Megaciella lobata Lehnert & Stone, 2015, n. sp.

Megaciella lobata n. sp.

(Figs. 3 & 4, Table 2)

Material examined. Holotype: ZSM 20150382, collected by Jay Orr with a research survey bottom trawl (haul #166) from the FV Ocean Explorer; 17 July 2012, 91 m depth, 2.1 km north of western Kiska Island, western Aleutian Islands, Bering Sea (51°59.5740' N, 177°23.0100' E). Water temperature = 4.3°C. Complete specimen in ethanol.

Description. Habitus: This is a small, brown-colored sponge of firm, only slightly elastic consistency. It has an almost circular outline where several lobes radiate from a center (Fig. 3 A). The lobes are 0.5–2 cm in thickness and up to 2 cm long, starting from a common center, 3.5 x 4.4 x 5.3 cm. Lobes may be partially fused. The surface is hispid, due to projecting spicules of choanosomal spicule tracts (Fig. 3 B).

Skeletal structure: The ectosome is a thin membrane and contains scattered anisotylotes with microspined bases and microscleres (Fig. 3 C). In the choanosome, plumose tracts, cored by smooth styles (Fig. 3 D) and echinated by acanthostyles (Fig. 3 B & E), ascend to the surface with the end of the tracts as the cause of the hispid surface.

Spicules: Ectosomal anisotylotes have microspined ends, one end more inflated, the other often looking broken but, upon closer examination is complete due to micro-spination, 355–508 x 4–6 µm (Fig. 3 F). Coring the tracts are single, long smooth styles, mostly broken in spicule preparations, 1056–1645 x 19–32 µm (Fig. 3 E). Choanosomal styles, varying from completely smooth or with slightly microspined bases only, to microspined areas at both ends of the style, 735–928 x 42 –55 µm (Fig. 3 D), acanthostyles, 440–710 x 42 –53 µm (Fig. 4 A). Microscleres are toxa in two categories: long, thin toxa, 130–720 µm (Fig. 4 C) and short, thicker toxa, 29–47 µm (Fig. 4 B) and palmate isochelae, 22–47 µm (Fig. 4 D).

Discussion. The WPD currently recognises 14 species of Megaciella including two species previously described from the Aleutian Island Archipelago region (Lehnert et al., 2006b; Lehnert & Stone, 2014b). Megaciella are non-fistular branching, lobate, flabellate, or encrusting sponges of the family Acarnidae with a confused choanosomal skeleton divided into primary ascending multispicular tracts and secondary interconnecting uni- and bispicular tracts cored by basally spined styles, with or without echinating acanthostyles (Hooper, 2002a). We compare with 9 species co-occurring in the North Pacific Ocean, including one from off the Californian Coast, another from off the Pacific Coast of Mexico, and with the second new Megaciella, described below (Table 2). The two species we describe here are the only Megaciella with a third category of thin styles. Megaciella lobata n. sp. differs from the species compared with in the following characters:

M. anisochelae: Northwest Pacific Ocean (central Aleutian Islands). A stalked cluster of tubes with shorter and thicker styles, no acanthostyles, two categories of isochelae (both smaller), anisochelae, but no toxa or echinating spicules.

M. fragilis: Northwest Pacific Ocean and Sea of Okhotsk. A dactylate or lobate sponge, light yellow in color, with shorter tylotes, shorter and thinner styles, no acanthostyles, smaller isochelae, both categories of toxa are shorter.

M. microtoxa: Northeast Pacific Ocean (Coast of Mexico). A massive sponge with shorter tylotes, choanosome with acanthostyles only, shorter isochelae, and one category of toxa that are intermediate in length to those of M. lobata.

M. ochotensis: Northwest Pacific Ocean and Sea of Okhotsk. A lobate to dactylate sponge with shorter tylotes, choanosome with acanthostyles only, shorter isochelae, and only one category of toxa.

M. pituitosa: Northwest Pacific Ocean (Aleutian Islands). A stalked and fan-shaped sponge with shorter tylotes, shorter and thinner styles, shorter and thinner acanthostyles, smaller isochelae, and smooth toxa of different size categories.

M. spirinae: Northwest Pacific Ocean, Sea of Okhotsk, and central Aleutian Islands. An irregularly massivelobate sponge with smaller tylotes, choanosome with acanthostyles only which are much smaller, only one category of choanosomal styles, only one category of toxa.

M. toxispinosa: Northeast Pacific Ocean (Mexican Tropical Pacific). A thinly encrusting sponge with shorter tylotes, choanosome with acanthostyles only, two categories of isochelae, shorter categories of toxa.

M. zenkevitchi: Northwest Pacific Ocean and Sea of Okhotsk. A sponge with shorter but thicker tylotes, choanosomal styles are shorter and thinner, small toxa are longer.

M. triangulata n. sp.: Northwest Pacific Ocean (Aleutian Islands). A stalked and funnel-shaped sponge with shorter but thicker tylotes, shorter and thinner styles and acanthostyles, two categories of isochelae (both smaller), microspined toxa of different sizes, small category of anisochelas.

Etymology. From the latin lobatus—referring to the sponge’s lobate habitus.