Gyrophyllum hirondellei Studer, 1891

Figs 3–11

Gyrophyllum hyrondellei Studer, 1891: 94 .

Gyrophyllum hyrondellei – Studer 1901: 35. — Roule 1905: 456. — Kükenthal & Broch 1911: 394 (in text). — Kükenthal 1915 (in text): 120. — Hickson 1916: 252 (in text). — Thomson 1927: 56. — Deichmann 1936: 286. — Tixier-Durivault & d’Hondt 1974b: 1420. — Williams 1995a (in text).

Material examined

NORTH EASTERN ATLANTIC – Azores • 1 spec.; North São Miguel; 38º36.5′ N, 28º17.5′ W; depth 1260– 1258 m; 26 Nov. 1971; BIAÇORES 1971 exped.; stn.139; complete colony, 158 mm in length; MNHM OCT.A.579; MNHM. – South Rockall Slope • 1 spec.; 56º08.71′ N, 17º34.64′ W –56º07.25′ N, 17º34.89′ W; depth 997– 101 m; 29 Sep. 2020; SCOTIA 1420S; stn. S20321 #8008; complete colony, 103 mm in length; NMS.Z. 2022.1.1 - BECA (G-3832); NMS • 1 spec.; 56º08.71′ N, 17º34.64′ W –56º07.25′ N, 17º34.89′ W; depth 997– 101 m; 29 Sep. 2020; SCOTIA 1420S; stn. S20321 #8009; complete colony, 78 mm in length; NMS.Z. 2022.1.2 - BECA (G-3835); NMS • 1 spec.; 56º08.71′ N, 17º34.64′ W –56º07.25′ N, 17º34.89′ W; depth 997– 101 m; 29 Sep. 2020; SCOTIA 1420S; stn. S20322 #8010; complete colony, 110 mm in length; NMS.Z. 2022.1.3 - BECA (G-3831); NMS • 1 spec.; 56º08.83′ N, 17º29.77′ W –56º10.40′ N, 17º29.57′ W; depth 902–905 m; 29 Sep. 2020; SCOTIA 1420S; stn. S20322 #11835; 1 fragment; BECA OPEN-665 (G-3834); BECA • 1 spec.; 56º24.30′ N, 17º23.04′ W –56º22.80′ N, 17º22.72′ W; depth 761–771 m; 30 Sep. 2020; SCOTIA 1420S; stn. S20323 #8006; complete colony, 112 mm in length; BECA OPEN-660 (G-3832). – South West Rockall Slope • 1 spec.; 57º07.11′ N, 19º59.63′ W –57º04.87′ N, 20º00.47′ W; depth 1002–1009 m; 3 Oct. 2020; SCOTIA 1420S; stn. S20331 #7706; complete colony, 84 mm in length; BECA OPEN-659 (G- 3830). – West Rockall Slope • 1 spec.; 56º42.59′ N, 16º30.85′ W –56º42.31′ N, 16º37.05′ W; depth 721–792 m; 14 Apr. 2021; SCOTIA 0421S; stn. S21172 #11670; complete colony, 203 mm in length; NMS.Z. 2022.1.4 - BECA (G-4015); NMS • 1 spec.; 56º42.59′ N, 16º30.85′ W –56º42.31′ N, 16º37.05′ W; depth 721–792 m; 14Apr.2021; SCOTIA 0421S; stn. S21172 #11671;complete colony, 215 mm in length; BECA OPEN-661 (G-4016); BECA • 1 spec.; 56º42.59′ N, 16º30.85′ W –56º42.31′ N, 16º37.05′ W; depth 721–792 m; 14 Apr. 2021; SCOTIA 0421 S; stn. S21172 #11672; incomplete colony, lacking peduncle; NMS.Z. 2022.1.5 - BECA (G-4017); NMS • 1 spec.; 56º42.59′ N, 16º30.85′ W –56º42.31′ N, 16º37.05′ W; depth 721–792 m; 14 Apr. 2021; SCOTIA 0421 S; stn. S21172 #11678; complete colony, 218 mm in length; NMS.Z. 2022.1.6 -BECA (G-4018); NMS • 1 spec.; 56º42.59′ N, 16º30.85′ W –56º42.31′ N, 16º37.05′ W; depth 721–792 m; 14 Apr. 2021; SCOTIA 0421S; stn. S21172 #11801; incomplete colony, lacking peduncle; BECA OPEN-662 (G-4019); BECA. – South East Rosemary Seamount • 1 spec.; 59º05.85′ N, 09º52.94′ W –59º04.70′ N, 09º55.40′ W; depth 1051–1070 m; 10 Nov. 2021; SCOTIA 1621S; stn. S21553 #11834; complete colony, but peduncle eroded, 80 mm in length; BECA OPEN-663 (G-4095); Beca • 1 spec.; 59º05.85′ N, 09º52.94′ W –59º04.70′ N, 09º55.40′ W; depth 1051–1070 m; 10 Nov. 2021; SCOTIA 1621 S; stn. S21553 #11833; complete colony, 121 mm in length; BECA OPEN- 664 (G-4096); BECA .

