Terebellides toliman, Schüller, Myriam & Hutchings, Pat, 2013

Schüller, Myriam & Hutchings, Pat, 2013, New species of Terebellides (Polychaeta: Trichobranchidae) from the deep Southern Ocean, with a key to all described species, Zootaxa 3619, pp. 1-45 : 25-28

Terebellides toliman sp.n.

Figs 18, 19 , 20

Holotype: ANDEEP-SYSTCO, St. 16-1, RD (ZMH-26016)

Paratype: ANDEEP-SYSTCO, St. 16-1, RD [SEM, stub MI566 & MI567] (AM W38720)

Description: (Based on both holotype and paratype)

Holotype in two pieces, anterior part 22 mm in length, 4 mm in width, for 16 chaetigers, posterior part 23 mm in length, 2 mm in width, for 37 uncinigerous segments, extreme posterior missing. Body robust, colour preserved pale cream.

Head region: Prostomium with fleshy and markedly expanded tentacular membrane with curved glandular slightly folded margins, internal walls, corrugated and glandular. Tentacles numerous, of two kinds: short, uniform in thickness ones and long ones with expanded tips ( Figs 18, 19 A–C). Peristomium consisting of an upper lip and compact lower lip. Segment 2, glandular and expanded ventrally, visible ventrally and laterally, dorsally as narrow ring ( Fig. 19 C).

Branchiae: Stalk stout and short, weakly annulated ( Fig. 18). Four branchial lobes, almost completely fused together except for proximal quarter of lobe, without filamentous tips ( Fig. 19 B). Anterior two lobes largest, with compact numerous lamellae ( Fig. 19 A).

Anterior chaetigers: Notopodia from segment 3, only 17 pairs present, (posterior thorax missing, so suggest that 18 originally present). First five notopodia smaller than subsequent ones, first three pairs more ventrally displaced, first chaetiger very small with poorly developed chaetal lobes and chaetae appearing to arise directly from body wall ( Figs 18, 19 A). Posterior notopodia more erect than anterior ones, marked from chaetiger 4 onwards. Notochaetae, capillaries, graded in length within fascicle, with inflated thecae ( Fig. 19 D). First neuropodia on chaetiger 6, 6 smooth spines, only weakly bent (about 120°) ( Fig. 19 E). Thoracic neuropodia sessile pinnules, but posteriorly become increasingly erect, and on posterior abdominal segments form inverted triangular erect pinnules. Thoracic neuropodia from chaetiger 7 with uncini arranged in several rows (about 3), long shafted, denticulate with long and stout main fang and several multidentate rows of teeth above, not vertically aligned, so providing a dental formulae not possible ( Fig. 19 F, G). Abdominal uncini numerous within a torus and with elongate main fang and two to three rows of 4–5 elongate accessory teeth, head with unsorted multiple denticles ( Fig. 19 H).

Lateral lappets: Present from TC-1–6, with TC-1>2>3>4=5<6.

Ventral pads: Entire ventrum glandular, individual pads separated by non-glandular intersegmental rings.

Nephridial papillae: None visible in holotype, but nephridial pores present, present in paratype on segments 3, 5, 6, 7, accentuated by methyl green staining.

MG staining pattern of thorax resembles pattern 8 ( Figs 2 , 20 ): Anterior ventrum of thorax darkly stained with only narrow white bands between each segment. Between chaetigers 11–14, distinct white bands connecting notopodia ( Fig. 20 A). Staining posteriorly not fading, but mid ventral glandular stripe stained as well as neuropodial tori ( Fig. 20 B), lateral margins of branchiae also stained.

Pygidium: Unknown.

Remarks: Terebellides toliman sp.n., is characterised by four pairs of branchiae partially fused along their length, with filamentous tips absent, composed of densely packed lamellae, with lateral lappets continuing until thoracic chaetiger 6 and geniculate hooks weakly bent. This new species most closely resembles T. canopus sp.n., (this paper) but can be separated by the shape of the geniculate hooks. Other species with four branchial lobes, partially fused, and densely packed lamellae include T. horikoshii Imajima & Williams, 1985 and T. japonica Moore, 1903 , which both differ from T. toliman sp.n., by having lateral lappets until chaetiger 5 only. Terebellides horikoshii in addition has notopodia of chaetigers 1 and 2 well developed whereas in T. toliman sp.n., they are poorly developed. For details on other species see the key.

Another distinguishing character is that this species has reached a much greater size than any other species described, and is the only species collected on the one shelf station in this paper or by Schüller and Hutchings (2012).

Habitat: Eastern Weddell Sea shelf in 486– 488 m. Known only from type locality.

Etymology: The specific name toliman refers to the brightest star in the Centaurus, it is the third brightest star in the sky and the closest star to the Sun.

Figures

FIGURE 2. MG staining patterns of observed species, adapted and extended from Schüller & Hutchings (2010).

FIGURE 19. Terebellides toliman sp. n. (AM W 38720), A—anterior thorax, lateral, B—anterior thorax, dorsal, C—anterior thorax, ventral, D—median thoracic notopodium, E—geniculate neuropodial hooks on TC- 6, F—median thoracic neuropodium, G—uncini of thoracic neuropodia, H—uncini of abdominal neuropodium.

FIGURE 20. Terebellides toliman sp. n. (ZMH- 26026), MG staining, A—thorax, ventral view, B—abdominal segments.