Polydorella prolifera Augener, 1914

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 : 645-647

Polydorella prolifera Augener, 1914

( Figs 6, 7)

Polydorella prolifera Augener, 1914: 16 –20, pl. I, fig. 3, textfigs. 2 a–d.

Pseudopolydora prolifera .— Blake & Kudenov 1978: 271 –273, fig. 50 k–n.

Material examined. Queensland: AM W. 45231, MI QLD 2435 (20); MIMB 28115, MI QLD 2435 (15); AM W. 45512, MI QLD 2447 (30); MIMB 28116, MI QLD 2447 (20).

Adult morphology. Most individuals reproducing asexually by paratomy and appearing as chains of joined stocks and stolons at various stages of growth and regeneration. Single individuals up to 1.3 mm long, 0.25 mm wide for 14–15 chaetigers (15–16 segments). One female about 1.5 mm long for 16 segments. Paratomic growth zone situated in some worms between segments 10 and 11 and in others between segments 11 and 12 ( Fig. 6 A, B). Pigmentation greatly variable; dense fine net of black pigment present on dorsal and ventral sides of body in some individuals ( Fig. 6 A–C) while pigmentation weakly developed or absent in others.

Prostomium incised to bilobed anteriorly, extending posteriorly to end of segment 1 as a low caruncle. Nuchal organs short, wide ciliary bands, almost forming oval ciliary patches on sides of caruncle ( Fig. 6 C). Occipital antenna absent. One pair of white irregularly rounded eye-spots present in life, but not seen in preserved specimens. Palps as long as 10–15 segments, with longitudinal frontal groove lined with fine cilia, and short compound non-motile cilia arising directly from palp surface and scattered on fronto-lateral, lateral and abfrontal palp surfaces; fronto-lateral papillae absent.

Segment 1 reduced, poorly demarcated from peristomium; chaetae and notopodial lamellae lacking; small neuropodial lamellae present ( Fig. 6 A). Segments 1–7 short as if compressed, while subsequent segments longer ( Fig. 6 A). Notopodia from segment 2 (chaetiger 1) onwards and neuropodia of segments 2–7 with fascicles of unilimbate capillaries. Posterior notopodia with only capillaries.

Segment 5 (chaetiger 4) similar in size to segments 4 and 6, with up to five dorsal superior winged capillaries shorter than those on segments 4 and 6 ( Fig. 7 C), two kinds of heavy notopodial spines ( Fig. 7 A), and six ventral winged capillaries same as those on segments 4 and 6 ( Fig. 7 G); notopodial postchaetal lamellae lacking but low neuropodial lamellae same as on segments 4 and 6. Anterior-row notopodial spines up to six in a series, distally enlarged and flat, with denticulate upper edge; lateral sides of flat distal part enveloped by thin sheath covered with tiny scales; one side of distal part with a pointed capillary extension ( Fig. 7 D, E). Posterior-row spines up to four in a series, simple acicular ( Fig. 7 F).

Hooks in neuropodia from segment 8 (chaetiger 7), up to four in a series, not accompanied by capillaries. Hooks bidentate; shaft slightly curved, with constriction in upper part and a low boss on concave side below constriction ( Fig. 7 B, H).

Single pair of branchiae present on segment 7 (chaetiger 6). Branchiae free from notopodial lamellae, flattened, with surfaces oriented parallel to body axis, with longitudinal row of cilia along inner side ( Fig. 6 A). Nototrochs from segment 3 onwards, except segment 5, composed of single row of ciliated cells; longest nototroch cilia on segment 7 extending onto branchiae.

Pygidium elongated and rounded posteriorly, without appendages; anus terminal ( Fig. 6 A, B).

Glandular pouches in neuropodia from segment 1, largest in segments 6–7.

Oesophagus extending through 6–7 segments. Ventral buccal bulb and gizzard-like structure in digestive tract absent.

Main dorsal blood vessel without heart body. Blood red, without globules.

Nephridia from segment 4 (chaetiger 3) onwards.

Reproduction. Most P. prolifera examined in August 2013 were reproducing asexually by paratomy. One female had vitellogenic oocytes developing in segments 13–16; 2–3 oocytes were present in an ovary on each side of each fertile segment, with about 20 oocytes were present in total. The oocytes were up to 65 µm in diameter with a germinal vesicle about 13 µm and a single nucleolus 5 µm in diameter. The oocyte envelope was thin and smooth, less than 1 µm thick.

Remarks. Polydorella prolifera was originally described from Sharks Bay, South Passage, Western Australia by Augener (1914). Blake & Kudenov (1978) redescribed two syntypes of the species and also described Pseudopolydora stolonifera (= Polydorella stolonifera ) from Victoria, Australia.

Polydorella from Lizard Island appear identical to P. prolifera and are referred to this species. The worms also appear very similar to P. dawydoffi originally described from Nhatrang Bay, South-China Sea, Vietnam, by Radashevsky (1999) and re-described based on material from Philippines and the Red Sea, Egypt, by Williams (2004). They differ, however, in that the posterior-row notopodial spines of segment 5 are simple acicular in P. prolifera and acicular with subdistal shelf on convex side in P. dawydoffi .

Habitat. Adult P. prolifera live in tiny silty tubes on the surface of various sponges ( Fig. 6 D–F). The worms capture food particles by elevating their paired palps into water currents produced by the sponges. The tubes are 160–220 µm in diameter and 2.5 –5.0 mm long. Two separate individuals often inhabit one tube looking out and feeding from opposite openings of the tube. Having occupied a sponge, worms live in colonies of tens of individuals per one square centimetre. Dense colonies are formed due to asexual reproduction of worms by paratomy.

Distribution. Western Australia and Queensland, Australia.