Plakina paradilopha, Cruz-Barraza & Vega & Carballo, 2014

Cruz-Barraza, José Antonio, Vega, Cristina & Carballo, José Luis, 2014, Taxonomy of family Plakinidae (Porifera: Homoscleromorpha) from eastern Pacific coral reefs, through morphology and cox 1 and cob mtDNA data, Zoological Journal of the Linnean Society 171 (2), pp. 254-276 : 262-263

PLAKINA PARADILOPHA SP. NOV.

( FIGS 2C , 4 )

Material examined

Holotype: MNCN-1.01/695, Playa Blanca , Socorro Island (Revillagigedo), 18°48′59″N, 111°02′42″W, 0.5 m depth, 6.v.2008 . Paratype: LEB-ICML-UNAM-1652, same collection data as holotype.

ZooBank LSID: urn:lsid:zoobank.org:act:5.

Etymology

The species name is derived from the similarity of this species to the Mediterranean Plakina dilopha , mainly because of the composition of the dilophose spicules.

Diagnosis

Whitish to bluish, thinly encrusting sponge with rounded edges, surface smooth but rough to the touch, with abundant subectosomal spaces and slightly elevated oscula irregularly distributed over the surface. Spicules are diods and simple calthrops, which constitute a dense and sometimes confuse choanosomal alveolar structure, whereas dilophose calthrops are arranged in a thin ectosomal layer.

Description

Encrusting sponge from, 0.2 to 0.4 mm thick, covering a small area of 10 × 3 cm on dead coral fragments of the genus Pocillopora . The surface is smooth with rounded edges, and rough to the touch. It is also characterized by abundant subectosomal spaces homogeneously distributed, which are visible to the naked eye ( Fig. 2C ). They are rounded to ovalshaped, from 100 to 250 μm in diameter. Oscules are circular to oval-shaped, of 1 to 2 mm in diameter, which are irregularly distributed and slightly elevated. The consistency is firm but easy to tear. Choanosomal aquiferous canals are common. They measure from 75 to 125 μm in diameter. Colour in life is cream to greyishblue and greyish beige in ethanol preserved.

Spicules: diods, calthrops, and dilophose calthrops ( Table 3). Diods are robust, curved, or straight, with an irregular, slight thickening in the middle of the shaft ( Fig. 4A ). Diods are very abundant. They are 62–100 μm long and 2.5–7.5 μm wide. Simple calthrops possess rays with a sharp point. These spicules are characterized by having one or two short rays as a knob, and the other one slightly larger than the others. The rays are commonly slightly curved at the end ( Fig. 4B ). Calthrops are also abundant; the rays are 15–35 μm long (total length 30–67.5 μm). Dilophose calthrops are less abundant, and they are characterized by having two lophose rays ramify medially into four or five small rays, which in turn ramify distally into two or three rays with spined tips ( Fig. 4C ). The simple rays measure 12.5–22.5 μm long and the lophose rays 5–12.5 μm long (total spicule length 22–42.5 μm).

Skeleton: ectosomal structure is formed mainly by dilophose calthrops with rays toward the surface. The choanosome is formed mainly by diods and simple calthrops, forming a dense structure, but sometimes with confuse alveolar reticulation with meshes measuring from 20 to 37.5 μm in diameter ( Fig. 4D ).

Ecology and distribution

The species was collected at Playa Blanca (Socorro Island, Revillagigedo archipelago; Fig. 1 ), at 0.5 m depth. Individuals were found between branches and bases of dead coral.

Remarks

Plakina paradilopha sp. nov. displays similar characteristics to the Plakina dilopha species complex. However, the species differs in details of the surface; Plakina paradilopha sp. nov. presents a regular smooth surface characterized by subectosomal spaces homogenously distributed and oscules slightly elevat- ed, whereas Plakina dilopha possesses rounded holes of various sizes and oscules that do not protrude at the borders (sensu Schulze, 1880; see Muricy et al., 1998). Calthrops and diods are very scarce in Plakina dilopha (see Schulze, 1880; Topsent, 1895), but they are relatively abundant in Plakina paradilopha sp. nov. In addition, Plakina dilopha possesses triods ( Desqueyroux-Faúndez & van Soest, 1997), which are absent in Plakina paradilopha sp. nov. Specimens of Plakina cf. dilopha with triods have also been cited from Ascension Island in the Atlantic ( Díaz & van Soest, 1994).

Plakina microlobata is the only species of the Plakina dilopha species-complex found in the eastern Pacific region. This species is characterized by a smooth but strongly undulating, microlobate surface, which gives it the specific name ( Desqueyroux-Faúndez & van Soest, 1997), whereas Plakina paradilopha sp. nov. has a smooth surface, even under the stereoscope. Skeletal differences are also important in both species; diods are larger in Plakina paradilopha sp. nov. (62.5– 100 μm long and 2.5–7.5 μm wide) than in Plakina microlobata (45–60.5–72 × 1.5–2.75–4 μm). Additionally, Plakina microlobata possesses triods, which are absent in Plakina paradilopha sp. nov.

Plakina elisa ( de Laubenfels, 1936) from the Caribbean possesses dilophose calthrops but also monolophose calthrops and diods with several sharp spines ( de Laubenfels, 1936), which are absent in the diods of Plakina paradilopha sp. nov. (see Table 2).

Figures

Figure 1. Distribution and sample localities of Plakinidae species from the Mexican Pacific coast. Numbers refer to different species as follows: 1, Plakina muricyae sp. nov.; 2, Plakina paradilopha sp. nov.; 3, Plakortis clarionensis sp. nov.; 4, Plakortis albicans Cruz-Barraza & Carballo, 2005; 5, Plakinastrella clippertonensis van Soest et al., 2011.

Figure 2. External morphologies of plakinid species from the eastern Pacific. A, B, Plakina muricyae sp. nov. C, i, Plakina paradilopha sp. nov.; ii, Plakina muricyae sp. nov. D, Plakortis clarionensis sp. nov. E, Plakortis albicans Cruz-Barraza & Carballo, 2005. F, Plakinastrella clippertonensis van Soest et al., 2011.

Figure 4. Scanning electron microscopy and light microscopy images of spicules and skeletal structure of Plakina paradilopha sp. nov. A, diods. B, triods. C, dilophose calthrops. D, transversal view of the choanosome.