Rhamphobrachium (Minibrachium) nutrix, Paxton, Hannelore & Budaeva, Nataliya, 2015

Paxton, Hannelore & Budaeva, Nataliya, 2015, Minibrachium, a new subgenus of Rhamphobrachium (Annelida: Onuphidae) from Australia with the description of three new species, Zootaxa 4019 (1), pp. 621-634 : 623-626

Rhamphobrachium (Minibrachium) nutrix n. sp.

( Figs 1–4 )

Type material. Holotype: AM W.46046, Queensland, Lizard Island, outer Yonge Reef, 14º36’S, 145º28’E, dead coral, 10 m, coll. P.A. Hutchings & P.B. Weate, 25 Jan 1977, Collection Event Code 77 LIZ 56-2. Paratypes: AM W.47873 (3), same data as holotype; AM W.46045 (9), Queensland, Lizard Island, outer Yonge Reef, 14º36’S, 145º28’E, dead coral, 9 m, coll. P.A. Hutchings & P.B. Weate, 15 Jan 1977, Collection Event Code 77 LIZ 48-4.

Other material examined. AM W.47874 (35, 1 on slide, 1 on SEM stub), same data as holotype; AM W.47875 (28, 1 on slide, 2 and 1 juvenile on SEM stub), Queensland, Lizard Island, outer Yonge Reef, 14º36’S, 145º28’E, dead coral, 9 m, coll. P.A. Hutchings & P.B. Weate, 15 Jan 1977, Collection Event Code 77 LIZ 48-4; AM W.46043(1), Queensland, Yonge Reef, outer slope, 14º36’S, 145º38’E, reef rock with Halimeda and Lithothamnion , 36 m, coll. P.A. Hutchings & P.B. Weate, 9 Jan 1975, Collection Event Code 75 LIZ D-1.

Diagnosis. Very small, up to 0.5 mm wide. Diagnosis and description based on holotype and paratypes wider than 0.2 mm at chaetiger 10 excluding parapodia. Bidentate distally recurved spiny hooks on chaetigers 1 and 2; two subacicular hooks with spiny hoods from chaetiger 5, hoods becoming gradually less spiny, resembling typical subacicular hooks by about chaetiger 20; pectinate chaetae with 12–14 moderately long teeth. Pygidium with one pair of anal cirri.

Description. Holotype incomplete, measuring 16 mm in length for 55 chaetigers, 0.55 mm wide; largest complete specimens 9.4–11.0 mm long for 40–54 chaetigers, 0.4–0.5 mm wide. Alcohol stored specimens overall cream-coloured, lacking colour pattern.

Prostomium anteriorly rounded, wider than long, with paired globular frontal lips ( Fig. 1 A–C). Ceratophores of palps and antennae with one proximal ring and one longer distal ring; ceratostyles short and subulate, palps reaching to peristomium, lateral and median antennae reaching to chaetiger 1. Nuchal grooves curved laterally, with small middorsal separation. One pair of small eyespots at bases of lateral antennae. Peristomium shorter than first chaetiger; peristomial cirri absent.

First two pairs of parapodia modified, projecting anterolaterally, directed ventrally ( Fig. 1 B). Each of parapodia 1 and 2 with three short papilliform lobes and one ovate postchaetal lobe ( Fig. 1 E, F). Unmodified parapodia lacking distinct parapodial lobes. Dorsal cirri subulate on chaetiger 1 and 2, then becoming digitate. Ventral cirri subulate on chaetiger 1 and 2, replaced by rounded ventral pads from chaetiger 3. Branchiae absent.

Modified parapodia with three long, pseudocompound recurved hooks ( Figs 1 D, 2A), each projecting from a papilliform lobe ( Fig. 1 C, E). Shafts of hooks with two rows of long moveable spines below pseudoarticulation and irregularly distributed small spines; slight swelling before distal curvature of hook and small secondary hook, resulting in bifid recurved hook ( Figs 2 A, 3A–C). Internal chaetal sacs to chaetiger 20–22.

Unmodified parapodia from chaetiger 3, supported by two to three very thick aciculae ( Fig. 3 D, F). Limbate chaetae from chaetiger 3, decreasing in length from upper to lower position ( Fig. 3 D). Spinigers absent. Two bidentate subacicular hooks with spiny hoods from chaetiger 5 ( Figs 2 B, 3F); hoods initially almost enclosing distal part of hooks, gradually opening up, becoming smoother and changing to divided hoods, one on either side of distal part of hook by about chaetiger 20, resembling typical subacicular hooks ( Fig. 3 G–I). Slightly oblique pectinate chaetae with 12–14 moderately long teeth from chaetiger 12 ( Fig. 3 E). Pygidium with one pair of anal cirri. Fragile mucous tube without incrustations. Mandibles and maxillae extremely small and fragile, not clearly visible.

