Anobothrus wilhelmi Schüller & Jirkov, 2013, n.sp.

Anobothrus wilhelmi n.sp.

Figs 13–15

Holotype: ANDEEP III—st 16-10, EBS, 41°07.55'S – 41°07.02'S, 09°55.94'E – 09°54.85'E, South Africa / South Atlantic, 4720 m [ZMH-26068].

Paratypes: ANDEEP III—st 16-10, EBS, 41°07.55'S – 41°07.02'S, 09°55.94'E – 09°54.85'E, South Africa / South Atlantic, 4720 m (2 specimens, both incomplete), st 21-7, EBS, 47°39.87'S – 47°38.52'S, 04°15.79'E – 04°14.94'E, South Africa / South Atlantic, 4574 m (1 specimen, incomplete), st 74-6, EBS, 71°18.42'S – 71°18.33'S, 13°58.21'W – 13°57.65'W, eastern Weddell Sea, 1047 m (8 specimens, 2 complete), st 78-9, EBS, 71°09.52'S – 71°09.34'S, 14°00.76'W – 13°58.85'W, eastern Weddell Sea, 2182 m (1 specimen, incomplete), st 81-8, EBS, 70°31.08'S – 70°32.23'S, 14°34.82'W – 14°34.90'W, eastern Weddell Sea, 4419 m (7 specimens, 1 x SEM, 2 complete), st 133-2, EBS, 62°46.73'S – 62°46.33'S, 53°02.57'W – 53°04.14'W, central Weddell Sea, 1582 m (1 specimen, complete), st 150-6, EBS, 61°49.13'S – 61°48.52'S, 47°27.51'W – 47°28.16'W, South Orkney Islands, 1970 m (1 specimen, incomplete), st 154-9, EBS, 62°32.52'S – 62°31.31'S, 64°39.45'W – 64°38.66'W, King George Island, 3784 m (1 specimen, incomplete) [ZMH-26069–26077].

Diagnosis: The species is easily recognized by the reduced size of the outermost pair of branchiae, giving the impression that the species only bears three pairs of branchiae, and the “hidden” position of the first notopodium directly posterior to the paleal base.

Description: Holotype 16 mm long and 1.7 wide, incomplete with 5 AUs (Fig. 13 A–C). Complete paratypes (22 specimens, thereof 2 juveniles and 1 ovigerous) 2–10 mm long and about 0.1–1.2 mm wide, with 12–13 AUs when complete. Colour in ethanol white.

Prostomium trilobed, middle lobe anteriorly rounded, without ridges (Fig. 14 A). Lower lip not enlarged. Nuchal organs and eyes present (Figs 13 A–C, 14B). Buccal tentacles smooth. TS-2 laterally only visible as a narrow lobe from which paleae originate, otherwise indistinct from TS-3. TS-3 notopodium (TC-1) reduced in size and shifted dorsally, positioned directly behind paleae, completely covered by these, giving TS-2 and TS-3 (TC-1) a fused appearance. TS-2 bearing about 10 paleae [8–12], positioned laterally directly below branchiophore ridge. Paleae of medium length, stout, gradually tapering, basally arranged in a straight line, paleal fan arranged spirally. Four pairs of branchiae, arranged in an almost straight line forming a prominent transverse ridge over dorsum (Fig. 13 D). The two outermost pairs distinctly smaller in diameter than two innermost, positioned close to each other, easily mistaken for only one pair. Branchiae smooth. 15 TCs. Notochaetae simple, limbate in upper half, arranged in two rows in anterior half of thorax, anterior row with short chaetae, posterior row with chaetae about twice as long (Fig. 14 C–D). 12 TUs, starting in TC-4 (TS-6). Thoracic uncini very small [dental formula: MF-2-3-2-3-(1 to 3) (Fig. 15)]. Thoracic neuropodial tori whitish in methyl green staining, slightly decreasing in size towards posterior. Circular white band present in anterior half of TU-2 (TC-5, TS-7). Notopodia of 5th to last TC (TC-11, TU-8) shifted slightly dorsally and connected by a low ridge. Notopodial lobes of shifted parapodia slightly enlarged, notochaetae and neuropodial uncini not modified. [12–13 AUs.] Neuropodia of AU-1 and AU-2 sessile tori, of same type as thoracic neuropodia. Uncini not apparent in AU-1 and AU-2. Abdominal neuropodia from AU-3 distinct, prolonged erect pinnules with uncini in marginal position [dental formula: MF-3-3-3-∞]. Rudimentary abdominal notopodia absent. All thoracic and abdominal noto- and neuropodia without cirri. [Pygidium with two lateral triangular papillae.]

TC-5 with a pair of spherical nephridial papillae anterior to and slightly dorsal to notopodia (Fig. 14 C). A pair of nephridial papillae behind the branchial ridge not observed.

Tube loosely covered with fine sediment and sponge spicules.

Remarks: The species is very numerous in the material of ANDEEP I–III enabling documentation of intraspecific variability. Small, possibly juvenile, specimens bear only minute paleae or lack them altogether. Also, eyes are not always apparent in preserved specimens. While buccal tentacles were retracted in most specimens, one paratype showed smooth buccal tentacles. In Antarctic waters, A. wilhelmi n.sp. can easily be mistaken for small specimens of A. pseudoampharete at first sight. However, A. wilhelmi n.sp. is characterized by a circular white band in TU-2 which is only known for A. rubropaleatus n.sp. and A. laubieri. An outstanding character of A. wilhelmi n.sp. is the appearance of the two outermost branchial pairs. These are reduced in diameter and positioned close to each other. As a result, under low magnification only three pairs of branchiae are apparent. In contrast to the further described species of Anobothrus herein, A. wilhelmi n.sp. was not found to possess nuchal organs in the upper part of the crest separating the prostomium in three lobes. Also, nephridial papillae behind the innermost branchial pairs were not observed. As examined specimens were of comparably small size it might be that the features were present, but merely too difficult to discern.

Etymology: The name was chosen in honour of the first author’s deceased father Wilhelm Schüller who will always be special to her.