Aplysina sciophila, Rützler, Klaus, Piantoni, Carla, Van, Rob W. M. & Díaz, Cristina, 2014

Rützler, Klaus, Piantoni, Carla, Van, Rob W. M. & Díaz, Cristina, 2014, Diversity of sponges (Porifera) from cryptic habitats on the Belize barrier reef near Carrie Bow Cay, Zootaxa 3805 (1), pp. 1-129 : 98-100

Aplysina sciophila new species

( Figures 4 g, 43)

Material. Holotype: USNM 1229149, Carrie Bow forereef, 25 m; crevice entrance bottom; M. C. Diaz, col. 8 Sep 2009.

Paratypes: USNM 1191344, Carrie Bow forereef cave, 18 m; K. Ruetzler col. 19 May 1979. USNM 1191340, 1191341 Carrie Bow forereef, 22 m; under ledge in deep shade; M. C. Diaz and E. Villamizar col. 23 Jul 2008. USNM 1191343, USNM 1229150, Carrie Bow forereef, 25 m; crevice entrance bottom; M. C. Diaz col. 8 Sep 2009.

Other material examined: USNM 1191339, Carrie Bow forereef, 22 m; under ledge in deep shade; M. C. Diaz & E. Villamizar col. 23 Jul 2008. USNM 1191342, Carrie Bow forereef, 20 m; under ledge in deep shade; M. C. Diaz & E. Villamizar col. 23 Jul 2008.

Diagnosis. Thinly ramose Aplysina in Caribbean reef caves and in the shaded parts of ledges and overhangs. Branches less than 4 mm in diameter and up to about 150 mm long, arising from a small cushion. Delicate fibers, measuring less than 50 Μm in mean diameter and forming meshes averaging 0.7 x 0.4 mm. Color yellow to ochre, not changing to purple or black upon exposure to air.

External morphology. The holotype consists of a small cushion, 23 x 14 x 13 mm in dimensions and supporting one whip-like branch, 154 mm long, 2–3 mm thick. Other specimens have similar dimensions, with a base 1–5 cm 3 in volume; there may be 1–8 branches extending from one base, 3–180 mm in length, 1–4 mm in diameter, with no tendency to subdivide. The surface pattern is very finely conulose and interrupted, here and there, by very small (<1–2 mm) oscula, most located on the base cushion but also along the side of branches. The consistency is soft but elastic. Color: dull yellow to reddish tan in life, some specimens with a bluish, luminescent hue over the reddish tan background; reddish tan after fixation in alcohol.

Skeleton structure. The typical (for Aplysina ) golden yellow, pithed fibers of the holotype measure 20–63 (42) Μm in diameter, with the pith occupying two thirds of the thickness (an average of 67 %). These fibers form meshes of (largest perpendicular diameters) 260– 1520 x 110–650 (682 x 349) Μm. Fiber diameters of all specimens measured combined ranged 20–81 (47) Μm, meshes 220– 1520 x 110–650 (641 x 376) Μm.

Cellular fine structure. Transmission electron microscopy (TEM) revealed choanocyte chambers of about 25 Μm diameter and the typical (for genus Aplysina ) spherulous cells (24–28 Μm) and pocket-type bacteriocytes (28–32 Μm). Symbiotic bacteria, numerous inside bacteriocytes and throughout the mesohyle, are heterotrophic; no cyanobacteria were seen.

Ecology. Occurs on walls, ceilings, and ledges in medium to deeply shaded caves and under overhangs on the forereef, 20– 25 m.

Distribution. The material studied by us is from the Belize barrier reef but one of us (MCD) found specimens in similar environments in the Cayman Islands.

Etymology. The species name is derived from the Greek words skia (shade) and philia (love, fondness). Comments. Judging from its shape and color (and the lack of aerophobic color change when removed from the water and preserved in formalin or alcohol), this species is closest to Aplysina cauliformis ( Carter, 1882) with which it co-occurs in the same reef environment. The latter flourishes in full exposure to ambient light but in places its distribution extends into caves, thus overlapping with that of our new species. For comparison, we collected a piece of A. cauliformis , a specimen taken nearby on a reef in South Cut, in 4 m depth, and subjected it to the same processing techniques (fixation, fiber and mesh measurements). It too has branches that originate from a cushionshaped base and do not usually subdivide. But the branches are often clavate and their diameter ranges from 5 to 20 mm, the length can reach 50 cm or more. The color may be dull yellow to brown, reddish brown, and purple. As in our new species, there is no strong color change upon exposure to air or fixative. The fiber diameter measured in A. cauliformis is about double that of A. sciophila , 65–120 (90) Μm, and fibers form considerably coarser meshes: 620– 2800 x 330–660 (1164 x 478) Μm. From the fine structure, cell types and inclusions in both species are identical except that in A. cauliformis more than a third of the bacterial symbionts are photosynthetic (cyanobacteria). Similar observations were made by Vacelet (1967, 1975) when comparing cellular structures in a similar photophilic and sciophilic species pair in the Mediterranean, Aplysina aerophoba Nardo and A. cavernicola (Vacelet) (both as Verongia ). It was later shown that specimens of A. cavernicola transplanted to illuminated habitats retained its original bacterial symbionts and did not acquire cyanobacteria from their new environment ( Thoms et al., 2003).

Another yellow, rope-like Aplysina species on the Belize forereef is Aplysina fulva (Pallas) . Its branches, however, are 5–25 mm in diameter and up to 28 cm long and the dimensions of fibers and skeleton meshwork are coarse, the same as in A. cauliformis , and we never found it in cryptic environments. Above all, A. fulva is aerophobic and turns dark purplish to almost black when it is exposed to air and subjected to fixation, thus making it easily identifiable. Kobluk & van Soest (1989) list A. fulva from a framework cave in 12–24 m in the Netherlands Antilles, but it is likely that this material belongs to our new species.

Figures

FIGURE 4. In-situ photographs of new sponge species reported in this contribution (measurements in parentheses are picture widths): a, Wigginsia curlewensis (8 cm); b, Phorbas aurantiacus (10 cm); c, Myrmekioderma laminatum (12 cm); d, Niphates arenata (10 cm); e, Siphonodictyon occultum (10 cm); f, Xestospongia purpurea (8 cm); g, Aplysina sciophila (20 cm).