Xenospongia patelliformis Gray, 1858

Sutcliffe, Patricia R., Hooper, John N. A. & Pitcher, Roland, 2010, The most common sponges on the Great Barrier Reef seabed, Australia, include species new to science (Phylum Porifera), Zootaxa 2616, pp. 1-30 : 15-19

Xenospongia patelliformis Gray, 1858 .

( Figures 8 , 9 , Table 3 )

Xenospongia patelliformis Gray, 1858: 229 ; Hooper & Wiedenmayer, 1994 (2005 web version): 427; Fromont, 2003: 408; Sara, 2002: 265.

Material examined. Holotype BMNH 1883.1.25.9 dry, Torres Strait, QLD, 10°25'S 142°10'E. Paratypes BMNH unregistered 2 specimens, dry (D.A.38); BMNH unregistered slide 2/57.

New material. QMG331025 (SBD513104), seabed north of Heron Island, adjacent to Haberfield Shoal, Great Barrier Reef, 22° 57΄ 53ʺ S 151° 47΄ 0 5ʺ E, 55m depth, epibenthic sled, 22 ix. 2004, coll. RV Lady Basten. QMG329286 (SBD537920), seabed between Capricorn-Bunker Group and Swains Reef, Great Barrier Reef, 22° 55΄ 30ʺ S 151° 58΄ 29ʺ E, 76 m depth, epibenthic sled, 9 xi. 2005, coll. RV Lady Basten. QMG329285 (SBD537858), inner shelf seabed between Herald’s Prong No.2 and the mainland, Great Barrier Reef, 22° 12΄ 17ʺ S 150° 59΄ 42ʺ E, 22 m depth, epibenthic sled, 10 xi. 2005, coll. RV Lady Basten.

Other material: 102 specimens collected between Wyborn Reef at the tip of Cape York to the seabed adjacent to northern Fraser Island in the south ( Figure 8 ). Housed at the Queensland Museum, Brisbane, Australia.

Description. Shape. Distinctive disc shape, ranging in thickness from 3–6 mm. All specimens show a concave structure, which allows them to be raised above the seabed.

Colour. A beige or grey colour on the surface, when the sponge is turned over, the underside is mottled as the incorporated sand grains are more highly visible.

Oscules. No oscules were visible in these specimens.

Texture and surface characteristics. Flexible due to the thin shape of the specimens, this sponge is otherwise firm, incompressible, easily torn and becomes very brittle when dry. Spicule bundles and large singler spicules protrude from the ectosome and give the surface a hispid appearance, although the longer spicules are easily broken. The extremities of the disc also have large spicules echinating through the ectosome, allowing the entire sponge to be raised above the seabed. The surface is frequently grooved. Grooves originate from the apex of the sponge and run to the extremities of the disc, with variable degrees of branching.

Skeletal structure. Spicules are concentrated almost exclusively in the ectosomal layer on the upper, exposed side. Styles in two size classes are arranged tangentially, forming a matted layer which lies directly below the ectosomal crust of asters. Specialised styles form dense bundles which project through the ectosome, surrounding a single, large, specialised style which extends to a distance of about 1.5 mm. The choanosome is filled almost entirely with sand grains ( Figure 9 ).

Megascleres ( Table 3 ). Large styles (Type I) are the most abundant, have smooth heads, rounded tips and can be flexuous. They form the tangential ectosomal layer as well as the dense ectosomal brushes and range from 530–1447 μm in length. The upper length limit of these styles, however, may be very conservative as a result of the fragility of these larger spicules. Smaller, thinner styles (Type II) have slightly swollen heads, approaching subtylote, with sharply pointed tips and a straight shaft. They are also located in the tangential ectosomal layer. Very fine, elongate styles (Type III) are the single styles arising from the centre of ectosomal brushes to a distance of approximately 1.5 mm.

Microscleres ( Table 3 ). Oxyasters are large and regular, with a small centrum and smooth, slightly recurved, conical rays. These are slender, uniform asters with approximately 11 rays per aster.

Strongylasters are very compact and robust, with 7–8 stout rays. These have been previously described as tylasters, but our examination shows that the spination is spread along the entire length of the rays, with larger, more sharply pointed spines at the tips of each ray in some asters, giving the appearance of being swollen, thus simply a manifestation of the size of spines and not a true tylaster morphotype. The short tuberculate spines on the shaft of the rays give a warty appearance and can conceal the centrum in smaller asters, due to the shaft width and elaborate spination on the rays.

Habitat and distribution. Distributed throughout the Great Barrier Reef, this species has also been recorded from the Torres Strait, Western Australia and allegedly Sri Lanka. Specimens from the GBR were collected in depths ranging from 10 to 87 m, from predominantly sandy and carbonate dominated substrata.

Remarks. This species has an unusually distinctive habit which is relatively well known by many marine invertebrate researchers, and as recently as 2003 was recorded from Western Australia ( Fromont, 2003), where specimens reach a much larger size than any of those reported here. Type II and Type III styles have not been previously recorded in descriptions of this species. Type III styles were possibly overlooked due to handling of the degraded type specimens causing the larger megascleres to break, giving the false impression that the ectosomal megascleres were the only megasclere component. Smaller, Type II styles were also previously overlooked.