Remarks. Rhamphobrachium (M.) nutrix n. sp. differs from R. (M.) fractum n. sp. and R. (M.) talboti n. sp. in being much smaller, having bidentate instead of unidentate distally recurved hooks, having two subacicular hooks per parapodium from chaetiger 5 instead of multiple hooks from chaetiger 3, and having one pair of anal cirri instead of two. Furthermore, R. (M.) nutrix has pectinate chaetae with 12–14 moderately long teeth while the other two new species have pectinate chaetae with 9–13 very long and 8–10 long teeth respectively.

Etymology. The species name nutrix (nurse) in Latin refers to the ability of the individuals of the new species to brood their young.

Biology. Despite their small size the specimens of the new species brood their young and thus are considered fully grown individuals. The holotype and several paratypes have two to four juveniles inside their tubes. Several similarly sized juveniles are present in the examined samples; presumably they have detached from their parents because of the destruction of the very fragile tubes. None of the specimens has an intact tube and the number of juveniles per parent could not be established with certainty; however, judging from the size of the juveniles, only few of them (possibly not more than 10) could fit with a single brooding parent.

Examined juveniles have about 16–20 chaetigers and are about 1 mm long, 0.2 mm wide, with developed palps and antennae but lacking fully formed frontal, upper and lower lips ( Fig. 4 A, B). The anterior two pairs of parapodia have subulate dorsal and ventral cirri but are not enlarged and lack chaetal lobes and recurved hooks. Limbate chaetae are present from chaetiger 3 ( Fig. 4 C); pectinate chaetae are absent. Subacicular hooks with spiny hoods number up to three per parapodium from chaetiger 3 ( Fig. 4 D, E). In posterior chaetigers hoods on subacicular hooks become smaller and less spiny ( Fig. 4 F).

Type locality. Pacific Ocean, Outer Yonge Reef, Lizard Island, Queensland; 14º36’S, 145º28’E.

Distribution. This species is only known from Lizard Island, Great Barrier Reef, Queensland, Australia; in 9– 36 m depth.

Figures

FIGURE 1. Rhamphobrachium (Minibrachium) nutrix n. sp., AM W. 47875. A. Lateral view; B. Anterior part of body, lateral view; C. Prostomium and chaetigers 1 – 2, ventral view; D. Recurved hooks from chaetiger 1; E. Parapodium from chaetiger 1; F. Parapodium from chaetiger 2. Abbreviations: dc = dorsal cirrus, fl = frontal lip, la = lateral antenna, ll = lower lip, ma = median antenna, p = palp, per = peristomium, psl = postchaetal lobe, ul = upper lip, pl = papilliform lobe, vc = ventral cirrus.

FIGURE 2. Rhamphobrachium (Minibrachium) nutrix n. sp. (A, B), R. (M.) fractum n. sp., (C – G) and R. (M.) talboti n. sp., (H – I). A. Distal part of recurved hook from chaetiger 1; B. Subacicular hook from chaetiger 20; C. Anterior part of body; D. Distal part of recurved hook from chaetiger 1; E. Compound subacicular hook from chaetiger 3; F. Pseudocompound subacicular hook from chaetiger 3; G. Simple subacicular hook from chaetiger 4; H. Mandibles; I. Part of maxillary apparatus (MxI, MxII and MxIII are shown).

FIGURE 3. Rhamphobrachium (Minibrachium) nutrix n. sp., AM W. 47875. A – B. Distal bidentate parts of the recurved hooks from chaetiger 1; C. Spiny shaft of recurved hook from chaetiger 1; D. Parapodium from chaetiger 3; E. Pectinate chaeta from chaetiger 25; F. Parapodium from chaetiger 5; G. Subacicular hooks from chaetiger 6; H. The same from chaetiger 14; I. The same from chaetiger 22.

FIGURE 4. Juvenile of Rhamphobrachium (Minibrachium) nutrix n. sp., AM W. 47875. A. Ventral view; B. Anterior part of body, ventral view; C. Parapodia from chaetigers 3 and 4; D. Parapodium from chaetiger 6; E. Subacicular hooks from chaetiger 9; F. The same from chaetiger 12. Abbreviations: fl = frontal lip, la = lateral antenna, ll = lower lip, ma = median antenna, p = palp, ul = upper lip.