Alternatipathes longispina, 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 : 248-251

Alternatipathes longispina sp. nov.

( Fig. 2–4 ; Table 2 )

Material examined. Holotype: MBM286472 , station FX-Dive 172 (17°23’28”N, 153°05’45”E), Kocebu Guyot in the Magellan Seamount Chain in the Western Pacific, depth 1336 m, 1 April 2018.

Diagnosis. Corallum monopodial and unbranched, maximum width nearly two times as long as corallum height. Lower unpinnulated stem slightly shorter than upper pinnulated stem. Pinnules simple, arranged bilaterally and alternately, about 19 cm long, length decreasing from the lowermost to the uppermost. Pinnular density 9‒11 per 3 cm for both sides. Spines on pinnules conical with slightly rounded point, with four to five rows of spines visible in lateral view. Polypar spines 0.29‒0.58 mm high and abpolypar spines 0.06‒0.24 mm high. Polyps about 4–6 mm in transverse diameter, with 1 or 2 polyps per cm.

Description of holotype. Colony was reddish brown in situ and became yellowish brown after being preserved in alcohol ( Fig. 2 ). The holotype is about 19 cm high and 39.3 cm wide, with the holdfast about 0.6 - 1.1 cm in diameter. The lower unpinnulated section of stem is about 9 cm in length and the stem diameter is about 1.9 mm near the basal plate. Stem curved to abpolypar side. Pinnules arranged bilaterally and alternately along stem. Pinnules elongated, curved to abpolypar side. The length of pinnules ranges from 5.8 cm to 19.1 cm, decreasing from the lowermost to the uppermost of corallum ( Fig. 3 ). The distance between adjacent pinnules on the same side is 4‒6 mm, increasing from the bottom to apex of corallum, about 9‒11 per 3 cm for both sides. The distal angle between pinnules and stem ranges from 60° at lower part of stem to 70° at upper part. The internal angle between two lateral rows of pinnules varies from 110° at lower part of stem to 140° at upper part.

Spines on pinnules are simple, smooth, conical with blunt apex, and nearly perpendicular to the axis ( Fig. 4 ). On the middle part of the pinnules, the polypar spines are 0.29‒0.58 (0.44±0.06, n=20) mm high and 0.50‒0.79 (0.66±0.09, n=20) mm wide at the base, and the abpolypar spines are 0.06‒0.24 (0.12±0.05, n=20) mm high and 0.25‒0.58 (0.43±0.09, n=20) mm wide at the base. On the basal part of the pinnules, the polypar spines are 0.20‒0.50 mm high and the abpolypar spines are 0.04‒0.27 mm high. Along the distal parts of the pinnules, the polypar spines are 0.22‒0.58 mm high, and the abpolypar spines are 0.06‒0.21 mm high. Spines are arranged in 4‒5 longitudinal rows in lateral view. There are usually four rows of larger polypar spines and two rows of smaller abpolypar spines. The distance between adjacent spines of the same row is 0.61‒1.81 mm, about 1‒2 spines per millimeters. Spines on middle and distal part of stem are simple, smooth, and conical with blunt apex ( Fig. 5 ). Few spines on lower part of unpinnulated stem ( Fig. 5A ). Spines on middle stem are 0.04‒0.06 mm high and 0.14–0.28 mm wide at the base. Spines are arranged in 5–6 rows in lateral view, 0.05‒0.10 mm high and 0.17–0.36 mm wide at base on upper part of stem. Polyps are in poor preservation, about 4–6 mm in transverse diameter, and 1 or 2 polyps per centimeter.

Type locality. Kocebu Guyot in the Magellan Seamount Chain in the Western Pacific Ocean with water depth of 1336 m .

Etymology. Composite of the Latin adjective longus (long) and the Latin noun spina (spine), referring to the long spines of the species, a main feature of the species.

Distribution and habitat. Found only from the Kocebu Guyot in the Magellan Seamount Chain with water depth of 1336 m, where the colony attached on rocky substrate. The water temperature was about 3.1°C and salinity about 35.8.

Remark. Alternatipathes longispina sp. nov. is placed in the genus Alternatipathes based on the alternately arranged pinnules, and the decrease in the length of pinnules to the apex of the corallum. To date, there are four species in the genus Alternatipathes : Alternatipathes alternata (Brook, 1889) , Alternatipathes bipinnata ( Opresko, 2005) , Alternatipathes mirabilis Opresko & Molodtsova, 2021 and Alternatipathes venusta Opresko & Wagner, 2020 .

Alternatipathes longispina sp. nov. is most similar to A. alternata (Brook, 1889) in possessing a monopodial and unbranched corallum and a relatively short unpinnulated lower stem ( Molodtsova & Opresko 2017). However, the new species differs from A. alternata by the much larger polypar spines (maximum height 0.58 mm vs. 0.06 mm) and a lower density of spines (1‒2 per mm vs. 4‒5 per mm) ( Molodtsova & Opresko 2017, Table 2 ). Alternatipathes longispina sp. nov. is different from the type species of the genus, A. bipinnata , by the unbranched colony (vs. branched), the very prominent polypar spines (height 0.29‒0.58 mm vs. 0.22‒0.30 mm), the relative short unpinnulated stem (ratio of the length of unpinnulated stem to the total height of stem about 0.47 vs. 0.69), and the relatively much longer pinnules (ratio of the length of the longest pinnule to the total height of corallum 1.0 vs. 0.07) ( Opresko 2005, Table 2 ). Alternatipathes longispina sp. nov. is distinguished from A. venusta and A. mirabilis by the larger polypar spines (height 0.29‒0.58 mm vs. 0.11‒0.22 mm and 0.04–0.06 mm, respectively), the relative short unpinnulated stem (ratio of the length of unpinnulated stem to the total height of stem about 0.47 vs. 0.70 in the latter two species), and the relatively much longer pinnules (ratio of the length of the longest pinnule to the total height of corallum 1.0 vs. 0.23 and 0.32, respectively) ( Opresko & Wagner 2020, Opresko & Molodtsova 2021). In addition, the new species also differs from A. venusta by the larger distance between adjacent spines (0.61–1.81 mm vs. 0.2–0.46 mm, Table 2 ).

Figures

FIGURE 2. The external morphology of Alternatipathes longispina sp. nov. A. The holotype in situ. Laser dots were spaced at 33 cm for measuring dimension. B, C. The holotype after collection in different view. D. Arrow points indicate the prominent spines on pinnules. Scale bar: 10 cm (B); 5 cm (C).

FIGURE 3. Variation of left and right pinnule length (holotype) from the lower section of stem to the upper section, viewing from the polypar side.

FIGURE 4. The spines on pinnules of Alternatipathes longispina sp. nov. A, B. Spines on the middle part of pinnules. C, D. Spines on the distal part of pinnules. E. An abpolypar spine with the measured minimum height of 0.04 mm. F. A polypar spine with the measured maximum height of 0.58 mm. G. An abpolypar spine with the height of 0.08 mm. H. A polypar spine with the height of 0.45 mm. Scale bars: 1 mm (A–D in the same scale); 0.1 mm (E, G in the same scale) 0.2 mm (F, H in the same scale).

FIGURE 5. The spines on stem of Alternatipathes longispina sp. nov. A. Spines on the lower part of stem. B, D, E. Spines on the middle part of stem. C. Spines on the upper part of stem. Scale bars: 1 mm (A–C in the same scale); 0.1 mm (D, E in the same scale).