Granulogorgia amoebosquama Tang, Alderslade & Xu 2025, gen. et sp. nov.

Granulogorgia amoebosquama Tang, Alderslade & Xu, gen. et sp. nov. (Figs. 2‒9, Table 1) urn:lsid:zoobank.org:act: F9B3D4A2-CCDE-476C-962C-FA698DB7B2E1 Material examined. Holotype: MBM287322, M6 Seamount; stn. FX-Dive 217; 140°14′46″E, 10°06′52″N; depth of 946 m; 5 June 2019. Paratype: MBM287323; same seamount; stn. FX-Dive 218; 140°14′21″E, 10°07′22″N; depth of 925 m; 6 June 2019. Diagnosis. Colony planar with proteinaceous axis possessing a hollow, cross-chambered central core. Polyps retractile. Calyces tall, volcano-shaped, scattered on all sides or missing on back side of branches. Polyp armature is in a collaret and points arrangement formed from large, curved spindles with tall, well-spaced warts and small tubercles. Tentacles with small rods or spindles, some curved. Sclerites in calyx wall are elongate plates or scales, often tapering at one or both ends, with irregularly lobed, granulated margins. The coenenchyme contains warty rods and spindles together with irregular branched forms. Description. The holotype is planar and about 85 cm tall and 164 cm wide (Fig 2A, B). The axis is proteinaceous with a hollow cross-chambered core and arises from conical holdfast, about 12 cm long, 8 cm wide, and 4.5 cm tall (Fig. 2B). The main stem is about 2.5 cm in diameter at the base, and 4 cm long before the first branch. About 8 cm above the latter, the stem gives off a main branch, and shortly after bifurcates resulting in a colony formed of more-or-less three fans, the largest of which is about 74 cm long and 40 cm wide. Branching throughout the colony is irregularly lateral, dense, and occasionally anastomosing. The small branches arise about 7‒21 mm apart and terminal branchlets are 2‒2.5 mm in diameter and up to 70 mm long (Fig. 2). The polyp calyces are volcano-shaped, predominantly occurring on three sides of the colony, irregularly dispersed, and about 1‒5 mm apart. They are sparsely distributed on one face of the colony and along the stem and main branches. The polyps are capable of complete retraction into the calyces, but many are preserved partially exsert with the polyp head, 0.6‒1.4 mm in height and 0.9‒2.0 mm in diameter, sitting atop the calyx rim (Fig. 3A‒F). Polyp armature is arranged as a collaret and points (Fig. 3E‒G) and is formed from large, curved spindles. Below the base of a tentacle, the collaret sclerites may form a triangle with the neighboring proximal chevron-arranged point sclerites (Fig. 3G), while on other polyps some collaret sclerites become obliquely angled and become merged with the point sclerites (Fig. 3E). The point sclerites distal to the triangular group are mostly smaller and form a longitudinal row that extends to the tentacle base. In each octant the number of collaret sclerites varies from about 3‒6; 2 rows of 1‒3 sclerites form the sides of a points triangle; and there are about 5 point sclerites in the longitudinal row distal to this (Fig 3G). The spindles in the collaret and points are curved to various degrees and occasionally branched, some become flattened and widened in the central part. Those in the points measure 0.24‒0.68 mm long and 0.04‒0.13 mm wide, and may have a smooth or granulated proximal tip (Fig. 4C), while those in the collaret are 0.28‒0.68 mm long and 0.03‒0.10 mm wide and often have a smooth or granule-ornamented tip at each end (Fig. 4D). The sclerites are ornamented with large, well-spaced warts and smaller tubercles. The polyp neck below the collaret is devoid of sclerites, as is the pharynx. The tentacle rachis contains small rods or spindles. They are ornamented with large, well-spaced warts and smaller tubercles (Fig. 4A) and measure 0.08‒0.27 mm long and 0.02‒0.06 mm wide. Mostly they are longitudinally arranged (Fig. 3H) but they can be en chevron in the distal end. Most pinnules lack sclerites; however, in a few pinnules, a single rod or scale, 0.10‒0.13 mm long and 0.02‒0.03 mm wide, is occasionally present, aligned longitudinally along the pinnule. (Figs 3I, 4B). The calyces are 0.6‒1.4 mm tall and 1.0‒ 1.7 mm in diameter at the base with eight, low, longitudinal ridges in the wall formed by accumulations of longitudinally arranged sclerites (Fig. 3A‒F). The sclerites are elongate plates or scales, 0.22‒0.63 mm long and 0.05‒0.19 mm wide, and both have irregular lobed edges. The scales are thinner and smoother than the plates, which have large warts ornamented with numerous short granules. The lobes on the scales and plates are also ornamented with granules (Figs. 5A, 6A). Some of the calicular sclerites taper distally and slightly resemble thornscales, but lack any differentiation into a basal root and a distal thorn-like process, lack a palisade-like arrangement, and they do not protrude from the calyx rim or wall. Other calyx sclerites taper at both ends and others are rather blunt. The thin coenenchyme contains spindles, sometimes with lateral processes, and irregular branched forms (Fig. 7). The sclerites are ornamented with large, well-spaced warts of various sizes, and the ends of the spindles and the rays of the branched forms are usually ornamented with granules. The spindles are 0.12‒ 0. 