Gorgonocephalus chilensis novaezelandiae Mortensen, 1924

Figs 9–10

Gorgonocephalus chilensis var. novaezelandiae Mortensen, 1924: 109–110, pl. 4 fig 1.

Gorgonocephalus chilensis – Baker 1980: 51–52. — McKnight 2000: 45–46, pl. 19. [non G. chilensis chilensis Philippi, 1858]

Material examined

CHINA • 1 spec.; South China Sea, SE of Zhongsha Islands, seamount; 13° 58.68′ N, 114° 52.09′ E; depth 1550 m; 25 Sep. 2020; collection event: stn SC013; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 198761; IDSSE EEB-SW0007 .

Description (IDSSE EEB-SW 0007)

MEASUREMENTS. Disc diameter 15.5 mm.

DiSC. Dorsal disc slightly inflated, interradials slightly indented. Radial shields elongated and narrow, extending nearly toward center of disc but not meeting in center, tapering at distal ends, densely covered by large, tall conical granules. Skin between radial shields also covered by conical granules, but less dense and smaller than on radial shields, but disc center covered with compacted conical granules. Disc periphery covered with few larger conical granules (Fig. 9A–F). Ventral disc covered with small, scattered, low granules, extending onto oral area (Fig. 9E). Genital slits conspicuous, interradial margin covered by two irregular rows of larger, higher than wide granules (Fig. 9D). Single madreporite. Oral area covered by smooth skin, partly exposing adoral shield outlines and few scattered smaller granules (Fig. 9E). Adoral shields short, square. Oral papillae spiniform (Fig. 9E).

ARMS. Branched at least six to seven times, flexible dorso-ventrally, flat ventrally, high rounded dorsally (Fig. 9A). Ventral arm along first branch and near base covered by smooth skin, distalwards scattered with smaller granules (Fig. 9G). Dorsal arm surface covered by domed scales, on proximal segments with naked scales and naked areas corresponding to pedicellarial bands. Dorsal arm surface densely covered by compact granules after second arm fork. Pedicellarial bands start at second arm fork with three to four isolated clumps on each side of arm and becoming continuous across arm. From sixth arm fork, raised pedicellarial bands give an annulated appearance to arm (Fig 9H). First arm segment lacks spines, next three with two arm spines, next nine to ten with three arm spines and thereafter four arm spines per segment, decreasing to three after fifth branch (Fig. 9G, I–J). Ventral arm spines smaller, slightly flattened, unevenly pointed, distally turning into multi-toothed hooks (Fig. 9J–L). Pedicellariae with small secondary tooth (Fig. 9K–L).

COLOR. Creamy white in alcohol specimen, with light brown disc and darker arms when alive (Fig. 9A–B).

OSSiCLE MORPHOLOGY. Pedicellarial band formed by approximately six articulating tubercles on middle arm region and eight articulations at curved distal end (Fig. 10A–B). Tubercles form two parallel rows with single foramen (Fig. 10A–B). Ventral arm spines distally transformed into hooks with two or three secondary teeth (Fig. 10C). Pedicellariae on pedicellarial band with single secondary tooth and apophysis (Fig. 10D). Pedicellariae on pedicellarial band differ from ventral arm spine by smooth apophysis. Vertebrae with hourglass-shaped streptospondylous articulation with smooth lateral furrows (Fig. 10E–I). Paired openings in lateral side of vertebrae for lateral water canals, no oral bridge (Fig. 10F–G).

Remarks

The subspecies G. chilensis novaezelandiae is currently unaccepted and considered a junior synonym of G. chilensis (Philippi, 1858) (Stöhr et al. 2021) . Our molecular results (see below) place this specimen with other New Zealand material in a sister clade to G. chilensis from Antarctica and the Southern Ocean. We consider the New Zealand clade sufficiently different from the Antarctic clade to reinstate the subspecies name for it, pending further investigation that may result in raising it to full species status. For the Antarctic clade, the name G. chilensis chilensis should be used for the time being, although the type locality is in Southern Chile, and if future molecular data find the Chilean population to be in the same clade as the New Zealand and South China Sea material, a new name would need to be found for the Antarctic clade. The only morphological difference between the two subspecies mentioned by Mortensen (1924) is a sparser distribution of the dorsal disc granules in G. chilensis novaezelandiae . The specimen from the present study is smaller and thus probably younger than the holotypes of both subspecies and the New Zealand specimens described by Baker (1980) and McKnight (2000). However, McKnight (2000) also reported two specimens of the same size as ours (16 mm disc diameter) with a dense cover of disc granules. This character may either be variable or age-related. We consider it highly likely that the specimens studied by Baker (1980) and McKnight (2000) represent G. chilensis novaezelandiae . The morphological characters of our specimen varied slightly from their descriptions, particularly in the number of branches in the arms, which is size dependent. According to Baker (1980) the shields indirectly contributed to thickening the periphery of the disc, but other species of Gorgonocephalus showed a distinct gap in granulation at the end of the shields and granules on the periphery of the disc. Therefore, this morphological feature can be used to distinguish G. chilensis within the genus Gorgonocephalus . Considering other morphological characters, G. tuberosus Döderlein, 1902 is similar to G. chilensis by having a dense cover of coarse, conical, or hemispherical granules on the disc, small and closely arranged in the dorsal angle of the interradial space (Döderlein 1902).

H.L. Clark (1923), Seno & Irimura (1968) and Mortensen (1936) reported on younger individuals that were attached to the mature adult individuals, which prompted H.L. Clark (1923) to consider G. chilensis as viviparous. Mortensen (1936) suggested that it is not viviparous and these younger specimens simply attached to mature specimens as a host, like larger specimens attach to gorgonians (Olbers et al. 2019). This is the first record of G. chilensis novaezelandiae from the Indo-Pacific region and far from previously recorded occurrences, which may suggest that other non-Antarctic records also belong to this subspecies. Its true bathymetric and geographic distribution is currently unclear, because most previously recorded specimens were reported as G. chilensis and need to be re-examined, preferably with molecular methods. The taxonomic value of the disc granulation should be tested by examination of a large number of specimens, which could also find other distinguishing characters.

Distribution

1550–1830 m depth. New Zealand, South China Sea (Mortensen 1924; this study).