Oscarella filipoi, Perez & Ruiz, 2018

Perez, Thierry & Ruiz, Cesar, 2018, Description of the first Caribbean Oscarellidae (Porifera: Homoscleromorpha), Zootaxa 4369 (4), pp. 501-514 : 504-506

Oscarella filipoi sp. nov.

Holotype: Muséum National d’Histoire Naturelle de Paris , MNHN—DJV193 : Martinique, Le Diamant, Caribbean Sea. Site « Tunnel du Diamant » (14°26.556' N, 61°2.408' W), 10 m depth, on a vertical wall of the tunnel, date 11/ 06/2011. Sample code : 120325 -MT1TP14 collector T. Pérez ( Fig. 2 ). GenBank accession number: KX3482268. Paratype 1: Muséum National d’Histoire Naturelle de Paris , MNHN—DJV194 : Martinique, Le Diamant, Caribbean Sea. Site « Grotte Fer à Cheval » (14°27.882' N, 61°01.162 W), 17 m depth, overgrowing an octocoral in the cave entrance, date 25/03/2012. Sample code : 120325 -MT4bTP01, collector T. Pérez.

Paratype 2: Muséum National d’Histoire Naturelle de Paris , MNHN—DJV195 : Saint Martin, Caribbean Sea. Site « Rocher Créole » (18°07.038' N, ' 063°03.419' W), 10 m, under an overhang, date 26/05/2015. Sample code: 150526 -SN3CR08 collector C. Ruiz.

Other material examined: Martinique, 131203 -MT3CR1, Grotte Couleur at 8 m depth, Anses d'Arlet, collector C. Ruiz ; 120325 -MT1TP12, 120325 -MT1TP13, 120325 -MT1TP14, Tunnel du Diamant at 15 m depth, collector T. Pérez. This material is kept in the collection of the Station Marine d’Endoume (Marseille—France).

Etymology: the new species is dedicated to Philippe Thélamon, a resourceful diver of Anses d’Arlet. Known by his nickname “Filipo”, he is deeply involved in nature conservation and the promotion of Martinique’s marine biodiversity. Filipo was the first to take us to the type locality of the new species.

Diagnosis. The largest Oscarella recorded world-wide, covering up to 1m ², inhabiting shaded habitats. Color from purple to yellow and light green, with the largest specimens always purple, thick, with a pale-green base. Large specimens are often associated to tiny hydroids. Thick ectosome, especially in the basal part, is mostly devoid of cells. Ovoid to spherical eurypylous choanocyte chambers. Only one type of vacuolar cell is abundant and is grouped in clusters in the mesohyl.

Description. External morphology: An encrusting sponge with irregular clathrate surface and small lobes. Size up to 1 m ² and 2–3 cm thick. Different color morphotypes have been observed: the most common is deep purple, but light green and light orange were also observed in natural conditions ( Fig. 2 ). The surface is mostly colored while the basal part is pale or green in large specimens, turning green in all cases when put in alcohol. The consistency is soft, fragile and easy to tear. The surface presents small lobes that converge to oscula of about 1–4 cm diameter. Large and heavy specimens tend to partially detach from the substrate, often hanging from the ceiling of semi-dark caves and tunnels.

Soft tissue organization: No spicule or fiber skeleton. The ectosome is 20 to 50 µm in the apical zone, but can be considerably thicker than 100 µm in the basal part ( Fig. 3A ). Inhalant canals, 13 to 22 µm wide, often run perpendicular to the surface. The exhalant canals run towards a well-developed system of irregular basal cavities from 2 to 150 µm in diameter before finally reaching the oscula of the sponge. Eurypylous choanocyte chambers are ovoid to spherical, from 30 to 72 µm in diameter ( Fig. 3 ). Apopylar cells are located around the apopyle of the choanocyte chambers. Basopinacocytes delimit the basal part from the substrate ( Fig. 3 ). The ectosome is mostly devoid of cells, with only a few vacuolar cells distributed randomly underneath the pinacocytes ( Fig. 3 ).

