Thelepus longtongensis, Hsueh, Pan-Wen & Li, Kuo-Rong, 2016

Hsueh, Pan-Wen & Li, Kuo-Rong, 2016, New species of Thelepodidae (Terebelliformia, Polychaeta) from Taiwan, Zootaxa 4170 (3), pp. 510-524 : 520-522

Thelepus longtongensis sp. nov.

Fig. 6 A–H

Material examined. Holotype ( NMNS 2572-1024 ), Longtong Bay (25°06´08˝N, 121°55´11˝E), New Taipei, subtidal hard-bottom, 2 m deep, 5 June, 1996.

Description. Holotype complete, brownish in alcohol ( Fig. 6 A); body length 221 mm with 157 segments, maximum width 11.4 mm on segment 18.

Prostomium at base of upper lip; upper lip with large lobe, triangular ( Fig. 6 B); lower lip almost straight-line, low ridge, with a thin lappet ventrally ( Fig. 6 B); buccal tentacles thick, elongate, with medium groove, basal part of prostomium moderate high and large ( Fig. 6 C); eyespots absent; peristomium forming lips and continue dorsally; ventral surface of anterior segments corrugated.

Lateral lobes absent. Three pairs of branchiae on segments 2 to 4 ( Fig. 6 A, C), filaments thin and elongate, most filament lengths exceeding seven body segments, arising from swollen glandular areas, arranged in transverse bands ( Fig. 6 C); counting branchial scars, segment 2 with about 30 simple filaments on each side, segment 3 with about 20 simple filaments per side, and segment 4 with about 20 simple filaments; medial gap present between within branchial filaments of each branchiferous segment, but less conspicuous on first pair.

Notopodia present from segments 3 to segment 48. Anterior parapodia elongate, rectangular, with distinct glandular pre-and postchaetal lobes, notochaetae emerging from between lobes ( Fig. 6 D), mid to posterior notopodia becoming triangular, less glandular than anterior ones; notopodia on segment 3 shorter and clearly ventral than following ones ( Fig. 6 C), reaching maximum length on segment 4, thereafter becoming shorter progressively. Notochaetae of anterior segments with two rows of winged chaetae, anterior row slightly shorter than those from posterior row, tapering to tips ( Fig. 6 E).

Neuropodia rectangular from segments 5 to 28, uncini arranged in single line, dental formula MF:2:1 ( Fig. 6 F), neuropodia from segments 29 to 49 remain rectangular but progressively narrower and thinner, neuropodia from segment 50 to last segment becoming trapezoid; uncini arranged in single line, with squared prow and moderately upturned terminal button, dental formula MF:2:1 ( Fig. 6 G–H).

Nephridial papillae present on segments 5 to 7, near bases of notopodia, round and conspicuous. Pygidium round.

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

Type locality. Longtong Bay , New Taipei, Taiwan.

Distribution. Only known from type locality.

Remarks. Comparing available information on uncinial dental formula of anterior tori of known species in the genus, seven are noted with identical or similar dental formula to Thelepus longtongensis sp. nov., which are T. abranchiatus ( Hartman & Fauchald, 1971) (type locality: New England), T. dubius Caullery, 1944 (type locality: Malay Archipelago), T. fraggleorum Capa & Hutchings, 2006 (type locality: Panama), Thelepus japonicus Marenzeller, 1884 (type locality: Japan), Thelepus taamensis Caullery, 1944 (type locality: Red Sea), Thelepus triserialis ( Grube, 1855) (type locality: Mediterranean Sea), and Thelepus verrilli ( Treadwell, 1911) (type locality: Florida) ( Table 1). However , T. longtongensis sp. nov. can be readily distinguished from these seven species by examining morphological characters such as number of branchial filaments and the presence and absence of eyespots. Among those seven species, only T. abranchiatus has no eyespots as in T. longtongensis sp. nov.; however, the former species has no branchial filaments, whereas the latter species has many branchial filaments ( Table 1). Thelepus longtongensis sp. nov. can be separated from Thelepus dubius , T. fraggleorum , T. japonicus , T. taamensis , T. triserialis , and T. verrilli by having different number of branchial filaments on each side of parapodia (~30:~20:~20 vs. 10–12:5–6:5–6, 10:7:5, ∞:∞:∞, 4–5:4–5:4–5, 14:14:14, and 2:2:4, respectively) ( Table 1).

