Sarametra subtilis, Mao & Zhang & Eléaume & Zhou & Zhang & Sun & Sha & Wang, 2025

Sarametra subtilis sp. nov. ( Figs 7, 11–13)

ZooBank registration: urn:lsid:zoobank.org:act:.

Material examined: Holotype RSIOCRI0108, Northwest Pacific, 13.3520°N, 134.5292°E, depth 1807 m, 6 August 2020, collected by ROV Hailong IV. Paratypes, RSIOCRI0016, Northwest Pacific, 12.6948°N, 156.5382°E, depth 1670 m, 29 September 2017, collected by ROV Haima ; RSIOCRI0102, Northwest Pacific, 13.3316°N, 134.5094°E, depth 2097m, 3 August 2020, collected by ROV Hailong IV. RSIOCRI0253, Northwest Pacific, 12.8623°N, 157.0395°E, depth 1947 m, 19 July 2023, collected by HOV Jiaolong.

Diagnosis: A rounded, conical aboral pole on a conical centrodorsal with a height-to-diameter ratio ( H/D) ranging from 1.3 to 1.5. Two or three columns of cirrus sockets per radial area separated by weak interradial ridges. Long, fine spines webbed with tissues densely distributed on the radials and proximal brachials. P 1 7.0–10.0 mm, 11–17 pinnulars. The first pinnular of P 1 with L/W = 1.7–1.8.

Description of holotype RSIOCRI0108: Centrodorsal conical in shape, H/D = 1.4 ( 5 mm / 3.6 mm). The aboral pole rather flat. The interradial ridges weakly developed restricted to the centrodorsal periphery ( Fig. 11A). Tegmen naked, domed, with mouth central or subcentral. Surface of tegmen level at IIBr 5–6 ( Fig. 11B). Radials spiny, with a shallow U-shaped distal margin.

Cirri XLVII (functional sockets), arranged in two or three columns per radial area in basal half of centrodorsal. Each column with 3–5 functional sockets. 2–4 obsolete sockets per radial area. Fulcral bowl of cirrus sockets surrounding central lumen, with fine marginal crenulations of sockets. Cirri of 49–63 segments, 23–40 mm long. The longest cirral with L/W = 2.2. Proximal several cirrals cylindrical with distinctly concave aboral margins. c 1–4 are very short, measuring twice as wide as long ( Fig. 11F). c 5–7 are the longest. The following cirrals become shorter, with distal cirrals wider than long. Few cirri with opposing spine. The terminal claw is tapered and exhibits a weak curvature.

Basals visible from each interradius. The radials are short with spines. Arms 10, all broken. IBr 1 short, W = 2.6 mm, L = 0.7– 1.0 mm, W/L = 2.6. The distal margin of IBr 1 is longer than the proximal margin. Distal margin of IBr 1 slightly raised from the axillary. Axillary (IBr 2) rhombic in shape, W/L = 1.1 (3.0 mm/ 2.8 mm). The proximolateral and distal margins are slightly concave. IIBr 1 short, W = 1.8–2.0 mm, L = 0.7–0.8 mm, W/L = 2.5–2.8. Distal margin V-shaped, longer than proximal margin, IIBr 2 cuneate, W = 1.9–2.2 mm, L = 1.0– 1.3 mm, W/L = 1.5–2.0.

Syzygies at IIBr 3+ 4, IIBr 9+ 10 and IIBr 14 +15 (or IIBr 15+ 16, IIBr 17 +18); subsequent interval 2–8. First syzygy W = 1.5 mm. Second syzygy W = 2.1 mm. In one case the second syzygy is at IIBr 7 +8, and the third syzygy at IIBr 10 +11, and in a second case the second syzygy at IIBr 8 +9 ( Fig. 11B). Long, fine spines webbed with tissues, densely distributed on both the proximal and distal edges of the proximal brachials ( Fig. 11B). IIBr 5–8 rectangular, with W/L ranging from 1.3 to 1.4. Middle brachials W/L = 1.3–1.5. Distal brachials W/L = 0.9–1.2. Brachials exhibit concave lateral margins and occasionally with weakly alternating articular tubercles ( Fig. 11E).

