Baseodiscus hemprichii, (EHRENBERG, 1831)

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 : 529

BASEODISCUS HEMPRICHII (EHRENBERG, 1831)

( FIG. 2O )

Nemertes hemprichii Ehrenberg, 1831 in Ehrenberg (1828 –1831): 64. For additional synonyms, see: Gibson (1979), Kazmi & Gibson (1994), Kajihara & Kato (2008) and Shrinivaasu et al. (2011).

Material examined: Four specimens; extracted total DNA and remaining body preserved in 99% EtOH. ICHUM 6314 , 6315 , 22 May 2008, rocky intertidal, Iheyajima (27°02′09″N, 127°58′02″E), Okinawa, Japan, collected by K. Kakui ; ICHUM 6316 , 6317 , 25 May 2001, Tanegashima , Kagoshima (30°49′28″N, 131°02′18″E), Japan, SCUBA, ~ 5 m depth, collected by H. Kajihara.

Sequences: From ICHUM 6314 : LC178593 , 18S (1793 bp) ; LC178623 , 28S (2107 bp) ; LC178668 , 16S (510 bp) ; LC190946 , COI (658 bp). From ICHUM 6315 : LC178594 , 18S (1794 bp) ; LC178624 , 28S (1095 bp) ; LC178669 , 16S (512bp) ; LC190947 , COI (658bp). From ICHUM 6316 : LC178595 , 18S (1794 bp) ; LC178625 , 28S (2007bp) ; LC178670 , 16S (510 bp) ; LC190948 , COI (658 bp). From ICHUM 6317 : LC178671 , 16S (510 bp) .

Description: Body white, with cephalic patch and middorsal stripe ( Fig. 2O ), anterior end of latter widening laterally and reaching ventral side.

Distribution: Widely distributed in the Indo-Pacific from the Red Sea to Easter Island (summarized in Kajihara & Hookabe, 2019, fig. 1).

Remarks: Baseodiscus hemprichii is one of the few nemertean species that can be reliably identified by only the external appearance, even after preservation. It can reproduce asexually by fragmentation followed by anterior regeneration ( Kajihara & Hookabe, 2019). Kajihara & Kato (2008) listed the diagnostic external features in this species, which include ‘whitish body, with head demarcated from the body by a transverse furrow encircling the neck; minute secondary furrows may be present in life, running anteriorly from the main transverse furrow, difficult to confirm in preserved state; numerous ocelli arranged along the margin of the head; a single dark-coloured (purplish, dark brown or black) cephalic patch situated at the posterior portion of the dorsal surface of the head; and a dorsal and ventral stripe of the same coloration as the cephalic patch; the anterior end of the dorsal stripe laterally widened to form a T-shaped collar’.

Kazmi & Gibson (1994) reported an individual from Karachi, Pakistan, in which the mid-dorsal stripe was discontinuous and regularly interrupted, as in B.edmondsoni Coe, 1934 from Hawaii ( Coe, 1934, 1947). Given the sister-taxon relationship ( Fig. 1 ) between B. hemprichii and a clade containing two ‘banded’ species ( B. mexicanus and B. zebra ), B. hemprichii sensu Kazmi & Gibson (1994) may possibly represent a hybrid between B. hemprichii s.s. and one of these banded forms, or yet one more new species.

Baseodiscus unistriatus ( Isler, 1900) , with a whitish body and a dark-coloured (olive green or black) middorsal stripe, is known from Sri Lanka ( Isler, 1900), Maldive Islands ( Punnett, 1903) and the Red Sea ( Gibson, 1974). Although our study does not include B. unistriatus , the body coloration of that species suggests a close relationship to B. hemprichii . Baseodiscus hemprichii seems to feed on terebellid polychaetes (see Potential food items below).

Figures

Figure 1. Maximum-likelihood (ML) tree showing the phylogenetic relationships among 41 newly sequenced specimens of pilidiophorans (indicated with solid blue circles). Numbers near nodes are support values, ML bootstrap/Bayesian inference (BI) posterior probability. Nodes with yellow triangles are fully supported, with 100% ML bootstrap and 1.00 BI posterior probability. New species names are indicated in bold. Some nodes were polytomous in the BI tree (indicated by hyphens in place of posterior probability values).

Figure 2. A, Eopilidion misakiense gen. et sp. nov., holotype, ICHUM 6303, lateral view, head to the right; B, Oxypolella hiebertae sp. nov., holotype, MIMB 42256; C, Cephalomastax brevis Iwata, 1957, ICHUM 6304; D, E, Valencinura jambio sp. nov., holotype, ICHUM 6305, anterior body fragment (D) and enlargement of intestinal region (E) showing yellowish proboscis (indicated by arrowheads); F, Baseodiscus takakurai Gibson, 1995, ICHUM 6306; G, Baseodiscus profundus sp. nov., holotype, MIMB 42257; H, I, Baseodiscus narusei sp. nov., holotype, ICHUM 6310, anterior end of body, dorsal (H) and ventral (I) views; J, Baseodiscus paracelensis sp. nov., holotype, MIMB 33132; K, Baseodiscus komatsui sp. nov., holotype, NMNS-Ne 1; L, Baseodiscus unicolor Stiasny-Wijnhoff, 1925; M, Baseodiscus giribeti sp. nov., holotype, MCZ IZ-135324; N, Baseodiscus cf. amboinensis (Staub, 1900); O, Baseodiscus hemprichii (Ehrenberg, 1828-1831), specimen from Okinawa, different from any voucher specimens in this study; P, Baseodiscus zebra sp. nov., holotype, RUMF-ZN-00001; Q, Baseodiscus quinquelineatus (Quoy & Gaimard, 1833), ICHUM 6319. Photographs by H. Kajihara (A, C, D, E, F, O), A.V. Chernyshev (B, G, J), T. Naruse (H, I), H. Komatsu (K), G. Giribet (L, M), D. Uyeno (P), and R.Yoshida (Q).