Onuphis uschakovi, Wu, Xuwen & Xu, Kuidong, 2017

Wu, Xuwen & Xu, Kuidong, 2017, Neotypification of Onuphis fukianensis Uschakov & Wu, 1962 and description of a new species of Onuphis (Annelida: Onuphidae) from China seas, Zootaxa 4291 (2), pp. 347-360 : 355-360

Onuphis uschakovi sp. nov.

Figures 1 , 7–9 ; Table 2

Type material. Holotype: MBM 009427 , East China Sea near the southern Yellow Sea , 31°30'N, 124°00'E, coarse sand and shell fragments, coll. Yuheng Cui, 15 January 1959 . Paratypes: MBM 009434 (n=2), southern Yellow Sea , 32°30'N, 122°45'E, brown silt and shell fragments, 35 m, coll. Liren Cheng, 23 January 1959 ; MBM 009439 (n=1), southern Yellow Sea near the East China Sea, 31°45′N, 122°45′E, coarse sand and shell fragments, 34.6 m, coll.

Liren Cheng, 23 October 1959; MBM 009444 (n=1), southern Yellow Sea , 32°00'N, 122°45′E, silt and shell fragments, 34 m, coll. Liren Cheng, 13 May 1959 .

Type locality. East China Sea, near border with the southern Yellow Sea , coarse sand and shell fragments (31°30'N, 124°00'E).

Diagnosis. Peristomium and anterior 20 chaetigers each with a faint transverse band. Ceratophores long with 27–32 rings on lateral antennophores. One or two eyespots present near bases of palpophores. Branchiae starting from chaetiger 1 as single branchial filament, branched from chaetiger 23–29, with a maximum of 3 or 4 filaments. Subulate ventral cirri present in first six chaetiger, distinctly subulate postchaetal lobes in first 22–29 chaetigers. Interramal papillae present from chaetiger 5 to 12. Pseudocompound hooks tridentate, present in first four chaetigers; slender long-appendage hook absent. Subacicular hooks from chaetiger 12 or 13. Pectinate chaetae flat, distally oblique with 8–10 teeth.

Description. Mainly based on holotype, complemented with data from paratypes.

Holotype well-preserved, 29 mm long with 78 chaetigers (without posterior end), maximum width 2.1 mm excluding parapodia. Peristomium and anterior 5 chaetigers cylindrical, becoming dorsoventrally flattened from chaetiger 6. Body light yellow or pale in alcohol, epithelium slightly iridescent. Peristomium and anterior 20 chaetigers each with an indistinct transverse band ( Fig. 7 A–E).

Prostomium small, subtriangular, anterior margin rounded with a pair of subulate frontal lips ( Fig. 7 H–K). Palps situated on anterolateral region of prostomium, extending posteriorly to chaetiger 3 with 24 basal rings ( Fig. 7 A). Antennae arranged on median part, lateral antennae reaching chaetiger 21 with 32 basal rings, median antenna reaching chaetiger 13 with 18 basal rings ( Fig. 7 A). Eyespot observed near base of left palpophores in holotype ( Fig. 7 H), and on both sides in three paratypes ( Fig. 7 J, K). Nuchal grooves straight. Peristomium slightly shorter than chaetiger 1, possessing a pair of slender peristomial cirri inserted at anterior margin, slightly longer than peristomium ( Fig. 7 A–E).

Maxillae well sclerotized, yellow to brown. Carriers triangular, about 2/3 as long as Mx I. Maxillary formula: Mx I = 1+1, Mx II = 8+7, Mx III = 7+0, Mx IV = 6+11, Mx V = 1+1. Posterior teeth smaller posteriorly in both Mx II and Mx III. Mx V reduced to an edentate plate ( Fig. 8 E). Mandibles shorter than maxillae with slender and less sclerotized shafts; cutting plate (slightly broken) smooth in frontal edge ( Fig. 8 F).

