Anobothrus rubropaleatus, Schüller, Myriam & Jirkov, Igor A., 2013

Schüller, Myriam & Jirkov, Igor A., 2013, New Ampharetidae (Polychaeta) from the deep Southern Ocean and shallow Patagonian waters, Zootaxa 3692 (1), pp. 204-237 : 221-223

Anobothrus rubropaleatus n.sp.

Figs 10–12

Holotype: Knipovich 258, 34°34‘S, 53°14‘W, 50 m [ZMH-26065].

Paratypes: Knipovich 258, 34°34‘S, 53°14‘W, 50 m (64 specimens, 1 x SEM, complete and incomplete) [ZMH-26066–26067].

Diagnosis: The species is characterized by its bright red paleae even in preserved material, and the lack of notopodia in TS-3.

Description: Holotype 6 mm long and 0.5 wide, with 13 AUs, complete. Complete paratypes 2–8 mm long and about 0.1–0.7 mm wide, with 12–13 AUs ( Fig. 10 A). Colour in ethanol white, paleae light red.

Prostomium trilobed, middle lobe anteriorly rounded, without ridges or eyes ( Figs 10 B, 11A). Lower lip not enlarged. Presence of nuchal organs unresolved. Buccal tentacles all retracted. TS-2 bearing about 8–12 reddish paleae, positioned laterally directly below branchiophore ridge ( Fig. 11 A, B). TS-2 laterally visible as a prominent lobe from which the paleae originate, otherwise more or less fused to TS-3. TS-3 achaetous. Paleal base distinctly stouter than best developed notochaetae of subsequent thoracic segments. Paleae flat, saber-like, width of paleae abruptly decreasing in distal third, from there chaetae fine, tapering to a pointed tip ( Fig. 11 B). Four pairs of branchiae ( Fig. 10 C). Anterior three pairs of branchiophores attached to each other across dorsum, arranged in an almost straight line forming a prominent dorsal ridge. Forth branchial pair attached behind the second outermost pair and connected to notopodia of TC-2 (TS-5). Outermost branchial pair connected with notopodia of TC-1 (TS- 4). Diameters of all branchial scars almost equal. All branchiae lost, branchial surface structure unknown. 14 TCs, 1st pair of notopodia present in TS-4, well developed. Notochaetae limbate ( Fig. 11 C). 12 TUs, starting in TC-3 (TS-6). Thoracic neuropodia large tori, slightly decreasing in size towards the posterior. [Thoracic uncini with a main fang surmounted by 4 to 5 transverse rows of 2 teeth ( Fig. 11 D).] Circular band present in anterior half of TU- 2 (TC-4, TS-7) [hardly visible in most specimens] ( Fig. 10 A, C, D). Notopodia of 5th to last TC slightly shifted dorsally and connected by a prominent ridge ( Fig. 10 A). Chaetae and uncini of 5th to last TU not modified ( Fig. 12 A, B). 13 AUs, neuropodia of AU-1 and AU-2 of similar type to thoracic neuropodia, only slightly erect tori. [Uncini not observed in AU-1 and AU-2 under SEM.] Abdominal neuropodia from AU-3 distinct, prolonged erect pinnules with uncini in marginal position ( Fig. 12 C). [Abdominal uncini with dental formula with main fang surmounted by a transverse row of 7–8 teeth, surmounted by numerous small teeth.] Rudimentary abdominal notopodia absent. All thoracic and abdominal noto- and neuropodia without cirri. Pygidium with two lateral oval to cirriform papillae ( Fig. 12 D).

A pair of nephridial papillae positioned slightly apart from each other behind branchial ridge dorsally on TS-5 (TC-2) ( Fig. 10 C) [under SEM, additional papillae observed dorsally associated with notopodia of TU-3].

Tube membranous, covered loosely with fine sediment and detritus, brightly stained in methylene blue and methyl green.

Remarks: All paratypes are either minute in size or incomplete. In complete specimens the distinguishing characters of the species are difficult to observe due to the small size. Hence, a large but incomplete specimen in good condition is chosen as holotype here to display all important characters for species recognition. A characteristic trait of Anobothrus is a circular whitish band anterior of parapodia of TU-2 or TU-3. While most species bear this feature in TU-3, the newly described species, A. rubropaleatus n.sp., bears it in TU-2, which has only been reported for Anobothrus laubieri (Desbruyères, 1978) and A. wilhelmi n.sp. The most outstanding character of A. rubropaleatus n.sp. however is the unique reddish colouration of the paleae. In shape they resemble those of Anobothrus pseudoampharete Schüller, 2008 with their medium size, stout base and an abruptly tapering distal quarter with a fine but pronounced tip. Under SEM, a simple accessory chaetae dorsal to the paleae was observed ( Fig. 11 B). The surface of this chaeta was covered by regularly scattered holes, that were also present (but less numerous) on the paleal surface. This type of chaeta has never been described for the genus before and only further observation of material under SEM will help to resolve its significance as a taxonomic character. Anobothrus rubropaleatus n.sp. together with Anobothrus mancus Fauchald, 1972 are the only species of the genus with only 14TCs. Additionally, among the examined material, a few specimens bear only 11 neuropodia on one side, starting in TC-4 (TS-7). While uncini were not observed in AU-1 and AU- 2 in the species, under SEM, a surface structure that might resemble uncini in development was observed in midline of the neuropodia of AU-1, however, the true identity of this structure is unknown.

Etymology: The name refers to the bright reddish colour of the paleae that remains present even in ethanolpreserved specimens.

Figures

FIGURE 10. Anobothrus rubropaleatus n. sp. (paratype, Knipovich 258, ZMH- 26067) A—habitus lateral view, Bprostomium, dorso-frontal view, C—anterior end, dorsal view, D—anterior end, lateral view.

FIGURE 11. Anobothrus rubropaleatus n. sp. (paratype, Knipovich 258, ZMH- 26066) SEM A—prostomium, dorso-frontal view, B—paleae, arrow—chaeta of unknown origin associated with paleae, C—notochaetae of TU- 9, D—uncini of neuropodium of TU- 9.

FIGURE 12. Anobothrus rubropaleatus n. sp. (paratype, Knipovich 258, ZMH- 26066) SEM A—notochaetae of TU- 8, Buncini of neuropodium of TU- 8, C—neuropodium of mid-body AU, D—pygidium.