Trichogorgia utinomii, Cordeiro, 2019

Cordeiro, Ralf T. S., 2019, A review of the genus Trichogorgia (Cnidaria, Octocorallia), including descriptions of new species, Zootaxa 4706 (4), pp. 517-530 : 520-522

Trichogorgia utinomii sp. nov.

Figs. 1–2

Not Malacogorgia capensis Hickson 1904: 226–227 , pl. VII, fig. 5, pl. VIII, figs. 10–11.

Malacogorgia capensis . Utinomi 1964: p. 9, fig. 5, pl. II, figs. 4–5.

Holotype: Eltanin R /V, USAP expedition, st. 1521, 54°07’59”S, 52°12’29”W (Scotia Sea), 419–483 m, 30 Jan 1966 ( USNM 77385 , one colony and three fragments).

Paratypes: Eltanin R /V, USAP Expedition, st. 428, 57°48’29”S, 62°40’01”W, 662–1120 m, 5 Jan 1963 ( USNM 77374 , one colony and one fragment) ; Eltanin R /V, USAP Expedition, st. 1520, 54°08’31”S, 52°04’01”W, 1244– 1771 m, 30 Jan 1966 ( USNM 77384 , two small colonies)

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Description: Uniplanar flabellate and dichotomously branched colonies, up to 17 cm tall and 13 cm wide, all lacking holdfasts, which probably were attached to solid substrata ( Fig. 2 A–C). Colonies quasi-bilaterally symmetrical and slightly concave. Main stem 3.7–12.7 mm long and 0.7–2.6 mm in diameter. Axis calcified, circular in cross-section ( Fig. 3B,E ), not undulated, with concentric layers ( Fig. 3B,D,E,F ) and inconspicuous longitudinal canals perforating its medular region ( Fig. 3A,C ). Axis golden in basal parts, becoming pale iridescent to translucent towards branchlets. Branchlets arising up to the 5 th order ( Fig. 2A,B ). Primary branchlets 5.5–13 mm long and new branchlets distant 11.2–22 mm from each other. Main stem and proximal branchlets usually shorter, stiff and oriented upwards, whereas distal branchlets are long and flexible. Terminal branches up to 14 cm long. Polyps well separated, 0.78± 0.55 mm from each other (n = 30), occurring on the entire coral, except on the main stem ( Fig. 2B,C ), longitudinally arranged in two alternate rows on the branchlets ( Fig. 2D ), slightly facing the concave face of the colony. Distally, polyps arranged in a single line. Each of the eight tentacles of polyps bears 8–15 pairs of pinnules (~ 0.15 mm long) on both sides ( Fig. 2E ). Based on measurements of 30 zooids randomly chosen among the specimens, mean polyp length when fully expanded is 2.06± 0.48 mm, and polyp width 0.89± 0.2 mm. When completely contracted, polyps are 0.58± 0.1 mm long and 1.15± 0.29 mm wide. Coenenchyme transparent throughout colonies. Pharynx slightly darker than rest of soft tissues, visible through the polyp body wall. Polyps and coenenchyme completely devoid of sclerites.

Comparisons: The new species differs from its congeners in having no sclerites at all, which would group it with Trichogorgia lyra Bayer & Muzik, 1976 and T. capensis ( Hickson, 1904) . I examined specimens of T. lyra (including types) and, contrary to expectations, most showed very rare translucent and fragile scales in the main stem coenenchyme ( Fig. 6B ). According to Hickson’s description, fully expanded polyps in T. capensis are less than 1 mm tall (up to 0.65 mm), whereas in T. utinomii they often exceed 2 mm in similar colony sizes ( Table 1 ), being opposite and alternately disposed, respectively (see Hickson, 1904, pl. VII fig. 5 and pl. VIII figs. 10–11). Moreover, T. capensis is known from depths <100 m, in contrast with a much deeper range for the new species (see Distribution).

Remarks: This species was first recorded by Utinomi (1964) as Malacogorgia capensis Hickson, 1904 in the Southern Ocean (500–590 m). Our specimens were collected almost contemporarily with Utinomi’s, and there are no reports of new collections since then. Regarding ecological associations, several amphipods were found on branches of the holotype. Besides that, some polyps are oddly swollen in their proximal portion, indicating sexual maturation ( Fig. 2F )

Etymology: Named in honor to Dr. Huzio Utinomi, a prominent octocoral taxonomist, who first record this species in the Southern Ocean.

Distribution: Known only from the type locality, the Scotia Sea, 419–1244 m.

Figures

FIGURE 1. Forms and distribution of the genus Trichogorgia. A: four common colony shapes in the genus (left to right): lyrate, flabellate, slender planar and bushy, respectively; B: comparison between bathymetric ranges of Trichogorgia species; C: distribution map for the genus. Depth given in meters (m).

FIGURE 2. Specimens of Trichogorgia utinomii sp. nov. Colony view of the holotype (A, USNM 77385) and paratypes (B and C, USNM 77384 and 77374, respectively); D: detail of a terminal branch with several polyps clustered; E: polyp extended; F: reproductive contracted polyp.

FIGURE 3. Morphological details of the axis in Trichogorgia utinomii sp. nov. A, C: central core in cross-section with several longitudinal channel-like pores (arrows); B: cross-section of the axis, showing its circular form; D, F: lateral view of axes exposing their concentric lamellae; E: cross-section showing regular superposition of layers around the central core.

FIGURE 6. Scale-shaped sclerites under polarized light showing concentric extinction patterns. A: Stephanogorgia diomedea (USNM 75108); B: Trichogorgia lyra (USNM 52875); C: S. wainwrighti (USNM 1112682); D: T. muzikae sp. nov. (USNM 77155, holotype).