Granulogorgia amoebosquama Tang, Alderslade & Xu, 2025

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

( Figs. 2‒9 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 , Table 1 View TABLE 1 )

urn:lsid:zoobank.org:act:F9B3D4A2-CCDE-476C-962C-FA698DB7B2E1

Material examined. Holotype: MBM287322 View Materials , M6 Seamount; stn. FX-Dive 217; 140°14′46″E, 10°06′52″N; depth of 946 m; 5 June 2019 GoogleMaps . Paratype: MBM287323 View Materials ; same seamount; stn. FX-Dive 218; 140°14′21″E, 10°07′22″N; depth of 925 m; 6 June 2019 GoogleMaps .

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 View FIGURE 2 ). 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 View FIGURE 2 ). 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 View FIGURE 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 View FIGURE 3 ). Polyp armature is arranged as a collaret and points ( Fig. 3E‒G View FIGURE 3 ) 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 View FIGURE 3 ), while on other polyps some collaret sclerites become obliquely angled and become merged with the point sclerites ( Fig. 3E View FIGURE 3 ).

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 View FIGURE 3 ). 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 View FIGURE 4 ), 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 View FIGURE 4 ). 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 View FIGURE 4 ) and measure 0.08‒0.27 mm long and 0.02‒0.06 mm wide. Mostly they are longitudinally arranged ( Fig. 3H View FIGURE 3 ) 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 View FIGURE 3 , 4B View FIGURE 4 ).

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 View FIGURE 3 ). 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 View FIGURE 5 , 6A View FIGURE 6 ). 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 View FIGURE 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 View FIGURE 7 ); the irregular branched forms are 0.13‒ 0. 30 mm long and 0.06‒0.20 mm wide ( Fig. 7B View FIGURE 7 ). 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 View FIGURE 8 ). 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 View FIGURE 8 ).

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 View FIGURE 2 , 8A View FIGURE 8 ), becoming brown after fixation in ethanol, but appearing whitish due to the sclerites covering the surface ( Figs. 3A, B View FIGURE 3 , 8C View FIGURE 8 ).

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 calyx with the polyp head, and armature (his “crown”), visible and sitting on the calyx rim, and he states that, “The spicules of the crown of the polyp are straight or curved spindles”. His detailed description of the polyp “crown” concludes with, “The spindles forming the ring also overlap one another, but not to such an extent as those in the triangular areas. There appear to be about ten spicules at any one place in this ring, enumerating in a proximo-distal direction”. This is a description of that portion of the polyp armature referred to in modern literature as the collaret. He further states that, “Distally to this ring, spicules of another form are situated on the polyp wall. These are very protuberant, and stand more or less in a vertical direction. These spicules are “ Blattkeulen ” and pass over basally into small spicules of the same general form as those of the general surface of the coenenchyme namely “ Kalkkörper ”. “ Blattkeulen ” are calicular sclerites, so Thomson’s description only makes sense if reworded, for example, as follows, “ Proximal to this ring, spicules of another form are situated on the verrucal wall. These are very protuberant, and stand more or less in a vertical direction. These spicules are “ Blattkeulen ” and pass over basally into small spicules of the same general form as those of the general surface of the coenenchyma namely “ Kalkkörper ”. In fact, his statement, “The spicules of the lower part of the polyp [read verruca] differ, as a rule, in shape from those of the upper crown. Many of the spicules from this part are “ Blattkeulen ”, would seem to confirms that his intention was as suggested above.

Any proposed close relationship between M. fusca and G. amoebosquama gen. et sp. nov. can be eliminated by looking at Thomson’s sclerite illustrations. His Plate 44, Fig.4b View FIGURE 4 represents three sclerites from the calyx (“lower polyp”). One of these, when reoriented, clearly depicts a “Blattkeulen” ( Fig 6B View FIGURE 6 ). None of the sclerites in the group are the same as the calyx sclerites of G. amoebosquama gen. et sp. nov. The sclerites in Thomson’s Fig.4a View FIGURE 4 are from the polyp, and they also are quite different to those of G. amoebosquama gen. et sp. nov. Figure 4c View FIGURE 4 represents sclerites from the coenenchyme and although they show a small resemblance to the sclerites of G. amoebosquama gen. et sp. nov., they are not the same.

Placogorgia dentata Nutting, 1910 View in CoL has irregularly lobed plates or scales (“discs”) in the calyces and therefore has similarities to Granulogorgia amoebosquama gen. et sp. nov. But Nutting described the scales as having “One edge of each is exposed on the surface of the calyces, and the other is embedded in the coenenchyma of the walls” and that “The margin is surrounded by a circlet of rather prominent blunt points.” He also stated that “The coenenchyme of the stem and branches is filled with similar spicules…There are few, if any, regular spindles except those forming the opercula”. Tixier-Durivault (1972: 45) identified a specimen from the Island of Europa off Mozambique as P. dentata View in CoL but provided no description other than a figure of some irregularly lobed scales that look different to those depicted by Nutting (1910: pl. XXII, Fig. 10), so it remains uncertain if the specimens are the same species.

Tixier-Durivault did not state from what part of the colony the figured scales came from, but they are very similar to those in the calyces Granulogorgia amoebosquama gen. et sp. nov.: some have a number of large warts and others are much smoother. However, the fact that Tixier-Durivault’s figure contained only lobed scales conforms to Nutting’s statement that, except for the polyps, the sclerites in his material were virtually only “discs”, indicating that Tixier-Durivault’s specimen may at least have represented the same genus as Nutting’s material. Placogorgia View in CoL , however, is defined as having well developed thornscales in the calyces and spindles with or without spines in the coenenchyme, and Placogorgia dentata View in CoL clearly does not belong in that genus. Regarding Granulogorgia amoebosquama gen. et sp. nov., the sclerites in Tixier-Durivault’s figure look very similar to those of the new species. But G. amoebosquama gen. et sp. nov., can be distinguished from both Tixier-Durivault’s and Nutting’s material as it only has scales in the calyx, and the polyp armature is relatively complex and consists of numerous sclerites, whereas Nutting reported for P. dentata View in CoL that, “The operculum is elevated and composed of two long, bent, longitudinal spindles on the dorsal surface of each tentacle, with a third shorter one between their bases.” Although the exact form of the armature can vary from species to species in a genus, the general style is usually maintained.