Alaskagorgia splendicitrina, Horvath & Stone, 2018

Horvath, Elizabeth A. & Stone, Robert P., 2018, Another unusual new gorgonian (Anthozoa: Octocorallia: Plexauridae) from the Aleutian Islands of Alaska, Zootaxa 4524 (1), pp. 112-120 : 114-119

Alaskagorgia splendicitrina n. sp.

( Figs. 2–4 )

Material examined: Holotype USNM 1498741 , whole specimen dry (originally in ethanol), collected by Roger Clark on 18 June 2002, 184 m depth, Stalemate Bank, western Aleutian Islands , Alaska, (52°56'12.84" N, 170°59'00.24" E), Station 89, bottom water temperature = 3.6 ° C. Supplemental holotype material USNM 1498741 , 2 dry branch tips (5 and 7 cm long), wet (70% ETOH) branch section (2 cm long), vials of sclerites in 70% ETOH and SEM stubs.

Diagnosis. Fan-like, branches robust, numerous, slightly curling back towards center and base, convoluted; branch ends conspicuously clavate. Large, exposed polyps with coenenchyme conspicuously raised around polyp orifices; small base (holdfast) present. Axis dark reddish brown/black, horny (hard to cut), with hollow chambered central core.

Description. Vibrantly-colored ( Figs. 2A, B ), upright colony (~ 12 cm high), arborescent, extensively laterally branched, but rather squat, very broad (~ 25 cm wide), with many long, stout ended-branches ~5.0 mm in diameter (excluding polyps), often with clavate tips up to 1.0 cm in diameter (nearly as wide as trunk diameter). Branching generally lateral; primary branches hard to distinguish from secondary (and any tertiary from secondary), but latter also range ~5.0 mm in diameter, with branches somewhat convoluted, tending to curl in all planes; tendency to curl down and back towards base, over front or rear of colony, branches often seeming to tangle themselves together, giving overall appearance of colony being flat, but not actually in one plane; branching pattern “bushy lateral.” Curling became more pronounced as colony dried ( Fig. 3A ), with branches reminiscent of the writhing snakes seen atop the Gorgon Medusa’s head. Curled and convoluted pattern more pronounced at distal ends of secondary and smaller branches, a few making a really tight curl, such that distal tip of branch met/touched base attachment of branch. Despite tight curling and convolutions, no sign of branch anastomosing. Primary branch length (difficult to accurately measure due to curling) 16.5 cm; secondary branch lengths ranged from 8.0 cm to nearly 16.5 cm. Holotype with main trunk roughly 3.5 cm tall, nearly 8.0 mm wide, bearing proximally small, flat base (round in circumference), ~ 1.5 cm in diameter. At distal end of trunk, at least two primary branches come off, one to each side at roughly 90°. From each of these, two or more secondary branches immediately split off, at ~45° before advent of seemingly numerous tertiary branches. Branches (irregularly) slightly flattened “front to back,” more evident at branch ramification points. Branchlets (tertiary branches) extend to roughly 7.5 cm in length. Axis black at base, dark olive-brown/maroon in branches.

Polyps large, exposed, numerous ( Figs. 2B , 3B ), scattered on all sides of major, secondary and tertiary branches, with few to none on main trunk and holdfast. Anthocodiae (tentacles of polyp) fully retractile into moderate to very thick coenenchyme, but are commonly preserved exert ( Fig. 3B ). Coenenchyme sometimes displayed grooves or folds, depending on degree of extension and orientation of polyp. Often, cortex (which appeared to be loculated) conspicuously raised around polyp openings (when polyps fully retracted), forming short, cylindrical protuberances as broad, rounded domes (“grooved pyramids”) up to 3.0 mm tall, up to 3.0 mm in diameter; aperture opening ~2.0 mm across, round to oblong in shape, eight-lobed. Equally, protuberances could be reduced to barely visible raised and lobed rim (“collar”) at top of protuberance with eight notches around exert polyp. Tentacles of polyps appear rather long, extending out beyond aperture edge some 3.0 mm. Polyp tentacles often all joined together to form a tall “grooved column,” extending directly perpendicular to branch, but also pointed upwards, downwards, or to either “side” of polyp (generally, pointing in any direction). Spacing between polyps from immediately adjacent (seen out towards branch tips and at distal-most end, clustered to form swollen ball; Fig. 3B ) to widely spaced (5.0 mm apart) on primary branches; coenenchyme surface between polyps appeared fairly smooth.

