Ophryotrocha cf. akessoni Blake, 1985

Zhang, Dongsheng, Zhou, Yadong, Yen, Nicole, Hiley, Avery S. & Rouse, Greg W., 2023, Ophryotrocha (Dorvilleidae, Polychaeta, Annelida) from deep-sea hydrothermal vents, with the description of five new species, European Journal of Taxonomy 864, pp. 167-194 : 175-176

Ophryotrocha cf. akessoni Blake, 1985

Fig. 3

Material examined

EAST PACIFIC OCEAN • 6 specs (5 fixed in formalin, 1 fixed in ethanol and the posterior end used for DNA extraction); Southern East Pacific Rise, German Flats Vent Field , active hydrothermal vents; 37.793° S, 110.916° W; depth 2216 m; 22 Mar. 2005; Greg Rouse, Nerida Wilson and Robert Vrijenhoek leg.; collecting event: HOV Alvin dive 4088; GenBank: OP311735 (COI); SIO-BIC A14105 • 2 specs (1 fixed in formalin, 1 fixed in ethanol and the posterior end used for DNA extraction); same collection data as for preceding; GenBank: OP311736 (COI); SIO-BIC A14106 • 1 spec. (fixed in ethanol and the posterior end used for DNA extraction); Southern East Pacific Rise, active hydrothermal vents; 31.151° S, 111.932° W; depth 2237 m; 29 Mar. 2005; Greg Rouse, Nerida Wilson and Robert Vrijenhoek leg.; collecting event: HOV Alvin dive 4094; GenBank: OP311737 (COI), OP304892 (16S), OP311647 (H3); SIO-BIC A14107 .

Description

Body about 7.5 mm in length and ~ 30 segments ( Fig. 3A ). Prostomium rounded, wider than long, slightly rise medio-posteriorly, with paired digitiform antennae inserted dorsally, paired digitiform palps similar in length with antennae, inserted ventral-laterally ( Fig. 3A ). Peristomium with two rings, subequal in length to the following segments, with ciliary band on each ring ( Fig. 3A ). Mandibles heavily sclerotized, with rod-like shafts, curved shape cutting plates, with single blunt peak, lateral wings weakly sclerotized ( Fig. 3B ). Maxillae P-type, forceps comb-like, with large main fang. Two rows of 7 free denticles, posterior most denticles (D1) comb-like, with smaller main fang. The other six denticles (D2–D7) small, shovel-shaped, with fine teeth ( Fig. 3C ). Parapodia uniramous, with long dorsal cirri and short stubby ventral cirri, acicular lobes sub-triangular distally ( Fig. 3D ). Supra-acicular chaetae simple, distally serrated, tapering into a main fang ( Fig. 3D–E ). Sub-acicular chaetae compound, with serrated blades ( Fig. 3F–G ). Sub-acicular chaetal lobe holds one simple chaeta ( Fig. 3D, G ). Pygidium with two short nub-like papillae laterally ( Fig. 3A ).

Remarks

The specimens were collected from two sites of hydrothermal vents on the southern East Pacific Rise, also known as the Pacific Antarctic Ridge. Though collected well south of the type locality, they agree with Ophryotrocha akessoni described from Galapagos Rift vents in most characters, though there are differences in jaw structure. Blake (1985) described a replacement of mandibles in O. akessoni from serrated cutting plates in juveniles to curved cutting plates in adults. In our specimens ( Fig. 3B ), mandibles with curved cutting plates resemble the adult mandibles in O. akessoni . Paxton (2004) and Macnaughton et al. (2010) inferred that mandibles of a range of species of Ophryotrocha show basically adult size and shape of cutting plates since the larval stage, they only lengthen and enlarge their proximal shafts with maturity. It is possible that the juvenile mandibles in Blake’s (1985) original description of O. akessoni may belong to another Ophryotrocha . Furthermore, O. akessoni was described with a P-type tending to K-type maxillae, with lateral teeth on the forceps ( Blake 1985). However, the forceps of K-type maxillae are unidentate or bidentate with the lateral dentition completely reduced ( Paxton 2004; Macnaughton et al. 2010). Thus, according to the original description, it may be that O. akessoni has P-type maxillae as seen in our specimens ( Fig. 3C ). Blake (1985) described the presence of two anal cirri but provided no further details or drawings. Our specimens had two short papillae which could correspond to those of Blake’s specimens, but examination of the types is needed. Based on the variation in morphological characters ( Table 3 ) and the lack of any DNA sequences for O. akessoni from the type locality, we consider it prudent to report our specimens as O. cf. akessoni .

Figures

Fig. 3. Ophryotrocha cf. akessoni Blake, 1985. A. Dorsal and ventral views of live specimen (SIO-BIC A14105). B. Mandibles (SIO-BIC A14107). C. Maxillae (SIO-BIC A14107). D. Parapodium (SIO-BIC A14105). E. Simple supra-acicular chaetae (SIO-BIC A14105). F. Compound sub-acicular chaetae (SIO-BIC A14105). G. Simple sub-acicular chaeta (SIO-BIC A14106).