Terebellides jitu, Schüller, Myriam & Hutchings, Pat A., 2010

Schüller, Myriam & Hutchings, Pat A., 2010, New insights in the taxonomy of Trichobranchidae (Polychaeta) with description of a new Terebellides species from Australia, Zootaxa 2395, pp. 1-16 : 7-11

Terebellides jitu sp. nov.

Figures 2–4

Terebellides narribri — Hutchings and Peart 2000; 247–254, in part.

Material examined. Holotype. AM W35501 (ripe male): Northern Territory, Arafura Sea, 948.46' S 13315.24' E, 158m, coll. May 2005.

Paratypes. AM W7059 (1 specimen, part on SEM stub), AM W23828 (1 specimen): Queensland, East channel, off Tangalooma Point, Moreton Island, Queensland, Australia, 2712' S 15321 ' E, Dec 1972; AM W34026 (1 specimen on SEM pins), AM W34027 (1 specimen on SEM pins), AM W34028 (1 specimen, gravid), AM W34030 (1 specimen), AM W34031 (1 specimen), AM W34034 (1 specimen, gravid): Arafura Sea, 913.9' S 13329.25' E, 158m, coll. 21-05-2005 from Area C South, Australia.

Additional material examined. AM W36139 (8 specimens): New South Wales, Port Hacking, 344.6’ S 1516.25’ E, 27 Oct 1994; AM W27473 (1 specimen, ripe male): Western Australia, 1km north east of Legendre Island, 2035.6’ S 11635.37’ E, 6 Aug 2000; AM W27490 (1 specimen): Western Australia, between Enderby & Lewis Islands, 2035.6’ S 11635.37’ E, 28 Jul 2000; AM W23839 (1 specimen): Western Australia, Duffield Ridge, Rottnest Island, 322.30’ S 11528.39’ E, 10 Jan 1991.

Description. Holotype complete, 15 mm long and ~ 2.5 mm wide for 20 abdominal segments, mature. Additional specimens 0.3–2.9 mm long, some with coelomic gametes. Dorsum and ventrum smooth, colour yellow to reddish brown in preserved specimens.

Prostomium compact, expanded tentacular membrane with numerous folds. Buccal tentacles of two kinds, uniformly tapered and with expanded tips. Remains of numerous scattered eyespots may be visible in preserved specimens dorsally on prostomium after MG staining. Peristomium consisting of hidden upper lip. And large, expanded lower lip. Second segment reduced, narrow, almost completely covered by third segment ( Figs 2 a & 3a). Lateral lappets on segments 1–6, well developed ( Figs 2 a & 3a), largest on segments three and four. Ventral glandular bands and glandular areas around parapodia absent. Nephridial papillae inserted dorsally to notopodia of segments 3, 6, and 7 ( Fig. 2 a).

Branchiae as single structure dorsally on segments 3 and 4, consisting of 4 distinct lobes; fused for about half their length, all of similar length ( Fig. 2 b). Anterior ones broader than posterior ones, projecting anteriorly to form a seemingly 5th lobe. Posterior lobes with distinct distal tip. All lobes composed of tightly packed lamellae, each one with transverse ridges on its surface ( Fig. 2 b).

FIGURE 3. Terebellides jitu sp. nov. SEM a–c AM W34026 a—Anterior front end showing well developed lateral lappets with elevated anterior margins, b—Chaetiger 3 with 2 tiers of notochaetae, c—close up of notochaetae of chaetiger 3. d–f AM W7059 d—8th thoracic neuropodia, e—lateral view of thoracic uncini from 8th neuropodia, f—Close up of single posterior abdominal uncinus. g–h AM W34027 g—Head on view of posterior abdominal uncini, h—More lateral view of posterior abdominal uncini. Scales: a-100 µm, b-20 µm, c-2 µm, d-10 µm, e-10 µm, f-2 µm, g-2 µm, h-2 µm

