Chrysogorgia binata, Xu, Yu, Li, Yang, Zhan, Zifeng & Xu, Kuidong, 2019

Xu, Yu, Li, Yang, Zhan, Zifeng & Xu, Kuidong, 2019, Morphology and phylogenetic analysis of two new deep-sea species of Chrysogorgia (Cnidaria, Octocorallia, Chrysogorgiidae) from Kocebu Guyot (Magellan seamounts) in the Pacific Ocean, ZooKeys 881, pp. 91-107 : 91

Chrysogorgia binata sp. nov. Figs 4 , 5 , 6 , 7 ; Table 1

Holotype.

MBM286346, station FX-Dive 173 (17°28.69'N, 153°09.95'E), Kocebu Guyot, depth 1669 m, 7 April 2018. GenBank accession number: MK431862.

Diagnosis.

Chrysogorgia ("group C, Squamosae typicae") with a biflabellate colony and a short main stem. Polyps 3-5 mm tall. Scales smooth and thin in the basal part of polyps body with various shape, up to 1 mm long. Scales in the upper part of polyps of various shapes, converged to form an inconspicuous and blunt point at the base of a naked tract below each tentacle. Scales bluntly lancet-shaped, often with numerous coarse granules, longitudinally arranged around both sides of each naked tract. Scales irregular and coarse, usually with lobed edges in the back of tentacles. Scales of coenenchyme slipper-shaped with a medial contraction. Nematozooids absent from coenenchyme.

Description.

Specimen with two attached individuals of the crustacean genus Galathea Fabricius, 1793 ( Fig. 4C ). Main stem short with a principal bifurcation, forming two roughly parallel, fans ( Fig. 4A, F ). Calcareous holdfast small and white, about 7 mm in diameter ( Fig. 4F ). Major branches of each fan subdivided dichotomously or sympodially. Specimen about 16 cm long and 15 cm wide with a brilliant golden axis, and the stem about 1.5 mm in diameter at base ( Fig. 4C ). Internodes about 5-9 mm long, each with a single polyp except the terminal twigs, which may sometimes have two polyps. Polyps large and orange in situ, about 3-5 mm tall by 1-2 mm wide, with sclerites forming an inconspicuous blunt point at the base of a naked tract below each tentacle ( Figs 4D , 5A ). Terminal polyps usually with a long and narrow body ( Fig. 4E ).

In the basal part of the polyp body, the sclerites comprise transversally arranged, large, smooth scales. They represent a variety of shapes, a few with broad marginal lobes, length by width measuring 216-936 × 58-283 μm, with an average of 549 × 166 μm, ( Figs 5B , 6A ). There are also scales in the upper part of polyps of various shapes, sometimes thick and with a medial contraction, often sharp at one end, broad and lobed at the other, which combine to form an inconspicuous and blunt point at the base of a naked tract below each tentacle; measuring 275-635 × 77-254 μm, with an average of 451 × 151 μm ( Figs 5B , 6B ). Above these points are irregular, elongate or lancet-shaped scales mostly with coarse granules on surface, that are arranged longitudinally around the sides of each naked tract. The scales measure 337-650 × 45-85 μm with an average 431 × 70 μm ( Figs 5B , 7A ). The scales in the back of tentacles are coarse, of various shapes, mostly flat and lobed, and densely and transversally arranged, measuring 88-352 × 19-149 μm, with an average of 183 × 55 μm ( Figs 5A , 7B ). The scales in the pinnules are curved at an obtuse angle, and are sometimes thick with a few lobes on their edges; measuring 87-196 × 19-34 μm, with an average of 152 × 27 μm ( Fig. 7D ). The scales of the coenenchyme are generally slipper-shaped, some elongate elliptical, occasionally with indentations in their edges, and measure 138-361 × 40-87 μm, with an average of 222 × 56 μm ( Fig. 7C ). The coenenchyme is thin with no nematozooids.

Etymology.

The Latin adjective binatus (binate) refers to the biflabellate structure of the species.

Distribution.

Found only from the Kocebu Guyot in the Magellan seamounts with water depth of 1669 m.

Habitat.

Colony attached to a rocky substrate with a small holdfast ( Fig. 4B ).

Remarks.

Within the known species of Chrysogorgia , seven species mainly possess a planar structure (Table 1 ). Among these, including our specimen, C. desbonni Duchassaing & Michelotti, 1864 and C. pinnata Cairns, 2007 belong to the Chrysogorgia "group A, Spiculosae"; Chrysogorgia chryseis Bayer & Stefani, 1988 and C. stellata Nutting, 1908 belong to the "group B, Squamosae aberrantes". Chrysogorgia binata sp. nov.; C. electra Bayer & Stefani, 1988 and C. scintillans Bayer & Stefani, 1988 belong to the "group C, Squamosae typicae". The species C. upsilonia Cordeiro, Castro & Pérez, 2015 belongs to the "group D, Spiculosae aberrantes". Based on the arrangement of the sclerites, Chrysogorgia binata sp. nov. can easily be distinguished from the species in groups A, B and D.

Both Chrysogorgia binata sp. nov. and C. electra have a biflabellate colony. However, the new species differs from the latter by its larger polyps (3-5 mm vs. generally 1.75-2.00 mm in height), eight short and blunt points beneath the tentacles (vs. inconspicuous), scales of various shapes with low and broad marginal lobes in the body wall (vs. elongate with narrow prominent marginal lobes), scales mainly slipper-shaped in coenenchyme (vs. elongate tapered with prominent marginal lobes) ( Bayer and Stefani 1988). Chrysogorgia binata sp. nov. differs from C. scintillans by its larger polyps (3-5 mm vs. up to 2.8 mm in height), larger sclerites in the body wall (maximum length 0.93 mm vs. 0.65 mm), scales in the upper part of polyps (irregular and usually with sharp end vs. regular and usually with smooth end), scales around the sides of each naked tract (lancet-shaped and usually with coarse granules vs. twisted, flat and often lobed) ( Bayer and Stefani 1988, Cairns 2018).

Figures

Figure 4. External morphology of the holotype and polyps of Chrysogorgia binata sp. nov. A Two planar fans of the colony after fixation B The holotype (arrow) in situ. Laser dots spaced at 33 cm used for measuring dimensions C The colony after collection D A single polyp under SEM E Single terminal polyp under light microscope F Short trunk with the first bifurcation of branches after fixation. Scale bars: 10 cm (A); 5 cm (C); 1 mm (D, E); 1 cm (F).

Figure 5. Polyps of Chrysogorgia binata sp. nov. A Three polyps under SEM B Head and body of one polyp under SEM. Scale bars: 2 mm (A); 1 mm (B).

Figure 6. Sclerites of Chrysogorgia binata sp. nov. A Sclerites in the basal part of the polyp body B Sclerites in the point at the base of a naked tract below each tentacle. Scale bar: 300 μm (all at the same scale).

Figure 7. Sclerites of Chrysogorgia binata sp. nov. A Sclerites around the sides of each naked tract B Sclerites in the back of tentacles C Sclerites of the coenenchyme D Sclerites in pinnules. Scale bar: 100 μm (all at the same scale).