Diplopathes antarctica Opresko & Stewart & Voza & Tracey & Brugler 2022, sp. nov.

Diplopathes antarctica sp. nov. Opresko & Brugler

(Figs 1–3)

Material examined. Holotype: NIWA 38070, Stn TAN0802/199, 68.108 S, 179.312 W, Site C 31, Scott Seamount B, Southern Ocean, Pacific Antarctic Ridge, inside 60 o South, 662.0‒605.0 m, 2 March 2008 (USNM 1491422, SEM stub 458; Genbank ON572254). Paratype: NIWA 38674, Stn TAN0802/256, 67.340 S, 179.932 W, Site C 34, Scott Seamount B, Southern Ocean, Pacific Antarctic Ridge inside 60 o South, 1130–1235 m, 8 March 2008 (USNM 1491412, SEM stub 456; Genbank ON572249). Other material: NIWA 38071, Stn TAN0802/199, 68.108 S, 179.312 W, Scott Seamount B, 1130‒1235 m, 08 March 2008; NIWA 38203, Stn TAN0802/256, Site C 31, Scott Seamount B, 67.340 S, 179.932 W, 1130‒1235 m, 08 March 2008; NIWA 38495, Stn TAN0802/237, 67.408 S, 179.809 W, Scott Seamount B, 1520–1560 m, 7 March 2008; NIWA 38639, Stn TAN0802/251, 67.380 S, 179.989 E, Site C 34, Scott Seamount B, 1450–1541 m, 8 March 2008.

Type locality. Southern Ocean, Pacific Antarctic Ridge, Scott Seamount B, 662.0‒605.0 m.

Distribution. Known only from Scott Seamount B, Southern Ocean,PacificAntarctic Ridge(Fig.1), 605‒1560m.

Diagnosis. Corallum planar with very sparse branching to the first order; pinnules bilateral and alternating, usually 2–4 cm long (maximum 7 cm long); pinnular density 16–22 per 3 cm (total for both rows); polypar spines up to 0.1 mm tall; abpolypar spines up to 0.06 mm tall; 3–4 spines per mm in each row; polyps up to 4 mm in transverse diameter; polyp density 2–3.5 per cm.

Description. The holotype (NIWA 38070) is about 20 cm tall and about 18 cm wide (Fig. 2A). There is no basal plate, and the stem is pinnulated down to its broken basal end. The corallum has one large branch about 14 cm long and several very short branches; all the branches lie in the same plane as the stem. The pinnules are arranged bilaterally and alternately in two rows. The pinnules do not occur in more than two rows on any part of the corallum. The interior angle formed between the two rows of pinnules is near 180, and the pinnules are slightly inclined such that the distal angle formed with the stem or branches is mostly 70‒80. The length of most pinnules is in the range of 3‒4 cm, but the maximum length is 7 cm, with a basal diameter of 0.5 mm. The pinnules are spaced 3‒5 mm apart in each row, with 8‒10 per 3 cm in each row. Counting the pinnules in both rows, there are 16‒18 per 3 cm, and 28‒30 pinnules per 5 cm.

The spines (Fig. 2B) on the pinnules are conical, smooth, with an acute apex. The polypar spines are larger than the abpolypar spines. On pinnules 0.24‒0.40 mm in diameter, the polypar spines are 0.086 ‒0.103 mm tall, the abpolypar spines 0.05‒0.06 mm. The spines are arranged in axial rows, with 4‒6 rows visible in lateral view. Within the rows, the spines are spaced 0.22‒0.37 mm apart, resulting in 3‒4 spines per mm. On some pinnules spines become bifurcated or trifurcated at the apex and eventually form double and triple spines. Thus, on parts of some pinnules, and especially near the proximal end, there can be many more spines present than those in the primary axial rows.

Polyps are arranged uniserially on one side of the pinnules; they are 2.5‒3 mm in transverse diameter, resulting in 3‒3.5 polyps per cm.

The paratype (NIWA 38674, Fig. 3A) is similar to the holotype in being only sparsely branched to the first order with bilateral alternating pinnules. The pinnules are mostly 2‒4 cm long (maximum about 5 mm) and the pinnular density is 18‒22 (total for both rows) per 3 cm. As in the holotype, the spines (Fig. 3C) are conical and acute, and some are bifurcated or trifurcated. On a pinnule 0.23 mm in diameter, the polypar spines are 0.09 mm and the abpolypar spines 0.04 mm. On a pinnule 0.32 mm, the polypar spines are 0.07 mm, and the abpolypar spines 0.05 mm. The density of the spines is 3‒4 per mm in each axial row. The polyps (Fig. 3B) are slightly larger than those in the holotype; measuring up to about 4 mm in transverse diameter, with 2‒2.5 per cm.

DNA sequencing indicated that the paratype (NIWA 38674) possessed the same cox3 -IGR- cox1 haplotype as the holotype (NIWA 38070). The other four specimens assigned to this species (NIWA 38071, NIWA 38203, NIWA 38495, and NIWA 38639) also had the same cox3 -IGR- cox1 haplotype as the holotype. Sequence data corresponding to nuclear SRP54 were obtained for four of the six specimens (the holotype NIWA 38070, the paratype NIWA 38674, NIWA 38071, and NIWA 38495) and revealed a unique genetic signature for the paratype (NIWA 38674) when compared to the other four specimens (the SRP54 gene for NIWA 38674 contained five nucleotide substitutions and three deletions [2, 9, and 21 bp in length]).

Comparisons. Diplopathes antarctica sp. nov. forms a sparsely branched corallum similar to that seen in D. tuatoruensis sp. nov. (see below). It differs from D. tuatoruensis in having smaller pinnules (typically 2‒4 cm vs. 5‒7 cm), a slightly greater pinnular density (16‒22 per cm vs. 14‒16 per cm), larger spines (up to 0.103 mm vs. up to 0.045 mm) and less crowded spines (3‒4 per mm vs. 5‒7 per mm) (see also Table 3).

Genetic Distances. A K2P-based genetic distance analysis based on cox3-cox1 indicated a 0.61% separation between D. antarctica sp. nov. (NIWA 38070) and D. multipinnata sp. nov. (NIWA 88617), and a 1.73% separation between D. antarctica (NIWA 38070) and D. tuatoruensis sp. nov. (NIWA 16055).

Etymology. The species name antarctica is in reference to the fact that the type material was collected from Scott Seamount B, along the Pacific Antarctic Ridge, in the Southern Ocean.