Metallogorgia macrospina Kuekenthal , 1919

Xu, Yu, Zhan, Zifeng & Xu, Kuidong, 2020, Morphology and phylogenetic analysis of five deep-sea golden gorgonians (Cnidaria, Octocorallia, Chrysogorgiidae) in the Western Pacific Ocean, with the description of a new species, ZooKeys 989, pp. 1-37 : 1

Metallogorgia macrospina Kuekenthal, 1919 Figures 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ; Tables 2, 3

Metallogorgia macrospina Kükenthal, 1919: 504-505, figs 227-229, Taf.XXX, Fig. 6 .

Type locality.

0°58.2'S, 90°43.2'E, West Sumatra, 1280 m depth ( Kükenthal 1919).

Voucher specimens.

MBM286484, station FX-Dive 210 (10°04.68'N, 140°12.07'E), depth 911 m, 28 May 2019. MBM286487, station FX-Dive 215 (10°04.97'N, 140°10.75'E), depth 986 m, 2 June 2019. MBM286488, station FX-Dive 215 (10°04.82'N, 140°10.90'E), depth 902 m, 2 June 2019. MBM286489, station FX-Dive 223 (10°04.63'N, 140°15.12'E), depth 1072 m, 11 June 2019. They were collected from three seamounts (tentatively named as M5, M7 and M8) located on the Caroline Ridge.

Diagnosis

(extended on the basis of Kükenthal 1919). In adults, main stem monopodial with branches forming a similar spiral on the top. Strong branches subdivided dichotomously, with branchlets forming a sympodium pattern in each plane. In juveniles, main stem monopodial and thin/gracile with branches occurring on the lateral of the trunk randomly and subdivided dichotomously in multiple planes. Polyp cylindrical, some of them with a slightly expanded base, absent on stem of adults but present in juveniles. Sclerites relatively coarse with many small warts on surface, cross-shaped occasionally. Rods relatively regular, longitudinally arranged in tentacles and the upper part of the polyp body, and partially crosswise or transversely arranged on the body bottom. Scales and rods elongated, usually coarse with serrated edges, transversely arranged in coenenchyme. Nematozooids not present.

Description.

In juvenile (specimen MBM286484), colony slightly bottlebrush-shaped, with branches occurring on the lateral side of the stem randomly. Main stem monopodial and gracile. Branches subdivided dichotomously in multiple planes. Polyps cylindrical, occasionally present on the top of the stem. The branch coenenchyme well differentiated with a layer of sclerites. In the adults (specimen MBM286487-286489), colony like a tree shape with branches forming a similar spiral on the top of the stem. Main stem monopodial and strong. Branches subdivided dichotomously with branchlets forming a sympodium pattern in each plane. Polyps cylindrical, some of them with a slightly expanded base, absent from the stem. Branch coenenchyme usually not well differentiated.

Sclerites with same forms and arrangement in juveniles and adults, both relatively coarse with many small warts on surface, cross-shaped occasionally. Rods relatively regular, longitudinally arranged in tentacles and the upper part of the polyp body, and partially crosswise or transversely arranged on the body bottom. Scales and rods elongated, usually coarse with serrated edges, transversely arranged in coenenchyme. For detailed morphological measurements, see Table 2 .

Distribution.

West Sumatra ( Kükenthal 1919); the unnamed seamounts on the Caroline Ridge in the Western Pacific (present study); Southwest Pacific ( Pante et al. 2012), 720-1280 m depth.

Remarks.

According to Kükenthal (1919), the sclerites in the M. macrospina polyps contain rods and spindles, and those in coenenchyme are slender rods, some of them flat or irregular. The sclerites in our specimens match well with the original description as well as pictures. Therefore, we identify our specimen as M. macrospina .

