Terebellides yangi, Zhang & Hutchings, 2018

Zhang, Jinghuai & Hutchings, Pat, 2018, Taxonomy and distribution of Terebellides (Polychaeta: Trichobranchidae) in the northern South China Sea, with description of three new species, Zootaxa 4377 (3), pp. 387-411 : 396-402

Terebellides yangi n. sp.

Figures 7–11

Material examined. Holotype. MBM 286028 in IOCAS: Weizhou Island, Guangxi, Beibu Gulf, South China Sea, 20.6462° N 108.9855° E, 35.0 m, mud, May 2014.

Paratypes. MBM286029 and MBM286030 (2 specimens mounted for SEM), MBM286031 (9 specimens), MBM286032 (6 specimens), MBM286033 (5 specimens) in IOCAS: Weizhou Island , Guangxi, Beibu Gulf, South China Sea, 20.6462° N 108.9855° E, 35.0 m, mud, May 2014 ; MBM286034 (1 specimen) in IOCAS: Guangdong, Daya Bay, South China Sea, 22.6675° N 114.6642° E, 17.5 m, silt, Aug 2016 ; MBM286035 (3 specimens) in IOCAS: Weizhou Island , Guangxi, Beibu Gulf, South China Sea, 21.0299° N 109.0668° E, 12.0 m, mud, May 2014 ; MBM286036 (4 specimens) in IOCAS: Weizhou Island , Guangxi, Beibu Gulf, South China Sea, 21.0480° N 108.9509° E, 23.0 m, mud, May 2014 .

Description (Based on both holotype and paratypes). Holotype complete, 19.2 mm in length and 0.4–2.8 mm in width (from posterior end to anterior chaetigers (excluding chaetae) respectively), with distinct demarcation between thorax and abdomen; with 30 abdominal segments; body tapering posteriorly with segments ( Figs 8A & 11A–B ). Dorsum and ventrum smooth, colour pale to reddish in preserved specimens.

Buccal tentacles of two types on dorsal margin of large tentacular membrane, uniformly tapered and with expanded tips ( Figs 7A ; 8B–C & 11C). Prostomium compact almost completely hidden by tentacular membrane. Eyespots absent. Peristomium consisting of expanded lower lip which forms an elongate rectangular structure and upper lip often covered by lower lip and tentacular membrane ( Figs 7A–B ; 8B–C; 10A & 11C). Segments 1–2 with small lateral lappets; segment 1 with inconspicuous ventral collar; segment 2 with conspicuous ventral collar ( Figs 7B ; 8C & 11D). Segments 3–7 with lateral lappets, and with a conspicuous dorsal rounded projection on lateral lappets and largest on segment 5; forming thickened ventral membranous collars (ventral lobes) on anterior margins of segments 3–7, lobes those of segment 5 largest; ventral lobes of segment 3 with an inverted “n” shaped invagination in centre, others with uniform smooth margins ( Figs 7A–B ; 8B–C; 10A & 11C–D). Lateral lappets with conspicuous projection, largest on segment five ( Figs 7C ; 8B–D; 10B & 11C). Ventral glandular bands and glandular areas around parapodia absent.

Branchia as single elongate structure dorsally on segments 2–4, consisting of two pairs of posterior lobes and pair of anterior lobes ( Figs 7A ; 8B, E; 10C & 11E). BL5–6 fused completely, and distinctly prolonged about 1/2 posterior lobes. Posterior lobes fused for about 1/4 their length. BL1–2 much longer and greater than BL3–4. BL1– 2 and BL5–6 with large lamellae, without distal tip; lamella of BL1–2 and BL5–6 with longitudinal ridges with cilia, without a row of papilla; BL3–4 with small lamellae and distal tip ( Figs 8E–G & 10C ).

