Tethya sorbetus, Sim-Smith & Hickman & Kelly, 2021

Sim-Smith, Carina, Hickman, Cleveland & Kelly, Michelle, 2021, New shallow-water sponges (Porifera) from the Galápagos Islands, Zootaxa 5012 (1), pp. 1-71 : 53-55

Tethya sorbetus sp. nov.

( Fig. 25 )

Material examined. Holotype —MCCDRS9477, Punta Vicente Roca , Isabela Island, 0.049° S, 91.558° W, 4 m, 15 Jan 2003.

Type locality. Punta Vicente Roca , Isabela Island .

Habitat and distribution. Only known from the type locality. Found growing on a rock wall; 4 m.

Description. Globose sponge, 20 mm in diameter, covered in flattened, slightly irregular tubercles. Surface on preserved specimen appears rugose rather than verrucose. A cluster of oscules is present on the apex. Colour in life is pale greenish yellow, colour in ethanol is tan ( Fig. 25A ). Texture is firm, slightly compressible.

Section. Ectosome is well-developed with a dense layer of tylasters at the surface. Tylasters and spherasters are abundantly scattered throughout the ectosome ( Fig. 25C ). Bundles of strongyloxeas radiate out from the centre of the sponge, spreading out into terminal fans near the surface. A palisade of smaller auxiliary strongyloxeas is present in the periphery of the choanosome, aligned perpendicular to the surface ( Fig. 25B ). Spherasters and tylasters are abundantly scattered throughout choanosome.

Spicules. Megascleres —Strongyloxeas, 679 (224–1267) × 9 (4–19) µm (n=50) ( Fig. 25E ). No clear size separation between between auxiliary and main strongyoxeas. Microscleres (megasters) —Spherasters I, with sharply pointed conical rays, 46 (32–61) µm in diameter (n=40); ray:centrum ratio is 0.75 ( Fig. 25F ). Microscleres (micrasters) —Spherasters II, less abundant than spherasters I with conical or slightly rounded rays, 15 (4–25) µm in diameter (n=41); ray:centrum ratio is 0.77 ( Fig. 25G ). Tylasters with spined tips, 8 (5–12) µm in diameter (n = 20) ( Fig. 25D ).

Etymology. Named for the lemon sorbet colouration of this species (Latin nominative singular in apposition, coined from Spanish sorbete = ‘sorbet’).

Remarks. Two species of Tethya have been previously described from the Galápagos Islands; T. sarai Desqueyroux-Faúndez & Van Soest, 1997 and T. strongylata Sarà, Bavestrello & Calcinai, 2000 . Tethya sorbetus sp. nov. can be differentiated from T. sarai by the possession of only one size class of tylasters while T sarai has two size classes. Tethya sorbetus sp. nov. can be differentiated from T. strongylata by the morphology of the tylasters—those of T. sorbetus sp. nov. are only spined at the tips, while those of T. strongylata are spined along the entire length of the rays.

Twelve other species of Tethya have been described from the eastern Pacific that differ from T. sorbetus sp. nov. as follows:

• T. melinka Hajdu, Desqueyroux-Faúnde, Carvalho, Lôb-Hadju & Willenz, 2013 , T. deformis Thiele, 1898 , T. californiana De Laubenfels, 1932 , T. ensis Sarà, Gómez & Sarà, 2001 , T. ovum Sarà, Gómez & Sarà, 2001 , T. ornata Sarà, Bavestrello & Calcinai, 2000 , T. papillosa ( Thiele, 1905) , T. paroxeata Sarà, Gómez & Sarà, 2001 and T. vacua Austin, Ott, Reiswig, Romagosa & McDaniel, 2014 have strongylasters instead of, or in addition to, spined tylasters;

• T. taboga De Laubenfels, 1936 and T. mexicana Sarà, Gómez & Sarà, 2001 also possess smooth oxyasters;

• T. socius Sarà, Gómez & Sarà, 2001 has oxyspherasters with long thin rays (very high R:C ratio) (see Hajdu et al. 2013 for more details).

Figures

FIGURE 25. Tethya sorbetus sp. nov. holotype, MCCDRS9477: A. In situ. B. Cross section of the ectosome showing the radiating brushes of the main strongyloxeas at the surface, and the palisade of auxiliary strongyloxeas below the ectosome (arrow). C. Cross section showing the dense layer of tylasters at the surface of the ectosome. D. Tylasters. E. Strongyloxea. F. Spherasters I. G. Spherasters II.