Sclerites generally displayed those forms typical of the genus; anthocodiae are rather densely armed with somewhat pointed, tuberculate spindles (lying longitudinally on tentacle surface), many nearly 0.5 mm long; few attain a length slightly greater than 0.5 mm ( Fig. 4A ). It was difficult to determine if introvert was devoid of sclerites but none of the anthocodial sclerites appeared to have projecting processes.

Coenenchyme divided into three layers; remaining sclerite forms overlap somewhat across layers ( Figs. 4 C-1, 2). Surface layer of coenenchyme quite thin, containing small oval capstans ( Fig. 4D ) ranging in length from 0.07 to 0.09 mm, collectively falling at the larger end of the range for those seen in A. aleutiana . Progressing inwards toward colony axis, sclerites of large middle coenenchyme layer (containing many, dense gastric cavities) were oval capstans ( Fig. 4C ) ranging in length from 0.03 to 0.18 mm. In the deepest layer, also quite thin, which included the axial sheath, there are generally simple or modified octoradiate sclerites ( Fig. 4B ), ranging in length from 0.1 to ~ 0.2 mm. Surface of coenenchyme is covered with thick layer of epidermal tissue. Sclerites not visible to the naked eye; but layer of smallest sclerites lies beneath epidermal tissue. While many sclerites appeared colorless (typical of the genus), careful examination with light microscopy showed most sclerites were a very pale yellow. Coenenchyme bright, vibrant lemon-yellow when freshly collected and presumably in situ, color accentuated by numerous peachy-orange brittle stars entwined in branches ( Fig. 2A, B ).

Type locality. Stalemate Bank , western Aleutian Islands, (52°56'12.84" N, 170°59'00.24" E), 184 m.

Distribution and ecology. Presently known only from the type locality ( Fig. 1 ). Despite extensive collections from bottom trawl, longline, and crab pot fisheries and research surveys throughout the region during the past several decades and systematic surveys of seafloor habitat in the central Aleutian Islands with submersibles and remotely operated vehicles ( Stone 2006; Stone 2014) only the single specimen has been collected or observed. We speculate that it emanated from the much less explored region to the west including the Commander (Komandorskie) Islands and Kamchatka Peninsula of the Russian Far East and that it is endemic to the Northwest Pacific region.

The single specimen was collected with a bottom trawl so there were no in situ observations of the seafloor setting where it was collected. But based on the invertebrate (sea stars— Pteraster militaris (O.F. Müller, 1776) and Solaster endeca (Linnaeus, 1771) , as well as Fusitriton oregonensis (Redfield, 1846) — Oregon triton) and fish (skates, soles, sculpins, sandlance and rockfishes) catch in the trawl we can surmise that the species is found in areas of sand, pebble, and small cobble with moderate bottom currents. The shape and morphology of the specimen’s holdfast indicate that it was attached to a small cobble or large pebble.

Etymology. The species designation is derived from the Latin word for “bright” or “vibrant” (=splendius) and the Latin for “lemon-yellow” (=citrina).

Common name. Lemon-yellow Squat Gorgonian.

Taxonomic discussion. Sclerites were illustrative; tuberculate spindles of species described here nearly double in length of those observed in A. aleutiana Sánchez and Cairns, 2004 : Figs. 3 I-J, 5F-J and 6G, I-J, where longest shown measured roughly 0.26 mm. There may be a typographical error in the description text (page 268 in Sánchez and Cairns 2004), where a maximum length was given as 0.6 mm; however this does not correspond to values given in any of the figures. Anthocodial sclerites displayed no projecting processes, seen in some examples of this form in A. aleutiana . Small, densely warted double heads reported for the surface layer in the holotype of A. aleutiana were not detected in multiple sample preparations of sclerites done for this specimen. However, paratypes for A. aleutiana did not have these sclerites in their outer surface. Examinations of other specimens of this species would need to be done to see if these smaller double heads ever occur. Oval capstans of middle coenenchyme layer slightly smaller than or as large as those in A. aleutiana . While these sclerites become longer, more ornamented in deeper layers of the coenenchyme in A. aleutiana , they did not do so in this species. Octoradiates of the deepest layer, at their largest, were slightly smaller than the axial sclerites of A. aleutiana . All sclerites in the species described here displayed less developed ornamentation when compared to those of A. aleutiana .

