Onuphis fukianensis Uschakov & Wu, 1962

Onuphis fukianensis Uschakov & Wu, 1962 View in CoL

Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 ; Table 1

Onuphis fukianensis Uschakov & Wu, 1962: 93 View in CoL –94, 104, Pl. I, E–K. Heptaceras fukianensis ( Uschakov & Wu, 1962) View in CoL . Paxton, 1986: 60.

Type material. Neotype: MBM 283399 View Materials , East China Sea, Nanji Islands , Dasha’ao, 27°28'N, 121°03'E, intertidal sandy beach, coll. Kuidong Xu, Yuhang Li, 12 August 2015 GoogleMaps . Paraneotypes: MBM283400 (n=12), same collection information as above. MBM 283034 View Materials (n=1), same locality as the neotype, 14 May 2014 GoogleMaps ; MBM 283035 View Materials (n=1), East China Sea, same locality as the neotype, coll. Kuidong Xu, 8 August 2014 GoogleMaps . MBM 283080 View Materials (n=1), East China Sea, Nanji Islands , Huokun’ao, 27°28'N, 121°05'E, intertidal sandy beach, 14 August 2015 GoogleMaps .

Neotype locality. Intertidal zone of Zhejiang Nanji Islands in the southwest of East China Sea (27°28'N, 121°03'E). GoogleMaps

Diagnosis. Peristomium and anterior 16–39 chaetigers each with a brown transverse band, gradually becoming narrower and lighter in color posteriorly. Ceratophores very long, with 1–5 distinct pigment spots in underside and 36–46 rings on lateral antennophores. Eyespots usually absent in adults. Branchiae starting from chaetiger 1 as single branchial filament, branched from chaetiger 43–54, with a maximum of 3–6 filaments. Subulate ventral cirri present in first five chaetiger, distinctly subulate postchaetal lobes in first 43–82 chaetigers. Interramal papillae absent. Pseudocompound hooks tridentate in adults, and mostly bidentate in juveniles (less than 2.0 mm in width), present in first four chaetigers; slender long-appendage hook absent. Subacicular hooks from chaetiger 10. Pectinate chaetae flat, distally oblique with about 11 teeth.

Description. Mainly based on neotype, complemented with data from paraneotypes.

Neotype well-preserved, 48 mm long with 81 chaetigers (without posterior end), maximum width 2.7 mm excluding parapodia ( Fig. 2 View FIGURE 2 B). Peristomium and anterior 4 chaetigers cylindrical, becoming dorsoventrally flattened from chaetiger 5.

Body flesh colored in alcohol, epithelium slightly iridescent. Peristomium and anterior few chaetigers each with a wide brown transverse band situated near anterior margin; bands gradually becoming narrower and lighter in color posteriorly, disappearing by chaetiger 21 ( Fig. 2 View FIGURE 2 ). Dark pigment forming 2–4 distinct spots in underside of palpophores and antennophores ( Figs 2 View FIGURE 2 ; 3F–H). Brown patches usually occurring on anterior part of prostomium ( Fig. 3 View FIGURE 3 F, G), bases of frontal lips ( Fig. 3 View FIGURE 3 F), ceratostyles and branchiae after chaetiger 5 or 6.

Prostomium small, subtriangular, anterior margin rounded with a pair of subulate frontal lips ( Fig. 3 View FIGURE 3 F, G). Palps situated on anterolateral region of prostomium, extending posteriorly to chaetiger 1 or 2 with 19–27 basal rings ( Fig. 2 View FIGURE 2 ). Antennae arranged on median part, lateral antennae reaching chaetiger 11–13 with 36–46 basal rings, median antenna reaching chaetiger 4–7 with 22–34 basal rings ( Figs 2 View FIGURE 2 ; 3H). Eyespots not observed in neotype, but present near bases of palpophores in some paraneotypes ( Fig. 3 View FIGURE 3 F, G). Nuchal grooves straight. Peristomium slightly shorter than chaetiger 1, possessing a pair of slender peristomial cirri inserted at anterior margin, as long as peristomium ( Fig. 3 View FIGURE 3 H).