In the original description, Gray (1858) noted that oscules were visible in the surface grooves of the adult specimen, and infrequently situated on the surface of the main body of the sponge. Sollas (1888) agreed and added that small pores could be seen in rows situated externally to the grooves. In the specimens collected as part of the GBRSBD no oscules were visible, possibly due to the nature by which they were collected, and preserved frozen.

Although the officially recorded distribution of this species is relatively limited to date, it is possible that it is widespread throughout Australasia on the inter-reef seabed. The holotype was collected in the Torres Strait ( Gray, 1858). Dendy (1905) recorded a single specimen from Sri Lanka, but conspecificity has never been confirmed. The older (non GBRSBD) collections of the Queensland Museum contain one specimen from the Gulf of Carpentaria, one from Yeppoon (Queensland coastal waters) and six specimens from four sites in Torres Strait. The Western Australian Museum, however, has specimens ranging the West Australian coast from Rottnest Island to Broome (Jane Fromont, pers. comm.), which is a far more southern reaching distribution. Collections from South Australia also suggest an abundant southern distribution, however, identification of these specimens have not been confirmed (Shirley Sorokin, pers. comm.). To our knowledge at least, there are no other records of this species, despite it being the third most abundant sponge on the GBR seabed, with 415 specimens recorded from 96 sites.

Predicted distributions and biophysical preferences. Distributed throughout the northern and southern regions of the GBR, the highest concentrations were found in the southern coastal regions ( Figure 8 ). This species was collected from 86 sled sites (biomass 900 g) and 8 trawl sites (biomass 126.9 g) between 10 and 87m depth in benthic habitats dominated by sandy sediments and carbonate dominated sediments ( Figure 3 ). The low occurrence of this species in the northern regions of the GBR, which has similar benthic habitats to the southern GBR regions (e.g. coastal region in proximity to Townsville), is curious considering that previously known distribution on the East coast was only from these northern regions (Torres Strait and Yeppoon). This high abundance in the southern GBR, as well as records from southern Western Australia, suggest that this species has a stronger distribution in southern regions. X. patelliformis showed preference for shallow water, sandy environments with high deviation in oxygen content.

Figures

FIGURE 3. Substrate composition plot, showing the relative composition of sand, carbonate, gravel and mud for four species (Dercitus xanthus sp. nov., Xenospongia patelliformis Gray, 1858, Coscinoderma nardorus (Lendenfeld, 1886) and Spheciospongia vagabunda (Ridley, 1884 )).

FIGURE 8. Model distribution map displaying predicted and actual distribution and biomass of Xenospongia patelliformis Gray, 1858 from the Great Barrier Reef seabed, displaying: OTU code for this species (TSQMSB. BRS 203863), P-AUC: Area Under the Curve performance diagnostic for the Presence / Absence model; Dev. Ratio: Deviance Ratio (P-AUC) performance diagnostic for the Biomass model; Measuresled: a device factor accounting for the difference in sampling rates between devices; Measuretrawllog (AreaHa) and Measuresledlog (AreaHa): offsets accounting for the swept area sampled by the trawl and sled; and influential predictor variables including: CRS _ O 2 _ SD: oxygen (ml / l) standard deviation, GA _ SAND: sand grainsize fraction (%), GBR _ BATHY: bathymetry.

FIGURE 9. Xenospongia patelliformis Gray, 1858 (QMG 331025 (SBD 513104 )) A, Specimen (scale bar 5 mm) B, Margin of discoid sponge, showing long echinating styles protruding from the tangential ectosomal layer as well as from brushes perpendicular to the surface (scale bar 3 mm). C, Ectosome, displaying the high concentration of asters and arrangement surface brushes (scale bar 500 μm) D, Ectosome in cross section, with long style protruding from ectosomal bundles. Dense, tangential arrangement of styles and highly arenaceous choanosome are also visible (scale bar 1 mm). E, Large oxyaster (scale bar 15 μm). F, Strongylasters (scale bar 10 μm). G, Style (Type II) (scale bar 50 μm). H, Style (Type I) (scale bar 200 μm). I, Style head (Type II) (scale bar 10 μm). J, Style tip (Type II) (scale bar 20 μm). K, Style (Type III) (scale bar 250 μm).

Tables

TABLE 3. Measurement of spicules for Xenospongia patelliformis Gray, 1858, as range (and mean) of length x width in μm, N = 30. Asters are measured by overall diameter from tip of ray to opposing tip of ray.

Specimen number	Styles (Type I)	Styles (Type II) Styles (Type III)	Oxyasters	Strongylasters
Q M G 3 3 1 0 2 5 (SBD513104)	535–1275 x 5–13 (1020 x 9)	145–600 x 2–6 1500–2600 x 8–12 (380 x 4) (2000 x 11)	14–65 (45)	3–11 (5)
QMG329285 (SBD537858)	930–1447 x 8–12 (1100 x 10)	245–485 x 2–4 1600–3000 x 9–11 (330 x 3) (2100 x 10)	21–65 (38)	3–18 (8)
QMG329286 (SBD537920)	850 –2100	205–445 x 4–8 1500–3000 x 9–12 (350 x 5)	20–80 (45)	3–10 (7)