Thorax with 20 segments without dorsal hump. Notopodia 18 pairs, present on segments 3–20 (chaetigers 1– 18). First three pairs inserted more dorsally to subsequent ones; first two pairs strongly reduced with shorter and finer chaetae than following ones, notochaetae appearing to arise from body wall ( Figs 7A, C ; 8B–D; 10A–B & 11C). Chaetae arranged in 2 tiers, lower tier with finely pointed chaetae and upper tier with narrowly–winged chaetae; chaetae of lower tier finer and about 2/3 length of those of upper tier ( Fig. 9D–G ). Neuropodia beginning from segment 8 (chaetiger 6), and present on all subsequent segments. Thoracic neuropodia as sessile pinnules. First neuropodia with 6 geniculate acicular hooks; geniculate hooks arranged in single row throughout with pointed tips and sharply bent, and showing different degrees of bending depending on size; ventral geniculate hooks smaller and more bent than dorsal ones ( Figs 7D ; 9A & 10D–E). Subsequent thoracic neuropodia with one row of 8–10 long-handled uncini per torus; uncini with main fang and several rows of secondary teeth, with 2–4 major teeth in first row above main fang ( Figs 7E ; 9B–C & 10F–G).

Abdomen with 30 segments with length gradually decreasing posteriorly. Abdominal neuropodia as foliaceous pinnules with about 36 avicular uncini; arranged in single row ( Figs 9H & 10H ). Abdominal uncini with strongly crested head, covered with numerous small and scale-like teeth ( Figs 7F ; 9J–I & 10I). Pygidium blunt without appendages ( Figs 10J & 11F ).

The methyl green staining similar to pattern 5 of Schüller & Hutchings (2010), compact green colour of the first five segments, a likely J-shaped glandular region in segment 5, then becoming striped and gradually fading to weak striped in posterior abdominal segments ( Fig. 11A–B ). Margin of lower lip without white stripe on peristomium. Thoracic notopodia, abdominal neuropodia and branchial tips and lamellae all lacking any staining.

Variability. Complete individuals ranging from 6.9–25.9 mm in length, 1.4–3.0 mm in width of anterior chaetigers excluding the chaetae and 29–32 abdominal segments. Large specimens with greater width and more abdominal segments than smaller ones ( Fig. 12A ). LRTA ranging from 0.7–1.8, showing large specimens possibly with a smaller LRTA and relatively long abdomen ( Fig. 12B ). Geniculate hooks ranging from 5–7 in number, with larger specimens tending to have more geniculate hooks. Thoracic neuropodia with 6–10 uncini per torus, number increasing with size of individual which is presumably linked to age.

Remarks. Terebellides yangi n. sp. is characterised by a pair of anterior branchial lobes which are distinctly prolonged, lateral lappets of segments 3–7 which have a conspicuous rounded projection (largest on segment 5), neuropodia in segment 8 (chaetiger 6) which have sharply bent geniculate hooks and subsequent thoracic neuropodia which have few (6–10) uncini per torus arranged in a single row.

According to published descriptions, there are another 10 species like Terebellides yangi n. sp. with pair of anterior branchial lobes distinctly prolonged, with geniculate acicular chaetae in TC6 only, and without thoracic dorsal hump ( Schüller & Hutchings 2013; Parapar & Hutchings 2014). Terebellides yangi n. sp. is distinguished from Terebellides kobei Hessle, 1917 (type locality Japan), Terebellides longicaudatus Hessle, 1917 (type locality Southern Ocean) and Terebellides reishi Williams, 1984 (type locality south-central California) by the arrangement of thoracic neuropodial uncini. Terebellides yangi n. sp. has only a single row of thoracic neuropodial uncini, whereas in the other species thoracic neuropodial uncini are present in double or partial double rows. Terebellides yangi n. sp. and Terebellides woolawa Hutchings & Peart, 2000 (type locality Australia) are different from Terebellides bisetosa Hartmann-Schröder, 1965 (type locality Chile), Terebellides brevis Imajima & Williams, 1985 (type locality Japan), Terebellides gracilis, Malm, 1874 (type locality Norwegian North Sea), Terebellides kerguelensis McIntosh, 1885 (type in Southern Ocean), Terebellides malvinensis Bremec & Elias, 1999 (type locality Argentina), Terebellides narribri Hutchings & Peart, 2000 (type locality Australia) and Terebellides stroemii Sars, 1835 (type locality Norwegian North Sea) by having less well developed notopodia of TC1 and TC2 compared to those of subsequent notopodia. Terebellides yangi n. sp. is easily distinguished from Terebellides woolawa as in the new species, BL1–2 are much longer and wider than BL3–4, posterior lobes fused for about 1/4 their length; neuropodia with sharply bent geniculate acicular hooks in TC6, and few (6–10) uncini per torus in subsequent neuropodia. In contrast in Terebellides woolawa , BL1–2 and BL3–4 are almost equal, posterior branchial lobes fused for about half of their length; neuropodia with weakly bent geniculate acicular hooks in TC6, and more uncini (10–20) per torus in subsequent neuropodia. In addition, species with characters similar to Terebellides yangi n. sp. are recorded from very different geographical regions.