Notopodia 18 pairs, starting on segment 3. First one strongly reduced, notochaetae seemingly originating from body wall but not apparently shorter than subsequent ones. Anterior notopodia shifted slightly dorsal. Chaetae arranged in 2 tiers, consisting of narrow - winged, finely pointed capillaries (Fig. 3b) with shaft consisting of numerous compact filaments with tips slightly splayed so that surface appears plumose (Fig. 3c). First neuropodia from segments 8 (chaetiger 6), continuing through abdomen. Thoracic neuropodia sessile pinnules with varying number of long-handled uncini (varying between 6–20 per torus, specimens observed under SEM with about 13 uncini per torus, Fig. 3d), except first neuropodia; with ~ 6 acicular hooks, with pointed tips and sharply bent ( Fig 2 c). Long - handled uncini with a dental formula of MF: 3–6:5:~:~~. Back of uncini very striated, rows of teeth intercalated ( Figs 2 d & 3e).

Abdomen length possibly depending on size of specimens, usually with more than 30 segments present. Abdominal neuropodia erect pinnules with>15 avicular uncini ( Figs 2 e–f & 3f–h), with a dental formula of MF:6–7:6–8:~~:~~. Abdominal uncini with strongly crested head, covered with numerous small and scalelike teeth ( Fig. 2 e, 3f). Length of abdominal segments gradually decreasing, caudally terminating into blunt pygidium without appendages ( Fig. 2 f).

The staining with MG results in compact green coloration of the first 3–5 segments before turning into striped pattern ( Fig. 4 ). Stripes are gradually fading posteriorly and vanish from about segment 12 to 15. Additionally, pronounced staining of ventro-anterior margins of segments 1–6 and thoracic noto- and neuropodia is present. Buccal tentacles with expanded tips show distinct dotted staining in contrast to the weakly stained uniformly tapering ones.

Remarks. All observed material is part of the polychaete collection of the Australian Museum, Sydney, NSW, Australia. Specimens newly described as Terebellides jitu sp. nov., were originally identified as Terebellides narribri by the authors of this species ( Hutchings & Peart 2000). Hutchings and Peart (2000) had already reported the presence of two variations in their material stating the occurrence of “large, white, oval, glandular patches present on chaetiger 3 as the distinguishing character. A re-examination of the material, especially after staining with MG confirmed this character for many specimens, including the holotype of T. narribri . However, all specimens with this trait were also characterized by the lack of a truly apparent reduction of the first chaetiger in contrast to the description by Hutchings and Peart (2000). Specimens without glandular patches showed reduced first notopodia, lateral lappets on segments 1–6, and also presented pronounced filamentous tips on the posterior branchial lobes. Adding up to now four distinct characters between the two variations, the species T. narribri is split up. Specimens with glandular patches on chaetiger 3, first chaetiger only slightly reduced in size compared to subsequent ones, lateral lappets on the first 5 segments, and absence of filamentous tips on posterior branchial lobes belong to Terebellides narribri . Specimens with a purely solid—striped staining pattern, strongly reduced first chaetiger, lateral lappets on segments 1–6, and pronounced tips on posterior branchial lobes are placed into the new species T. jitu sp. nov. These include two paratypes of T. narribri (AM W7059, AM W23828) which were collected at Moreton Bay, Queensland, the type locality of T. narribri . A differentiation based on sampling locality could not be made between the two species suggesting that the species may coexist in the same habitat.

Distribution. Australian waters in shallow to moderate depths

Etymology. “ Jitu is the Aboriginal (Kariyarra) word for ibis. The acicular hooks of the first neuropodia resemble the shape of the beak of the Australian white ibis (Threskiomis molucca) which is very common in Australia, especially in the area around the Australian Museum, Sydney where the material is deposited.

Figures

FIGURE 2. Terebellides jitu sp. nov. holotype AM W 35501, a—anterior region, b—branchiae, c—acicular hooks (segment 8), d—detail head of thoracic uncinus, e—detail head of abdominal uncinus, f—pygidium and posterior segments [* — position of nephridial papillae, arrows—filamentous tip of branchiae and transverse ridges]

FIGURE 4. Methyl green staining of Terebellides jitu sp. nov. holotype AM W 35501, anterior region in lateral view.