Ototyphlonemertes (parmula) nakaoae 1863

Kajihara, Hiroshi, Tamura, Kotaro & Tomioka, Shinri, 2018, Histology-free Descriptions for Seven Species of Interstitial Ribbon Worms in the Genus Ototyphlonemertes (Nemertea: Monostilifera) from Vietnam, Species Diversity 23 (1), pp. 13-37 : 24-27

Ototyphlonemertes (parmula) nakaoae sp. nov.

( Figs 9 , 10 )

Material examined. Five specimens: ICHUM 5366 (holotype) (from Dam Trong); four paratypes, ICHUM 5367 (from Dam Trong), ICHUM 5368–5370 (from Dam Ngoai) .

Description. Body length 4.1–6.2 mm (6.2 mm in holotype), width 0.2–0.3 mm (0.2 mm in holotype) (n =4). Epidermis whitish ( Fig. 9A, D, E ); cephalic furrow postcerebrally; tissues around brain slightly reddish ( Figs 9B, E, F , 10A, B ); cirri present in both anterior and posterior ends of body; cephalic cirrus formula (cf. Norenburg 1988b) observed in two specimens: A=2+2, B=0, C=9, D=6, E=4, tail= 14 in ICHUM 5368 (paratype); A=0, B=2, C=7+5, D=4+5, tail= 8 in ICHUM 5369 (paratype). Foregut–in-testine junction not markedly distinct. Statolith polygranular ( Fig. 10 C–F), 8–11 µm (9 µm in holotype) in diameter (n =4), consisting of 7–8 (7 in holotype) granules; statocyst 19.2–26.1 µm (19.2 µm in holotype) in diameter (n =4). Proboscis diaphragm short ( Figs 9F , 10A, B, G ); gland-secretion ring situated posterior to hind end of basis; accessory-stylet pouches two, each containing 2–5 accessory stylets (3 in each in holotype) per pouch (n =4 individuals ×2 pouches), directing both forward and backward; central stylet (as well as accessory stylets) spiral ( Fig. 10 H–K), 32–46 µm (32 µm in holotype) long; basis 39–52 µm (42 µm in holotype) long, 8–12 µm (8µm in holotype) wide (n =4), with each ridge twisting 1.5–2 (1.5 in holotype) times; basis length/width ratio 4.27–5.16 (5.16 in holotype); middle chamber bulbous; posterior chamber opaque, with specialized anterior part ( Figs 9B, F , 10A, B ). Intestinal diverticula deep. Posterior adhesive plate containing cells with orange contents ( Fig. 9C ). Gonads found in posterior 1/2 to 3/4 of intestinal region, alternating more or less regularly with intestinal lateral diverticula.

Distribution. So far recorded from the islands of Dam Trong (type locality) and Dam Ngoai, Vietnam.

Etymology. The specific name is a noun in the genitive case, after the Japanese ostracode biologist Dr Yuriko Nakao at Nihon University, Japan, who devotedly arranged our sampling trip to Phu Quoc.

Remarks. In the phylogenetic tree, Ototyphlonemertes ( parmula ) nakaoae sp. nov. was sister to O. ( parmula ) tsukagoshii sp. nov. ( Fig. 2 ). Out of the seven species discovered in this study, O. ( parmula ) nakaoae turned out to be the only species that occurred at both the localities surveyed, the islands of Dam Trong and Dam Ngoai. Following O. ( macintoshi ) ani , it was the second most abundant species recovered in the present survey.

Figures

Fig. 9. Ototyphlonemertes (parmula) nakaoae sp. nov. A, D, Entire body; B, F, composite photomicrographs of squeezed specimens; C, posterior end of body; E, enlargement of head, anaesthetized specimen. A–C, ICHUM 5366 (holotype); D–F, ICHUM 5368 (paratype).

Fig. 10. Ototyphlonemertes (parmula) nakaoae sp. nov. A, B, Composite photomicrographs of squeezed specimens; C–F, statoliths; G, stylet apparatus; H–K, central stylets and bases. A, E, J, ICHUM 5367 (paratype); B, F, K, ICHUM 5369 (paratype); C, G, H, ICHUM 5366 (holotype); D, I, ICHUM 5368 (paratype).

Fig. 2. Part of the phylogenetic tree resulting from the maximum-likelihood analysis of COI (ln L=−15264.650301), along with results of three species-delimitation analyses, ABGD, PTP, and TCS, as indicated by vertical bars. Numbers near nodes indicate maximum-likelihood bootstrap support value.