Abderos minotaurus Schüller & Jirkov, 2013, n.sp.

Abderos minotaurus n.sp.

Figs 1–2

Holotype: ANDEEP III—st 142-5, EBS, 62°11.36'S – 62°11.36'S, 49°27.62'W – 49°29.57'W, central Weddell Sea, 3404 m [ZMH-26046].

Paratypes: ANDEEP III—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, SEM, incomplete) [ZMH-26048].

Additional material: ANDEEP III—st 142-5, EBS, 62°11.36'S – 62°11.36'S, 49°27.62'W – 49°29.57'W, central Weddell Sea, 3404 m (1 specimen, very poor condition) [ZMH-26047].

Description: Holotype 7 mm long and 0.5 mm wide in broadest region, complete with 11 AUs (Figs 1 A–C), mature, entire body cavity filled with small eggs. Paratypes 11 mm long and about 1 mm wide. Colour in ethanol white.

Prostomium weakly trilobed (Figs 1 B, 2A), middle lobe anteriorly rounded, without ridges, nuchal organs or eyes. Buccal tentacles broad and few, seemingly covered with minute papillae under low magnification [annulated with four longitudinal rows of pinnules in paratype (Fig. 2 B)]. First segment (TS-1) with a pair of forwardly directed, large (notopodial size) lateral papillae (Figs 1 A, 1B, 2A), these much darker in methylene blue staining than remaining body surface. Paleal and rudimentary notopodia in TS-2 absent. Two pairs of branchiae in a more or less transverse row (Fig. 2 C), inner pair separated by a distance of about two branchial diameters, connected by a distinct ridge. Inner branchiae belong to TS-2 (paleal segment), outer branchiae to TS-3. 14 TCs, starting in TS-4. Thoracic segments all similar, notopodia of first anterior segments slightly smaller than subsequent ones. Notochaetae keeled, accompanied by fine accessory chaetae (Figs 2 D, 2E). [Notochaetae of last two parapodia not keeled under SEM.] Notopodia of 3rd to last TU shifted dorsally. 2nd to last and last notopodia also shifted, not as far as 3rd to last. 12 TUs, neuropodia small, similar throughout thorax with 10 to 12 uncini deeply imbedded in sessile tori (Fig. 2 F). Neuropodial tori of last two TCs more prominent than former ones, somewhat swollen. [Thoracic uncini all of same kind, with three to four rows of paired teeth, and numerous small teeth in apical region (Fig. 2 F).] 11 AUs without rudimentary notopodia, noto- and neuropodial cirri. First two abdominal neuropodia similar to thoracic ones, with tori only slightly erect from body wall. From AU-3 all neuropodia distinct erect pinnules with uncini positioned along distant margin. [Abdominal uncini avicular with numerous rows teeth gradually decreasing in size.] Pygidium bearing two long lateral cirri (Fig. 1 C).

One pair of nephridial papillae situated directly behind outer branchial pair, dorsally behind notopodial lobe of TS-4 (TC-1) (Figs 2 A, C). [Notopodia of TC-3 (TU-1, TS-6) accompanied by a glandular papilla dorsally (Fig. 2 D).]

Tube unknown.

Remarks: To date only four genera with two branchial pairs and 12 TUs are known (Reuscher et al. 2009). Auchenoplax Ehlers, 1887 and Melinnoides Benham, 1927 differ from the new genus by the presence of prolonged thoracic neuropodia in anterior segments. The presence of the tegumentary projections in the first segment found in A. minotaurus n.sp. has never before been reported for Ampharetidae: The combination of characters in the new species is unique and justifies the erection of the new genus. The unusual tegumentary projections of the first segment in this genus may represent rudimentary notopodia as they mirror the subsequent thoracic notopodial tori in shape. The exact position of modifications and dorsal shifts of parapodia in the new species remains unclear since only three specimens were found, all in different state of prservation. Only one branchostyle was intact in a paratype, suggesting that the species’ branchiae are cirriform and covered with minute papillae. Also, the true surface structure of the buccal tentacles remains ambiguous until further material is available for examination. Since in the holotype minute papillae are visible under low magnification, it is likely that the buccal tentacles are truly papillated as found on the paratype. Despite this ambiguity, specimens match each other in numbers of TCs and AUs, arrangement of branchiae, position of nephridial papillae and general development of noto- and neuropodia throughout the body and are thus considered the same species.

Etymology: The name refers to the distinct forwardly directed lateral tegumentary projections of segment 1 that have the appearance of two lateral horns. The species thus has the appearance of a worm with a bull’s head resembling the minotaur, a Greek mystic figure, part human, part bull.