Bathypathes longicaulis, Lü & Zhan & Li & Xu, 2024

Lü, Ting, Zhan, Zifeng, Li, Yang & Xu, Kuidong, 2024, Alternatipathes longispina sp. nov. and Bathypathes longicaulis sp. nov., two black corals (Antipatharia, Schizopathidae) from seamounts in the Western Pacific, Zootaxa 5437 (2), pp. 245-261 : 253-258

Bathypathes longicaulis sp. nov.

( Fig. 6 , 7 ; Table 3 )

Material examined. Holotype: MBM286468 , station FX-Dive 220 (10°04’55”N, 140°15’20”E), M7 seamount, depth 1088 m, 8 June 2019 . Paratypes: MBM286469 , station FX-Dive 209 (10°04’40”N, 140°12’12”E), M5 seamount, depth 998 m, 27 May 2019 . MBM286470 , station FX-Dive 213 (10°04’08”N, 140°11’36”E), M5 seamount, depth 1011 m, 31 May 2019 . MBM286471 , station FX-Dive 209 (10°04’40”N, 140°12’13”E), M5 seamount, depth 1001 m, 27 May 2019 .

Diagnosis. Corallum monopodial, unbranched and pinnulate, with long unpinnulated lower stem. Pinnules simple, arranged bilaterally and alternately, with longest pinnule near the middle section of pinnulated stem. Pinnular density 3–4 per cm. Spines smooth, conical with blunt point. Spines on pinnules usually in 6 longitudinal rows, three to four rows in lateral view. Polypar spines 0.034 ‒0.056 mm high and abpolypar spines 0.024 ‒0.040 mm high. Spines 0.34–0.65 mm apart in each row, 2 or 3 spines per millimeter.

Description of holotype. Colony was slightly pink in situ and became reddish brown after being preserved in alcohol. The holotype is approximately 38.1 cm high, 16 cm wide, with lower unpinnulated section of stem 28.1 cm in length, occupying about 3/4 of stem length ( Fig. 6A, E ). Basal stem is about 1.62 mm in diameter, while only 0.81 mm in diameter near the base of lowermost pinnules and 0.25 mm in diameter on the apex of corallum.

Pinnules simple, usually arranged alternately in two lateral rows along the upper portion of stem, with a few exceptions. The distance between pinnules of the same row is 4–12 mm (mostly 6–9 mm), about 3 pinnules per centimeter on both sides. The length of pinnules ranges from 3 cm to 8 cm, increasing from lower section of pinnulated stem to middle part, then decreasing towards apex. The distal angle between pinnules and stem is near 90° along the pinnulated section. The interior angle between the two rows of pinnules varies from 130° to 150°.

Spines on pinnules ( Fig. 7A ) simple, smooth, conical with blunt point. Spines on the same side nearly equal in size and projecting outwards at approximately right angles to axis ( Table 3 ). On the middle part of the pinnules, the polypar spines are 0.034 ‒0.056 (0.045±0.006, n=18) mm high and 0.18‒0.29 (0.24±0.03, n=18) mm wide at base, and the abpolypar spines are 0.024 ‒0.040 (0.033±0.005, n=18) mm high and 0.14‒0.27 (0.20±0.04, n=18) mm wide at base. On the basal part of the pinnules, the polypar spines are 0.028 ‒0.059 mm high and the abpolypar spines are 0.024 ‒0.038 mm high. Along the distal parts of the pinnules, the polypar spines are 0.027 ‒0.043 mm high, and the abpolypar spines are 0.018 ‒0.042 mm high. Spines on pinnules are usually arranged in 6 longitudinal rows when viewed from the cross section and in 3‒4 rows from the lateral view. The distance between adjacent spines of same row is 0.34‒0.65 mm, about 2‒3 spines per millimeter in each row. Spines on stem simple, smooth, conical with blunt apex ( Fig. 7D ). Spines on the middle part of pinnulated stem are 0.023 ‒0.036 mm high and 0.09–0.22 mm wide at base, arranged in 2–4 rows in lateral view. Polyps are in poor condition in alcohol-preserved colony.

Type locality. A seamount tentatively named as M 7 in the Caroline Ridge in the tropical Western Pacific Ocean with water depth of 1088 m .

Etymology. Composite of the Latin adjective longus (long) and the Latin noun caulis (stem) refers to the longer unpinnulated stem of species.

Distribution and habitat. Found from the M5 and M7 seamounts located in the Caroline Ridge in the tropical Western Pacific, with water depth of 998‒1088 m. The water temperature was about 4.4‒5.1°C and the salinity about 34.3–34.7.

Remarks. The genus Bathypathes Brook, 1889 contains currently 15 species ( Molodtsova et al. 2022, Chimienti et al. 2022). Like the new species, only three congeners have alternately arranged pinnules, Bathypathes platycaulus Totton, 1923 , Bathypathes pseudoalternata Molodtsova, Opresko & Wagner, 2022 and Bathypathes thermophila Chimienti, 2022 .

Bathypathes longicaulis sp. nov. differs from B. platycaulus by the number of pinnules (15–20 per 5 cm vs. 25– 30 per 5 cm). In addition, the stem diameter of the new species decreases from the base to the apex, while the stem diameter of B. platycaulus increases from 1.5 mm to 1.75 mm in the first 7 cm and then decreases to 0.28 mm at the apex ( Totton 1923, Molodtsova et al. 2022). Bathypathes longicaulis sp. nov. is different from B. pseudoalternata by the relatively much longer unpinnulated stem (ratio of the length of unpinnulated stem to the total height of stem 0.74 vs. 0.25), less rows of spines visible in lateral view (3–4 vs. 5–6) and the number of spines (2–3 per 1 cm vs. 5–6 per 1 cm) ( Molodtsova et al. 2022). Bathypathes longicaulis sp. nov. can be easily distinguished from B. thermophila by the corallum form (unbranched vs. branched), the relatively much longer unpinnulated stem (ratio of the length of unpinnulated stem to the total height of stem 0.74 vs. 0.05), the number of pinnules (9–12 per 3 cm vs. 14–18 per 3 cm), the larger spines (0.024 ‒0.056 mm vs. 0.017 –0.022 mm), the larger distance between adjacent spines (0.34–0.65 mm vs. 0.20–0.31 mm,) and the spine rows visible from lateral view (3–4 vs. 6–7) ( Chimienti et al. 2022, Table 3 ).

Figures

FIGURE 6. External morphology of Bathypathes longicaulis sp. nov. The holotype MBM286468 (A, E) and paratype specimens MBM286469 (B), MBM2864670 (C, F), and MBM286471 (D, G) in situ (A–D) and after collection (E–G). Two laser dots spaced at 33 cm (A–D). Scale bars: 10 cm (E–G in the same scale).

FIGURE 7. Spines of the holotype of Bathypathes longicaulis sp. nov. under SEM.A, B. Spines on the middle part of pinnules. C. Spines on the distal part of pinnules. D. Spines on the middle part of pinnulated stem. E. An abpolypar spine with the measured minimum height of 0.024 mm. F. An abpolypar spine with the height of 0.030 mm. G. A polypar spine with the measured maximum height of 0.056 mm. H.A polypar spine with the height of 0.047 mm. Scale bars: 0.5 mm (A–D in the same scale); 0.1 mm (E‒H in the same scale).