short yellow line extending for 1 cm mid-ventrally at anterior end of body; same as Joubin’s (1890) form reported from Banyulssur-Mer, France; and (4) ventrally snow white in colour, 6–7 cm long, 3 mm wide ( Bürger, 1895a, pl. 4, fig. 17).

Our specimens from Japan agree with Hubrecht’s (1879) original description, as well as with Bürger’s (1895a) form iv (with snow-white underside) in that the brown longitudinal stripes are lacking on the ventral surface of the body. The taxonomic identity of Bürger’s (1895a) forms i, ii, and iii need to be investigated with molecular data.

There are various records of valenciniid heteronemerteans under the name curtus , curta or curtum from different parts of the world, with a varying degree of reliability in terms of taxonomic identity. Verrill (1900) reported a form as Taeniosoma curtum from Bermuda; slenderer than B. curtus and lacking dorsal stripes on the head in front of the cephalic furrows, it thus appears to be a different species. Joubin (1904) did not mention whether stripes were also present on the ventral surface of the body in material from Djibouti that he identified as Eupolia curta ; it could have been either B. curtus or another species such as B. delineatus . Timofeev (1911: 39) provided no information on the body colour of his ‘ Baseodiscus curtus ’ from Villefranche-sur-Mer, the identity of which cannot be confirmed. StiasnyWijnhoff (1925) admitted that her specimens from Curaçao, which she identified as B. curtus , were also consistent with B. delineatus in having stripes also on the ventral surface of the body. Coe (1940) regarded curtus as a variety of B. delineatus , listing ( Coe, 1940: 261) the distribution as ‘Mediterranean, East Indies, Polynesia, Mauritius, Bermuda, West Indies, on the Pacific coast in the Gulf of California, and on the coast of Chile’. Coe (1940) mentioned that the body markings in B. delineatus var. curtus comprise small, red or brown dots or larger spots without definite pattern, instead of interlacing longitudinal lines. These markings are also seen in B. maculatus , B. maculosus and B. amboinensis , suggesting that Coe’s (1940) B. delineatus var. curtus probably included several species. Corrêa (1956) reported three specimens from Naples that she identified as B. curtus [ Bürger’s (1895a) form ii], although they also had stripes also on the ventral body surface. Gibson’s (1974) material from Jidda, reported as B. curtus , is more similar to B. insignis Punnett & Cooper, 1909 from Zanzibar in that the stripes, also present ventrally, are discontinuous beyond and behind the cephalic furrow; this also applies to what Gibson (1979) identified as B. delineatus from the Great Barrier Reef.

Figures

Figure 3. A, Baseodiscus aff. marmoratus (Bürger, 1890) (voucher DNA, ICHUM 6322); B, Baseodiscus aff. maculosus (Bürger, 1895a) (voucher DNA, ICHUM 6324); C–E, Baseodiscus delineatus (Delle Chiaje, 1822-1829), ICHUM 6326; F, Baseodiscus cf. curtus (Hubrecht, 1879), ICHUM 6328; G, H, Baseodiscus urgorrii sp. nov., holotype, MCZ IZ-135319, entire body (G) and protruding proboscis (indicated by an arrowhead, H); I, Baseodiscus punnetti (Coe, 1904), specimen different from any voucher specimens in this study; J, K, Baseodiscus kakuii sp. nov., holotype, ICHUM 6334, anterior body (J) and