Morphological description

Colonies stout and clavate, pinnate distally (Figs 3–4), up to 218 mm in length in the preserved state. Rachis in two distinct parts: distally a bilaterally symmetrical section bearing polyp leaves, and proximally a stalk of shorter length. Complete rachis is up to 110 mm in length (50.46% of overall length in the whole examined material) and up to 18 mm in width (measured at mid-length of distal rachis part, not including polyp leaves). Rachis-peduncle limit slightly prominently swollen (Figs 3–4). Peduncle up to 108 mm in length (49.54% of overall length) and up to 11 mm in width at the widest point (the limit rachis-peduncle). Rachis with up to seven fleshy polyp leaves on each side, projecting somewhat obliquely and extending ventrally upward (Fig. 3B, F). Polyp leaves placed nearly oppositely, difficult to observe in preserved and contracted state (Figs 3B, E, 4D), increasing in size along the rachis until the mid-zone to last third, then quickly decreasing in size towards the distal part. Rachis with distinctive wide dorsal (Figs 3B, E, 4C) and reduced ventral track (Figs 3F, 4B) due to accumulation of ventral portion of polyp leaves bases. Polyp leaves nearly rectangular, not triangular, maximum length ~ 30 mm, maximum width ~ 45 mm. Axis present throughout colony, X-shaped in cross section, up to 2 mm in maximum diameter at rachis-peduncle limit, becoming progressively asymmetric with age (Fig. 5A– B). Autozooids numerous, up to approximately 45–50 in the largest polyp leaves, arranged in one or two (three?) indistinct rows (Figs 3C, F, 4B, 6A–D) appearing at different levels near the atutozooid apertures along ventral edge of polyp leaf. Anthocodiae up to 3.4 mm in length (excluding tentacles) and 2.4 mm in width, completely retractile into spiculiferous, and not-always evident ‘calyces’ usually equipped with one prominent lateral blunt to pointed process (BPP hereinafter) up to 3.4 mm in length (not always present or well developed even in the same polyp leaf, see Discussion) (Figs 3C, F, 4B, 7A). Along ventral edge of polyp leaves, autozooids and spiculiferous BPPs alternate (Fig. 7). Tentacles of autozooid up to 3.5 mm in length in preserved state, with two kinds of processes, standard pinnules arranged in two lateral series (Figs 8F, 9C), and numerous filiform structures only present along the oral axial surface (Figs 8C, E–H, 9A–C). Siphonozooids minute, 0.32–0.55 mm in diameter (average 0.46 mm, N = 20), numerous, scattered on the lateral (actually proximal and distal) sides of polyp leaves (Fig. 6E), and rachis dorsal track (more difficult to detect).

Sclerites differentially distributed in various parts of colony: densely placed in rachis, including polyp leaves, calycular BPP (Fig. 6D), and along dorsal and ventral tracks, around openings of siphonozooids (Fig. 6E), along abaxial side of tentacular axis of autozooids (Fig. 8G–H); however, much more scattered on body of autozooids (Fig. 8C–D). Sclerites present in a reticular manner on polyp leaves, observable not only on surface (Fig. 6E) but also internally. Walls between consecutive autozooids thinner than outer surrounding wall (Fig. 8A–B). Similar reticular structures visible at rachis-peduncle limit (Fig. 6F) and on penduncle. Sclerites absent in pinnules (including filiform processes), polyp body, and pharynx. No minute bodies observed in peduncle.

Sclerites from polyp body and tentacular axis as blunt tree-flanged rods up to 0.25 mm and 0.31 mm in length, respectively (Figs 8C–D, 10A). Sclerites from polyp leaves (including those surrounding siphonozooids), calycular BPPs, rachis and peduncle as elongated three-flanged rods. Those from polyp leaves up to 0.52 mm in length (Fig. 10B). Sclerites from calycular BPPs up to 0.48 mm (Fig. 10C). Sclerites from exterior surface of rachis up to 0.44 mm in length (Fig. 10D). Sclerites from inner rachis up to 0.48 mm in length (Fig. 11A). Sclerites from surface of peduncle up to 0.36 mm in length (Fig. 11B). Sclerites from inner peduncle up to 0.35 mm in length (Fig. 11C).

Colour

Freshly collected colonies were light brown at peduncle, rachis stalk and the section of rachis bearing polyp leaves dorsally, but darker brown on surfaces of polyps and calycular BPPs with the sclerites visible as whitish trabecular structures. The autozooids themselves were dark brown. Preserved colonies are whitish to light brown (Figs 3–4) while all sclerites are colourless.

Geographical and depth distribution

At present, Gyrophyllum hirondellei is known from the North Atlantic, from Rosemary Seamount and Rockall and Hatton Banks to Azores and Bahamas, over a bathymetric range of 721–2220 m depth, the shallower records being those in reported in this paper (see Table 1) (Studer 1891; 1901; Roule 1905; Deichmann 1936; Tixier-Durivault & d’Hondt 1974b; present account).