Polycirrus rhombolabiatus, Çinar & Erdoğan-Dereli, 2023

Çinar, Melih Ertan & Erdoğan-Dereli, Deniz, 2023, Polychaetes (Annelida: Polychaeta) off Kıyıköy (Black Sea, Türkiye) with descriptions of three new species, Zootaxa 5383 (4), pp. 537-560 : 552-557

Polycirrus rhombolabiatus n. sp.

urn:lsid:zoobank.org:act:AEA6B0DA-287C-408B-ABE1-35C5EC049C7A

Figures (10-12), Table 4

Material examined: Holotype. ESFM-POL/2022-009 , 25.09.2022, station H3 , Paratypes. ESFM-POL/2022-010 , 25.09.2022, station H2, 1 specimen ; ESFM-POL/2022-012 , 25.09.2022, station H3, 1 specimen .

Description: Holotype complete, 10.72 mm (6.02–19.45 mm in paratypes) mm long and 1.08 mm (0.5–1.5 mm in paratypes) mm wide with 58 chaetigers (37–80 in paratypes). Colour in alcohol yellowish.

Antero-dorsum surface weakly tessellated to segment 11; smooth from segment 12 to posterior part; strongly annulated in posterior part, body somewhat cylindrical, abruptly tapering in posterior part ( Figs 11A ; 12 A−C).

Transverse prostomium attached to dorsal surface of base of upper lip; basal part as thick crest across dorsum, extending laterally, slightly curved ( Fig. 12B ). Buccal tentacles missing on all specimens. Peristomium forming lips; upper lip somewhat rectangular in shape, wider than long, with a single prominent median lobe only, margin of lobe straight; lower lip rhomboidal with rounded edges and pointing toward mouth with smooth surface, extending to anterior margin of segment 4 ( Figs 11A ; 12A, B ).

Segment 1 (SG1) and 2 (SG2) reduced, SG2 hardly visible ventrally ( Fig. 12A ).

Ventro-lateral inflated pads present from SG3 to SG11, distinctive with smooth surface and transversely ridged until SG10, subsequent ones not ridged ( Figs 10A , 11A ; 12A ). Midventral groove from SG3, present until end of body as a stripe.

Notopodia from SG3, extending to 17 segments in holotype (14–17 in paratypes); first pair shorter, bilobed, postchaetal lobe digitiform, larger than prechaetal one ( Figs 10A, C ; 11D ; 12E ). Notochaetae one type, bilimbate, with inconspicuous hirsute surface under light microscopy ( Figs 10B, C ; 11C, D ; 12D, E ). Neuropodia beginning from SG15, 14–30 uncini per row. Neuropodial tori ridged, similar in size along body. Uncini with short occipitium (Type 1); crest with three rows of teeth above main fang; first row, just above main fang, including a solitary, sharp, slightly curved tooth, reaching the distal third of main fang; second row including approximately 14 teeth; third row including 8 small teeth; subrostral process as low protuberance and positioning on proximal third, heel triangular with rounded tip, base nearly straight ( Figs 10D ; 11E, F ; 12F, G ).

Nephridial papillae present from segment 3 to 10, spherical in shape, situated at the ventral base of notopodia ( Figs 10A , 11B , 12A ).

Pygidium rounded with ventral papilla ( Figs 11A ; 12C ).

Methyl green pattern. Only first six pairs ventro-lateral pads are stained intensely.

Etymology. This species is named after its rhomboid-like lower lip.

Habitat. It occurs at 11–13 m depth on rocks with Cystoseira crinita , Cladophora sp. and Phyllophora crispa .

Remarks. Polycirrus rhombolabiatus n. sp. is mainly characterized by having an upper lip with a medial lobe only and a rhomboidal lower lip; transversely ridged ventral pads; 14-16 pairs of notopodia; neuropodia commencing in the anterior region; and type 1 uncini only with a subrostral process. In terms of the number of notopodia (13–21 pairs) and the shape of the upper lip (having medial lobe only), Polycirrus rhombolabiatus n. sp. is similar to P. catalanensis Lavesque, Hutchings, Daffe & Londoño-Mesa, 2020 , P. elisabethae McIntosh, 1915 , P. nogueirai Lavesque, Hutchings, Daffe & Londoño-Mesa, 2020 , P. norvegicus (Wollebaek, 1912) , P. plumosus (Wollebaek, 1912) and P. readi Lavesque, Hutchings, Daffe & Londoño-Mesa, 2020 .