Distribution. Known from Beibu Gulf and Daya Bay of the northern South China Sea ( Fig.1 ).

Habitat. Found in muddy substrates in shallow water (12.0–35.0 m depths).

Etymology. The species is named after Professor Dejian Yang, for his contributions to the taxonomy of Chinese polychaetes.

Figures

FIGURE 1. Distribution of Terebellides in the northern South China Sea; TG Terebellides guangdongensis n. sp.; TY Terebellides yangi n. sp.; TE Terebellides ectopium n. sp.

FIGURE 7. Terebellides yangi n. sp. holotype MBM286028, A. anterior region, lateral view; B. anterior region, ventral view; C. notopodia of TC1–4, lateral view; D. geniculate hook (segment 8); E. detail head of thoracic uncini; F. detail head of abdominal uncinus. Abbreviations: BL, branchial lobes; BT, Buccal tentacles; ll, lower lip; SG, segment; NI, n-type invagination; TC, thoracic chaetiger; TM, tentacular membrane.

FIGURE 8. Terebellides yangi n. sp. SEM paratypes MBM286029.A. entire worm; B. anterior end, lateral views; C. anterior end, lateral-ventral views; D. thoracic chaetiger 1–6; E–G. close ups of branchia. Abbreviations: BL, branchial lobes; BT, buccal tentacles; cr, cilia ridge; ll, lower lip; SG, segment; TC, thoracic chaetiger.

FIGURE 9. Terebellides yangi n. sp. SEM paratypes MBM286029, A. neuropodial spines, segment 8 (chaetiger 6); B. neuropodial uncini, chaetiger 7; C. neuropodial uncini, chaetiger 13; D–G. close ups of notochaetae, chaetiger 17; H. neuropodium, chaetiger 19; I. uncini, chaetiger 32; J. uncini, posterior chaetiger. Abbreviations: CUT, chaetae of upper tier; CLT, chaetae of lowertier.

FIGURE 10. Terebellides yangi n. sp. SEM paratypes MBM286030. A. anterior end, lateral views; B. thoracic chaetiger 1–4; C. branchia; D–E. close ups of neuropodial spines, chaetiger 6; F. neuropodial uncini, chaetiger 7; J. neuropodial uncini, chaetiger 16; H. neuropodium, chaetiger 19; I. uncini, chaetiger 48; J. pygidium and posterior segments. Abbreviations: BL, branchial lobes; BT, buccal tentacles; ll, lower lip; TC, thoracic chaetiger.

FIGURE 11. Methyl green staining of Terebellides yangi n. sp. holotype MBM286028.A. anterior region, left lateral view; B. posterior region, lateral view; C. anterior end, lateral views; D. anterior end, anterior-ventral views; E. branchia; F. pygidium and posterior segments. Abbreviations: BL, branchial lobes; BT, buccal tentacles; ll, lower lip; NI, n-type invagination; TC, thoracic chaetiger; TM, tentacular membrane.

FIGURE12. A. Relationof width andnos of abdominal segments with length of body of Terebellides yangi n.sp.; B. Relation of the length ratio of thorax and abdomen (LRTA) with length of body.