Plakinastrella clippertonensis, Van, Rob W. M., Kaiser, Kirstie L. & Syoc, Robert Van, 2011

Van, Rob W. M., Kaiser, Kirstie L. & Syoc, Robert Van, 2011, Sponges from Clipperton Island, East Pacific, Zootaxa 2839, pp. 1-46 : 5-8

Plakinastrella clippertonensis n. sp.

( Figs 2A , 3 A–D)

Holotype. MNHN DCL 4042–A, Jean-Louis Etienne Expédition Clipperton 2005, station 18, 55 m, on dead corals, 20–01–2005. 1 specimen.

Description. Cake-shaped ( Fig. 2A ), elongate mass of 3.5 x 1.5 x 1 cm. Surface smooth, but faintly grooved. Color light beige in alcohol. Consistency rather firm, but easily damaged.

Skeleton. A dense mass of diods and triods arranged around the aquiferous system. At the surface the skeleton is alveolar consisting of rounded meshes of approx. 50–100 µm diameter surrounded by tangential diods. The tangential crust of diods is carried by perpendicular bundles of diods mixed with triods, making small subdermal cavities. In the overall spiculation diods dominate, but there is a relatively large proportion of triods, and there are also rare small calthrops.

Spicules. Diods ( Fig. 3 A), centrotylote or crooked in the middle, occasionally two crooks occur, and small spines or incipient rays issue from the middle; size relatively small but quite variable, rendering computation of averages meaningless, 4–75 x 0.2–7 µm, the smallest ( Fig. 3 B) being irregular sinuous microdiods which do not appear a separate spicule category. A frequent size of the larger diods is 60– 70 x 5–6 µm.

Triods ( Fig. 3 D) either equiangular, with conical rays, or Y shaped, variable in size, most frequently with a ‘cladome’ of 40–45 µm, rays ranging from 5– 33 x 1–3 µm. The smallest are comparable in size with the microdiods, but their frequency is too low to consider them a separate microtriod category.

Calthrops ( Fig. 3 C), rare, mostly small, but ranging from 15–24 µm in overall diameter of the cladome, with rays 9–15 µm in length, usually unequal (N=12).

Ecology. Encrusting dead corals in deep reef habitat (55 m).

Etymology. Named after the locality.

Remarks. By the possession of calthrops this species is assigned to Plakinastrella but it appears close to many Plakortis species. Most Plakinastrella species, with the exception of Plakinastrella clathrata ( Kirkpatrick, 1900 as Placinastrella) described from Funafuti, Tuvalu, and Plakinastrella microspiculifera Moraes & Muricy, 2003 described from Northeast Brazil have calthrops much larger and in a similar size range of the diods. A recent definition of the genus ( Muricy & Díaz, 2002) emphasizes the occurrence of calthrops in three size categories. This supports the above suggestion that both the present new species and Plakinastrella clathrata and Plakinastrella microspiculifera would fit better in Plakortis than in Plakinastrella . Plakinastrella clathrata differs from our new species in the overall larger size of all spicule categories and by diods in two size categories, 140 and 36 µm, the smaller of which form an ectosomal palisade. Triods predominantly have a Y shape, they are up to 120 µm in cladome size; calthrops have rays 18–36 µm. Plakinastrella microspiculifera is very close in spiculation to our new species, but diods reach an upper size of 128 µm and triods are Y shaped and rare. The inter-ocean occurrence of both precludes the possibility that Plakinastrella clippertonensis n. sp. and Plakinastrella microspiculifera are conspecific.

Plakinastrella polysclera Lévi & Lévi, 1989 from the Philippines has much larger spicules and calthrops of 200–400 µm. This also applies to Plakinastrella mammillaris Lendenfeld, 1907 from Western Australia, but additionally this species appears to lack triods. Atlantic representatives of the genus, Plakinastrella copiosa Schulze, 1880 and Plakinastrella onkodes ( Uliczka, 1929) are likewise different in overall spicule sizes.

Like Moraes & Muricy (2003) we believe that the affinities of Plakinastrella with small calthropses lie with Plakortis Schulze, 1880 . If such spicules would be overlooked in casual studies this would result in a classification as Plakortis . To avoid a possible confusion, we compare our new species here with regional representatives of Plakortis as well. The comparison is also facilitated by a summary table (Table 1).

The new species appears close to Plakortis albicans Cruz-Barraza & Carballo, 2005 from the Pacific coast of Mexico. Color is white vs. light beige in our specimen. Size of diods and triods are basically similar, although diods in Plakortis albicans have a larger upper size range (132 µm vs. 75 µm in the new species). The smallest diods in Plakortis albicans are larger (12 vs. 4 µm in the new species) and appear less sinuous. There are microtriods like in Plakinastrella clippertonensis n. sp. The major difference is the apparent absence in Plakortis albicans of small calthrops. The second tropical East Pacific Plakortis species, Plakortis galapagensis Desqueyroux-Faúndez & Van Soest, 1997 shares the beige color with our new species, but diods are larger (up to 165 µm) and a distinct category of larger (126–165) and smaller (27–92) diods is reported. No calthrops were recorded and do not appear to be present in the type material (re-examined). The Japanese species Plakortis japonica ( Hoshino, 1977 as Monotria ) differs from Plakortis albicans and Plakortis galapagensis in a larger upper range of the diods (200 µm), but likewise lacks small calthrops.

The Pacific Plakortis lita De Laubenfels, 1954 recorded from the Caroline Islands, Indonesia, Papua New Guinea and Japan, shares the extremely small sinuous microdiods (see Díaz & Van Soest 1994), but has very few if any triods and has a peculiar liver-like consistency. A further Pacific species is Plakortis quasiamphiaster Diaz & Van Soest, 1994 from Vanuatu, which has strongly spined diods and triods.

Hooper (1994) recorded the Red Sea species, Plakortis nigra Lévi, 1953 from reef atolls of the Sahul Shelf. This is a black species and it has neither triods nor calthrops.

Spicule sizes of Pacific Plakinastrella and Plakortis species compared in Table 1.

Figures

FIGURE 3. Plakinastrella clippertonensis n. sp., spicules of holotype MNHN DCL 4042 – A. A. diods, B. microdiods, C. calthrops, D. triods, including ‘ microtriod’ (at right).

FIGURE 2. A. Plakinastrella clippertonensis n. sp. habit of holotype, MNHN DCL 4042 – A. B – D. Oscarella carmela Muricy & Pearse, 2004, B. habit of specimen MNHN DCL 4050 – A, C – D. Oscarella carmela Muricy & Pearse, 2004, C. histological cross section showing basal lacunae and embryos, D. detail of the same showing choanocyte chambers separated by peripheral grooves.