In Table 1, there are four species, which lack any information on uncinial dental formula of anterior tori for making comparison to T. longtongensis sp. nov. These are: Thelepus leptoplocamus ( Grube, 1878) (type locality: Philippines), Thelepus mcintoshi Grube, 1877 (type locality: Kerguelen Islands), Thelepus nucleolata (Claparède, 1869) (type locality: Gulf of Naples, Italy), and Thelepus parcus ( Grube, 1878) (type locality: Philippines). Among those four species, T. mcintoshi and T. nucleolata are the two species least similar to T. longtongensis sp. nov.; both species have eyespots, while T. longtongensis sp. nov. lacks them. In addition, Thelepus mcintoshi has fewer pairs of notopodia than T. longtongensis sp. nov. (31-39 vs. 46), and T. nucleolata has fewer number of branchial filaments on each side of notopodia than T. longtongensis sp. nov. (6:4:0 vs. ~30:~20:~20) ( Table 1). Thelepus leptoplocamus and T. parcus are also noticeably different from T. longtongensis sp. nov. in terms of the ratio of the length of notopodia to the total body length, despite both these species have no eyespots and number of pairs of notopodia, which is similar to or within the range to that of the latter species (~40, ~40–90 vs. 46) ( Table 1). Notopodia of both T. leptoplocamus and T. parcus continue almost to end of the body ( Grube, 1878), but in T. longtongensis sp. nov. they continue only for less than one-third of the total body length. Moreover, T. leptoplocamus has thin branchial filaments, but none of them with length exceeding two-body segments length (Grube 1978: 238–9, Pl. XIII, fig. 5). Thelepus longtongensis sp. nov. also has thin filaments but many of the filaments their length exceed the length of three-body segments ( Fig. 4 A). Thelepus parcus has fewer branchial filaments on each side of parapodia than that of T. longtongensis sp. nov. (24:10:10 vs. ~30:~20:~20) ( Table 1).

Lastly, T. longtongensis sp. nov. can be distinguished from T. taiwanensis sp. nov. by the morphology of prostomium and peristomium, the origin and number of branchial filaments, number of pairs of notopodia, morphology of notochaetae of anterior segments and neurochaetae, and type of habitat. Thelepus longtongensis sp. nov. has large upper and lower lips, branchial filaments thin and quite elongate and arising from swollen glandular areas, up to 20–30 branchial filaments on each side of notopodia, 46 pairs of notopodia, and uncinial dental formula MF:2:1 throughout, whereas T. taiwanensis sp. nov. has small upper and lower lips, branchial filaments thick and moderately elongate and arising from body wall, up to 8–16 branchial filaments on each side of notopodia, 36 pairs of notopodia, and uncinial dental formula MF:2 throughout ( Table 1; Figs 5 B–H, 6B–H). Thelepus longtongensis sp. nov. was collected from shallow rocky bottom, whereas T. taiwanensis sp. nov. was collected from offshore sediment bottom in bathyal depths (765–806 m).

Figures

FIGURE 4. Streblosoma wuchiensis sp. nov.; holotype (NMNS 7516 - 2): A, close-up view of neuropodia on middle segments; B, frontal view of uncinus, segment 9; C, close-up view of neuropodia on posterior segments; D, frontal view of uncinus, segment 27. Scale: A, C, 0.5 mm; B, D, 0.05 mm.

FIGURE 5. Thelepus taiwanensis sp. nov. Holotype (NMNS 7516 - 21): A, lateral view of anterior region; B, closed-up lateral view of anterior body; C, close-up ventral view of view anterior body; D, close-up view of notopodium, segment 13; E, closeup view of notochaetae, segment 10; F, frontal view of uncini, segment 10; G, frontal view of uncinus segment 34; H, lateral view of uncinus, segment 37. LL, lower lip; P, Prostomium; UL, Upper lip. Numbers indicate segment number. Scale: A, 10.0 mm; B – D, 1.0 mm; E, 0.1 mm; F – G, 0.05 mm; H, 0.1 mm.

FIGURE 6. Thelepus longtongensis sp. nov. Holotype (NMNS 2572 - 1024): A, lateral view of anterior body; B, closed-up ventral view of anterior body; C, close-up lateral view of anterior body; D, close-up lateral view of anterior body; E, notochaetae, segment 19; F, frontal view of uncinus, segment 7; G, lateral view of uncinus segment 40; H, line draw of uncinus, segment 40. LL, lower lip; P, Prostomium; UL: Upper lip. Scale: A, 10.0 mm; B – D, 1.0 mm, E, 0.5 mm; F – H, 0.1 mm.