Proximal pinnulars compressed, following pinnulars gradually narrower, becoming extremely slender to tip. Pinnules 7.1– 14.0 mm in length, with 10–14 pinnulars. Pinnulars 0.9–1.2 mm in length. P 1 8.3–10.0 mm long with 15–17 pinnulars. The first pinnular of P 1 with L/W = 1.7–1.8 ( Fig. 11C). Middle pinnular of P 1 L/W = 2.7–4.0. Distal pinnular of P 1 L/W = 4.0. P 2 9.1–10.2mm long with 16 pinnulars. The following pinnules have a broad base, the first pinnular is short, and the distal pinnulars are extremely slender ( Fig. 11D). P a 5.0– 8.7 mm, 6–14 pinnulars.

Description of paratypes: RSIOCRI0016, centrodorsal H/D = 1.3 ( 5.1 mm / 3.8 mm). Cirri XLIX (functional sockets). Obsolete sockets 1–3 per radial area. Functional cirrus sockets in one or three columns per radial area. Spines conspicuous, webbed with tissues, densely distributed on proximal brachials ( Fig.12C). IBr 1 short, W/L = 3.8 (2.9/ 0.7 mm). Distal margin broadly V-shaped, longer than the proximal margin. Axillary (IBr 2) rhombic, W/L = 1.1. The proximolateral and distal margins are slightly concave. IIBr 1 short, distal margin V-shaped, longer than proximal margin. W/L = 2.8. IIBr 2 cuneate. W/L = 1.5. First syzygy at IIBr 3 +4, W = 1.8 mm. Second syzygy at IIBr 9+ 10, rectangle-shaped, W = 1.7–2.1 mm. IIBr 5–8 square-shaped, W/L = 1.4. Pinnule length 7.1–11.4 mm, 10–13 pinnulars. Pinnular length 0.4– 1.0 mm.P 1 7.8mm, 14 pinnulars.ThefirstpinnularofP 1 L/W = 1.8. P 2 6.7 mm, 8 pinnulars. P a 7.5 mm, 13 pinnulars.

RSIOCRI0102, centrodorsal H/D = 1.5 ( 5.9 mm / 3.8 mm). Cirri XL (functional sockets). Four to eight obsolete sockets per radial area. Cirri of 40–54 segments, 20–30 mm long. Longest cirral L/W = 2.8. Few cirri with opposing spine. IBr 1 short, W/L = 3.5 (2.1/ 0.6 mm). Distal margin broadly V-shaped, longer than the proximal margin. Axillary (IBr 2) rhombic, W/L = 1.1 (2.6/ 2.4 mm). The proximolateral and distal margins are slightly concave.IIBr 1 short, distal margin V-shaped, longer than proximal margin. W/L = 2.5. IIBr 2 cuneate. W/L = 1.4. First syzygy at IIBr 3 +4, W = 1.7 mm. Second syzygy at IIBr 9 +10, rectangle shaped, W = 1.7 mm. IIBr 5–8 square shaped, W/L = 1.4. Pinnule length 10.0– 17.6 mm, 10–20 pinnulars. Pinnular length 0.4–1.1 mm. P 1 7 mm, 11 pinnulars. The first pinnular of P 1 with L/W = 1.8. P 2 7 mm, 9 pinnulars. P

a

6.4 mm, 8 pinnulars.

