Paralophaster ferax Mah 2023, n. sp.

Paralophaster ferax n. sp.

FIGURE 20A–F

Etymology

The species epithet ferax is Latin for fertile or fruitful, alluding to the brooding behavior found in this species.

Diagnosis

Body shape weakly stellate (R/r=1.7), arms short, triangular, disk large (Fig. 20A, C). Body thickened. Interradial arcs weakly curved. Largest R= 2.5 cm. Abactinal plates paxillate, each with spines, 10–25, each bearing pointed, jagged hyaline tips (Fig. 20B). Plates separated by membranous skin. Marginal plates 26–28 per interradius (13–14 per arm), widely spaced, single series of marginals observed, superomarginals not clearly discerned, these either weakly expressed or irregular. Marginal plates are large, paxillate with trunk-like shaft, head of paxilla with curved head, each bearing spines, 8–30 on plate surface. Actinal region small, with 1–4 small, round plates, each bearing 1–3 spinelets. Furrow spines, 2–4, palmate arrangement with basal webbing (Fig. 20F). Subambulacral spines two, decreasing to a single spine distally along arm, arranged transversely on adambulacral plate. Oral plates with 10 furrow spines, no suboral plates. No pedicellariae. Brooded juveniles in coelomic cavity (Fig. 20D, E).

Comments

This species displays closest resemblance to Paralophaster paucispinus n. sp. with which it shares a similarly low number of marginal plates, approximately 13–14 per arm, a single discernible marginal series with no clear superomarginal plates, similar numbers of furrow spines and a similar overall body shape. It differs in having significantly more abactinal spines, 10–25 versus 3–5 in P. paucispinus and in having abactinal paxillae with lobate rather than round bases in P. paucispinus. There are also more spines on the marginal paxillae, 8–30, than are on P. paucispinus, which only shows 4–10.

Occurrence

Scotia Sea, 3138–4429 m.

Description

Body weakly stellate (R/r=1.6–2.22), arms short, triangular in shape, disk large. Body strongly thickened. Interradial arcs weakly curved (Fig. 20A, C). Surface covered with membranous skin.

Abactinal plates paxillate with spines, 10–25, each with pointed, jagged hyaline tips, shaft short, stocky (Fig. 20B). Spinelets triangular in cross-section. Paxillae, widely spaced, each with 3–5 lobes radiating at base forming open papular spaces between plates which are filled with thin membranous skin. These skin-filled spaces widest proximally on disk but become arranged more closely together distally. Madreporite diamond shaped, raised with irregular sulci. No pedicellariae.

Marginal plates 20–28 per interradius (13–14 per arm), widely spaced, single series of marginals observed (Fig. 20C), superomarginals not clearly discerned, these either weakly expressed or irregular. Marginal plates are large, paxillate with trunk-like shaft, head of maxilla with curved head, each bearing spines, 8–30 on plate surface. Paxillar spines similar to those on abactinal paxillae, slender hyaline tipped with multiple tips, triangular in cross-section.

Actinal surface relatively small, limited only to disk (Fig. 20C). Marginal plates (possibly inferomarginals?) along arm in direct contact with adambulacral plates. Actinal intermediate region small, filled with membranous dermis bearing small plates, 1–4, present on actinal intermediate region round to irregular, bearing slender spines, 1–4.

Adambulacral plates lobate in shape, with distinct, skin-filled gap between each plate. Furrow spines, 2–4, palmate arrangement with basal webbing. Subambulacral spines two, decreasing to a single spine distally along arm, arranged transversely on adambulacral plate (Fig. 20F). Oral plates pronounced with furrow spines, 10, blunt, widely spaced. Center of oral plate with distinct ridge on either side of central fossae. No spines present on oral plate surface.

Brooded juveniles. USNM 1675790 and 1676505 contain brooded juveniles in their coelomic cavity (Fig. 20D, E), enclosed within tissue, these occur directly above the oral region. Approximately 8–10 individuals, most with R=3.0 mm, r= 0.5 mm. Actinal surface facing upward towards abactinal surface of adult. Furrow spines, 1 or 2, subambulacral spines 2, both with hyaline, finely denticulate tips. Inferomarginal plates mound-like with hyaline spines, 3–6, bearing denticulate tips. Abactinal plates, including presumptive superomarginals identical.

Holotype. USNM 1675790, East of South Georgia Island, Scotia Sea, South Atlantic, −56.033, −33.967, 3138– 3239 m. Coll. R/V Eltanin, 8 Sept. 1963. 1 dry spec. R=1.7 r=1.0 (contains brooded juveniles).

Paratype. USNM 1675789, East of South Georgia Island, Scotia Sea, South Atlantic, −56.033, −33.967, 3138– 3239 m. Coll. R/V Eltanin, 8 Sept. 1963. 2 dry specs. R=1.7 r=1.0, R=1.7 r=1.0 (no brooding).

USNM 1676503, Southern Ocean, −64.75, −82.53, 4429 m. Coll. R/V Eltanin, USAP, 27 Oct. 1963. 1 dry spec. R=2.0 r=0.9 (no brooding).

USNM 1676504, South Georgia Island, Scotia Sea, South Atlantic, −55.092, −39.842, 2886–3040 m. Coll. R/V Eltanin, USAP, 8 Feb. 1966. 1 dry spec. R=1.9 r=0.7, R=1.7 r=0.7, R=2.0 r=0.9, R=2.0 r=0.6, R=1.3 r=0.4 (no brooding).

USNM 1676505, South Georgia Island, Scotia Sea, South Atlantic, −55.092, −39.842, 2886–3040 m. Coll. R/V Eltanin, USAP, 8 Feb. 1966. 1 dry spec. R=1.9 r=0.7. (brooding specimen).

USNM 1676568, South Atlantic, −54.925, −14.842, 3947–4063 m. Coll. R/V Eltanin, 28 Feb. 1966. 1 dry spec. R=2.5 r=0.9 (no brooding).

USNM 1676577, South Atlantic Ocean, −54.925, −14.842, 3947–4063 m. Coll. R/V Eltanin, 28 Feb. 1966. 1 dry spec. R=1.2 r=0.4 (no brooding).

USNM 1676578, NE of Candlemas Island, South Sandwich Islands, Scotia Sea, South Atlantic. Coll. John Dearborn et al. R/V Islas Orcadas, 22 May 1975. 3 wet specs. R=2.3 r=1.0, R=2.1 r=1.0, R=1.2 r=0.6 (no broodingbut gametes present).