Aonides cf. nodosetosa Störch, 1966

Radashevsky, Vasily I., 2015, Spionidae (Annelida) from Lizard Island, Great Barrier Reef, Australia: the genera Aonides, Dipolydora, Polydorella, Prionospio, Pseudopolydora, Rhynchospio, and Tripolydora, Zootaxa 4019 (1), pp. 635-694 : 638-641

Aonides cf. nodosetosa Störch, 1966

( Figs 1 , 2 )

Aonides nodosetosa Störch, 1966: 174 –175, pl. 2, fig. 3a–d.

Material examined. Queensland: AM W.45224, MI QLD 2379 (2); MIMB 28110, MI QLD 2379 (2).

Adult morphology. Up to 5 mm long, 0.25 mm wide for 50 chaetigers; smallest examined individual 2.5 mm long for 31 chaetigers. Worms fragile, with thin cuticle easily destroyed during treatment and fixation. No pigmentation on body and palps. Prostomium elongated, conical, anteriorly rounded, posteriorly blunt to rounded, not extending over chaetigers as a caruncle. Eyes and occipital antenna absent. Ciliary bands or patches of nuchal organs absent on posterior sides of prostomium. Peristomium reduced to a small ring around mouth. Palps as long as 5–10 chaetigers, with frontal longitudinal groove lined with fine cilia, and up to 15 short transverse ciliary bands regularly arranged on inner lateral surface; lateral bands fewer in small individuals; long cilia of bands beating towards distal end of palp ( Fig. 1 A).

Chaetiger 1 with capillaries and small postchaetal lamellae in both rami. Postchaetal lamellae on succeeding chaetigers elongated in both rami ( Fig. 1 A). Dorsal crests, lateral pouches and ventral flaps absent.

Hooks in notopodia from chaetigers 9–13 ( Fig. 2 B), up to three in a series among capillaries. Hooks in neuropodia from chaetigers 8–13 ( Fig. 2 B), up to four in a series, accompanied by 1–5 alternating capillaries and 1–3 inferior capillaries throughout. Alternating capillaries alimbate, hair-like ( Fig. 1 F). Sabre chaetae absent. Hooks in both rami tridentate, with two upper teeth arranged vertically above main fang; upper part of shaft characteristically bent ( Fig. 1 D, E). Outer hood open distally; small membrane present below main fang, resembling inner subdistal hood ( Fig. 1 E).

Branchiae up to 10 pairs, from chaetiger 3 to chaetiger 12, fewer in small individuals ( Figs 1 A, 2A). Branchiae long on anterior chaetigers and gradually diminishing on 2–3 posterior chaetigers, up to 2.5 times as long as notopodial lamellae, free from lamellae, robust, flattened, with surfaces oriented perpendicular to body axis, with longitudinal bands of cilia along inner and outer edges. Afferent and efferent blood vessels of branchiae forming a loop and interconnected by radial capillaries giving branchiae annulate appearance.

Dorso-lateral dense bands of short cilia from chaetiger 1 to chaetiger 11, fewer in small individuals. Bands short, extending between successive notopodia. Short nototrochs present on branchiate chaetigers, each composed by single row of short cilia.

Pygidium with five cirri of similar length, comprising one pair of ventral cirri, one pair of dorsal cirri and a midventral cirrus ( Fig. 1 C). Ventral cirri with weak yellow pigment.

Oesophagus extending through 9–10 anterior chaetigers. Ventral buccal bulb below oesophagus extending to middle of chaetiger 2 ( Fig. 1 B). Gizzard-like structure in digestive tract absent.

Main dorsal blood vessel transformed into gut sinus in anterior part of midgut. Narrow heart body present in main dorsal vessel in anterior chaetigers. Blood red, without elements.

Nephridia from chaetiger 4 to chaetiger 12, fewer in small individuals ( Fig. 2 C).

Reproduction. All individuals of A. cf. nodosetosa collected in August 2013 were immature.

Remarks. Aonides nodosetosa was originally described from near Gaftun (Giftun) Island, El Ghardaqa (Hurghada) in the Red Sea by Storch (1966). Worms were collected from coarse sand with pebble in shallow water off wavy beach (die Grobsandzone des Brandungsstrandes in der Nähe der Insel Gaftun bei Ghardaqa). They were up to 5 mm long for 59 chaetigers and had a prostomium anteriorly rounded and posteriorly not extending as a caruncle, 8–9 pairs of branchiae beginning from chaetiger 3, pygidium with 2–3 pairs of short cirri, and tridentate hooks in noto- and neuropodia from chaetigers 11–12. Eyes and occipital antenna were absent. Aonides nodosetosa has never been redescribed or reported from a place other than type locality.

Aonides from Yonge Reef in Australia appear similar to A. nodosetosa from the Red Sea, Egypt in the shape of the prostomium, arrangement of branchiae and hooks and also shape and dentition of the hooks. Worms from the two localities slightly differ in number of cirri on the pygidium, 4–6 in A. nodosetosa and five in Aonides from Yonge Reef, but this may result from an individual variability and the small number of individuals examined in Australia. The Australian Aonides with branchiae from chaetiger 3 are tentatively referred to as A. cf. nodosetosa .

Aonides nodosetosa appears similar to other Aonides but differs from them in having branchiae from chaetiger 3 instead of chaetiger 2. Remarkably, the examined worms from Yonge Reef were small juveniles and it is likely that the Red Sea worms described by Storch (1966) were also juveniles. Mature individuals should be examined to verify if start of branchiae from chaetiger 3 is an adult or temporary juvenile condition prior to the development of definitive adult characters. Retarded development of branchiae on anterior chaetigers is characteristic for other spionids including Boccardia , Boccardiella , Laonice , Malacoceros , Microspio , Prionospio , Spio and can be misleading in identification of small individuals ( Radashevsky 2012).

By having a pygidium with five cirri and tridentate hooks with upper teeth situated one above another A. nodosetosa appears similar to A. selvagensis Brito, Núñez & Riera, 2006 from Selvagens Islands in the Eastern Central Atlantic. Adults of both species also have no eyes and occipital antenna on the prostomium. They differ however in the beginning of branchiae, from chaetiger 2 in A. selvagensis and from chaetiger 3 in A. nodosetosa . The largest described specimen of A. selvagensis was 9.25 mm long with 52 chaetigers, i.e., by the number of chaetigers smaller than A. nodosetosa , but it had branchiae beginning from chaetiger 2.

Habitat. In this study, adult Aonides cf. nodosetosa were found on the outside of the Great Barrier Reef at about 10 m depth. Worms were likely crawling free in the coral sand.

Distribution. Red Sea, Egypt;? Queensland, Australia.

Figures

FIGURE 1. Aonides cf. nodosetosa. AM W. 45224. A. Anterior end of a 50 - chaetiger individual in left lateral view with right palp missing; B. Same, optical section, showing ventral buccal bulb below anterior part of oesophagus; C. Posterior end of same individual in left lateral view; D – F. Chaetae from a middle neuropodium; D. Tridentate hooded hook in frontal view; E. Same in lateral view; F. Hair-like alimbate alternating capillary.

FIGURE 2. Aonides cf. nodosetosa. A. Relationships between distribution of branchiae (referring to number of the last branchiate chaetiger) and total number of chaetigers in worm; B. Relationships between anterior position of hooks in neuro- and notopodia (in chaetiger numbers) and total number of chaetigers in worm; C. Relationships between anterior and posterior position of excretory metanephridia (referring to number of the first and the last chaetigers bearing nephridiopores) and total number of chaetigers in worm.