Prionospio lylei , 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: 664-666

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Prionospio lylei

n. sp.

Prionospio lylei  n. sp.

( Figs 18View FIGURE 18, 19View FIGURE 19)

Type material. Queensland: Holotype: AM W. 45260, MI QLD 2365. Paratypes: AM W. 45263, MI QLD 2410 (1); AM W. 45264, MI QLD 2440 (1); AM W. 45261, MI QLD 2379 (2); AM W. 45262, MI QLD 2382 (1).

Adult morphology. Largest complete individual, holotype, 14 mm long, 0.25 mm wide for 60 chaetigers. Pigmentation in life absent. Prostomium round anteriorly, extending posteriorly to end of chaetiger 1 as a prominent caruncle. Three small knobs with short non-motile sensory cilia present on frontal and fronto-lateral edges of prostomium. Occipital antenna absent. Two pairs of red eyes arranged trapezoidally comprising one pair of median eyes and one pair of lateral eyes situated anteriorly and set wider apart; median eyes small in small worms and very large, crescent-shaped in large individuals ( Figs 18View FIGURE 18 A, B, 19 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 moderate elevated ear-shaped structures. Palps as long as 5–10 chaetigers, with longitudinal frontal groove lined with fine cilia, short transverse bands of cilia regularly arranged on inner surface, and narrow longitudinal band of cilia running on outer fronto-lateral side along frontal groove on distal half of palp; cilia of transverse bands beating towards the distal end of palp, while cilia of longitudinal band beating towards frontal groove.

Chaetiger 1 with short capillaries and small postchaetal lamellae in both rami; notopodial lamellae fused to posterior dorsal parts of peristomium forming elevated ear-shaped structures; neuropodial postchaetal lamellae oval. Notopodial lamellae of chaetigers 3–5 largest, triangular, gradually becoming smaller and rounded 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 ( Fig. 19View FIGURE 19 A).

Dorsal crest on chaetiger 7 high ( Figs 18View FIGURE 18 A, 19 A, B); notopodial postchaetal lamellae on succeeding chaetigers extended towards dorsal midline but not joined to form crests; low dorsal folds present from chaetiger 8 on 4–6 succeeding chaetigers in some individuals (on chaetiger 8 in holotype). Lateral pouches and ventral flaps absent.

Sabre chaetae in neuropodia from chaetiger 10, usually one, occasionally two in a group in first two-three neuropodia, thick, robust, with narrow limbation and fine granulation on distal end of shaft; chaetae largest in chaetiger 10, gradually diminishing in size on succeeding chaetigers towards midbody ( Fig. 19View FIGURE 19 C, D), then gradually increasing again.

Hooks in notopodia from chaetigers 22–38, up to five in a series among capillaries. Hooks in neuropodia from chaetigers 11–12, up to nine in a series, accompanied by inferior sabre chaetae and alternating capillaries throughout. Alternating capillaries 2–2.5 times as long as hooks, in anterior chaetigers slender, with narrow limbation, in posterior chaetigers hair-like, alimbate. Hooks multidentate, with 4–5 pairs of thin upper teeth arranged in two vertical rows above main fang, with inner and outer hoods; shaft slightly bent ( Fig. 19View FIGURE 19 E).

Four pairs of branchiae on chaetigers 2–5 ( Figs 18View FIGURE 18 A, 19 A, B). Branchiae on chaetigers 2 and 5 cylindrical, similar in length to each other or chaetiger 5 pair longer, up to three times as long as notopodial lamellae. Branchiae of chaetiger 2 with 1–2 pairs of short pinnae (1 pair in holotype), apinnate in some individuals; branchiae of chaetiger 5 with 1–4 pairs of digitiform pinnae on low part (three pairs in holotype). Branchiae on chaetigers 3 and 4 apinnate, robust, flattened, with surface oriented perpendicular to body axis, similar in length or slightly longer than notopodial lamellae. Longitudinal bands of cilia running on inner and outer edges on each branchia; ciliation heavier on branchiae on chaetigers 3 and 4. Afferent and efferent blood vessels interconnected by numerous radial capillaries making also loops inside pinnules.

Nototrochs on chaetigers 2–5. Dorso-lateral longitudinal ciliation present on chaetigers 3–6 as short bands of dense cilia extending between successive notopodia.

Pygidium with long thin, transparent middorsal cirrus and one pair of short, thick and yellowish ventral cirri ( Fig. 18View FIGURE 18 C).

Oesophagus extending through 6–7 anterior chaetigers. Ventral buccal bulb below oesophagus extending to end of chaetiger 1. Gizzard-like structure in digestive tract absent.

Main dorsal vessel transformed into gut sinus in anterior part of midgut. Soft heart body up to 40 µm in diameter present in main dorsal vessel from level of chaetigers 3–4 to chaetigers 8–9. Blood red, without globules or other elements.

Nephridia in chaetigers 4–6, greenish in life.

Reproduction. Prionospio lylei  n. sp. is gonochoristic. Both in females and males gametes develop from chaetiger 11 to chaetigers 50–55. Oogenesis is intraovarian. Vitellogenic oocytes develop in ovaries attached to segmental blood vessels. 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 lylei  n. sp. belongs to the P. steenstrupi  group (see above Remarks for P. anneae  n. sp.) and is characterized by short caruncle extending to the end of chaetiger 1, large median eyes, dorsal crest only on chaetiger 7, hooks beginning in neuropodia from chaetigers 11–12 and in notopodia from chaetigers 22–38, and sabre chaetae in neuropodia invariably from chaetiger 10. Most members of the group have the caruncle extending to the end of chaetiger 2 or longer. Short caruncles extend to the end of chaetiger 1 in P. fallax Söderström, 1920  , P. dubia Day, 1961  , P. anuncata Fauchald, 1972  , P. membranacea Imajima, 1990  , P. oshimensis Imajima, 1990  , P. variegata Imajima, 1990  , and P. phuketensis Hylleberg & Nateewathana, 1991  . Of these, only P. fallax  and P. membranacea  have single prominent dorsal crest on chaetiger 7. These two species also have large median eyes, ventrally pointed and elongated neuropodial lamellae on chaetiger 2, and sabre chaetae in neuropodia from chaetiger 10. Prionospio lylei  n. sp. differs from P. membranacea  in that adults of the latter species have numerous pinnae on the pinnate branchiae, and hooks beginning in neuropodia from chaetigers 13–16 and in notopodia from chaetigers 49–51. Prionospio lylei  n. sp. appears most similar to P. fallax  where adults have hooks beginning in neuropodia from chaetigers 10–13 and in notopodia from chaetigers 18–45. It differs, however, from the latter by having fewer numbers of pinnae on the branchiae. Remarkably, P. fallax  was originally described from Sweden by Söderström (1920) (redescribed by Sigvaldadóttir & Mackie 1993) and later reported from Australia by Day & Hutchings (1979), Hartmann-Schröder (1979), and Hutchings & Rainer (1979). These records should be verified to confirm the presence of the species in the Australian waters.

Etymology. The species is named in honour of Dr Lyle Vail, a co-director (with his wife Dr Anne Hoggett) of the Lizard Island Research Station, an avid enthusiast of marine biology and coral reef protection.

Habitat. Adults of P. lylei  n. sp. were found in coral sand and rubble at 6–21 m depth.

Distribution. Australia, Queensland, Great Barrier Reef.