Ototyphlonemertes (duplex) envalli 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 : 21-22

Ototyphlonemertes (duplex) envalli sp. nov.

( Fig. 5 )

Material examined. Four specimens, all from Dam Trong; ICHUM 5351 (holotype); ICHUM 5352–5354 (three paratypes) .

Description. Body length 5.0– 6.2 mm (6.2 mm in holotype), width 0.2 mm (n =3). Epidermis whitish ( Fig. 5A ); cephalic furrow post-cerebrally; tissues around brain reddish ( Fig. 5B, C ); cirri present in both anterior and posterior ends of body. Foregut-intestine junction distinct; foregut region translucent; intestine tinged with pale-yellow to whitish color ( Fig. 5A ). Statoliths bipartite ( Fig. 5D, E ), 8.5–9.2 µm in diameter (8.5 µm in holotype) (n =3); statocyst 23.8–25.6 µm in diameter (23.8 µm in holotype) (n =3). Proboscis diaphragm short ( Fig. 5F ); two accessory stylet pouches, lateral to central-stylet basis, each containing two accessory stylets (n =3); in two of three specimens examined, one of two accessory-stylet pouches contained one accessory stylet that directed backward; other accessory stylets directed forward; middle chamber bulbous ( Fig. 5F ); central stylet smooth ( Fig. 5G, H ), 23.9–31.6 µm long (23.9 µm in holotype); basis 29.6–31.6 µm long (29.6 µm in holotype), 7.4–8.1 µm wide (7.4 µm in holotype) (n =3); basis length/ width ratio 3.90–4.00 (4.00 in holotype) (n =3); posterior chamber opaque, without specialized anterior portion ( Fig. 5B, C, F ). Intestinal diverticula shallow. Mature oocytes up to 136 µm in diameter, accounting for ~35% of body width ( Fig. 5B, C ). Posterior adhesive plate well developed ( Fig. 5I ).

Distribution. So far known only from the type locality, the island of Dam Trong, Vietnam.

Etymology. The specific name is a noun in the genitive case, after Dr Mats Envall for his distinguished contribution to the Ototyphlonemertes systematics.

Remarks. Ototyphlonemertes ( duplex ) envalli sp. nov. was sister to O. ( duplex ) norenburgi sp. nov. in the phylogenetic analysis ( Fig. 2 ) and they look similar to each other. As far as the specimens observed, O. ( duplex ) envalli may be distinguished from O. ( duplex ) norenburgi in that the ratio of the oocyte diameter to the body width is smaller than in O. ( duplex ) envalli (oocyte / body-width ratio ~0.35) than in O. ( duplex ) norenburgi (oocyte/body-width ratio>0.4). Whether or not this character is reliable in discriminating these two species should be investigated in future studies, because the degree of oocyte matureness might have been different among the specimens examined. Also, the squeezed method might have skewed the actual diameters of the body and oocytes.

Figures

Fig. 5. Ototyphlonemertes (duplex) envalli sp. nov. A, Entire body; B, C, composite photomicrographs of squeezed specimens; D, E, statoliths; F, stylet apparatus; G, H, central stylets and bases; I, posterior end of body. A, B, D, G, ICHUM 5351 (jolotype); C, E, F, ICHUM 5353 (paratype); H, I, ICHUM 5352 (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.