There is no doubt that this specimen belongs in the genus Alaskagorgia ; its collection location, the long, thick, clavate terminal branches, thicker coenenchyme, darkly-colored horny axis with hollow chambered central core, and general colony shape place it squarely in this fairly new genus, as do the pronounced polyps and their apertures, with their raised rims bearing eight notches. The sclerite forms found in this specimen also closely match many of those found in A. aleutiana , the only other species in the genus. However, the extensive branching, the stout, yet broadly, lateral-branched colony shape, the unusual “curling back” of the branches on themselves, the vibrant lemon-yellow color of colony, and the pale yellow color of the sclerites, set it apart from A. aleutiana , as does the greater length of the anthocodial sclerites, and the lack of the small double heads. However, this latter form of sclerite only appeared in the holotype of A. aleutiana , not in the paratypes. It remains to be seen if other specimens of this new species might display a similar pattern of occurrence (or non-occurrence).

Alaskagorgia aleutiana is much more robust and far less arborescent than the new species described here. Sánchez & Cairns (2004) reported a maximum colony height of 60 cm, maximum branch diameter of 12–15 mm, clavate branch tips with maximum diameter of 17 mm, and a maximum of 5 total branches. Measurements made by us of our museum specimens indicate a maximum colony height of 71 cm, maximum branch diameter of 18 mm, clavate branch tips with maximum diameter of 20.7 mm, and a maximum of 7 total branches. Colonies do not start branching, if at all, until they attain a height of 13 cm. By contrast the new species has a colony height of only about 12 cm with a width of about 25 cm., while the maximum branch width (nearer the base) is about 8 mm with clavate branch tips slightly larger (~ 10 cm). The colony starts branching only 10 mm from the base and is richly branched (approximately 40 branches total).

Remarks. The condition of the sclerites in this specimen, overall, revealed a large degree of erosion. We speculate that the eroded nature of the sclerites was an indication of the colony’s relatively older age. This speculation is supported by previous work on plexaurid octocorals in Alaska waters indicting very slow growth (Stone et al. 2017).

Preliminary genetic analyses have been undertaken ( Thoma 2013) and additional work is ongoing to determine the similarities at the molecular level between this species, A. aleutiana , and an apparent third undescribed species of Alaskagorgia from deep-water (824 m) in the central Aleutian Islands (see Alaskagorgia sp. in Fig. 1 ). The status of the genus in regards to higher level taxa, such as family are also being investigated with molecular genetics (M. Everett, NOAA, NMFS, personal communication).

Associates. Brittle stars, Class Ophiuroidea (identified by Gordon Hendler of Los Angeles County Museum of Natural History), are common associates of gorgonian corals in the Aleutian Islands (R. Stone, personal observations). The holotype of Alaskagorgia splendicitrina was no exception, hosting 23 brittle stars including 20 Ophiosemnotes pachybactra H. L. Clark, 1911 and 3 Astronebris tatafilius Downey, 1967 , belonging to the Ophiacanthidae and Asteronychidae , respectively.

Figures

FIGURE 1. Map of the Aleutian Island Archipelago showing the distribution of Alaskagorgia specimens (expertly identified) collected in the region. Blue triangles indicate the location of Alaskagorgia aleutiana, the red circle indicates the location of A. splendicitrina n. sp., and the purple square indicates Alaskagorgia sp.

FIGURE 2. Holotype of A. splendicitrina n. sp. A, Whole, live colony upon collection. B, Close-up of several branches, showing distribution of polyps, shape of polyp, and arrangement of tentacles.

FIGURE 3. Holotype of A. splendicitrina n. sp. A, Whole colony, fully dried. Note curled nature of branches. B, Close-up of a large branch tip, showing the arrangement of polyps at the terminal branch end and clavate tip with large polyps and prominent tentacles.

FIGURE 4. SEM images of major sclerites. A, long, pointed tuberculate spindles of tentacles. B, Sclerites of axial sheath. C, Oval capstans of the middle tissue layer (containing gastric cavities); C 1 and C 2 longer than average. D, Small, oval capstans of the surface layer. Scale bar for A-D = 100 µm.