Prionospio Iberian Canyons sp. C

Paterson, Gordon L. J., Neal, Lenka, Altamira, Iris, Soto, Eulogio H., Smith, Craig R., Menot, Lenaick, Billett, David S. M., Cunha, Marina R., Marchais-Laguionie, Claire & Glover, Adrian G., 2016, New Prionospio and Aurospio Species from the Deep Sea (Annelida: Polychaeta), Zootaxa 4092 (1) : 18-19

Prionospio Iberian Canyons sp. C

(Figures 2.7, 9)

Material examined: 23 specimens examined.

Voucher specimens: Portuguese margin Nazaré canyon: St. 15765#2 39°35.00’N 10°19.04’W, 4336 m; 5 individuals.

Other material examined: Nazaré canyon: RSS Discovery 2005, St. 15758#2 39°34.94’N 10°19.00’W, 4332m, 8 individuals; St. 15758#6 39°34.99’N, 10°19.00’W 4335 m, 8 individuals;

RSS Charles Darwin 179 April/ May 2006, St. 56847#7 39°35.55’N 10°20.06’W, 4404 m, 2 individuals.

Diagnostic features. Eleven pairs apinnate branchiae, neuropodial hooded hooks and sabre chaetae not present in the first 31 chaetigers.

Description. Voucher specimen incomplete with 31 segments, measuring 1.6 mm long (length to chaetiger 10) and 0.22mm wide (at chaetiger 1). Body wide and somewhat flattened; appears divided into two parts: branchial region plus four following segments with enlarged notopodial lamellae and dense capillaries and postbranchial region, with abruptly smaller notopodial lamellae and less dense capillaries. Colour pale yellow colour in alcohol. Prostomium nearly oval, with anterior margin somewhat truncated, prostomial peaks absent; distinct caruncle not formed, posterior margin of prostomium reaching to chaetiger 1 ( Fig. 10 a); eyes not observed. Peristomium well developed, closely surrounding prostomium, ventrally distinct, dorsally incomplete; partially fused to chaetiger 1; lateral wings not formed. Palps missing.

Eleven pairs of branchiae present on chaetigers 2–12; branchiae only slightly longer than accompanying notopodial lamellae, all of similar shape and size throughout, but with last two pairs shorter; all apinnate, but heavily ciliated on both sides, except for the tip; branchiae rather narrow but somewhat flattened–strap-like, wider at the base and tapering into somewhat swollen tip ( Fig. 10 a,b).

Notopodial postchaetal lamellae enlarged in branchial region (chaetigers 2–12) (Fig. 2.7a–d), about three times longer than neuropodial postchaetal lamellae, reduced in size in chaetigers 13–16, then abruptly smaller from chaetiger 17 (Fig. 2.7e), similar in size to neuropodial postchaetal lamellae; notopodial postchaetal lamellae subtriangular in branchial segments, becoming more small, oval, somewhat produced into blunt tip in postbranchial segments. No dorsal crests in 31 segments. Interparapodial pouches absent.

Neuropodial postchaetal lamellae on chaetiger 2 small, oval with blunt distal tip; in other branchial segments enlarged, subquadrangular with produced tip dorsally; gradually becoming smaller and more oval assuming shape similar to the one on chaetiger 2 in postbranchial segments.

Only capillary chaetae present in incomplete 31chaetiger-long holotype. Capillaries long and dense in branchial region; straw-coloured, arranged in four rows: two rows of shorter and two rows of longer capillaries; capillaries in postbranchial segments less dense, arranged in single row. Neuropodial hooded hooks, sabre chaetae and notopodial hooded hooks absent in 31 segments. Pygidium unknown.

Methyl green pattern: Prostomium and peristomium stain strongly, the margins of notopodial and neuropodial lamellae in branchial regions also stained, more intensively in anteriormost segments.

Remarks. Given that in the voucher specimen all branchiae are apinnate, this species is similar to species grouped by many authors into Minuspio . Minuspio was erected by Foster (1971) to include all species with only apinnate branchiae. Maciolek (1985) in her revision of Prionospio suggested that Minuspio was only a sub-genus. Subsequent authors have been similarly divided in their designations and Minuspio has been used as a genus and subgenus. Many of the species designated to this taxon have more than four pairs of branchiae. Eleven pairs of branchiae are present on chaetigers 2–12 in the voucher of Prionospio spC, but branchiae are missing in all other specimens and their number may be variable. The absence of neuropodial sabre chaetae and neuropodial hooded hooks in 31 segments (the largest fragment) appears to be a unique feature of this species. In other species of Prionospio described to date, the neuropodial hooks usually start around segment 20 at the latest and sabre chaetae are usually present before this. However, given that the largest specimen available for examination was only 31 chaetigers long, it is possible that sabre chaetae/neuropodial hooks may start later in body. Given that no described species of Prionospio have the either neuropodial hooks or sabre chaetae starting so far back on the body, we consider that this is a distinct species but we are reluctant to formally classify it until we have more complete specimens. We therefore choose to describe but not name the species to enable future workers to identify it with the hope that complete specimens will be discovered and allow a more comprehensive description.

Distribution. Nazaré canyon (Portuguese margin) at 4364–4404 m.

Figures

FIGURE 10. Profiles of anterior chaetigers of the Aurospio species described.