Alcyonidium epispiculum Porter & Hayward 2004

"Alcyonidium epispiculum sp. nov. Figure 4A-H

Material examined

Holotype: USNM 21263, Palmer Archipelago, 64º48’38”S 4º00’W to 64º48’12”W, 70-150m, 19 March 1982.

Paratypes: USNM 21263, same data as holotype (27specimens).

Other material

The USNM 21226, South Georgia, 53º51’S 37º38’W to53º52’S 97-101m, 7 February 1966 (2 specimens); 21229,Anvers Island, Palmer Archipelago, 64º49’30”S 63º470W,73128m, 1 February 1969 (2 specimens); 21234, King George Island, South Shetland Islands, 62º17’30”S58º34’36”W to 62º17’54”S, 55-78 m, 21 December 1971(stripped from substratum); 21242, Palmer Archipelago, Antarctic Peninsula, 65º54’30”S 65º17’30”W, 246-270m,16 March 1982 (5 specimens); 21247, Palmer Archipelago,64º47’42”S 64º7’24”W, 100m, 28 January 1972 (cylinders mostly stripped from substratum); 21256, Biscoe Island, Palmer Archipelago, 65º35’S 67º19’W to 65º37’ S, 161m,8 February 1969 (large cylindrical colonies which have mostly been stripped from their urchin spine substratum).

Description

The colony forms a tough sheet investing the spines of regular sea urchins (Figure 4A); the sheet is ~1.5mmthick and consists of a single layer of autozooids, with small kenozooids both frontally and basally. In some specimens the colony has grown beyond its substratum, but maintains its basically single-layered structure. Sample21256 includes several colonies which have outgrown the urchin spine, producing unilaminar lobes; e.g. one specimen 6.3 cm long with diameter 5.3 mm, broadens to approximately 10mm for the distal third of the colony; another, 3 cm long, has a lobed expansion, 1.5 cm wide, constituting two-thirds of its length. The frontal body wall consists of a thick, laminated cuticle, and in cases where the colony has outgrown the substratum there is a basal body wall of almost equivalent thickness. In frontal view (Figure 4B) the autozooids are irregularly polygonal in outline, convex, with well-marked sutures between; the closed orifice is clearly visible close to the margin of the autozooid but is not especially prominent. Autozooids with orifice, vestibule and polypides visible are interspersed with others in which neither orifice nor polypides are present,but which appear to occupy the entire thickness of the colony, and small chambers that appear to represent frontally budded kenozooids (Figure 4C). Similar kenozooidal units are present between and below the autozooids in the basal portion of the colony. Polypides are oriented perpendicularly to the frontal plane of the colony. Lophophores with 20 to 21 tentacles (Figure 4E); zooid dimensions and tentacle counts are given in Table 4. Alcyonidium epispiculum is a broadcast spawner. Sections of specimen 21263 show an intertentacular organ (Figure 4G), and ovaries with large numbers of small oocytes, with very small lipid content, clustered around the gut (Figure 4D,F,H).

Etymology

Latin: epi, upon; spiculum, a little point.

Remarks

Waters (1904) described a new species, Alcyonidium antarcticum, from a single station of the ‘Belgica’ Expedition(70º20’S 83º23’W). He had four specimens, all encrusting echinoid spines, and noted that in two specimens the autozooids were hexagonal in shape, with papillate orifices, and in two they were ‘narrower’ with the orifices projecting only slightly. Sections of one of the latter revealed a lophophore with 24 to 26 tentacles, and Waters’ figure (1904: pl.7, figure 7a) shows a lophophore with 26 tentacles and an intertentacular organ; he noted the latter, remarking that the autozooids contained large numbers of small eggs, co-occurring with spermatozoa. It is clear that Waters’ species was a broadcast spawner, and it has been demonstrated (Porter, 2003) that reproductive mode is an important character in defining species in Alcyonidium. However, tentacle number is also now known to be an important specific character (Porter, 2003), and the great disparity between A. antarcticum (24-26 tentacles) and A. epispiculum (20-21 tentacles) strongly suggest that they are separate species. All of the USARP material originated from the region of the Antarctic Peninsula and the Scotia Arc." (Porter and Hayward, 2004:259-60)