RSIOCRI00253, centrodorsal H/D = 1.4 (5.0 mm/ 3.6 mm). Tegmen naked, domed, with mouth central ( Fig. 12B); surface of tegmen level with IIBr 3–4. Middle brachials W/L = 1.3. Distal brachials W/L = 1.4. Syzygies at IIBr 3 +4, IIBr 9+ 10, IIBr 14 + 15. Second syzygy appears in IIBr 11 + 12 in one arm. Cirri L (functional sockets). There are very few obsolete sockets, 2–3 per radial area. Functional cirrus sockets in two or three columns per radial area. There are spines on both the proximal and distal edges of the proximal brachials ( Fig. 12A). IBr 1 short, W/L = 2.7 (1.9/ 0.7 mm). Distal margin broadly V-shaped, longer than the proximal margin. Axillary (IBr 2) rhombic, W/L = 1.2 (2.4/ 2.1 mm). The proximolateral and distal margins are slightly concave. IIBr 1 short, distal margin V-shaped, longer than proximal margin. W/L = 2.6. IIBr

2

cuneate. W/L = 1.5. First syzygy at IIBr 3+ 4, W = 1.7 mm. Second syzygy at IIBr 9 +10, rectangle shaped, W = 1.8 mm. IIBr 5–8 square shaped, W/L = 1.1. Pinnule length 6.0– 12.3 mm, 6–15 pinnulars. Pinnular length 0.6–0.9mm. P 1 8 mm, 14 pinnulars. The first pinnular of P 1 L/W = 1.8. P 2 6.3 mm, 9 pp. The distal pinnules have oval-shaped and notably large plates ( Fig. 12D). Delicate side and covering plates present.

Ossicle morphology of RSIOCRI0016: Cirrus sockets are well separated by the weak interradial ridges. Concave fulcral stereom restricted to central bowl surrounding socket lumen; socket margins finely crenulate ( Fig. 13A). The centrodorsal ossicle exhibits a shallow depression on its edge in each interradius, designed for adhesion to the basal surface ( Fig. 13B, white arrow). The aboral pole at the centrodorsal was broken, possibly by erosion ( Fig. 13C). Basal circlet surrounding centrodorsal central cavity, with a fused rosette in the centre ( Fig. 5D), broken off during ossicle preparation ( Fig. 13D). Interradial processes of basal is broad, about as long as wide ( Fig. 13D). External end of basal pentagonal in shape, with a curved aboral margin ( Fig. 13E). The articular facet of each radial to the first brachial bears five fossae. The two adoral muscle fossae and two interarticular ligament fossae separated by a narrow ridge. Radial W = 2.0 mm with spines ( Fig. 13F). IBr 1 W = 2.8 mm with long spine ( Fig. 13G). Axillary (IBr 2) rhombic in shape, bears two articular faces distally ( Fig. 13H). In external view, axillary (IBr 2) bears long, lamellate spines densely distributed in several rows ( Fig. 13I). L = 2.8 mm, W = 3.0 mm, W/L =1.1. IIBr 1 W = 2 mm ( Fig.13J). IIBr 2 W = 2 mm with dense spines ( Fig. 13K). First syzygy IIBr 3+ 4. The syzygial articular surface on IIBr 3 has alternating radial ridges and depressions ( Fig. 13L), which are nearly circular.

Colour: Deep purple brown coloured ( Fig. 7D, E).

Etymology: The specific epithet ‘ subtilis ’ is a Latin adjective meaning ‘fine, thin, finely woven’, reflecting the long, fine spines webbed by tissues densely distributed on proximal brachials.

Distribution: Known from Weijia seamount, Roischesar Peak, Northwest Pacific. Depth range 1670–2097m. Attached to remnant coral stalk (RSIOCRI0108) or Caulophacus sponge (RSIOCRI0102, RSIOCRI0253).

Remarks: The new species Sarametra subtilis presented morphological similarities to Sarametra triserialis , the type species of the genus. In Sarametra triserialis , the P 1 measures 9.6 mm in length with 22 pinnulars, with the first segment as long as broad. P 1 of Sarametra subtilis is often longer than those in Sarametra triserialis , yet the number of pinnulars is less numerous. These differences in the P 1 dimensions, although minor, are consistent across all specimens. Furthermore, Messing and White (2001) described S. triserialis as having long, slender, webbed spines on proximal brachials. Here, webbed spines are less prominent and more or less restricted to IBr 1 and axillary ( Fig. 6F).