Metallogorgia macrospina is similar to M. melanotrichos by the branchlets forming a sympodium pattern in the large branches. In the original description, Kükenthal (1919) pointed out that M. macrospina differed from M. melanotrichos by its more densely arranged branches, larger polyps, longer sclerites in coenenchyme and different color. However, the polyps of M. macrospina in our specimens are generally smaller than those of M. melanotrichos (Table 2 ), and there are no conspicuous differences in color (almost brown to black) among these colonies. Therefore, based on the morphological features of our specimens, M. macrospina can be separated from M. melanotrichos by its sympodial branching part forming a spiral on the colony top (vs. monopodial), only rods in the polyp-body wall (vs. rods and scales), and rods and scales in coenenchyme (vs. only scales).

The juvenile of Metallogorgia macrospina (specimen MBM286484) has significant differences in the branching pattern from the adult specimens MBM286487, MBM286488 and MBM286489 in morphology. It differs also by having a slightly bottlebrush-shaped colony (vs. similarly tree-shaped colony), gracile and flexible stem (vs. hard and strong), monopodial branching part (vs. sympodial), branchlets in multiple planes (vs. forming a sympodium in one plane), and well differentiated coenenchyme with more sclerites (vs. not well differentiated and with relatively sparse sclerites). However, the same sclerites in polyps and coenenchyme, and particularly the mtMutS gene data analyzed below indicate these specimens belong to the same species.

Figures

Figure 6. Sclerites of Chrysogorgia carolinensis sp. nov. A sclerites in the back and at the base of tentacles B sclerites at the basal polyp body C sclerites in coenenchyme. Scale bar: 300 μm (all images at the same scale).

Figure 11. External morphology and polyps of juvenile Metallogorgia macrospina MBM 286484 A the colony in situ. Laser dots spaced at 33 cm used for scale B close-up of branches in situ C the colony after collection D a branch under a light microscope E, F a single polyp under a light microscope G three polyps under SEM H polyp-body wall under SEM I coenenchyme under SEM. Scale bars: 10 cm (C), 5 mm (D), 1 mm (G), and 500 μm (E, F, H, I; H, I at the same scale).

Figure 12. Sclerites of juvenile Metallogorgia macrospina MBM 286484 A some small rods in polyps B larger rods in polyps C rods and elongated scales in coenenchyme. Scale bars: 50 μm (A), 300 μm (B, C at the same scale).

Figure 13. External morphology and polyps of Metallogorgia macrospina MBM 286487 A the colony in situ. Laser dots spaced at 33 cm used for scale B close-up of branches in situ C the colony after collection D a branch under a light microscope E, F a single polyp under a light microscope G three polyps under SEM H head of a polyp under SEM I coenenchyme under SEM. Scale bars: 10 cm (C), 2 mm (D), and 500 μm (E-I; H, I at the same scale).

Figure 14. Sclerites of Metallogorgia macrospina MBM 286487 A some small rods in polyps B larger rods in polyps C rods and elongated scales in coenenchyme. Scale bars: 100 μm (A), and 300 μm (B, C at the same scale).

Figure 15. External morphology and polyps of Metallogorgia macrospina MBM 286488 A the colony in situ. Laser dots spaced at 33 cm used for scale B close-up of branches in situ C the colony after collection D a branch under a light microscope E, F a single polyp under a light microscope G three polyps under SEM H head of one polyp under SEM I coenenchyme under SEM. Scale bars: 10 cm (C); 2 mm (D), and 500 μm (E-I; H, I at the same scale).

Figure 16. Sclerites of Metallogorgia macrospina MBM 286488 A rods in tentacles B rods in the polyp-body wall C rods and elongated scales in coenenchyme. Scale bar: 200 μm (all images at the same scale).

Figure 17. External morphology and polyps of Metallogorgia macrospina MBM 286489 A the colony in situ. Laser dots spaced at 33 cm used for scale B the colony after collection C a branch under a light microscope D a terminal branchlet under a light microscope E, F a single polyp under a light microscope G three polyps under SEM H head of one polyp under SEM I coenenchyme under SEM. Scale bars: 10 cm (B), 2 mm (C), and 500 μm (D-I; H, I at the same scale).

Figure 18. Sclerites of Metallogorgia macrospina MBM 286489 A rods in tentacles B rods in the polyp-body wall C rods and elongated scales in coenenchyme. Scale bar: 300 μm (all at the same scale).