Baseodiscus amboinensis
Creators: name: Kajihara, Hiroshi
name: Abukawa, Shushi
name: Chernyshev, Alexei V.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Nemertea
Pilidiophora
Heteronemertea
Valenciniidae
Baseodiscus
Baseodiscus amboinensis

description: BASEODISCUS CF. AMBOINENSIS (STAUB, 1900)
(FIG. 2N)
? Eupolia amboinensis Staub, 1900: 594, 597–599 (78, 81–83 in an alternative pagination), pl. XLVII, fig. 1, 1a, 1b, pl. XLVIII, figs 1–5 (Ambon, Indonesia).
? Eupolia reticulata Staub, 1900: 594–595, 599–601 (78–79, 83–85 in an alternative pagination), pl. XLVII, fig. 2, 2a, pl. XLVIII, figs 6–9 (Ambon, Indonesia).
Baseodiscus delineatus: Chernyshev, 2011b: 22–23, fig. 1C (Cù Lao Thu Island, Vietnam).
Baseodiscus jonasii: Chernyshev, 2015: 548–549 (Cù Lao Thu Island, Vietnam); Chernyshev, 2016: 289, fig. 4A (Cù Lao Thu Island, Vietnam).
Material examined: One specimen (DNA voucher ICHUM 6313), 18 May 2010, among dead corals, 6–9 m depth, Cù Lao Thu Island (10°32′N, 108°55′E), Vietnam, collected by A. V. Chernyshev.
Sequences: From ICHUM 6313: LC178599, 18S (1804 bp); LC178629, 28S (2086 bp); LC178676, 16S (508 bp).
Description: In life, the specimen examined (Fig. 2N) was ‘about 1 m long, ground colour pale yellowish with numerous reddish brown longitudinal stripes situated irregularly on both dorsal and ventral surfaces; about 80–90 eyes on each side of head; transverse cephalic furrows present, each with 50–60 secondary grooves’ (Chernyshev, 2016: 289). The mouth is small and rounded, not slit-like (Chernyshev, 2016, fig. 4A).
Remarks: In the preserved state, Staub’s (1900) material of Eupolia amboinensis from Ambon, Indonesia, reached 30 cm in body length and 5 mm in width, with a dark background body colour having light-brown longitudinal stripes, which are interrupted, branched and reticulate. Eupolia reticulata, also from Ambon, reached up to 27cm long and 6 mm wide (Staub, 1900), and had nearly the same external appearance as Eupolia amboinensis, and thus can be regarded as conspecific; indeed, Gibson (1979) synonymized these two nominal species under Baseodiscus delineatus, although with some reservation.
Our specimen from the South China Sea has a bright yellowish background colour, entirely overlain with longitudinal, intermittent, reddish brown stripes, which are more closely set relative to one another than in Baseodiscus delineatus (Fig. 3C), making it difficult to tell which (bright yellow or reddish brown) is the background colour, especially in the posterior part of the body. The brown stripes appear to be narrower than those in Baseodiscus cf. curtus (Fig. 3F). Our specimen is thus compatible with Staub’s (1900) descriptions and illustrations of Eupolia amboinensis and E. reticulata. The geographical distance of ~ 2600 km between the South China Sea and Banda Sea localities leaves room for doubt as to the identification of our material as Baseodiscus amboinensis. Barcode sequences from topotypes will be necessary to resolve this uncertainty.
Due to insufficient knowledge of the genetic diversity among species of Baseodiscus in the tropical Indo-West Pacific, our material was tentatively identified first as Baseodiscus delineatus (Chernyshev, 2011b) and then as Baseodiscus jonasii (Chernyshev, 2015, 2016). The uncorrected p -distance for 16S sequences between our material (LC 178676) and Baseodiscus jonasii (AY 955231) was 4.3%, which is greater than some values known between congeneric lineid heteronemertean species that were confirmed to be biologically different by cross-fertilization experiments, e.g. 4.0% (Hiebert & Maslakova, 2015) between Maculaura alaskensis (Coe, 1901a) and Maculaura oregonensis Hiebert & Maslakova, 2015, and 2.8% (Ikenaga et al., 2021) between Kulikovia alborostrata (Takakura, 1898) and Kulikovia fulva (Iwata, 1954). Our specimen differs from B. jonasii in that the background and stripe colours are reversed between the two species: in B. jonasii, the background colour is reddish brown and the stripes are yellowish beige (Strand et al., 2005), as in Borlasia striata Quoy & Gaimard, 1833 from Guam. The latter has a red background colour with pale reddish stripes (Quoy & Gaimard, 1833: 286, pl. 24, figs 3, 4), and thus may be a senior synonym of B. jonasii.
description: Published as part of 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), pp. 503-548 in Zoological Journal of the Linnean Society 196 on page 528, DOI: 10.1093/zoolinnean/zlac015, http://zenodo.org/record/7037958