Rhamphobrachium (Minibrachium) talboti, 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 : 629-631

Rhamphobrachium (Minibrachium) talboti n. sp.

( Figs 2 , 6 )

Rhamphobrachium (Rhamphobrachium) sp.— Paxton 1986a: 19, fig. 13c; 1986b: 87.

Type material. Holotype: AM W.198967, New South Wales, Sydney, off Palm Beach, 33º35’03”S, 151º21’30”E, 31 m, coll. F. Talbot et al., 17 Mar 1978; Paratypes: AM W.47837(1), same data as holotype; AM W.47838.001, W.47839.001, 2 specimens on SEM pins, same data as holotype; AM W.198966 (14), New South Wales, Sydney, off Palm Beach, 33º35’03”S, 151º21’30”E, 31 m, coll. F. Talbot et al., 10 Dec 1977.

Diagnosis. Small, width up to 1.0 mm wide. Unidentate distally recurved spiny hooks on chaetigers 1 and 2; six to ten simple subacicular hooks with spiny hoods from chaetiger 3, hoods becoming gradually less spiny, resembling typical subacicular hooks by about chaetiger 20; pectinate chaetae with 9–13 very long teeth. Pygidium with two pairs of anal cirri.

Description. Holotype incomplete, measuring 27 mm in length for 72 chaetigers, 1.0 mm wide; complete paratypes ranging from 11–21 mm long for 67–110 chaetigers, 0.45–1.0 mm wide. Alcohol stored specimens overall cream-coloured, lacking colour pattern.

Anterior part of prostomium shovel-nosed, representing partly formed frontal lips ( Fig. 6 A, B). Ceratophores of palps and antennae with one to two proximal rings and one longer distal ring; ceratostyles short and subulate, palps reaching to peristomium or chaetiger 1, lateral and median antennae reaching to chaetiger 1. Nuchal grooves curved laterally, with narrow middorsal separation. One pair of small eyespots between the bases of palps and lateral antennae. Peristomium shorter than first chaetiger; peristomial cirri absent.

First two pairs of parapodia modified, projecting anterolaterally, directed ventrally ( Fig. 6 B). Neither of parapodia 1 and 2 fully extended, anterior ends inverted, hiding parapodial lobes. Unmodified parapodia lacking distinct parapodial lobes. Dorsal cirri subulate on anterior chaetigers, more posteriorly becoming digitate. Ventral cirri subulate on chaetiger 1 and 2, replaced by rounded ventral pads from chaetiger 3 ( Fig. 6 A, B). Branchiae absent.

Modified parapodia with three long, pseudocompound recurved hooks. Shafts of hooks with two rows of long moveable spines below pseudoarticulation and irregularly distributed small spines along whole length of shaft, but more dense above pseudoarticulation; slight swelling before distal curvature of hook ( Fig. 6 G–J). Internal chaetal sacs to chaetiger 30.

Unmodified parapodia from chaetiger 3, supported by two to three very thick aciculae ( Fig. 6 C, D). Limbate chaetae from chaetiger 3, decreasing in length from upper to lower position. Spinigers absent. Six to ten bidentate subacicular hooks with spiny hoods from chaetiger 3 ( Fig. 6 E, F); hoods initially enclosing distal part of hooks more closely, gradually opening up ( Fig. 6 C, D), becoming smoother and changing to divided hoods, one on either side of distal part of hook by about chaetiger 20, resembling typical subacicular hooks; concurrent with morphological change, number of hooks becoming gradually reduced to two per parapodium by chaetiger 20–30. Slightly oblique pectinate chaetae ( Fig. 6 K) from chaetiger 13; with 9–13 extremely long teeth, gradually decreasing in length from one side of comb to other. Pygidium with two pairs of anal cirri; dorsal pair longer than ventral one. Fragile mucous tube with attached sand grains.

Jaws very delicate and fragile. Mandibles ( Fig. 2 H) with long, slender shafts; cutting plates relatively small, covered with thin layer of calcium, protomandibles clearly visible. Maxillae ( Fig. 2 I) extracted only partially due to their delicate nature; elements almost transparent, hardly sclerotised. Incomplete maxillary formula: MxI = 1+1; MxII = 9+10; MxIII = 7+0; other elements not observed.

Remarks. Rhamphobrachium (M.) fractum n. sp. is most similar to R. (M.) talboti n. sp. described above, where the relationships of the two species have been discussed.

Etymology. It is a pleasure to dedicate this new species to Dr. Frank Talbot, former Director of the Australian Museum, under whose tenure Lizard Island Research Station was established, and who collected the material with his students.

Biology. No brooding specimens were encountered and hence we have no evidence that the specimens examined are adults. However, since they were collected at the same site three months apart with a similar size distribution and the chaetal characteristics showed no size dependent variations, we feel justified to assume that the larger specimens were fully grown.

Type locality. Pacific Ocean, off Palm Beach, Sydney, New South Wales; 33º35’03”S, 151º21’30”E.

Distribution. This species is only known from off Palm Beach, Sydney, New South Wales, Australia; in 31 m depth.

Figures

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 6. Rhamphobrachium (Minibrachium) talboti n. sp., AM W. 47838.001. A. Anterior part of body, ventral view; B. The same, lateral view; C. Parapodium from chaetiger 3; D. The same, enlarged; E. Parapodium from chaetiger 9; F. The same, enlarged; G. Distal part of recurved hook from chaetiger 1; H – J. Shafts of recurved hooks with movable spines; K. Pectinate chaeta from chaetiger 13. Abbreviations: la = lateral antenna, ll = lower lip, ma = median antenna, mx = maxillae, p = palp, per = peristomium, ul = upper lip, vc = ventral cirrus.