Anterior 4–6 chaetigers distinctly longer than followings. Chaetiger 1 longest, about 2 times as long as chaetiger 6, gradually becoming shorter posteriorly to normal length by chaetiger 12 ( Fig. 7 A). First 4 pairs of parapodia modified, directed anterolaterally, slightly larger than following. Dorsal cirri long and thick in anterior chaetigers ( Fig. 9 A–F), gradually diminishing thereafter and becoming short and narrow for majority of body ( Fig. 9 G–I). Ventral cirri subulate in first 6 chaetigers ( Figs 7 F, G; 9A–F), modified to glandular pads in subsequent chaetigers ( Fig. 9 G–I). Postchaetal lobes distinctly subulate in first 29 chaetigers ( Fig. 9 A–F), then reduced as small knobs posteriorly ( Fig. 9 G–I). Interramal papillae present in chaetigers 5–12, distinct in chaetigers 5–8, becoming short and thick in following ( Fig. 8 D).

Branchiae as single filament from chaetiger 1 to chaetiger 27, two filaments occurring from chaetiger 28, three from chaetiger 31, maximum 4 filaments by chaetiger 35, gradually decreasing in number thereafter. Branchial filaments subulate in anterior chaetigers, becoming short and digitiform in pectinate branchiae, longer than corresponding dorsal cirri ( Fig. 9 A–I).

Chaetigers 1–4 each consisting of 2–4 upper limbate chaetae with narrow wings and 3–4 pseudocompound hooks per parapodium ( Fig. 9 A–C, F, M). Pseudocompound hooks distally tridentate; distal tooth curved, longest; second one triangular, slightly smaller than distal tooth; proximal one smallest, slightly robust in large median hooks ( Fig. 9 J, K); slender long-appendage hook absent. Limbate chaetae from unmodified parapodia simple and slender with wings on both sides ( Fig. 9 L, N). Lower limbate chaetae replaced by two hooded subacicular hooks from chaetiger 13 ( Fig. 9 O). Pectinate chaetae flat and oblique with 8–10 teeth ( Fig. 9 P). Aciculae tapering with pointed tips, as many as 5 per parapodium in anterior chaetigers ( Fig. 9 A–C, F).

Methyl green staining pattern. Based on a single paratype (MBM009439; Fig. 8 A–C). Prostomium including palps and antennae lightly stained. Frontal lips, upper and lower lips stained evenly to deep blue. Dorsum of peristomium and first 4 chaetigers stained to deeper color than following. Dorsum of following chaetigers with only median areas stained. Venter with two parallel transverse stripes per chaetiger. Branchiae, dorsal cirri and postchaetal lobes deeply stained. Ventral cirri and ventral glandular pads lightly stained.

Variations. Morphological comparison of a total of five specimens is provided ( Table 2). Maximum width ranged from 1.0 to 2.1 mm. The transverse bands were usually faint on the dorsum but not observed in the specimens with pale epidermis ( Fig. 7 D, E) probably due to the poor fixation. Eyes were present as one or two dots on the anterolateral side of the prostomium but not observed in only one specimen (MBM009434-spec.1) ( Fig. 7 I). Branched branchiae started from chaetiger 23–29 with a maximum of 3 or 4 filaments. The number of chaetigers with subulate postchaetal lobes varied from 22 to 29, showing a positive relationship with the Size Index (y = 0.7175x + 19.241, R² = 0.8003, P <0.05). Interramal papillae usually started from chaetiger 5 and in only one specimen they started from chaetiger 7 (MBM009434-spec.1); the last chaetiger with interramal papillae varied from chaetiger 9 to 12. Subacicular hooks generally started from chaetiger 13 and in only one specimen (MBM009439) they started from chaetiger 12.

MBM009434-spec. 2 52 16 /3.0/1.0 16 29 16 1 pair faint Etymology. Onuphis uschakovi is named to honor the late Russian Professor P. V. Uschakov, in recognition of his contribution to the taxonomy of Chinese polychaetes, as well as the traditional friendship with Chinese colleagues.

