Galaxia gaviotensis, Turner, 2020

Turner, Thomas L., 2020, The order Tethyida (Porifera) in California: taxonomy, systematics, and the first member of the family Hemiasterellidae in the Eastern Pacific, Zootaxa 4861 (2), pp. 211-231 : 225-228

Galaxia gaviotensis sp. nov.

Material Examined. Holotype, CASIZ 235112 , Arroyo Quemado Reef , Santa Barbara County, California, United States of America (34.46775, -120.11905), 15 meters depth, 7/29/19.

Etymology. The area where this sponge was collected is known as the Gaviota Coast, and is the longest remaining undeveloped part of the Southern California coastline. As a common name, I suggest "Gaviota galaxy sponge".

Description. Macroscopic features. The sponge formed a pale-yellow crust with surface dimensions approximately 10 x 5 cm. Thickness only 200–650 μm. Field photos (figure 8) show darker spots on the surface; these disappeared in sampled fragments, so were likely oscules or pores that contracted when disturbed.

Microscopic features. Styles comprised 70% of megascleres. Some were tylostyles with well-formed oval heads, while others had weak heads (subtylostyles), and others had lumpy, irregular heads (fig. 9). Many also had subterminal heads or weak bands of slightly increased width near the head of the style. About 13% were unadorned, simple styles. Length varied greatly, from 176–1330 μm (mean = 751, N=45). Width from 2–9 μm, with a mean of 5.3 μm. The other 30% of megascleres were asymmetrical oxeas. These were sharply pointed at both ends, and gently bent at the thickest point, which was closer to one end. A minority (20%) of these had very weak centrylote swelling at the point of inflection. Length was less variable than for styles, from 174–464 μm (mean = 258, N=19); width 2–5 μm, with a mean of 3.7 μm.

Microscleres consisted of abundant and varied euasters. The most common type had thick, untapered rays ending in enlarged, spiny bouquets ("tylasters"). The ratio of ray length to centryole size varied greatly (fig. 9). Some were also spined along the rays, instead of merely at the tips. In some asters, the rays were greatly reduced, to hemispherical bulges around a large centrum, sometimes bearing spines and sometimes nearly smooth. Asters with conical rays (oxyspherasters) were also present. These ended in spined bouquets as well, but the bouquets were sometimes very small, resulting in nearly smooth, tapering, conical rays. Mean aster diameter was 10.6 μm (range 4–22 μm, N=62); sizes were not clearly different among types.

Spicule arrangement. Perpendicular sections through the sponge tissue revealed that it was packed with asters (figure 8). These formed a thick surface crust, but were also abundant throughout; no pattern of arrangement by type could be discerned. Megascleres were most dense in the lower half of the sponge, running parallel to the substrate; many were found in bundles. Bundles of megascleres were also oriented vertically, points up, piercing the surface of the sponge.

Geographic distribution. This sponge has been found at only a single location: Arroyo Quemado reef, approximately 0.15 km offshore of the small community of Arroyo Quemado (34.468801, -120.121233). This is an area of rocky reef and kelp forest that is part of the Santa Barbara Coastal Long-Term Ecological Research Station (sbclter.msi.ucsb.edu). It was found on "transect 3", which is a flat area 7.5–9.5 m deep, strewn with cobbles and boulders. It was growing on a single boulder. I made a total of 8 collecting dives at this reef (5 hours of cumulative search time) but no additional individuals were found. Seven months after collecting the initial sample, the transect 3 area was re-visited in an attempt to relocate the original sponge, without success. Many of the boulders at the site were coated in a fine layer of silt at this time, making it likely that the sponge was still present but concealed.

Remarks. Most encrusting sponges in the Tethyida are placed in the genus Timea . Timea is rejected in the current case due to the presence of oxeas and genetic data that places the species in the Hemiasterellidae . Encrusting Hemiasterellidae are known from only two genera: Leptosastra and Liosina . Leptosastra is monotypic, with the unusual L. constellata having acanthostyles, and tornotes; this is a very poor fit for the current species. Liosina includes at least one encrusting species (though thickly encrusting, with chimneys) and sometimes have oxeas; however, these species lack asters. Hemiasterella include some species with oxeas, but these species are all massive, digitate, or vase-shaped. Thus, this species has become the type for a new genus.