Thelepus taiwanensis Hsueh & Li, 2016, sp. nov.

Thelepus taiwanensis sp. nov.

Fig. 5 A–H

Material examined. Holotype (NMNS7516-21), offshore station CP235 (25°22´95˝N 122°43´63˝E), sediment bottom, 765–806 m deep, 22 July 2004.

Description. Holotype complete, brownish in alcohol (Fig. 5 A), body length 95.0 mm with 105 segments, maximum width 6.0 mm on segment 9.

Prostomium at base of upper lip, with large lobe (Fig. 5 B–C); upper lip large, with lobe, horseshoe-shaped; lower lip shallow, arch-shaped, low ridge (Fig. 5 B–C); buccal tentacles thick, with medium groove, basal part of prostomium short and compact; eyespots absent; peristomium forming lips and continue dorsally; ventral surface of anterior segments undetermined.

Lateral lobes absent. Three pairs of branchiae on segments 2 to 4 (Fig. 5 B), filaments thick and moderate elongate. Segment 2 filaments arising mostly from body wall with few from dorsal edge of lateral swollen glandular areas and few from body wall between medial gap, respectively; segments 3 and 4 have filaments arising directly from body wall at junction of two segments, transversely arranged. Counting branchial scars segment 2 has 16 simple filaments on each side with line of filaments extending laterally to notopodia, segment 3 with 12 simple filaments on each side, segment 4 with 8 simple filaments on each side; narrow medial gap between pairs of branchial filaments.

Notopodia present from segments 3 to 38. Anterior parapodia elongate, rectangular, with distinct glandular pre and post-chaetal lobes, notochaetae emerging between lobes (Fig. 5 B), mid to posterior notopodia becoming lobelike processes (Fig. 5 D), less glandular than anterior ones; notopodia on segment 3 shorter and clearly ventral than following ones, reaching maximum length on segment 6, similar in length to segment 14, thereafter becoming shorter progressively. Notochaetae with two rows of winged chaetae, anterior row slightly shorter than those from posterior row, all tapering to tips (Fig. 5 D–E).

Neuropodia rectangular, swollen on segments 5 to 11; neuropodia on segment 5 narrower but equal in length to following one, reaching maximum width and length on segment 11, thereafter becoming narrower and shorter progressively. Neuropodial uncini arranged in single line throughout, with moderately elongate prow and slightly upturned terminal button, dental formula MF:2 throughout (Fig. 5 F–H).

Nephridial papillae absent; pygidium round, with crenulated anal opening.

Etymology. The name is derived from the name of nearby island where the worm was collected.

Type locality. Offshore station CP235 of northeastern Taiwan.

Distribution. Only known from type locality.

Remarks. Unlike Streblosoma, information on the presence of lateral extension of branchiae on first pair of notopodia, uncini of segments arranged in curved rows, and posterior uncini arranged in straight rows for Thelepus was only available in a few descriptions, and re-examination type specimens of many species described in nineteen to early twenty centuries is not practical. Also unlike Streblosoma, information on some unstable morphological characters commented in previous Remark has improved with redescription and reviews for the genus by more recent studies (i.e. Hutchings & Glasby 1986; Glasby & Hutchings 1987; Hutchings & Glasby 1987; Hilbig 2000; Londoño-Mesa 2009). Here, the authors follows the work done by Reuscher et al. (2012) to create a synoptic table comparing some 40+ members of Thelepus. Above-mentioned morphological characters are also used for comparisons between congeners when it is applicable.

Examining available information on uncinial dental formula of anterior tori of all species in the genus, seven species are noted with identical or similar uncinial dental formula to that of Thelepus taiwanensis sp. nov. They are Species Branchial filaments Eyespots Notopodial Uncini dental formula Type locality

(II:III:IV each side) (P/A) pairs (anterior/posterior tori) (general region)

T. abranchiatus 1, 7 0:0:0 A 29 MF:2:1 7/n.a. New England, USA T. abyssorum 1 rudimentary gill filamentsA ~30 MF:4:5/n.a. Southeast China T. alatus 1 5–6:3–4:3 P>55a MF:2–3:1–3/MF:2–3:3–5 Queensland, Australia T. ambitus 1 ∞ A>6 7a MF:2–3:∞/ MF:2–3:∞ Argentina

T. angustitoris 1 few P n.a. MF:3:2/n.a. South East Asia T. antarcticus 1, 3 ~15:~12:0 3 P 3 n. a. MF:2 1 or MF:3:1–2 3/n.a. Antarctic Ocean T. australiensis 1 15–18:12–13: 10–12 P 64 MF:2–5:0–3/MF:2–4:0–3 South Australia T. binakayensis 1 6:3:2 P 34 MF:1:2/n.a. Philippines

T. boja 1 15–17:9–11:7 P 35 MF:2–3:4–8/MF:2–3:4–8 Victoria, Australia T. branchiatus 1 8:<8:1 A>30 MF:2/n.a. Hawaii

T. brevicauda 1 6:3:2 P 34 MF:1–3:5–7/MF:2–3:6–8 Victoria, Australia T. cincinnatus 1, 6 ∞:∞:0 6 P 40 MF:1?:1?:1?b/n.a. Arctic Ocean T. crassbranchiatus 12 4:2:0 P>38 MF:2/MF:2 Puerto Rico

T. crispus 1 ∞:∞:∞ A 84–131 MF:2:2–3:2–6/n.a. North East Pacific T. dubius 1 10–12:5–6:5–6 P 29 MF:2:1/n.a. Malay Archipelago T. extensus 1 17–18:9–10:10–11 P 34 MF:1–3:5–7/MF:2–3:6–8 South Australia T. fraggleorum 1 10:15:7 P 70 MF:2:1/MF:2:1–3 Panama

