Xestospongia ursa, Turner & Lonhart, 2023

Turner, Thomas L. & Lonhart, Steve I., 2023, The Sponges of the Carmel Pinnacles Marine Protected Area, Zootaxa 5318 (2), pp. 151-194 : 175-177

Xestospongia ursa sp. nov.

Figures 15 , 16

Material examined. Holotype: CASIZ236663 / IZC00048474 , Inner Carmel Pinnacle, (36.55852, -121.96820), 10– 24 m, 9/22/21; paratypes: IZC00048472 , Fire Rock, Pescadero Point, Carmel , (36.55898, -121.9511), 10–22 m, 8/10/21; SBMNH700926 , Tower house arches, Carmel , (36.56187, -121.95950), 9–21 m, 9/21/21; IZC00048473 , Whaler's Cove , Point Lobos , Carmel , (36.52172, -121.93894), 6–15 m, 11/23/19; SBMNH700921 , Whaler's Cove , Point Lobos , Carmel , (36.52172, -121.93894), 6–15 m, 11/23/19. Comparative material: Xestospongia diprosopia ( de Laubenfels 1932) , CASIZ190441 and CASIZ190442 , Rittenburg Bank , Farallon Islands , Northern California, 85 m, 10/9/12.

Etymology. Bright white and furry-looking, this sponge is named after Ursa maritimus.

Morphology. Thickly encrusting with irregular lobes and ridges; collected fragments are up to 3 cm thick, but sponges likely exceed this thickness in life. Oscules prominent but sparse and irregular, flush with surface, placed atop high points on lobes and ridges. Surface covered in minute conules that give the sponge a furry appearance. Chalky white alive, but often has brownish patches due to fouling by microscopic algae. Produces copious slime when collected. Very firm and incompressible.

Skeleton. Ectosome and choanosome possess a chaotic, reticulated network of single spicules and paucispicular bundles 3–7 spicules across; in some places these form a polygonal mesh. Spongin is not apparent.

Spicules. Oxeas, smoothly curved or with one or two subtle bends. Most commonly with two sharp points, but a substantial minority with one end tapering to a blunt tip; a small minority taper at only one end and are therefore styles. Some with extra spines forming a x-shape at one tip; this was very rare in any one sponge, but seen across multiple sponges. Spicules in one length category but variable in thickness; thickness unimodal but some much thinner than average; these may be immature. Holotype 218–290–332 x 4–13–18 μm (n=48), all samples pooled 185–281–332 x 2–14–21 μm (n=201). Mean lengths for each sample vary from 266 to 290 μm.

Distribution and habitat. Common on rocky reefs in the shallow subtidal from Pescadero Point, on the northern end of Carmel Bay, to the Carmel Highlands, just south of Carmel Bay; it was seen on six of eight locations in this region. Not seen at any other location to date, including the 6 reefs searched in nearby Monterey Bay.

Remarks. Xestospongia diprosopia ( de Laubenfels, 1930) is a deep-water species from Central California, and the type species for the genus. Xestospongia ursa sp. nov. is very similar in terms of skeletal structure, spicule shape, and gross morphology. To verify that X. ursa sp. nov. is not a shallow water form of X. diprosopia , we examined the spicules of two X. diprosopia from 85 m depth. The samples average 351 and 365 μm in length, matching published data from the holotype (352 μm; Desqueyroux-Faúndez & Valentine 2002). This is about 20% longer than X. ursa sp. nov., which averages 266–290 μm in length depending on the sponge. The holotype and other X. diprosopia also average about 60% thicker spicules (23–26 μm per sample, vs. 13–15 μm for X. ursa sp. nov.). We successfully sequenced a portion of the 28S locus from one X. diprosopia sample: this sequence was 6% divergent from X. ursa sp. nov. across the aligned 827 bp, supporting the species-level difference of these shallow and deep-water forms (figure 15). The genetic data also support the allocation of the new species to Xestospongia , as it is more closely related to the type species than any other species with publicly available data at this locus.

Previous phylogenies of the Haplosclerida have found that most families and genera are polyphyletic, and the position of X. disprotopia adds to this conclusion. Most Haplosclerida fall into five clades, designated A–E ( Pankey et al. 2022; Redmond et al. 2013): we include representatives of each in the 28S phylogeny shown in figure 15. The type species of Xestospongia falls within clade E, otherwise populated mainly by members of the Phloeodictyidae . In contrast, other Xestospongia have been found to be members of clades B and D ( Pankey et al. 2022; Redmond et al. 2013).

Two other Xestospongia are known from the region: X. dubia ( Ristau, 1978) has much smaller spicules and a different morphology, and X. hispida ( Ridley & Dendy, 1886) is hispid, with a different morphology and larger spicules.

Xestospongia ursa sp. nov. may be identifiable in the field due to its chalky white color, lobe-like growth form, and furry appearance. To date, all samples were correctly identified as conspecifics by the authors before looking at spicules, and no other samples were incorrectly identified as this species among the other samples collected.

Figures

FIGURE 15. Maximum likelihood phylogeny of the 28S locus for the Haplosclerida. Colors indicate well-supported clades, with letter names following Redmond et al. (2013). Genbank accession numbers are shown; bold indicates new sequences. Node confidence is based on bootstrapping. Scale bar indicates substitutions per site. Colors indicate clades containing new taxa, as referenced in the text.

FIGURE 16. Xestospongia ursa. Field photos of holotype (A) and SBMNH700926 (B). C, F: Thick and thin oxeas from IZC00048472. D: Cross-section showing choanosomal skeleton and tangential section showing surface skeleton, both from holotype.