Ophryotrocha jiaolongi, Zhang, Dong-sheng, Zhou, Ya-dong, Wang, Chun-sheng & Rouse, Greg W., 2017

Zhang, Dong-sheng, Zhou, Ya-dong, Wang, Chun-sheng & Rouse, Greg W., 2017, A new species of Ophryotrocha (Annelida, Eunicida, Dorvilleidae) from hydrothermal vents on the Southwest Indian Ridge, ZooKeys 687, pp. 1-9 : 1-3

Ophryotrocha jiaolongi sp. n. Figs 1, 2, 3, 4

Holotype.

(RSIO35301) Southwest Indian Ridge, Longqi vent field, HOV Jiaolong Dive 94, 49.6495°E; 37.7835°S, 2760m depth, 11 January 2015: ~ 10 mm long, 58 chaetigers; Paratypes: 21 specimens (RSIO35302) from same location as holotype; 7 specimens (RSIO35303) from Southwest Indian Ridge, Longqi vent field, 49.6501°E; 37.7836°S, 2737m depth; 8 specimens (SIO-BIC A6729) same locality as holotype.

Description.

In life, body translucent (Fig. 1a), becoming opaque white after preservation (Fig. 2a, b). Body shape elongated, slightly dorsoventrally compressed, length up to 10 mm for more than 50 chaetigers, width 1.1 mm, uniform throughout the body, slightly tapering posteriorly (Fig. 2a, b). Prostomium wider than long, anterior margin rounded, posterior medial area slightly raised. Paired antennae short, digitiform, inserted dorsally, reaching to the anteriorly rounded edge of the prostomium (Fig. 2c, Fig. 4a). Paired palps digitiform, similar length as antennae, inserted ventral-laterally on prostomium (Fig. 2d). Eyes not visible. Peristomium with two rings sub-equal in length to following segments, the first ring with two notches ventrally on both sides of the jaw (Fig. 2d). Complete ciliary bands are observed on peristomium segments and chaetigers. Pygidium with terminal anus, two digitiform pygidial cirri inserted laterally, similar in length with the parapodia on the last chaetigers, a small median papilla ventrally placed (Fig. 2a, b, Fig. 4b).

Mandibles rod-like, each cutting plate composed of two sub-triangular plates, dorsal plate larger than ventral plate, fused together from anterior and middle sides, distal edge smooth, with single blunt peak, no serration or teeth observed (Fig. 3a). Maxillae P-type (Fig. 3b, Fig. 4c), forceps comb-like with more than 30 teeth slightly decreasing in size distally (Fig. 3b), seven pairs of free denticles (D), posteriormost pair (D1) oval shaped, longer than wide, smaller than forceps, D2-D7 shovel shape, wide sub-equal with long, except D3 clearly longer than wide (Fig. 3b, d). D2-D3 with a slightly larger main fang and similar long sharp teeth (Fig. 3b, d), D4-D5 with alternating long and short teeth (Fig. 3c), D6-D7 with serrated margin similar as D4-D5 or with smooth margin (Fig. 3e). K-type maxillae not found.

Parapodia uniramous, slightly broadening distally with long sub-conical dorsal cirri and short nub-like ventral cirri (Fig. 4d). Supra-acicular chaetae simple, distally serrated, tapering abruptly into a fang, bearing several tiny spines on both sides distally (Fig. 3f), maximum 8 chaetae per fascicle. Sub-acicular chaetae compound, blades with distally curved main fang and double row of spines, heterogomph shaft with several spines distally (Fig. 3g), maximum 11 chaetae per fascicle. Some parapodiau appear to have sub-acicular retractable lobes with 1-3 simple chaetae (Fig. 3h).

Etymology.

Ophryotrocha jiaolongi sp. n. is named after the Chinese manned submersible Jiaolong, in recognition of its successful expedition to the hydrothermal vents of the Southwest Indian Ridge.

Remarks.

The complex pharyngeal jaw apparatus, which is morphologically well characterized by the presence of ventral mandibles and dorsal maxillae, is an important diagnostic feature in Dorvilleidae ( Rouse and Pleijel 2001). Mandibles of most Ophryotrocha species have been reported with a distally serrated edge or smooth anterior margin with anterior mandibular peaks. Ophryotrocha jiaolongi sp. n. has distinctive mandibles, with folded sub-triangular cutting plates, a distally smooth edge and a single anterior blunt peak, which easily distinguish it from other Ophryotrocha species. Among Ophryotrocha species, O. jiaolongi sp. n. most closely resembles O. akessoni Blake, 1985, in the general morphology of the prostomium, peristomium, ciliary bands, parapodia and chaetae, as well as in mandibular and maxillary structure. Ophryotrocha jiaolongi sp. n. differs from O. akessoni in having shorter antennae and palps and slight differences in jaw structure. The maxillae appear to be P-type in both species, although Blake referred to that of O. akessoni as tending towards K-type in the adult. Ophryotrocha jiaolongi has alternating large and small teeth on D4-D5, while O. akessoni has alternating large and small teeth on the forceps and D1.

DNA.

Sequences of Ophryotrocha jiaolongi sp. n. are deposited at NCBI Genbank with accession numbers CO1 KY906961-KY906965, 16S MF398963-MF398967, and H3 MF398968-MF398972. Preliminary phylogenetic analysis of the DNA data suggests that O. jiaolongi sp. n. is closely related to O. clava from whale bones. However, only one sequence of vent species ( O. globopalpata ) is currently available, which is located in a different clade from the new species. Further DNA data is being acquired from other vent Ophryotrocha species, which will help us to get a better understanding of the relationship among vents Ophryotrocha species in the near future (Zhang et al. in prep.).