Echinoclathria seguama Lehnert & Stone 2020, n. sp.

Echinoclathria seguama n. sp.

(Figs. 2 & 3, Table 1)

Material examined. Holotype: ZSM20200325, intact specimen, stored in ethanol then dried (sample retained in ethanol), collected by J. Orr with a research survey bottom trawl from the FV Dominator; 4 June 2000, 145 m depth, haul station 72, Seguam Pass, central Aleutian Islands (52° 03.76’ N, 172° 33.41’ W). Water temperature = 4.3 °C. Paratype: ZSM20200326, intact specimen, stored in ethanol then dried (sample retained in ethanol), collected by K. Pearson Maslenikov with a research survey bottom trawl from the FV Dominator, 11 June 2000, 240 m depth, haul station 82, Amukta Pass, eastern Aleutian Islands (52° 23.78’ N, 171° 22.25’ W). Water temperature = 4.1 °C.

Description. The holotype (Fig. 2A) is a stalked, tube shaped, light brown sponge, 40 cm in height with increasing tube diameter towards the top. The surface is smooth with irregularly distributed depressions, especially at the base. The consistency is cork-like in the dry state. The stalk is somewhat flattened, the narrower side 1.5 cm, the broader side 2.5 cm in diameter. The stalk is 12 cm long and then changing gradually into the tube starting by some ridges growing on the stalk and leaving open spaces between the ridges, not forming closed tube walls at the base. At the top the tube walls are approximately 1 cm thick with an apical opening of 3 cm in diameter.

The paratype (Fig. 2B) is somewhat smaller, of the same light brown color, 28 cm in height. The stalk is 5 cm long, 1.3–1.6 cm in diameter and merges into the tube with less depressions than the holotype and it has closed tube walls. The basal end of the stalk widens to 2.6 cm. At the top of the sponge the tube walls are 7–9 mm in thickness and the apical aperture is 3.5 cm in diameter. The inner walls have numerous circular openings 1–3 mm in diameter.

1 Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.

Skeletal architecture. The organization of the choanosome is not uniform as usual in Microcionidae and Echinoclathria. It consists of thick styles with numerous isochelae in between. Mainly in the interior and also near the inner tube walls a reticulate skeleton of single spicules and paucispicular tracts dominates (Fig. 2C). Close to the outer walls there are mostly plumose fibers running mainly obliquely, less often perpendicular or even parallel to the surface (Fig. 2D). The ectosomal skeletons of inner and outer tube walls differ also: at the inner walls the reticulate organization of thick styles extends until close to the surface and thin styles only occasionally form surface brushes but more often occur singly, oriented parallel to the surface between numerous isochelae (Fig. 2E). In places the ectosome of the inner tube walls consists of a thin veneer with abundant isochelae only. At the outer tube walls the choanosomal plumose spicule tracts of thick styles are replaced 1–2 mm below the surface by tracts of ectosomal thin styles fanning out into spicule brushes at the surface, perpendicular to the surface with points facing out (Figs. 2 F-H).

Spicules. Choanosomal thick styles (Fig. 3A, left) are smooth, curved, 395–454–535 x 13–21– 25 µm, ectosomal thin styles (Fig. 3A, right) are straight, curved or slightly sinuous and with microspined heads (Fig. 3B) and acute points (Fig. 3B), 270–588–805 x 5–7– 9 µm, microscleres are palmate isochelae (Fig. 3C), 13–19– 23 µm.

Discussion. The skeletal architecture of the new species with three different choanosomal spicule arrangements fits well in the concept of Microcionidae and the genus Echinoclathria. The renieroid reticulation of the inner parts changes into plumose, branching spicule tracts towards the outer tube walls and is then replaced just below the ectosome by thinner ectosomal spicules forming brushes at the surface.

We compared E. seguama n. sp. with congeners from the North Pacific Ocean and the Arctic Ocean. The four species occurring here differ in the following characters: Echinoclathria arborea Tanita, 1968: from Japan, is dichotomously branched with an arborescent appearance, has toxa and is lacking isochelae completely while E. seguama is tube shaped, has isochelae and is lacking toxa.

Echinoclathria beringensis (Hentschel, 1929): from the Arctic Ocean, the Bering Sea and the North Pacific Ocean is cup-shaped and lacks microscleres completely. Echinoclathria noto Tanita, 1963: from Japan, is lacking isochelae and has toxa. Echinoclathria vasa Lehnert et al., 2006: from the Aleutian Islands, it shares the vaseshaped habitus but differs in its choanosomal styles that are longer but half in width only, ectosomal styles are longer and again somewhat thinner, isochelae are larger and additionally differ in geometry.

Etymology. The species is named after Seguam Pass, where the holotype was collected.