Prionospio cooki, Radashevsky, Vasily I., 2015

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 : 658-660

Prionospio cooki n. sp.

( Fig. 15 )

Type material. Queensland: Holotype: AM W.45275, MI QLD 2379. Paratypes: AM W.45276, MI QLD 2385 (3).

Adult morphology. Largest individual intact holotype about 20 mm long, 0.5 mm wide for 80 chaetigers with caruncle extending to end of chaetiger 4 ( Fig. 15 A) (16 anterior chaetigers of the holotype deposited as AM W.45275, while the posterior chaetigers fixed in ethanol to be used in molecular analysis). There paratypes (AM W.45276) comprising 22-chaetiger anterior fragment of a big worm 0.7 mm wide with caruncle extending to end of chaetiger 4 ( Fig. 15 B), 60-chaetiger complete individual 0.35 mm wide with caruncle to end of chaetiger 3, and 16- chaetiger anterior fragment of a small worm about 0.3 mm wide with caruncle to end of chaetiger 3. All paratypes with branchiae missing but branchial scars present on chaetigers 2–5.

Pigmentation in life absent. Prostomium broadly-rounded anteriorly, extending posteriorly to end of chaetiger 4 as a distinct caruncle, shorter in small individuals. Small knobs with short non-motile cilia present on frontal and fronto-lateral edges of prostomium. Occipital antenna absent. Two pairs of small red eyes present ( Fig. 15 A, B). Nuchal organs U-shaped ciliary bands on lateral sides of caruncle. Posterior dorsal parts of peristomium fused to notopodial lamellae of chaetiger 1 forming ear-shaped structures. Palps as long as 10–15 chaetigers, with frontal longitudinal groove lined with fine cilia, short transverse bands of cilia regularly arranged on inner surface, and short compound motile cilia on fronto-lateral surfaces along frontal groove; cilia of transverse bands beating towards distal end of palp, while compound fronto-lateral cilia beating perpendicular palp axis towards frontal groove.

Chaetiger 1 with capillaries and lamellae in both rami; notopodial postchaetal lamellae fused to posterior dorsal parts of peristomium forming ear-shaped structures. Notopodial lamellae of chaetigers 2–5 largest, triangular, gradually becoming smaller and rounded on following chaetigers. Capillaries thick, with fine granulation in 10–15 anterior chaetigers, becoming thinner and smooth on succeeding chaetigers. Lower part of neuropodial postchaetal lamellae of chaetiger 2 acuminate and elongated ventrally. Neuropodial lamellae of chaetiger 3 trapezoidal, from chaetiger 4 onwards rounded, semicircular, diminishing in size on succeeding chaetigers.

Low dorsal crests present from chaetiger 7 on a series of succeeding chaetigers ( Fig. 15 B), at least to chaetiger 22, gradually diminishing in height posteriorly. Lateral pouches and ventral flaps absent.

Sabre chaetae in neuropodia from chaetiger 10, one in a group, with narrow limbation and fine dense granulation on distal end of shaft ( Fig. 15 C). Sabre chaetae large in chaetiger 12, gradually diminishing in size in succeeding chaetigers.

Hooks in notopodia from about chaetiger 30, up to five in a series among capillaries. Hooks in neuropodia from chaetigers 12–14 (in holotype three hooks present in chaetiger 14 and seven hooks in each of chaetigers 15 and 16), up to eight in a series, accompanied by inferior sabre chaetae and alternating capillaries throughout. Alternating capillaries thin, with narrow wing in anterior neuropodia, gradually becoming alimbate in posterior chaetigers, 2–3 times as long as hooks. Hooks with outer and small inner hoods, multidentate, with 4–6 pairs of small upper teeth arranged in two vertical rows above main fang; shaft slightly bent ( Fig. 15 D).

Four pairs of branchiae on chaetigers 2–5 almost equal in length and slightly longer than notopodial postchaetal lamellae; those on chaetigers 2 and 5 cylindrical, with numerous pinnae regularly arranged along lateral and posterior sides all along stem. Branchiae on chaetigers 3 and 4 apinnate, robust, flattened, with surfaces oriented perpendicular to body axis. Longitudinal bands of cilia running along inner and outer edges on each branchia; ciliation heavier on branchiae on chaetigers 3 and 4. Afferent and efferent branchial blood vessels interconnected by numerous radial capillaries which forming loops inside pinnae.

