Prionospio cf. tetelensis Gibbs, 1971

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 : 675-677

Prionospio cf. tetelensis Gibbs, 1971

( Fig. 26 )

Prionospio tetelensis Gibbs, 1971: 171 –173, fig. 13.

Prionospio (Aquilaspio) tetelensis .— Maciolek 1985: 331.

Material examined. Queensland: AM W.45510, MI QLD 2440 (1).

Adult morphology. Single 17-chaetiger anterior fragment 4.5 mm long, 1.25 mm wide (body without parapodia 0.75 mm wide). Pigmentation in life absent. Prostomium wide and rounded anteriorly, extending posteriorly almost to end of chaetiger 3 as an undulating caruncle. Occipital antenna absent. Two pairs of red eyes arranged trapezoidally, comprising one pair of small lateral eyes situated anteriorly and set wider apart, and one pair of large median eyes, each composed of a small rounded cup and a large wide pigment band oriented 1. Foster (1971) established a new genus Minuspio to encompass Prionospio members with only apinnate branchiae beginning from chaetiger 2. The taxon was treated as genus or a subgenus by following authors but Wilson (1990) and Sigvaldadóttir (1998) placed back those species into Prionospio sensu lato (see above Remarks to the Prionospio sensu lato section). In the absence of a phylogenetic hypothesis about relationships of the Prionospio members and support of monophyly of Minuspio , it would be however practical to recognize non-taxonomic groups of species based on shared simple diagnostic characters. One of those groups may include Prionospio members with only apinnate branchiae beginning from chaetiger 2 and be referred to as the Prionospio cirrifera group of species. Because of great number of species in this group (recently reviewed by Dagli & Çinar 2011), it can further be subdivided into smaller groups to facilitate their revisions and identification of species.

transversally ( Fig. 26 A). Nuchal organs U-shaped ciliary bands on lateral sides of caruncle. Posterior dorsal parts of peristomium fused to notopodial lamellae of chaetiger 1 forming prominent ear-shaped structures. Palps as long as 10–15 chaetigers, with frontal longitudinal groove lined with fine cilia and transverse bands of cilia regularly arranged on inner surface; cilia of inner transverse bands beating towards distal end of palp.

Chaetiger 1 with well developed capillaries and postchaetal lamellae in both rami; notopodial postchaetal lamellae fused to dorsal posterior parts of peristomium forming ear-shaped structures. Notopodial lamellae of chaetigers 2–4 triangular, small on chaetiger 2, largest on chaetiger 4; lamellae smaller and rounded on following chaetigers. Lower part of neuropodial postchaetal lamellae of chaetiger 2 rounded, slightly elongated ventrally.

Distinct low dorsal crests present from chaetiger 6 to end of fragment.

Sabre chaetae and hooks absent in fragment.

Three pairs of pinnate branchiae present on chaetigers 3–5 and a pair of scars present on chaetiger 2; branchiae gradually shorter on posterior chaetigers. All branchiae cylindrical, rounded in cross section, with longitudinal bands of cilia running along inner and outer sides; pinnae regularly arranged along lateral and posterior sides ( Fig. 26 B). Afferent and efferent blood vessels interconnected by circular capillaries which form loops inside branchial pinnae.

Oesophagus extending through 6–8 anterior chaetigers. Ventral buccal bulb below oesophagus extending to end of chaetiger 1. Gizzard-like structure in digestive tract absent.

Heart body about 30 µm in diameter extending inside main dorsal vessel from level of chaetigers 3–4 to almost end of fragment. Blood red, without globules or other elements.

Reproduction. The single individual of P. cf. tetelensis is a mature male with sperm present from chaetiger 13 to end of the fragment. Spermatogonia proliferate in testes; spermatogenesis occurs in the coelomic cavity. Spermatids are joined in tetrads. Spermatozoa are ect-aquasperm with small acrosome, spherical nucleus 2–3 µm in diameter, spherical mitochondria probably four in number, and a long flagellum.

Remarks. The single individual from Lizard Island has three pairs of pinnate branchiae on chaetigers 3–5, but has branchial scars on chaetiger 2 meaning that the first pair of branchiae on chaetiger 2 was lost. There is no described spionid with the first apinnate pair of branchia on chaetiger 2 and three more pairs of pinnate branchiae on succeeding chaetigers (see Maciolek 1985; Blake 1996; Sigvaldadóttir 1998), but four pairs of pinnate branchiae on chaetigers 2–5 are present in four Prionospio species: P. p e r u an a Hartmann-Schröder, 1962 originally described from Peru, P. tetelensis Gibbs, 1971 from Tetel Island of Solomon Islands, P. multipinnulata Blake & Kudenov, 1978 from New South Wales and Victoria, Australia, and P. pyramidalis ( Hutchings & Turvey, 1984) from South Australia. By having large median eyes, caruncle extending to end of chaetiger 3, dorsal crests arranged from chaetiger 6 on a series of succeeding chaetigers, and possible start of sabre chaetae and hooks after chaetiger 17, the specimen from Lizard Island appears very similar to P. tetelensis and is tentatively referred to this species.

The five type specimens of P. tetelensis have never been re-described and the species has never been reported from outside of the type locality. The single individual from Lizard Island differs, however, in having capillary notochaetae on chaetiger 1, which, according to Gibbs (1971), were absent in P. tetelensis . This may indicate the presence of a new species in the Australian waters that should be described when more material becomes available.

Habitat. A single individual of P. cf. tetelensis was found in fine coral sand at 14 m depth.

Distribution. Solomon Islands;? Queensland, Australia.

Figures

FIGURE 26. Prionospio cf. tetelensis. A, B—AM W. 45510. A, Prostomium, dorso-left lateral view, showing lateral eyes (la), median eyes (me) and associated transverse bands of red pigment (pi); B. Branchium of chaetiger 3 in frontal view, showing numerous pinnae arranged on lateral and rear sides. Scale bars: A, B— 50 µm.