Caulophacus (Caulophacus) miri, Tabachnick & Menshenina & Ehrlich, 2023

Caulophacus (Caulophacus) miri View in CoL sp.n.

Figs 19 View Fig , 20 View Fig .

MATERIAL. HOLOTYPE. IORAS 5/2/2054. RV ‘ Akademik Mstislav Keldysh’ – 22, sta. 2296, HOV ‘Mir-1’, Pacific side of Bering Island, 54°57.7′ N 165°42.85′ E, 5952 m. GoogleMaps

DESCRIPTION. BODY. The specimen is fungus-like with a discoidal ovoid body 140x 190 mm and 20 mm thick, the edge of the disc is everted down so that the atrial surface present also on the lateral edge of the discoidal body. The tubular peduncle was broken into several pieces during collection but was 180 mm long with walls 5 mm in thickness. The upper part of the peduncle is 20x 25 mm in diameter while the lower part is about 20 mm in diameter.

SPICULES. MEGASCLERES. Choanosomal spicules are diactins and hexactins. The diactins are sometimes thick but most were thin. The thick diactins have stout shafts and rounded outer ends, they are 2–2.7/ 0.032 –0.110 mm. The thin diactins have stout shafts, sometimes with a widening in the middle or four tubercle rudiments, their outer ends are rounded, smooth or rough, they are 1.5–1.9/ 0.008 – 0.024 mm. Choanosomal hexactins have rays 0.4– 1.6/ 0.015–0.1 mm with conically pointed outer ends. Hypodermalia and hypoatrialia are pentactins with conically pointed outer ends. Tangential rays of these pentactins are 0.2–1.4 mm long, the ray direct- ed inside the body 0.1–0.8 mm long, their diameter is 0.02–0.10 mm. Specific types of large hexactins are located beneath the atrial surface, each having a shortened ray directed outside the body with rough or short spiny rounded distal ends. Sometimes this ray is lanceolate in shape, and they do not protrude over the entire atrial surface. This outwardly protruding ray is about 0.6 mm long, whereas tangential rays are 1, 3 mm long. The ray directed inside the body is about 0.8 mm long and the diameter of these rays is 0.04–0.05 mm. The diactins of the peduncle have a diameter of 0.015 –0.053 mm and are connect- ed to each other by numerous synapticular junctions.

Dermalia and atrialia are pinular hexactins, they have rounded or conically pointed outer ends, tangential rays and the ray directed inside the body are short-spiny. Some rare dermal pentactins have no pinular ray; the unpaired ray is equal in shape to other rays. Pinular ray of dermal hexacins is spherical, 0.067 –0.107 mm in diameter (n=25, avg: 0.085 mm, std: 0.011 mm), tangential rays are 0.074 –0.141 mm in diameter (n=25, avg: 0.104 mm, std: 0.016 mm), the ray directed inside the body is 0.056 –0.111 mm in diameter (n=25, avg: 0.089 mm, std: 0.015 mm), the diameter of pinular ray is 0.019 –0.033 mm at base and 0.041 –0.063 mm in maximal mediate part, the diameter of other rays is 0.015 –0.019 mm at base. The pinular ray in atrial hexactins may also be spherical but often they are elongate, often with irregular shaft having a widening some distance from the base. Pinular ray of atrial hexacins is 0.074 – 0.463 mm in diameter (n=30, avg: 0.226 mm, std: 0.135 mm), tangential rays are 0.078 –0.152 mm in diameter (n=30, avg: 0.114 mm, std: 0.018 mm), the ray directed inside the body is 0.078 –0.152 mm in diameter (n=30, avg: 0.105 mm, std: 0.014 mm), the diameter of pinular ray is 0.019 –0.026 mm at base and 0.022 –0.052 mm in maximal mediate part, the diameter of other rays is about 0.015 mm at base.

MICROSCLERES. Most microscleres are thickrayed discohexactins, but there are rare discohemihexasters and sometimes discohexasters with 2–4 secondary rays. Lophodiscohexasters with 4–12 secondary rays are common close to the dermal and atrial surfaces. Some of these spicules have stout shafts, some have some secondary rays raised from the side of the primary rays, rarely lophodiscostaurasters are found. The diameter of discohexactin is 0.089 –0.185 mm (n=27, avg: 0.135 mm, std: 0.032 mm). The thick–rayed discohexasters are 0.059 – 0.104 mm in diameter (n=9, avg: 0.078 mm, std: 0.013 mm), the diameter of the primary rosette is 0.036 –0.044 mm (n=9, avg: 0.039 mm, std: 0.003 mm). The lophodiscohexasters are 0.036 –0.101 mm in diameter (n=25, avg: 0.067 mm, std: 0.016 mm), with the diameter of their primary rosette being 0.023 –0.063 mm (n=25, avg: 0.037 mm, std: 0.010 mm).

REMARKS. In comparison to other species in this subgenus, the new species has a notable and significant difference in the sizes between dermal and atrial spicules. This feature is observed also in the type species — Caulophacus (Caulophacus) latus Schulze, 1886 (re-described later: Schulze, 1887; Tabachnick, 2002b). Unlike it, the new species has dermal hexactins with spherical shape of pinular heads; atrial hexactins with widened pinular rays and often they have irregular overall shape of the pinular ray when it is thickest at base, close to the center of the spicule. Microscleres sizes are also quite different between these species. Caulophacus (Caulophacus) latus has calycocomes or lophodiscohexasters which are extremely large. Other species of Caulophacus (Caulophacus) which also have larger pinular ray in atrial hexactins and pentactins carry short spines on this ray.

ETYMOLOGY. The species is named after the HOV ‘Mir’ which collected this specimen.

DISTRIBUTION. Currently found only off the Pacific side of Bering Island, at 5952 m depth.