Pseudopterogorgia nanjiensis Sun, Xu & Zhan 2024, sp. nov.

Pseudopterogorgia nanjiensis Sun, Xu & Zhan sp. nov. Figs 2, 3, Table 2 Material examined. Holotype: MBM 287893, China-Zhejiang Prov. • Nanji Islands; 27 ° 28.53 ' N, 121 ° 08.13 ' E; 11 May 2023. Paratype: MBM 287892, China-Zhejiang Prov. • Nanji Islands; 27 ° 28.53 ' N, 121 ° 08.13 ' E; 14 m; 11 May 2022. Diagnosis. Colony non-pinnate and purplish. Branches divided dichotomously and irregularly, nearly in one plane. Polyp retracted and forming a small and oval-shaped protrusion. Sclerites in polyps small flat rodlets, colorless and rare to absent in numbers. Sclerites in coenenchyme red, mostly capstans, a few radiates and warty spindles, and rare scaphoids. Capstans have two whorls of tubercles and blunt ends with irregular arrangements of complex tubercles. Radiates and immature sclerites with two whorls of projections, spindles with 4–8 whorls of tubercles, and scaphoids with similar ornamentation of tubercles on both convex and concave sides. Description. Holotype upright and nearly planar but not pinnate, about 70 mm in length (Fig. 2 B). Holdfast nearly round, about 8 mm long and 7 mm wide at maximum. Trunk cylindrical, about 3 mm in length before first branch and 2 mm in diameter at base, divided into two primary stems, one with three secondary branches and the other with five secondary branches. Branches divided dichotomously and irregularly, nearly in one plane (Fig. 2 D). Distances between adjacent branches up to 20 mm. Branches usually cylindrical in the proximal part of the colony, and became flattened in the distal part of the colony. Terminal branchlets slender and a little curved, typically measuring 20–60 mm in length and 1–2 mm in width. Polyp retracted, forming small and oval-shaped protrusions with a recessed orifice (Fig. 2 E), measuring on average 1.00 mm in length and 0.65 mm in width. Each polyp’s orifice appears as a tiny and pale yellowish slit aligned lengthwise. Polyps usually closely and irregularly spaced on the branches and sparse at the basal part of the colony, some of them arranged into two opposing longitudinal rows on the terminal branchlets. Distance between polyps no more than 4 mm. Coenenchyme covered with dense sclerites, while the polyps sclerites rare to absent (Fig. 2 G, H). Sclerites in coenenchyme red with various shapes, arranged in two inconspicuous layers without a clear boundary, including abundant capstans, rare indistinct scaphoids, and occasional tuberculate spheroids and crosses in outer layers, a few radiates and warty spindles in inner layers. These sclerites range in length from 0.05 mm to 0.18 mm, but mostly less than 0.12 mm long (Figs 2 F, 3 A – E). Among them, capstans have two whorls of tubercles, up to 0.13 mm long, and blunt ends with irregular arrangements of complex tubercles (Fig. 3 A). The radiates and immature sclerites with two whorls of projections and often blunt ends, some of them covered with shallow longitudinal grooves on surface, measuring 0.05–0.09 mm (Fig. 3 B). The warty spindles with 4 to 8 transversely-aligned whorls of tubercles, up to 0.18 mm in length (Fig. 3 C). The scaphoids, not distinctly developed and resembling curved spindles, with 4–8 noticeable whorls of tubercles, up to 0.14 mm long (Fig. 3 D). The convex and concave sides have a similar degree of fine ornamentation on the whorls of tubercles, and there seems to be minimal variation in the tubercles between the two sides with those on the convex sides potentially being slightly shorter. Tuberculate spheroids and crosses occasionally present in coenenchyme, are up to 0.08 mm and 0.06 mm long, respectively (Fig. 3 E). Small rodlets in polyps flat and colorless, rare in numbers and only found in a few polyps, covered with sparse warts on the edges, up to 0.09 mm (Fig. 3 F). Holotype purplish in situ and after collection, and became deep purplish red after fixation. Variation of paratypes. The two specimens exhibited a high degree of morphological concordance, with discrepancies primarily noted in colony size and branching density. Paratype irregularly branched, about 140 mm in length and 90 mm in width (Fig. 2 C). The main trunk before first branch about 5 mm in length and 2 mm in diameter at base. The terminal branchlets 30–100 mm long and 1–2 mm wide. The oval-shaped protrusions formed by retracted polyps about 1.00 mm long and 0.75 mm wide. The warty spindles in coenenchyme up to 0.16 mm long. Type locality. The subtidal zone of Nanji Islands with water depth of 14 m. Etymology. Named after the type locality Nanji Islands. Distribution and habitat. Known only from the subtidal zone of the Nanji Islands on the Chinese coast of the East China Sea with a water depth of 14 m. Colony attached to a rocky substrate. The water temperature was 18 ° C and the pH was 8.13. Remarks. Given the non-uniform nature of these variations, they are treated as manifestations of intraspecific variability. Pseudopterogorgia nanjiensis sp. nov. is most similar to P. fredericki Williams & Vennam, 2001 in the irregular branching form and indistinct scaphoids, but differs by the sclerite forms and sizes (almost capstans, a few warty spindles and radiates, and rare indistinct scaphoids and small rodlets, mostly less than 0.12 mm vs. almost warty spindles and a few scaphoids, mostly more than 0.12 mm) and the purplish colony (vs. white, pink to deep rose) (Williams and Vennam 2001; Figs 2, 3, Table 2). Pseudopterogorgia nanjiensis sp. nov. is also analogous to P. formosa Nutting, 1910 in the irregular branching form, but distinct from P. formosa by the sclerite forms (capstans, spindles, radiates, and scaphoids vs. spindles, double heads, and scaphoids) (Nutting 1910; Table 2). In addition, the new species can be readily distinguished from the remaining congeners by its irregular branching form (vs. pinnate or lateral; Table 2). Genetic distance and phylogenetic analyses The new sequences were deposited in GenBank (Table 1). The alignments comprised 720, 575 and 717 nucleotide positions for the mtMutS, COI, and 28 S rDNA regions, respectively. Based on the aligned region of mtMutS, the interspecific distance of P. australiensis Ridley, 1884, P. fredericki, P. nanjiensis sp. nov. and P. rubrotincta Thomson & Henderson, 1905 ranged from zero to 0.44 %, while the intraspecific distance was zero, which was calculated from only two specimens of P. nanjiensis sp. nov. (Suppl. material 1: table S 1). The mtMutS genetic distances between P. nanjiensis sp. nov. and congeners are in the range of 0–0.28 %. For the 28 S rDNA and COI regions, only sequences of P. nanjiensis sp. nov. are currently available within the genus Pseudopterogorgia, and no genetic variation was detected between the two specimens analyzed (Suppl. material 1: tables S 2, S 3). The genetic distances between Pseudopterogorgia and other genera of Gorgoniidae are greater than 5.48 % for mtMutS, 5.74 % for 28 S, and 2.04 % for COI (Suppl. material 1: tables S 1 – S 3). The Bayesian inference (BI) tree is nearly identical to the maximum likelihood (ML) tree in topology for both the mtMutS - COI and 28 S rDNA regions, and thus only the BI tree annotated with support values from both inference methods is presented (Figs 4, 5). In the mtMutS - COI trees, all the Pseudopterogorgia species formed a monophyletic clade with full node support. The new species P. nanjiensis sp. nov. clustered with the clade comprising P. fredericki and P. australiensis (Fig. 4). In the 28 S rDNA trees, P. nanjiensis sp. nov. emerged as a distinct clade, with a basal branching position within the family Gorgoniidae (Fig. 5).