Maxillae well sclerotized, brown to dark brown. Carriers triangular, about 2/3 as long as Mx I. Maxillary formula: Mx I = 1+1, Mx II =6+7, Mx III = 7+0, Mx IV = 6+9, Mx V = 1+1. Mx V reduced to an edentate plate ( Fig. 3 View FIGURE 3 D). Mandibles shorter than maxillae; shafts slender, with posterior part less sclerotized; cutting plate with 3 or 4 irregular denticles in frontal edge ( Fig. 3 View FIGURE 3 D).

Anterior 5–8 chaetigers longer and slightly narrower than followings. Chaetiger 1 longest, gradually decreasing posteriorly to normal length ( Fig. 2 View FIGURE 2 ). First 4 pairs of parapodia modified, directed anterolaterally, slightly larger than following. Dorsal cirri subulate, long and thick in anterior chaetigers ( Fig. 4 View FIGURE 4 A–F, H–L), gradually diminishing thereafter and becoming short and slender for majority of body ( Fig. 4 View FIGURE 4 G, M, N). Ventral cirri cirriform to subulate in first 5 chaetigers ( Fig. 4 View FIGURE 4 A–E, H–K), modified to glandular pads in subsequent chaetigers ( Fig. 4 View FIGURE 4 F, G, L–N). Postchaetal lobes distinctly subulate in first 58 chaetigers ( Fig. 4 View FIGURE 4 A–F, H–L), then reduced to small knobs posteriorly ( Fig. 4 View FIGURE 4 G, M, N). Interramal papillae absent.

Branchiae as a single filament from chaetiger 1 to chaetiger 53, then increasing to a maximum of 3 filaments in pectinate arrangement in chaetiger 61. Branchial filaments subulate in anterior chaetigers, initially shorter than corresponding dorsal cirri ( Fig. 4 View FIGURE 4 A–D, H–J), becoming as long as or longer than dorsal cirri from chaetiger 5 ( Fig. 4 View FIGURE 4 E, F, K, L), then becoming short and digitiform in pectinate branchiae ( Fig. 4 View FIGURE 4 G, M, N).

Table 1. Comparisons of key characters of the specimens of Onuphis fukianensis Uschakov & Wu, 1962 . Abbreviations: MBM, Marine Biological Museum; spec., specimen; Chs, number of chaetigers; Lt, body length; L10, length from the tip of prostomial lobes to posterior margin of 10th chaetiger; Wm, maximum width with parapodia excluded; A1 rings, maximum number of rings of palpophore; A2 rings, maximum number of rings of lateral antennophore; A3 rings, number of rings of median antennophore; spots, number of spots palps or antennae; Eyes, numbers of eye spots; Bands, chaetigers with dorsal bands; VC, chaetigers with subulate ventral cirri; PCL, chaetigers with subulate postchaetal lobes; PCH, chaetigers with pseudocompound hooks; PCH type, tooth number of pseudocompound hooks; BBr start, first chaetiger with branched branchiae; Br max, maximum number branchial filaments; SH start, first chaetiger with subacicular hooks.

Chaetigers 1–4 each consisting of 2 or 3 upper limbate chaetae with very narrow wings ( Fig. 5 View FIGURE 5 K) and 4 or 5 tridentate pseudocompound hooks per parapodium ( Fig. 4 View FIGURE 4 A–D). Distal tooth large and curved, second one much shorter, proximal one smallest ( Fig. 5 View FIGURE 5 A–D), poorly defined or absent in juveniles ( Fig. 5 View FIGURE 5 E–G). Some tridentate hooks with middle and proximal teeth worn ( Fig. 5 View FIGURE 5 C, D) or with an extra tiny denticle between distal and middle ones ( Fig. 5 View FIGURE 5 C). Slender long-appendage hooks absent. Limbate chaetae from unmodified parapodia simple and slender with distinct wings on both sides ( Fig. 5 View FIGURE 5 J); lower limbate chaetae replaced by two hooded subacicular hooks from chaetiger 10 ( Fig. 5 View FIGURE 5 H). Pectinate chaetae flat and oblique with about 11 teeth, observed from chaetiger 10 with 1 or 2 per parapodium, but difficult to detect in large specimens ( Fig. 5 View FIGURE 5 I). Aciculae tapering with pointed tips, as many as 5 per parapodium in anterior chaetigers ( Fig. 4 View FIGURE 4 A–C).

