Nothria minima sp. nov.

urn:lsid:zoobank.org:act: A37FF597-3F0E-498C-AF3C-417E59D47874

Figs 1, 18–20, Tables 2, S 1

Holotype. Australian Museum (AM) W.51642, IN2018 _ V06 _184; 17 Dec 2018; Australia, Tasmania, St. Helen’s flat; 41.21– 41.20°S 148.80– 148.78°E; 1221– 1202 m depth . Paratypes (8): AM W.51641, IN2018 _ V06 _184 (1). AM W.51643, IN2018 _ V06 _184 (1). AM W.51644, IN2018 _ V06 _184 (1). AM W.53498, IN2018 _ V06 _ 184 (1 SEM on pin). AM W.53849, IN2018 _ V06 _184 (4).

Other material examined (82). AM W.51567, IN 2018_ V 06_184 (76). AM W.53848, IN 2018_ V 06_184 (6 in tubes).

Diagnosis. Eyes absent; antennae extending to chaetiger 5–9; branchiae absent; dorsal cirri absent from chaetiger 14–20; first 3 chaetigers with anterior hooks: slender bidentate pseudocompound to compound hooks on chaetiger 1 and 2; very slender bidentate compound hooks on chaetiger 3; pectinate and limbate chaetae from chaetiger 2; subacicular hooks from chaetiger 9–10.

Description. All examined specimens lacking posterior ends. Length of holotype 7.5 mm for 17 chaetigers, width 1.4 mm; paratypes 6.0–9.0 mm (17–22 chaetigers) long, 1.2–1.6 mm wide, non-type material ranging from 1.0– 1.8 mm in width.

Preserved specimens overall whitish to cream coloured without any colour pattern. Prostomium anteriorly rounded in holotype, rounded to subtriangular in other specimens, wider than long, with 2 rounded to ovoid frontal lips (Fig. 18A,B). Palpo- and antennophores very short, with 1–2 proximal rings and slightly longer distal ring. Palpostyles tapering, extending to chaetiger 1, antennostyles tapering gradually, lateral antennostyles extending to chaetiger 6 (4–7), median antennostyle with broken tip, reaching chaetiger (6–9). Nuchal grooves straight, with small middorsal separation. Eyes absent. Ventral upper lip rounded, lower lip subtriangular, neither with median section (Fig. 18B). Peristomium short, peristomial cirri inserted subdistally on peristomium, about as long as peristomium (Fig. 18A).

First chaetiger enlarged, about twice as long as peristomium, chaetiger 2 and 3 progressively shorter, following ones about as long as peristomium. Anterior 3 pairs of parapodia modified; first pair greatly enlarged, directed forward, extending far beyond anterior margin of prostomium (Fig. 18A,B) with narrow auricular, almost tongue-like prechaetal lobes and subulate postchaetal lobes (Fig. 18C). Second pair of parapodia much smaller, hardly prolonged, with smaller tongue-like prechaetal lobe (Fig. 18D). Third pair of parapodia (Fig. 18E) only slightly larger than subsequent ones, with prechaetal lobes further reduced, present as little knobs to posterior part of body, last postchaetal lobes on chaetigers 9 (8–12). Ventral cirri of first two chaetigers subulate, becoming rounded on chaetiger 3, as transitioning to glandular pads (Fig. 18B). Dorsal cirri weakly subulate to cirriform from chaetiger 1, becoming thinner and shorter, abruptly absent from chaetiger 15 (14–20). Branchiae absent.

First pair of parapodia (Fig. 18C) with 3–5 slender bidentate pseudocompound to compound hooks (Fig. 19A). Second pair (Fig. 18D) with 3 very slender bidentate pseudocompound to compound hooks (Fig. 19B), 2–3 limbate and 15–20 scoop-shaped pectinate chaetae with 16–20 teeth. Third pair of parapodia (Fig. 18E) with 3–5 very slender, bidentate compound hooks with serrated upper shafts and appendages (Fig. 19C), 2–3 limbate chaetae and numerous (up to 30) scoop-shaped pectinate chaetae (Fig. 18E). From chaetiger 4 anterior hooks absent, limbate and pectinate chaetae present to end of fragments, presumably end of body, although number of pectinate chaetae greatly reduced. Subacicular hooks present singly from chaetigers 9 (8–10), as pairs from chaetiger 10 (9–11). Pygidium unknown.

Mandibles (Fig. 19D) highly calcified, almost white, except for darkly sclerotized protomandibles. High cutting plates with two median teeth and large distal tooth. Maxillae (Fig. 19E) delicate with little sclerotization (MIV and MV hard to make out hence not included in drawing); MI very slender maxillary formula (based on 3 specimens): MI = 1+1; MII = 9 + 9 (left most distal tooth fang-like); MIII = 9 + 0; MIV = 7+8; MV = 1+1. Ratio of mandibles/maxillae = 1.2 (ratio for 3 jaw apparatuses ranged from 1.11–1.19 but a fourth result was 1.44, giving a mean of 1.22). Flattened tube (Fig. 20A), covered with similarly sized shells dorsally and ventrally, gaps filled in with foraminiferans; lining transparent .

Remarks. Nothria minima sp. nov. resembles N. solenotecton (Chamberlin, 1919), a deep-sea species from off Panama, as well as the new species to be described directly below, where the morphological similarities and differences between the three species are discussed.

Etymology. This species is the smallest, most delicate one encountered in the study, hence the epithet “ minima ”, meaning “small” in Latin.

Distribution. The new species was only collected in station 184 of cruise IN2018_V06, “ St. Helens flat” in 1202–1221 m depth (Fig. 20B).