The distinctive morphological characters of these species are indicated in Table 4 . Polycirrus rhombolabiatus n. sp. differs from all these species in terms of the following characters: 1) lower lip: rhomboidal with smooth surface in P. rhombolabiatus n. sp.; rectangular with longitudinal ridged surface in P. catalanensis ; subtriangular with ridged and grooved surface in P. elisabethae ; rounded and inflated with longitudinal ridged surface in P. nogueirai ; oblong, longer than wide with ridged and grooved surface in P. norvegicus ; sub-conical in P. plumosus ; oblong with ridged surface in P. readi ; 2) ventral pads: 9 pairs, surface smooth and transversely ridged in P. rhombolabiatus n. sp.; 8 pairs and surface corrugated and transversely ridged in P. catalanensis ; pairs unreported, surface smooth in P. elisabethae ; 11–12 pairs, surface smooth and transversely ridged in P. nogueirai ; 8–9 pairs, surface smooth and transversely ridged in P. norvegicus ; 9 unpaired after 4–5 paired; papillose, incised in P. plumosus ; 10 pairs, inflated surface smooth in P. readi , and 3) notochaeta: one type, winged with inconspicuous hirsute surface in P. rhombolabiatus n. sp. and P. catalanensis ; winged with conspicuous hirsute surface in P. elisabethae ; winged in P. nogueirai and P. readi ; hirsute in P. norvegicus ; pinnate and winged in P. plumosus .

Four species of Polycirrus have been reported up to date from the Black Sea: P. caliendrum Claparède, 1869 , P. haematodes ( Claparède, 1864) , P. jubatus Bobretzky, 1868 and P. pallidus ( Claparède, 1864) (Kurt-Şahin & Çinar, 2012) . Polycirrus rhombolabiatus n. sp. shows some affinities with P. jubatus Bobretzky, 1868 , which was originally described from the Black Sea ( Bobretzky, 1868). Both species have 17–18 pairs of notopodial segments and neurochaetae starting on segment 15, but P. rhombolabiatus n. sp. differs from P. jubatus in terms of the following characters: 1) the lower lip is rhomboidal in P. rhombolabiatus n. sp. vs. trapezoidal in P. jubatus , 2) the upper lip only has a medial lobe in P. rhombolabiatus n. sp. vs. trefoiled in P. jubatus , and 3) the ventral pads start on segment 3 in P. rhombolabiatus n. sp. vs. on segment 4 in P. jubatus . Polycirrus rhombolabiatus n. sp. is also similar to P. haemotodes , but the latter species has a very long upper lip, 2−2.5 times longer than wide. However, both P. jubatus and P. haemotodes have been considered as species inquirenda as the types of the species were presumably lost and the description and drawings of the species were insufficient ( Glasby & Hutchings, 2014).

Figures

FIGURE 10. Polycirrus rhombolabiatus n. sp. (Holotype, ESFM-POL/2022-009).A, Antero-ventral view of body; B, Limbate chaeta on chaetiger 9; C, Notopodium on chaetiger 6; D, Uncinus on abdominal chaetiger. Scale Bar: A, 660 µm; B, 18 µm; C, 52 µm; D, 12 µm.

FIGURE 11. Polycirrus rhombolabiatus n. sp.A, General view of body, stained with Methyl green (Holotype, ESFM-POL/2022- 009); B, Antero-ventral view body (Paratype, ESFM-POL/2022-012); C, Notochaetae on anterior chaetiger; D, Parapodia in mid-body; E-F, Uncini on abdominal chaetigers. Scale Bar: A, 656 µm; B, 83 µm; C, 39 µm; D, 113 µm; E-F, 12 µm.

FIGURE 12. Polycirrus rhombolabiatus n. sp. (Paratype, ESFM-POL/2022-012). A, Antero-ventral view of body; B, Anterodorsal view of body; C, Postero-lateral view of body; D, Notochaetae in mid-body; E, Notopodia in mid-body; F-G, Uncini on posterior neuropodium. Scale Bar: A, 411 µm; B, 276 µm; C, 316 µm; D, 21 µm; E, 57 µm; F, 4 µm; G, 11 µm.