Distribution. Southern Yellow Sea and East China Sea, near Changjiang (Yangtze River) Estuary (water depth 34–44 m) ( Fig. 1 ).

Remarks. Onuphis uschakovi sp. nov. can be distinguished from its congeners by a combination of characters as follows: long ceratophores with up to 27–32 rings; pseudocompound hooks tridentate, present in first 4 chaetigers; subulate ventral cirri present in first 6 chaetiger; branchiae present from chaetiger 1, branched from chaetiger 23–29, with up to 3–4 filaments; interramal papillae located from chaetiger 5 to 12; and subacicular hooks started from chaetiger 12 or 13.

Like O. fukianensis , Onuphis uschakovi sp. nov. has long ceratophores and tridentate pseudocompound hooks in the first 4 chaetigers. However, the two species can be easily separated by the distribution of subulate ventral cirri (chaetigers 1–6 vs. 1–5), the start of branched branchiae (chaetiger 23–29 vs. 43–54) and subacicular hooks (chaetiger 12 or 13 vs. 10), and the presence of interramal papillae in O. uschakovi (vs. absent in O. fukianensis ).

Onuphis uschakovi sp. nov. highly resembles O. eremita parva Berkeley & Berkeley, 1941 in possessing tridentate pseudocompound hooks in the first 4 chaetigers and subulate ventral cirri in the first 6 chaetigers. In addition, they are similar in the branchial characters, distributions of interramal papillae and subulate postchaetal lobes. However, O. uschakovi sp. nov. differs from O. eremita parva in the start of subacicular hooks (chaetiger 12 or 13 vs. 8), the maximum number of ceratophoral rings (27–32 vs. 21), and the shape of pectinate chaetae (oblique with 8–10 teeth vs. transverse with 15 teeth). Besides, O. uschakovi sp. nov. was found from the East China Sea and southern Yellow Sea, while O. eremita parva was recorded off California.

Figures

FIGURE 1. Distribution map of Onuphis uschakovi sp. nov. and O. fukianensis Uschakov & Wu, 1962 in the China seas based on examined material and original report.

FIGURE 7. Onuphis uschakovi sp. nov., holotype (A, F, H, MBM 009427) and four paratypes (B, C, G, I, J, MBM 009434; D, MBM 009439; E, K, MBM 009444). A – E, Anterior fragments, dorsal view; F, Anterior fragment, ventral view; G. Anterior fragment, lateral view; H – K, Close-up of prostomiums, arrows pointing to little eyespots. Scale bars: 1 mm (A, B, D, E, G), 0.5 mm (C, H), 2 mm (F) and 0.2 mm (I – K).

FIGURE 8. Onuphis uschakovi sp. nov., holotype (D, MBM 009427) and two paratypes (A – C, MBM 009439; E, F, MBM 009444). A, Anterior fragment of a same specimen stained with methyl green in dorsal (A), ventral (B, slightly broken in anterior segments) and lateral (C) views; D, Dorsum of several anterior chaetigers, arrows pointing to interramal papillae; E, Maxillae in dorsal view; F, Mandibles in ventral view, cutting plates slightly damaged. Abbreviation: Ch 5 referring to chaetiger 5, and so on. Scale bars: 1 mm (A – C), 0.5 mm (D) and 200 µm (E, F).

FIGURE 9. Parapodia and chaetae of Onuphis uschakovi sp. nov., paratype (A – P, MBM 009444), anterior views (A – F) and posterior views (G – I). A, Parapodium 1; B, Parapodium 2; C, Parapodium 4; D, Parapodium 5; E, Parapodium 6; F, Parapodium 2; G, Parapodium 19; H, Parapodium 27; I, Parapodium 39; J, K, Pseudocompound hooks; L – N, Limbate chaetae; O, Subacicular hook; P, Pectinate chaeta. Abbreviation: Ch 1 referring to chaetiger 1, and so on. Scale bars: 1 mm (A – I) and 50 µm (J – P).