Nototrochs present between branchial bases on chaetigers 3–5. Dorso-lateral longitudinal ciliation present on chaetigers 3–6 as short bands of dense cilia extending between successive notopodia.

Pygidium with one long middorsal cirrus and a pair of short ventral cirri; all cirri bearing non-motile sensory cilia.

Oesophagus extending through 6–10 anterior chaetigers. Ventral buccal bulb below oesophagus extending to end of chaetiger 1. Gizzard-like structure in digestive tract absent.

Main dorsal blood vessel transformed into gut sinus in anterior part of midgut. Soft heart body up to 20 µm in diameter extending inside main dorsal vessel from level of chaetigers 3–4 to chaetigers 9–13. Blood red, without globules or other elements.

Nephridia in chaetigers 4–6, greenish in life.

Reproduction. Prionospio cooki n. sp. is gonochoristic. In a female (holotype) and a male (paratype) gametes are present from chaetiger 13 onwards. Oogenesis is intraovarian. Vitellogenic oocytes develop in ovaries attached to segmental blood vessels. Intraovarian oocytes were up to 115 µm in diameter, with germinal vesicle about 50 µm and single nucleolus 20 µm in diameter. Oocyte envelope is 2–3 µm thick. 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. Prionospio cooki n. sp. belongs to the P. steenstrupi group (see above Remarks for P. anneae n. sp.) and is characterized by small red eyes, long caruncle extending to end of chaetiger 4, sabre chaetae in neuropodia from chaetiger 10, multidentate hooks in notopodia from around chaetiger 30 and in neuropodia from chaetigers 12–14, and gametes developing from chaetiger 13 onwards. Of the species of Prionospio occurring in Australian waters, the only other species with a caruncle extending over chaetiger 4 is P. paucipinnulata originally described from Port Phillip Bay, Victoria by Blake & Kudenov (1978). This species however has large median eyes, large dorsal crest on chaetiger 7, and different arrangement of pinnate branchiae (see below comments on this species). Adult P. cooki n. sp. appear similar to P. kuli n and P. multicristata in the shape of branchiae and neuropodial postchaetal lamellae on anterior chaetigers (with elongated acuminate lower part in chaetiger 2, trapezoidal in chaetiger 3, and rounded, semicircular from chaetiger 4 onwards), moderate dorsal crest on chaetiger 7 and lower crests on a series of succeeding chaetigers, arrangement of sabre chaetae and hooks, and hook dentition. They differ, however, in that P. c oo k i n. sp. has small eyes, caruncle extending to end of chaetiger 4, and gametes develop from chaetiger 13, whereas P. multicristata and P. kulin have large crescent-shaped eyes, gametes from chaetiger 12, and caruncle over chaetiger 3 and chaetiger 2 respectively.

Etymology. The species is named in honour of James Cook, a British explorer, navigator, cartographer, and captain in the Royal Navy who made three voyages to the Pacific Ocean. During the first voyage (1768–71) on the HMS Endeavour, on August 11, 1770, Cook climbed an island’s summit to find a way through the maze of reefs in the Great Barrier Reef ( Beaglehole 1968; Banks 2008). The only land animals on the island were lizards and Cook named the island Lizard Island. The opening through the reef was found and is now called Cook’s Passage, and the Lizard Island’s summit has since been called Cook’s Look. The Cook’s Passage (14.517°S, 145.567°E, the HMS Endeavour entered the Pacific Ocean through the Passage on August 13, 1770) is located north, next to the Yonge Reef, the type locality of P. cooki n. sp. (collected on the reef by diving on August 17, 2013).

Habitat. Adult P. cooki n. sp. were found off Yonge Reef, at the edge of the Great Barrier Reef in coral sand at 3–10 m depth.

Distribution. Australia: Queensland, Great Barrier Reef.

Figures

FIGURE 15. Prionospio cooki n. sp. A, C, D—AM W. 45249 (holotype); B—AM W. 45276. A. Anterior end, left lateral view; B. Anterior end, dorsal view; C, D. Neurochaetae from chaetiger 16; C. Inferior sabre chaeta; D. Multidentate hooded hook.