Suberites agaricus, Turner & Rouse & Weigel & Janusson & Lemay & Thacker, 2024

Turner, Thomas L., Rouse, Greg W., Weigel, Brooke L., Janusson, Carly, Lemay, Matthew A. & Thacker, Robert W., 2024, Taxonomy and phylogeny of the family Suberitidae (Porifera: Demospongiae) in California, Zootaxa 5447 (1), pp. 1-28 : 16-17

Suberites agaricus sp. nov. Turner, 2024

Figures 1–2 , 7

Material examined. Holotype: CASIZ 236793 , El cono, Point Loma, (32.69853, -117.27338), 21–26 m, 5/6/23.

Etymology. Named for its resemblance to cultivated “button” mushrooms in the genus Agaricus .

Morphology. Roughly spherical, 14 mm in diameter. Numerous small oscula (~ 1 mm in diameter) flush with surface in living specimen; constricted in preserved specimen. The substrate-facing side appears to have been attached to the substrate over a smaller surface than the entire diameter of the sponge, leading to an incipient stalked appearance, and making the overall morphology similar to the cap of the cultivated “button” mushroom. Pale yellow alive, white when preserved. Cross-section of the preserved sample reveals a visually distinct ectosomal layer 0.2–0.5 mm in thickness (figure 5D). Microscopically hispid.

Skeleton. Upright bouquets of tylostyles in the ectosome, with tips protruding 100–150 μm beyond sponge surface. Bouquets are supported by multispicular columns of tylostyles, creating a somewhat radial architecture, becoming increasingly confused towards the interior of the sponge.

Spicules. Large and small tylostyles, with overlapping size distributions. The distribution of tylostyle length is bimodal when all tylostyles are considered together, with modes at approximately 350 μm and 1050 μm. If 700 μm is used as a dividing point between classes, then the choanosome contains only long tylostyles, while the ectosome contains 20% long tylostyles and 80% short tylostyles. All tylostyles are straight or slightly curved, usually with symmetrical, round heads, but some heads are sub-terminal. Most spicules are thickest near head and gently tapering throughout their length, but some are slightly fusiform. The gradual tapering differentiates this species from the other Suberites found in California, but R. gadus is similar.

All spicules together: 204–598–1335 x 6–11–24 μm (n=161), modes at approximately 350 μm and 1050 μm.

Choanosome only: 860–1074–1335 x 11–17–24 μm (n=23)

Ectosome only: 223–548–1073 x 6–9–16 μm (n=87)

Only spicules <700 μm in length: 204–409–692 x 6–9–16 μm (n=107)

Distribution and habitat. Only seen at a single location to date: the kelp forest off of Point Loma, near the southern border of California. Numerous small, roughly spherical sponges matching the morphology of the sampled individual were seen at this location, which were all likely this species.

Remarks. This species could arguably be placed in either Suberites or Rhizaxinella . The body shape and somewhat radial skeleton are more consistent with Rhizaxinella , but sponges in this genus are carried on a long, often branching stalks, which are missing in this species. With the added evidence of a close genetic relationship to other Suberites , we feel this placement is a better fit. It is likely that the spherical body of the sponge has led to some convergent evolution of the skeleton from confused into a more radial architecture.

This species is quite closely related to S. lambei , with only 0.3% sequence divergence at the 28S locus. Divergence at the cox1 locus is higher (1.7%), and with consistent placement and both loci and very distinct spicule morphology, it is confidently assigned to a separate species. As discussed in the S. lambei section, tylostyles in that species have a unimodal length distribution, with average values between 282 μm and 499 μm per sample. We measured 750 spicules across 17 individuals throughout the range of S. lambei (including a sample from San Diego, near where S. agaricus was collected) and found the maximum spicule length to be 615 μm. This is in stark contrast to S. agaricus , where minimum sizes of the long tylostyles are longer than this maximum value for S. lambei . These long tylostyles also set the new species apart from all other Suberites in the region: S. latus , S. kumeyaay sp. nov., S. californiana sp. nov., S. concinnus Lambe, 1895 (which lacks tyles), and S. mineri de Laubenfels, 1935 (which is cup-shaped). Suberites baffini ( Brøndsted 1933) has spicules of similar length to S. agaricus , and also has a roughly radial architecture. These are unlikely to be conspecific, however, as S. baffini is described as having prominent spicular fibers, whereas no spongin or other fiber is present in S. agaricus ; moreover, S. baffini is known from deep water (1200 m) the far North Atlantic (Baffin Bay, Canada).

The spicules of the new species are similar to Rhizaxinella gadus . The spicules of R. gadus are significantly longer (Wilcox rank-sum test p <0.001), but examining more individuals may reveal overlap in size distributions. As described in the R. gadus section below, these species can be differentiated based on skeletal organization, the lack of a branching stalk in S. agaricus , and DNA sequence; they also likely have depth range differences, but further work could reveal overlap in depth range.

Figures

FIGURE 1. Maximum likelihood phylogeny of the 28S locus. Genbank accession numbers and collection locations (when known) are shown; bold indicates new sequences. Asterisks at nodes indicate SH-aLRT ≥ 80% and UFbootstrap ≥ 95%. Scale bar indicates substitutions per site. Asterisks in node names indicate type species of a genus.

FIGURE 2. Maximum likelihood phylogeny of the cox1 locus. Genbank accession numbers and collection locations (when known) are shown; bold indicates new sequences. Asterisks at nodes indicate SH-aLRT ≥ 80% and UFbootstrap ≥ 95%. Scale bar indicates substitutions per site. Asterisks in node names indicate type species of a genus.

FIGURE 7. Suberites agaricus. A: Field photo. B: Underside, post-preservation. C: Tylostyle. D: Cross-section, postpreservation. E: Skeletal structure in cross-section.All photos of holotype.