36 mm long and 0.05‒ 0.09 mm wide (Fig. 7A); the irregular branched forms are 0.13‒ 0. 30 mm long and 0.06‒0.20 mm wide (Fig. 7B). Elongated plates similar to those found in the calyces can occasionally be observed near the tips of the branchlets. Variability. The two main stems of the paratype were separated during collection, and both are planar. One is about 90 cm long and 82 cm wide, and the other is about 80 cm long and 50 cm wide (Fig. 8A, B). The paratype has the same branching pattern and sclerites as the holotype, but differs by having calyces distributed on all sides of the branches (Fig. 8C). Etymology. “ amoebo ” is in reference to the somewhat amoeboid outline of the calicular sclerites, combined with the Latin word for a scale: squama. Distribution and Habitat. Found only on the M6 Seamount on the Caroline Ridge in the western Pacific Ocean at water depths of 925‒ 946 m. Colonies attached to rocky substrate and inhabited by brittle stars (species of Euryalidae), hydrozoans (species of Lafoeidae), and/or crabs (Infraorder Brachyura). The water temperature ranged from 4.1℃ to 4.7℃, and the salinity of 36.6‒36.7 ppt. Color. bright yellow in situ (Figs. 2A, 8A), becoming brown after fixation in ethanol, but appearing whitish due to the sclerites covering the surface (Figs. 3A, B, 8C). Remarks. Astromuricea fusca (Thomson, 1911) as described by Williams (1992: 211‒214) has some marked similarities to Granulogorgia amoebosquama gen. et sp. nov. The genus Astromuricea was established by Germanos (1895, 1896) with two species, A. polyclados and A. theophilasi. However, the original descriptions were inadequate, leaving the taxa poorly defined. Nevertheless, it is clear that both species described by Germanos possess well-developed thornscales (Germanos 1895, 1896), which distinguishes them from G. amoebosquama gen. et sp. nov. Most of the species subsequently assigned to the genus have since been transferred to other genera (WoRMS database, November 2024) leaving three species considered as valid and A. formosa Thomson & Rennet, 1931 as “unassessed”. Williams (1992) transferred Muriceides fusca (Thomson, 1911) to Astromuricea, but the material described is quite different from A. polyclados and A. theophilasi, and seemingly from Muriceides fusca also. Williams described the calyx sclerites of his material as thornscales and diagnosed the genus as having “Permanent calyces with thorn scales, some of which have an elongated basal root and a tuberculated or serrated head that arises obliquely”, but the calyx sclerites in his Figure 18C do not appear to show that form and are better regarded as irregularly lobed plates and they are quite different from the thornscales illustrated by Germanos (1896: Plate 12, Fig. 21). These lobed plates also occur on the coenenchyme, as depicted in Williams’ Fig. 18A. The polyp armature of Germanos’ species also differs from Williams’ material. In Germanos’ description the armature is said to consist of eight triangles, but in Williams’ material the points are formed from long rows of spindles en chevron (Williams’ Fig. 18A). Germanos (1896) illustrated the coenenchymal sclerites of his two species in his Plate 11, Fig. 20. He described the coenenchymal sclerites of A. polyclados as, “The spicula of the coenenchyme are generally glass-clear stars, double stars and double wheels, usually with four rays… The middle part of the stars is usually thickened and bears strong tubercles, which are either completely separated from one another or partially fused and arranged in a circle around the center of the trunk”, and compared those of A. theophilasi as being, “larger and usually five- or morerayed stars …the fifth ray often forms a long, drawn-out extension, and the body of the star also becomes elongated, so that one ray appears to be a continuation of the spicule body, while the other four rays are to be regarded as lateral extensions”. The derivatives of 6-radiates along with lobed plates and lack of spindles in the coenenchyme of Williams’ Astromuricea fusca, the rows of numerous en chevron spindles in the polyp armature and the shape of the lobed plates in the calyces, clearly distinguish that taxon from Thomson’s Muriceides fusca and also Granulogorgia amoebosquama gen. et sp. nov. Thomson’s (1911) description of Muriceides fusca is confusing, but it does make sense if it is assumed that the author made two errors. These are his reference to the calyces (his “verrucae”) as polyps or the polyp body, and his reference to the positional relationship of a polyp and a calyx by using of the term ‘distal’ instead of ‘proximal’. Thomson states that, “In all the better expanded polyps, the crown of spindles is very apparent”. So in reading his relevant text, it would appear that his description refers to a caly