Sympagella abysslineae Herzog & Amon & Smith & Janussen 2018, sp. nov.

Sympagella abysslineae sp. nov.

(Fig 2, Tables 1.1, 1.2)

Material examined: Holotype (unicum), SMF 12104, CS_18, ABYSSLINE Project, RV Melville, cruise MV1313, UK-1 Stratum A, Clarion-Clipperton Zone, East Pacific, 10 October 2013, 13°50.997 N, 116°38.746 W, 3952 m, fixed in 96% ethanol.

Description: The single specimen collected by ROV Remora III was in good condition and shape (Figs 2a, i). The stalk of the specimen is 47 mm long and 35 mm thick. It is comparable to a stump, and the bottom is black colored, likely from contact with the polymetallic nodule it was adhered to. The body measures 135 mm in diameter and is 10 mm thick. It has a chanterelle-like shape and is slightly damaged on the edges.

Megascleres of the gastral and dermal sides are nearly identical. Beside a wide variety of choanosomal diactin and hexactins, hypodermal and hypoatrial pentactins, as well as dermal and atrial pinular hexactins, and pinular pentactins can be found. The hexactins (Fig 2b) and pentactins (not shown) are mainly smooth, sometimes slightly spiny on the proximal or distal endings and mostly with sharp or parabolic distal tips. Pentactins generally have a long distal ray and shorter tangential rays. Sometimes the distal ray is slightly curved. Hexactins mainly have thin long-shafted rays of different lengths and are less abundant than the pentactins. Pinular hexactins (Figs 2c, d) are very abundant, as are pinular pentactins (Fig 2e). In comparison, the pinular hexactins are slightly bigger than the pinular pentactins on the dermal side as well as on the gastral side. Both spicule tapes are bigger on the dermal side of the sponge. The rays, except the pinular ray, of both types have sharp pointed tips and are speckled with small spines. The pinular rays are longer than the other rays and have a tapered structure of distal pointed spines and a rounded end.

Microscleres are discohexasters and strobiloplumicomes. The discohexasters (Fig 2f) have short, smooth primary rays that split up in 3–4 long-shafted secondary rays. These bear small spines on the shaft and terminate in flat, slightly curved, star-shaped discs with 4–5 jags. Considerably smaller are the 20–25 µm-sized strobiloplumicomes (Figs 2g, h). These also have short smooth rays that terminate in a wreath with four rows of long, sigmoidal protruding hairs with tiny spines on the inner concave surface of their distal halves (similar to the ones described by Janussen & Reiswig 2009). From the center of the wreath arises a very short smooth strobe with a rounded tip. Whereas discohexasters are abundant, strobiloplumicomes are rare and difficult to measure because they are very fragile and often broken. Also because of their ability to ‘grasp’ other spicules' rays with the grappling hook-like hairs, they are mainly found in bunches of discohexasters and other strobiloplumicomes, which makes it even harder to measure them.

Remarks: The specimen clearly belongs to the genus Sympagella even though its mushroom-like appearance and the presence of atrial pinular pentactins suggest an affiliation to the genus Caulophacus. This is confirmed by the presence of strobiloplumicomes and the lack of discohexactins, which is a characteristic spicule type most representatives of the genus Caulophacus possess. The sponge is considered to be new to science for several reasons: Besides the fact that there are so far no known Sympagella species reported from the CCZ, only S. cantharellus (Lendenfeld, 1915) has a mushroom-like shape. Most of the species in the genus Sympagella show funnel-like, elliptical or saccular shapes. Our specimen differs from S. cantharellus by the presence of discohexasters. Also, discohexasters and strobiloplumicomes are the only microscleres in our specimen, whereas most of the other species of Sympagella have more than two types of microscleres, including onychohexasters or oxyhexasters.

Derivatio nominis: The specimen is named after the ABYSSLINE Project, during which it was collected.