T. haitiensis 12 35–43:25:20–30 A 43–46 MF:2/MF:2 Haiti

T. hamatus 1 ~5:~5:0 P>29a MF:2:1:2–3:1–3/MF:3:5:5:3 Alaska, USA T. japonicus 1 ∞:∞:∞ P 109 MF:2:1/n.a. Japan

T. leptoplocamus 1>20:>20:>20 A ~ 40 n. a. Philippines

T. longtongensis sp. nov. ~30:~20:~20 A 46 MF:2:1/MF:2:1 northeastern Taiwan T. malayensis 1, 7 1:0:0 A>13a MF:3:5–7: ∞ 7/n.a. Malaysia

T. marenzelleri 1 n.a. P n.a. MF:1:1–2/n.a. Southern Japan T. mcintoshi 1 n. a. P 31 – 39 n. a./n.a. Kerguelen Islands T. microbranchiatus 1 6:5:3 A 30 MF:2:3/n.a. South East Asia T. nucleolata 1 6:4:0 P n.a. n.a./n.a. Gulf of Naples, Italy T. opimus 1 10:6:6 P>55a MF:2:2–3: ∞ /MF:2–3:1–7:0–5 Hong Kong, China T. paiderotos 1 few:few:few P 31–35 MF:2:>2/MF:2:>2 Lizard Island, Australia

T. parcus 1 24:10:10 A ~40 – 90 n. a./n.a. Philippines

T. pascua 1, 7, 12 1:1:0 A 21 1, 32 7 MF:2–4:4–5:7/MF:2–4:4–5:7 1 Panama

T. paucibranchis 1 3–4:0:0 A n.a. MF:2/n.a. Philippines

T. pequenianus 1, 9 18–20:11 – 15:11 – 14 P 27 MF:1–3:1–6/MF:1–3:1–6 Namibia

T. pericensis 1 ∞ P ~193 MF:2/n.a. Panama

T. plagiostoma 7 20–30:11–20:8–15 P 58–119 MF:2–5:0–3/MF:2–4:0–1 New Zealand T. praecox 1 2:0:0 P 28 MF:2:2–4/MF:3–4:4–6 NSW, Australia T. pulvinus 1 15: 10 – 12:10 P 42 MF:2–3:2/MF:3:2 Hong Kong, China T. robustus 1, 10 38–50:20–35: 31–39 10 P 70–134 10 MF:1–3:0–3 10/MF:2–4:0–6 10 Philippines

T. setosus 1, 11, 12 5–15:5–15: 5–15 12 P1, 12 ~ 30–60 12 MF: 2 1, 12 /n.a. France

T. tenuis 7, 12 1:1:1 A 16–22 MF:2:1–3/MF:2:5 Bermuda

T. taamensis 1 4–5:4–5:4–5 P n.a. MF:2:1/n.a. Red Sea

T. taiwanensis sp. nov. 16:12:8 A 36 MF:2:/MF:2 northeastern Taiwan T. thoracicus 1, 2 30:<30:25 4 P 3 0 1, 48 2 MF:2:1:2 1 or MF:1 2/ MF:2–3 2 Red Sea

T. toyamaensis 1 11–12:7–8:6 P>32 a MF:2–3/MF:2–3 Japan

T. triserialis 1, 4 14:14:14 P4>39 a MF:2:1 4/n.a. Mediterranean Sea T. vaughani 1 few:few:few A>57 a MF:2:1:2/n.a. Gulf of Aden T. verrilli 1, 12 2:2:4 12 P12 33 MF:2:0–1/MF:2:0–1 12 Florida, USA Thelepus branchiatus Treadwell, 1906 (type locality: Hawaii), Thelepus crassibranchiatus Treadwell, 1901 (type locality: Puerto Rico), Thelepus haitiensis Treadwell, 1931 (type locality: Haiti), Thelepus paucibranchis (Grube, 1878) (type locality: Philippines), Thelepus pericensis Chamberlin, 1919 (type locality: Panama), Thelepus setosus (Quatrefages, 1866) (type locality: France), and Thelepus verrilli (Treadwell, 1911) (type locality: Florida) (Table 1). However, T. taiwanensis sp. nov. differs from T. crassibranchiatus, T. pericensis, T. setosus, and T. verrilli by lacking eyespots (Table 1). Numbers of branchial filaments on each side of parapodia in T. taiwanensis sp. nov. varies from that of T. crassibranchiatus, T. pericensis, and T. verrilli (16:12:8 vs. 4:2:0, ∞, and 2:2:4, respectively) (Table 1).

Thelepus branchiatus, T. haitiensis, and T. paucibranchis have no eyespots as in T. taiwanensis sp. nov., and their dental formula on anterior or both anterior and posterior tori are identical to that of T. taiwanensis sp. nov. (Table 1). However, T. taiwanensis sp. nov. can be separated from these three species by having different number of branchial filaments on each side of notopodia (16:12:8 vs. 8:<8:1, 35–43:25: 20–23, and 3–4:0:0, respectively) (Table 1). Moreover, T. branchiatus inhabits on coral sand bottoms, shells and foraminiferans near the continental shelf break (~257 to 220 meters) (Treadwell 1931). Thelepus haitiensis is known only from shallow water in Haiti (Londoño-Mesa 2009). Thelepus paucibranchis was reported from Bohol, Philippines (Grube, 1878), but T. taiwanensis sp. nov. was collected from offshore sediment bottom in bathyal depths (765–806 m).