Eopilidion misakiense, Kajihara & Abukawa & Chernyshev, 2022

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 : 516-517

EOPILIDION MISAKIENSE SP. NOV.

( FIGS 2A , 4A–C )

Zoobank registration: u r n: l s i d: z o o b a n k. org:act: DBA0D4FA-ACAC-4440-9EA3-894F582D62F0.

Material examined: Holotype, ICHUM 6303 , extracted total DNA (no morphological voucher remains); 12 February 2015, dredged at station 2 of the 5 th JAMBIO Coastal Organism Joint Survey ( Nakano et al., 2015), off Misaki (between 35°08′29′N, 139°32′34″E, 198 m depth, and 35°08′27″N, 139°32′12″E, 274 m depth), Sagami Bay , Kanagawa, Japan, collected by H. Kajihara.

Sequences: From the holotype: LC178608, 18S (1768 bp) ; LC178641, 28S (2144 bp) ; LC178690, 16S (506 bp) ; LC190962, COI (658 bp) .

Etymology: The new specific name is an adjective, derived from the type locality.

Description: Known from anterior fragment, 4 mm long, 1 mm wide, uniformly pale red in colour. Head anteriorly pointed ( Fig. 2A ), similar to that of capitellid polychaetes. Pre-cerebral region remarkably reduced, about 200 µm long, 320 µm in diameter at base; brain region 500 µm long, 700 µm wide. Transverse cephalic furrow present just behind brain ( Fig. 4A, C ), encircling head, without secondary furrows. Cerebral organ just behind cephalic furrow, elongated pit, 380 µm long along anterior–posterior axis, 130 µm wide along dorsoventral axis ( Fig. 4C ). Mouth ventral, small, opening 1.6 mm behind tip of head. Proboscis pore opening subterminal ( Fig. 4A–C ), immediately anterior to brain.

enlargement of the head (K); L, M, Baseodiscus aff. princeps ( Coe, 1901a) , ICHUM 6335, entire body (L) and enlargement of the head (M); N, Baseodiscus nipponensis ( Hubrecht, 1887) , ICHUM 6338; O–Q, Baseodiscus cf. princeps ( Coe, 1901a) , ICHUM 6339, entire body (O), ventral view of anterior end (P), and lateral view of head (Q). Photos by A. V. Chernyshev (A, B), H. Kajihara (C–F, N–Q), G. Giribet (G, H), T. C. Hiebert (I), and K. Kakui (J, K, L, M).

Distribution: Known only from the type locality, Sagami Bay, Japan.

Remarks: The unusually reduced precerebral region and the wide subventral proboscis pore opening just in front of the brain, as well as phylogenetic position as sister-taxon to all other molecularly known heteronemerteans, justify a new family for E. misakiense . However, information on the body-wall structure is lacking, and it remains to be determined whether Eopilidion misakiense belongs to the Heteronemertea (with cutis layer) or not (without cutis layer) (see Discussion below).

Figures

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).

Figure 4. A–C, Eopilidion misakiense gen. et sp. nov., holotype, ICHUM 6303, anterior end of body, ventral view, head to the right (A), frontal view (B), squeezed-slide preparation (C); D, Valencinura jambio sp. nov., holotype, ICHUM 6305, anterior end of body, ventral view. Photos by H. Kajihara.