Paralophaster lorioli (Koehler, 1907)

FIGURE 22 A–G

Solaster lorioli Koehler, 1907: 558 .

Paralophaster lorioli Fisher 1940: 175; Madsen 1955: 14; H.E.S. Clark 1963: 60; Hurtado-Garcia & Manjón-Cabeza 2022: 1221.

Diagnosis

Body strongly stellate, R/r=2.7–5.3 (Fig. 22A, C). Plates paxillate, 1 to 3 per plate, each with 4 to 12 slender, hyaline spinelets (Fig. 22A, D). Known specimens with 24–26 marginal paxillae per interradius (12–13 per arm) (Fig. 22C). Approximately 10–25 elongate, hyaline spines per inferomarginal paxillae at R= 1.6 cm. Furrow spines 2 to 3 webbing absent (Fig. 22F), subambulacral spines 4 to 5 with pronounced serrations, 7 to 12 along a single edge of each spine (Fig. 22E, G).

Coelomic brooding of juveniles present (Fig. 22B).

Comments

A widely occurring species which is present not only within the Southern Ocean but in the South Atlantic to abyssal depths (2897–4572 m). Paralophaster lorioli is distinguished from other Paralophaster by the pronounced serrations present on the subambulacral spines (Fig. 22F, G), which are absent from other known species. Function of these serrations is unknown.

Paralophaster lorioli and Paralophaster ferax n. sp. display comparable characters in that the abactinal paxillae display weak overlap in spine number, 4 to 12 in the former versus 10−25 in the latter as well as similar numbers of marginal plates per arm side 12−13 versus 13−14 in P. ferax and nearly identical numbers of furrow spines, 2−3 versus 2−4. The two species differ most significantly in that known specimens of P. ferax lack the serrated subambulacral spines present on Paralophaster lorioli and have higher numbers of spinelets on their abactinal paxillae. Bathymetric occurrence of both species is overlapping (220−4572 m in P. lorioli) versus 3138–4429 m in P. ferax . Although the two species are conceivably synonyms, character differences are present and further evidence evaluating the two species is desirable.

Occurrence

Tierra Del Fuego, Drake Passage (Chile), Weddell Sea, Elephant Island, Scotia Sea, Scotia Arc, Antarctic Peninsula, Kerguelen, Ross Sea, Argentina, Bridgman Island, Ross Sea. 220 –4572 m.

Description

Body strongly stellate (R/r=2.7–5.3). Disk sunken, interradial arcs acute. Arms petaloid, tapering distally (Fig. 22A, C).

Abactinal surface composed of thickened lobate plates, many weakly articulated, forming widely reticulate network (Fig. 22B); some with trilobate to quadrilobate bases. Abactinal dermis prevalent. Plates paxillate, 1 to 3 per plate, each with 4 to 12 slender, hyaline spinelets. Single paxillae on individual plate. Paxillae irregularly, widely distributed over surface. Madreporite irregularly round, strongly convex, bounded by approximately 2 to 3 plates forming around the base.

Marginal plates 18 (9 per arm side) at R=1.6 to 26 (13 per arm side) (Fig. 22C) per interradius at R= 2.5 to 3.9 cm. Only one marginal plate series is strongly defined and clearly observed, what is assumed to be the inferomarginal series owing to its position and near contact with the adambulacral plates. The presumptive superomarginals are weakly expressed with the plates while arranged serially, do not appear to be in close contact, especially those occurring distally, where they appear to be nearly absent. In contrast, the “inferomarginals” are very clearly observed and strongly expressed. These paxillae are widely spaced, thick, at least twice the thickness of the adjacent abactinal paxillae and cylindrical in cross-section. Approximately 10–25 elongate, hyaline spines per inferomarginal paxillae at R=1.6, 20–25 spines at R= 2.5 cm. Paxillar base of each inferomarginal similarly enlarged, thick with quadrate to round lobes. Inferomarginal plates sit in almost direct contact with adambulacral plate series.

Actinal intermediate region filled almost entirely with membranous-tissue, no actinal plates observed (Fig. 22C).

Adambulacral plates widely spaced, separated by membranous-tissue equal to the breadth of one or two adambulacral plates (Fig. 22F, G). Each adambulacral plate with 2 to 3 furrow spines (at R= 1.5 cm) to 4 to 5 furrow spines at R= 3.9 cm (Fig. 22F). Subambulacral spines 4 to 5, each with distinct, jagged serrations, approximately 6–12, along edge of each spine (Fig. 22E, G). Furrow spines on oral plates 10 with an 11th elongate spine directed into the mouth (thus a total of 20 furrow spines and 2 elongate spines directed into the mouth. Oral plates strongly arched, membranous tissue between first adambulacral and contact with oral plate.

Brooded juveniles

CASIZ 167622 (Fig. 22B) from 361−363 m was discovered with approximately 8−12 brooding juveniles within the coelomic cavity with oral cavity facing upward toward the abactinal surface. This is the second Paralophaster species which demonstrates this behavior. Brooding in this species will be further detailed in a subsequent manuscript.

Material Examined

USNM 13474, Clarence Island, South Shetland Islands, Antarctica, Southern Ocean, −61.27, −54.75, 293–294 m. Coll. Squires & Pawson, R /V Eastwind, 17 Feb. 1966. 1 dry spec. R=3.3 r=0.5.

USNM 1468788, Victoria Land, Southern Ocean, −70.542, 171.142, 2421 m. Coll. R/V Eltanin, USAP, 13 Feb. 1968. 1 dry specs. R=3.9 r=0.9.

USNM 1468789, Drake Passage, Tierra del Fuego, South Atlantic Ocean, −57.217, −62.8, 3733–3806 m. Coll. R/V Eltanin, USAP, 29 July 1962. 1 dry spec. R=3.4 r=0.7.

USNM 1660592, Scotia Sea, South Atlantic Ocean, −58.925, −53.983, 3817–3931 m. Coll. R/V Eltanin, USAP, 25 Jan. 1966. 3 dry specs. R=2.4 r=1.0, R=2.5 r=0.5, R=1.7 r=0.6.

USNM 1660593, Southern Ocean, Antarctica. −73.317, −174.875, 2897–2907 m. Coll. R/V Eltanin, USAP, 9 Feb. 1968. 2 dry specs. R=2.9 r=1.0, R=2.5 r=1.9 (arm tips broken on latter specimen).

USNM 1570997, Elephant Island, South Shetland Islands, Southern Ocean, Antarctica, −61.317, −56.158, 220– 240 m. Coll. R/V Eltanin, 31 Dec. 1962. 4 dry specs. R=2.6 r=0.9, R=1.7 r=0.4, R=1.8 r=0.4, R=2.9 r=0.6.

USNM 1573491, Drake Passage, Chile, −56.942, −74.808, 4209 m. Coll. R/V Eltanin USAP, 11 Nov. 1963. 1 dry spec. R=1.9 r=0.7.

CASIZ 167622, Off King George Island, South Shetland Island, − 61.775833, −57.390556, 361−363 m. Coll. R. Mooi & S. Lockhart, aboard R/V Yuzhmorgeologiya, 19 Aug. 2003. 1 wet spec. R=2.8 r=1.1.