Parajasonisis flabellata Xu, Watling & Xu 2024, sp. nov.

Parajasonisis flabellata Xu, Watling & Xu, sp. nov. urn:lsid:zoobank.org:act: 103C2F69-7481-455D-A380-8B8ECDDD0D8B Figs. 5–9 Material examined. Holotype: MBM287336, station FX-Dive 172 (17.3886°N, 153.0908°E), 1357 m, 1 April 2018. Paratype: MBM287337, station FX-Dive 175 (17.3317°N, 153.2147°E), 1670 m, 9 April 2018; MBM287338, station FX-Dive 175 (17.3350°N, 153.2103°E), 1430 m, 9 April 2018. They were all collected from the Kocebu Guyot on the Magellan Seamounts during the cruise of the R/V KeXue. Diagnosis. With the characters of the genus. Description. Colony. Holotype planar and flabellate with the holdfast not recovered, about 62 cm long and 68 cm wide in maximum extent (Fig. 5E). Colonial color pink in situ and became brown after collection, with the deepest color occurring on the distal part of the polyps, and the color not changed after fixation in ethanol. Surface of the colony is almost completely covered with a layer of thick and brown tegument. Main stem calcareous and solid, about 2 cm in diameter at base. Branches usually irregularly and pseudo-dichotomously branched from the nodes and in one plane, arising at less than 90º and tracing a distinct upward curve to eventually follow (more-or-less) the direction of the parent branch, forming a nearly lyrate pattern. Sometimes from one node three branches emerged in one plane, rarely four, occasionally producing more bushy lateral branchlets perpendicular to the colonial plane. Terminal branches bifurcated or trifurcated, with the unbranched branchlets up to 8 cm long (Fig. 5B). Internodes up to 4 cm long, partially hollow. Nodes brown and very short, concave inward, up to 1 mm in height. Polyps. Polyps tall and narrow, forming a cylindrical shape, 2.0–6.0 mm high and 1.5–2.0 mm wide (Fig. 5C). Polyps biserially arranged and well-spaced on branches, usually alternately but sometimes irregularly, perpendicular to the axis or slightly tilted, up to 9 mm apart. Tentacles contractile and tightly folded into the hollow oral disc or gathered on the distal end of polyps (Fig. 7). Sclerites. Sclerites densely arranged in polyps and coenenchyme, nearly smooth but often covered with more or less shallow grooves (Fig. 9B, C). Elongated and thick scales to flat rodlets in the tentacle rachis are longitudinally and densely packed, often with slightly toothed to irregular edges, occasionally branched or crossed, measuring 62– 174 × 15–75 μm (Figs. 7A–C, 8A). Scales in pinnules longitudinally arranged, thick and irregular, usually with an obvious medial constriction, measuring 43–79 × 7–25 μm (Figs. 7B, 8B). In some polyps, eight or fewer long rods/ needles longitudinally arranged at the base of tentacles, extending from the upper polyp body wall and projecting beyond the contracted tentacles, occasionally covered with sparse longitudinal ridges or grooves, measuring 745– 836 × 54–73 μm (Figs. 5C, D; 6E; 8D). The ends of these needles/rods usually pointed and sharp, some of them nearly round with shallow grooves. Flat rods/needles in the upper polyp body wall longitudinally or obliquely arranged, slender, some of them with irregular edges and large ridge-like projections, occasionally branched or crossed, measuring 182–736 × 23–223 (Figs. 7E, 8E). Flat rods/needles and elongate thick scales in the basal polyp body wall usually transversely arranged, some of them with irregular edges or a slightly medial constriction, occasionally became broad and stout, and with large warts on surface, measuring 123–682 × 27–214 μm (Figs. 7E, F; 8F). Sclerites in coenenchyme same as the basal polyp body wall, densely arranged along the branch, usually with a slightly medial constriction, some of them branched with irregular shape, measuring 75–726 × 23–178 μm (Figs. 7H, 9A). Rodlets in pharynx longitudinally arranged, irregular and abundant, covered with large and blunt lateral projections, measuring 53–94 × 11–34 μm (Figs. 7G, 8C). Variability of paratype: Paratypes MBM287337 and MBM287338 both incomplete and broken after collection (Fig. 6C). Internodes of MBM287337 up to 6 cm with its polyps occasionally up to 8 mm in height and 3 mm in width. Internodes of MBM287338 up to 6.5 cm and its unbranched terminal branchlets up to 20 cm long. Type locality: Kocebu Guyot on the Magellan Seamounts, 1357 m. Etymology: The Latin adjective flabellatus (flabellate) refers to the flabellate and planar external colony of this species. Genetic data: MBM287336, 28S rDNA: PP992072, cox1: PP991392, mtMutS: PP999495; MBM287337, 28S rDNA: PP992073, cox1: PP991393, mtMutS: PP999496. Distribution and habitat: Collected specimens from Kocebu Guyot on the Magellan Seamounts at water depths of 1357–1670 m. Colonies grow on rocky substrates with a solid disc-shaped calcareous holdfast in situ (Figs. 5A, 6A). The holotype attached with an individual of Comatulida AH Clark, 1908 in situ (Fig. 5A). At the site of collection, the water temperatures were 2.41–3.07℃ and the salinity 35.79–35.80 psu. This species is relatively common across the Central Pacific seamounts as seen in images taken by Okeanos Explorer and included in the Benthic Deepwater Animal Identification Guide (https://www.ncei.noaa.gov/maps/benthic-animal-guide/) under the name Jasonisis sp., including specimen USNM 94449 from Pensacola Seamount, south of Hawaii, 1500 m. From the NW Atlantic Ocean, specimen YPM IZ-044573 collected from Abaco Island, Bahamas, at 1972 m, and specimen YPM IZ-107119 from Northeast Providence Channel, Bahamas, at 2044 m, are genetically identical (mtMutS) to the Pacific specimens and so are assumed to belong to this species as well. Remarks: Parajasonisis gen. nov. resembles with the genus Jasonisis Alderslade & McFadden, 2012 in morphology, with the latter also with only one species J. thresheri, distributed in the southwest Pacific at water depths of 521–1813 m (Alderslade & McFadden 2012). Parajasonisis flabellata sp. nov. is similar to J. thresheri Alderslade & McFadden, 2012 in branching pattern, polyps and coenenchyme with thick tegument, sclerites of tentacles and pharynx. However, it differs from J. thresheri by polyps arrangement (usually alternately and biserially arranged vs. distributed on all sides of the axis), sclerites in polyp body wall (slender and flat rods/needles and thick scales with relatively regular edges and smooth surface vs. spindles and thin scales with lobed edges and warty surface), sclerites in coenenchyme with regular edges (vs. irregular and lobed) (Alderslade & McFadden 2012).