Neoanthomastus longistylus Li & Xu, 2025

Li, Xinlong, Xu, Ningxia, Ge, Meiling, Hu, Xuying, Li, Mengna, Wang, Zongling, Zhang, Xuelei & Xu, Qinzeng, 2025, Morphology and phylogeny of two new species of deep-sea mushroom soft corals (Octocorallia, Corallidae, Anthomastinae) from the Southern Mid-Atlantic Ridge, Zoosystematics and Evolution 101 (4), pp. 2103-2121 : 2103-2121

Neoanthomastus longistylus Li & Xu sp. nov.

Figs 2 , 3 , 4 , 5

Material examined.

Holotype • FIO-ATL 83 - JLBEN 26604 , collected by Qinzeng Xu using the HOV Jiaolong from the R/V Shenhai Yihao on 14 February 2024 at station JL 266 ( 22°59'2"S, 13°32'14"W), Southern Mid-Atlantic Ridge, at a depth of 1,860 m .

Paratypes • Two specimens (FIO-ATL 83 - JLBEN 26602 , part of a colony; FIO-ATL 83 - JLBEN 26603 ), same station as for holotype • Two specimens (FIO-ATL 83 - JLBEN 26704 ; FIO-ATL 83 - JLBEN 26705 , part of a colony), collected with the same vessel, gear, and by the same collectors as the holotype, on 15 February 2024 at station JL 267 ( 22°58'56"S, 13°29'50"W), Southern Mid-Atlantic Ridge, at a depth of 2,150 m .

Diagnosis.

Mushroom-shaped, capitate colony with a spherical capitulum separated from a cylindrical stalk. Stalk is long, typically at least three times longer than its maximum width, and approximately 2.5 times longer than the capitulum. Autozooids are large, retractile but not completely retracted. Siphonozooids are red, small, visible, and distributed across the surface of the capitulum and restricted to the upper 1 / 3 of the stalk. Sclerites include rods, clubs, spindles, multiradiates, and crosses; sclerite density on the capitulum surface, tentacles, and pharynx is abundant. Sclerites from the interior of the capitulum are absent. Anthocodial walls contain both curved rods and clubs. Pharyngeal sclerites are rodlets and crosses. Tentacular sclerites consist exclusively of straight rods and rods with one end unilaterally curved, lacking spindles and multiradiates.

Description of holotype.

Colony form and size. The specimen FIO-ATL 83 - JLBEN 26604 is a mushroom-shaped, capitate colony with a spheroidal capitulum supported by a conspicuous stalk (Fig. 1 B ). The capitulum is 17 mm in diameter and 15 mm high. The transition between the capitulum and the stalk is smooth. The conspicuous, longitudinally striated stalk is long ( 45 mm in height, 75 % of the colony), soft, and gradually tapers toward the capitulum ( 6 mm in diameter), while the base of the stalk is thicker ( 14 mm in diameter). In life, the specimen was attached to stone (Fig. 1 B ).

Polyps. The polyps are dimorphic. 28 autozooids are evenly arranged on the capitulum, retractile but not completely retracted. Upon retraction, the tentacles first contract into a spherical shape, followed by the autozooids retracting into the capitulum, leaving a protrusion on the surface of the capitulum. The largest autozooid has a diameter of 5 mm and a length of 33 mm, including the tentacles. The tentacles reach up to 12 mm with mostly 14–18 pairs of pinnules. The longest pinnules are located at the distal third of the tentacles. Siphonozooids are distributed on the capitulum and the upper third of the stalk, visible as red protrusions, and are usually 0.4–0.6 mm wide, spaced 0.15–0.6 mm apart (Fig. 1 D ).

Sclerites. Tentacular sclerites (Fig. 2 A ) are exclusively composed of rods, including straight rods ( 0.17–0.35 mm long) and rods with one end curved ( 0.18–0.34 mm long). Pharyngeal sclerites (Fig. 2 B ) are mostly rodlets ( 0.06–0.09 mm long) and a few crosses. Anthocodial sclerites (Fig. 3 A ) are straight rods ( 0.16–0.36 mm long), rods with one end curved ( 0.16–0.37 mm long), and a few clubs ( 0.18–0.25 mm long). Sclerites from the surface of capitulum (Fig. 3 B ) are straight rods ( 0.31–0.35 mm long), rods with one end curved ( 0.23–0.30 mm long), prominent tuberculated spindles ( 0.17–0.24 mm long), prominent tuberculated clubs ( 0.18–0.23 mm long), and multiradiates ( 0.12–0.15 mm long). Sclerites from surface of the stalk (Fig. 4 A ) are mostly multiradiates ( 0.11–0.14 mm long), a few rods ( 0.31–0.34 mm long), and prominent tuberculated spindles ( 0.15–0.28 mm long). Sclerites from interior of the stalk (Fig. 4 B ) are mostly rods ( 0.15–0.23 mm long) and a few rods with a short transverse axis ( 0.18–0.20 mm long). Sclerites of the holdfast (Fig. 4 C ) are rods ( 0.23–0.31 mm long), multiradiates ( 0.12–0.15 mm long), prominent tuberculated spindles ( 0.15–0.25 mm long), a few rods with a short transverse axis ( 0.22–0.27 mm long), and crosses. Sclerites from the interior of the capitulum are absent.