Tube membranous, cylindrical in shape, encrusted with coarse sand and grains ( Fig. 3 View FIGURE 3 E).

Methyl green staining pattern. Based on a single paraneotype (MBM283400; Fig. 3 View FIGURE 3 A–C). Prostomium slightly stained. Frontal lips deeply stained in basal portion, upper and lower lips stained evenly to light blue. Palps and antennae unstained. Peristomium and chaetiger 1 stained only on dorso-lateral areas. Dorsum and venter of anterior chaetigers each with a transverse stripe consisting of small blue dots. Branchiae of anterior 34 chaetigers deeply stained in bases to sub-distal part, gradually becoming lighter posteriorly. Dorsal cirri, postchaetal lobes, ventral cirri and ventral glandular pads lightly stained. Areas between neighbouring parapodia strongly stained, forming clear boundary with corresponding parapodia and ventral glandular pads.

Variations. Maximum width ranged from 1.5 to 3.1 mm. The morphological comparison of all 16 individual specimens is provided (Table 1) and the intraspecific variability of eight selected characters is illustrated in order to determine whether these characters are size-related ( Fig. 6 View FIGURE 6 ). Specimens with a smaller body size (less than 2.0 mm in width) are herein regarded as juveniles for they have rather different characters concerning the eyespots and the pseudocompound hooks, as indicated below.

The brown transverse bands were distinct on the peristomium and anterior few chaetigers, faded posteriorly and disappearing by chaetiger 17–40. Juveniles generally possessed 1 or 2 eyespots, which were usually absent in the adults especially in specimens more than 2.3 mm in width. Branched branchiae started from chaetiger 43–54 with a maximum number of 3–6 filaments by chaetiger 61–91. Subulate ventral cirri were usually present in the first 5 chaetigers, and in one specimen (MBM283400-spec.1) they continued to the right parapodium of chaetiger 6. The number of chaetigers with subulate postchaetal lobes varied from 43 to 82, showing no obvious relationship with the Size Index; this character is difficult to determine and is regarded as a poor character for O. fukianensis . Pseudocompound hooks were generally present in the first 4 chaetigers but also occurred in the left parapodium of chaetiger 5 in one specimen (MBM283400-spec.1). Pseudocompound hooks were tridentate in the adults, and bidentate hooks were commonly seen in the juveniles. Subacicular hooks always started from chaetiger 10.

Distribution. So far, the species has been reported only from the intertidal areas of Fujian Pingtan Island (holotype) and Zhejiang Nanji Islands (neotype and paraneotypes) in the southwest of the East China Sea ( Fig. 1 View FIGURE 1 ).

Remarks. The examined specimens agree well with the original description of Onuphis fukianensis made by Uschakov & Wu (1962) (Table 1), and both the holotype and our specimens were collected from the intertidal zone in the southwest of the East China Sea. The only difference is that the pseudocompound hooks in our material are mostly present in the first 4 chaetigers (with exception of a single specimen, on which they continue to chaetiger 5), while they occur in the first 3 chaetigers in the holotype. Since the original description of O. fukianensis was based on one specimen only, it is possible that it represented an anomalous individual, or was observed incorrectly. Another possibility is that the pseudocompound hooks in the fourth chaetiger of the holotype might have been broken or missing. Thus, we are convinced that the conspecificity is beyond reasonable doubt.

Onuphis fukianensis View in CoL is peculiar in the genus by having very long ceratophores (36–46 rings on lateral antennae) and a very late start of branched branchiae (chaetiger 43–54), which greatly exceed the normal ranges in the genus Onuphis View in CoL (10–25 ceratophoral rings and branched branchiae from about chaetiger 20) ( Paxton 1986; Arias & Paxton 2014). The specific characters give the species some similarity to members of the genus Heptaceras View in CoL which is characterized by having long ceratophores (20–60 rings) and a mid-dorsal notch on the peristomium. Thus O. fukianensis View in CoL was transferred to Heptaceras View in CoL without an investigation of the holotype. However, our examination confirmed that the species has definitely no mid-dorsal notch and thus should not be placed with Heptaceras View in CoL . Since the type material is not available and the taxonomic identity is threatened, we neotypify Onuphis fukianensis View in CoL with our specimens collected from the same intertidal area.