Plakortis spinalis Domingos, Moraes & Muricy, 2013, sp. nov.
Creators: name: Domingos, Celso
name: Moraes, Fernando
name: Muricy, Guilherme
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Porifera
Homoscleromorpha
Homosclerophorida
Plakinidae
Plakortis
Plakortis spinalis

description: Plakortis spinalis sp. nov.
(Fig. 3)
Specimens examined (1). Holotype: MNRJ 8597, Sapata Cave, Fernando de Noronha Archipelago, Brazil, 15 m depth. Fernando Moraes coll., 10 August 2004.
Specimens examined for comparison. P. angulospiculatus: UFRJPOR 3900, 4791, Fernando de Noronha Archipelago, Brazil. UFRJPOR 4032, Tamandaré, Pernambuco State, Brazil. UFRJPOR 4116, 4118, Carrie Bow Key, Belize.
Plakortis hooperi QMG 312880. Papua New Guinea.
Plakortis insularis: UFRJPOR 3917, 4803; MNRJ 2126, 2138; all from Fernando de Noronha Archipelago, Brazil.
Plakortis microrhabdifera: MNRJ 2165, 2170, 2940, all from Atol das Rocas, Brazil.
Plakortis petrupaulensis sp. nov. MNRJ 11828, 11817, 11826, 11839; all from São Pedro e São Paulo Archipelago, Brazil.
Plakortis potiguarensis sp. nov.: UFPEPOR 585, Urca do Tubarão, Potiguar Basin, Rio Grande do Norte State, Brazil.
Diagnosis. Plakortis thinly encrusting, gray in color, cartilaginous in consistency, with a vaguely reticulated tangential ectosomal skeleton and a disorganized choanosomal skeleton with fiber-like structures; spicules are diods and triods, some of which spined, and tuberculate microrhabds; smooth siliceous spheres are also present.
Description. Shape thinly encrusting (Fig. 3 A), 4.0 by 1.5 cm wide by 0.5 cm thick. External and internal color gray in vivo, becoming light brown to cream after fixation in ethanol. Surface irregular, rugose, coriaceous. Oscules contracted, not visible in the preserved specimen. Consistency cartilaginous, slightly compressible.
Skeleton. Tangential ectosomal skeleton reticulate, with ill-defined multispicular spicule tracts forming circular meshes, 30-39-70 µm in diameter (n=20; Fig. 3 B). In transverse sections, the ectosome is well differentiated and shows ascending spicule columns separated by ectosomal lacunae, 12–22-39 µm (Fig. 3 C, top). Subectosomal lacunae are absent. Choanosomal skeleton dense, disorganized, with a few denser, sinuous tracts parallel to the surface (Fig. 3 C, bottom). Some parts of the mesohyl show a golden color and look similar to illdefined spongin fibres (Fig. 3 D), but could not be easily separated form the mesohyl like common demosponge spongin fibers.
Spicules. Diods thin, slightly sinuous, with sharp endings and protuberant central torsion. Some diods have small spines along the actines or near the center (Fig. 3 E): 29-42.6-103 /1-2-4 µm (n = 20).
Triods smooth, Y-shaped, with sharp endings and center deformed like that of diods. Some triods also have small spines along the actines or near their intersection (Fig. 3 F): actines 24.7-37.5-49.4 / 1-3-5 µm (n=20). Microrhabds irregular, straight or curved, highly tuberculate (Fig. 3 G): 5-6.7-14 / 2-3-6 µm (n=20). Smooth siliceous spheres are common (Fig. 3 H): 1–20 µm (n=20).
Habitat and ecology. The only specimen was collected on a vertical wall inside a semi-obscure cave, 15 m depth. The sponge had no associated macrofauna.
Distribution. Endemic from Fernando de Noronha Archipelago, NE Brazil (Fig. 1).
Taxonomic remarks. Plakortis spinalis sp. nov. belongs to the group of Plakortis with microrhabds, which now also includes P. petrupaulensis sp. nov. as well as P. lita, P. microrhabdifera, P. hooperi and P. m y r a e. The new species is mostly similar to P. petrupaulensis sp. nov. by its thinly encrusting shape, disorganized choanosomal skeleton, and especially the tuberculate microrhabds; P. petrupaulensis sp. nov., however, differs by a smooth surface, light brown color, absence of triods, and absence of spined spicules. Plakortis spinalis sp. nov. differs from P. lita, P. microrhabdifera, P. myrae and P. hooperi by its gray color, presence of tubercles on microrhabds and presence of spines on diods and triods. It differs from all other species of Plakortis by the spined diods and triods, tuberculate microrhabds, and by the fiber-like structures in the choanosome (Fig. 3 D).
Etymology. The name spinalis refers to the presence of small spines on some diods and triods.
description: Published as part of Domingos, Celso, Moraes, Fernando & Muricy, Guilherme, 2013, Four new species of Plakinidae (Porifera: Homoscleromorpha) from Brazil, pp. 530-544 in Zootaxa 3718 (6) on pages 534-536, DOI: 10.11646/zootaxa.3718.6.2, http://zenodo.org/record/218896