Color. In alcohol, both the capitulum and the stalk appear red, with the stalk being slightly lighter in color than the capitulum. The tentacle tips and pinnules are pale yellow, and the sclerites are red.

Variation. Paratype FIO-ATL 83 - JLBEN 26602 is large, measuring 120 mm in total height, with a stalk height of 95 mm and bearing 28 autozooids. Paratype FIO-ATL 83 - JLBEN 26603 is attached to a dead coral branch, with a total height of 50 mm. The stalk measures 35 mm, approximately twice the height of the capitulum, and bears 12 autozooids. FIO-ATL 83 - JLBEN 26704 measures 75 mm in total height, with a stalk height of 55 mm and bears 18 autozooids. FIO-ATL 83 - JLBEN 26705 has a total height of 90 mm, with a stalk height of 72 mm and a relatively small capitulum ( 18 mm) bearing 9 autozooids.

Etymology.

The specific name longistylus refers to the long stalk, one of the characteristics of this species.

Distribution and habitat.

Known only from the Southern Mid-Atlantic Ridge, 1,860 –2,151 m.

Remarks.

N. longistylus sp. nov. has siphonozooids distributed across the capitulum’s surface and extending onto the stalk, with pharyngeal sclerites that are mostly rodlets. These characteristics distinguish it from other genera in the subfamily, placing it within the genus Neoanthomastus .

N. longistylus sp. nov. resembles N. giganteus in having an elongated stalk, siphonozooids scattered on the upper 1 / 3 of stalk. However, their sclerite characteristics differ. N. longistylus sp. nov. has abundant sclerites on its tentacles, pharynx, and capitulum surface, in contrast to N. giganteus (Tixier-Durivault, 1954) , which has sparse sclerites. The autozooid tentacles of N. longistylus sp. nov. contain unilaterally curved rods, and its anthocodial walls have both curved rods and clubs, features absent in N. giganteus . The surface of N. longistylus sp. nov. lacks the spiny dumbbells found on N. giganteus . In addition, N. longistylus sp. nov. colonies are soft and mostly curved, while N. giganteus colonies are rigid.

Beyond N. giganteus , the new species is also clearly separated from all other members of the genus. It is distinguished from N. purpureus and N. hicksoni by possessing a distinctly elongated stalk (at least three times longer than wide), as opposed to their short stalks. Furthermore, N. longistylus sp. nov. differs from N. stellatus , N. tahinodus , and N. elongatus, which have siphonozooids covering the entire stalk, whereas the siphonozooids of the new species are restricted to the upper one-third.

Figures

Figure 1. Morphology of Neoanthomastus longistylus sp. nov. A – D. The holotype FIO-ATL 83 - JLBEN 26604: A. In situ view; B. Colony; C. The tentacles of autozooids, indicated by arrows; D. The siphonozooids, indicated by arrows. E – H. Paratypes showing colony morphology: E. FIO-ATL 83 - JLBEN 26602; F. FIO-ATL 83 - JLBEN 26603; G. FIO-ATL 83 - JLBEN 26704; H. FIO-ATL 83 - JLBEN 26705. Scale bars: 10 mm (B); 2 mm (C, E).

Figure 2. Sclerites of Neoanthomastus longistylus sp. nov. (FIO-ATL 83 - JLBEN 26604). A. Sclerites from autozooid tentacles; B. Sclerites from pharynx. Scale bars: 0.10 mm (A); 0.05 mm (B).

Figure 3. Sclerites of Neoanthomastus longistylus sp. nov. (FIO-ATL 83 - JLBEN 26604). A. Sclerites from anthocodial wall; B. Sclerites from surface of capitulum. Scale bars: 0.10 mm.

Figure 4. Sclerites of Neoanthomastus longistylus sp. nov. (FIO-ATL 83 - JLBEN 26604). A. Sclerites from surface of stalk; B. Sclerites from interior of stalk; C. Sclerites from holdfast. Scale bars: 0.10 mm.

Figure 5. Morphological observation of Anthomastus mirabilis sp. nov. A – D. The holotype FIO-ATL 83 - JLBEN 27711: A. In situ view; B. Colony; C. Autozooids; D. the longitudinal section of capitulum, showing siphonozooids (arrows). E – H. Paratypes: FIO-ATL 83 - JLBEN 27712 in situ (E) and in preservation (F); FIO-ATL 83 - JLBEN 27713 in situ (G) and in preservation (H). Scale bars: 10 mm (B, D, F, H); 5 mm (C).