Cytology: Choanocytes have a rather pyramidal shape, 3 to 7 µm wide at the central part and 3.5 to 7 µm high. ( Fig.4 ). Their collar is 3 µm wide, composed of about 30 microvilli. Their nucleus is basal, centrally positioned, and 1.5 to 3 µm in diameter. Their cytoplasm usually contains 1 to 3 phagosomes of 0.8 to 1.7 µm in diameter, osmiophilic inclusions and mitochondria. Apopylar cells also have a pyramidal shape, and are about the same size as the choanocytes. Pinacocytes are flat and flagellated, 7 to 12 µm wide and 1 to 3 µm high. Their nucleus is ovoid, up to 2 µm in diameter. Several osmiophilic inclusions between 0.4 and 0.7 µm were observed only in the cytoplasm of endopinacocytes ( Fig. 4 ). No archaeocytes were observed in the mesohyl. One type of vacuolar cell, with an ovoid to irregular shape, 8 to 16 µm in diameter, is quite abundant and is grouped in clusters in the mesohyl ( Fig. 4 ). Its cytoplasm contains between 2 and 5 vacuoles, 3.5 to 10 µm in diameter, and their content is always clear. No bacteriocytes were observed. A single morphotype of symbiotic prokaryote is distributed in the mesohyl. It has a bacillus morphology, 1 to 1.5 µm long and 0.5 µm in diameter, with a cell wall consisting of many layers of dense filaments ( Fig. 4 ). Each bacteria is surrounded by a surface devoid of collagen fibers ( Fig. 4 ). No reproductive elements were observed.

Ecology. Oscarella filipoi sp. nov. was found in rather shallow waters, from 3 to 20 m depth. This new species prefers half-light conditions, and can thus be found on vertical walls of semi-dark marine caves, under overhangs, underneath rocks or inside crevices. The only sign of epibiosis is an undetermined tiny hydroids that grows into the lobes of the sponge, especially on large specimens. No sign of predation was observed.

Taxonomic remarks. The new species cannot be confused with the previous aspiculate Homoscleromorpha described in the Caribbean, as it has very classic Oscarella external morphology: it is clathrate with a very soft consistency, whereas A. madinina , for instance, has a cushion or globulous shape with a gelatinous consistency. On the other hand, the aspiculate P. nathaliae is a leaf-like, thinly encrusting sponge, which is a rather classic external morphology for Plakina . According to the in situ photos available in previous reports of Oscarella in the Caribbean Sea, the new species may well have formerly been called O. lobularis (e.g. Vacelet 1998). The external morphology (color, consistency and aspect of the surface) of the smallest specimens of O. filipoi sp. nov. is indeed very similar to the Mediterranean species, but the largest specimens do not correspond to any previous reports of Oscarella . The largest specimens tend to detach from the substratum, allowing a part of the body to hang like a curtain. The mesohylar content of the new species is very different from that of O. lobularis , as it includes abundant clusters of vacuolar cells, a trait shared with O. tuberculata ( Boury-Esnault et al. 1992) .

Figures

FIGURE 2. In situ pictures of Oscarella filipoi. A) O. filipoi is the biggest Oscarella species ever recorded, surface covered reaching 1m² in certain cases. B) Green chromotype, very rare. C) Orange chromotype, rare. D) Detailed view of a common tiny cerianthid associated with O. filipoi.

FIGURE 3. Histological sections of Oscarella filipoi sp. nov. A. General soft tissue organization. B. Detailed view of the mesohyl showing the aquiferoussystem and the ectosomelayer.C.Detailed view of the basal part of O.filipoi.cc: Choanocyte chamber; ect:Ectosome; bas:basopinacocyte; vc: Vacuolar cell.

FIGURE 4. TEM micrographs of Oscarella filipoi sp. nov. A) Detailed view of choanocytes. B) Detailed view of endopinacocytes.C) Detailed view of vacuolar cell. D) Detailed view of some of the few prokaryote morphotypes found in O. filipoi. Cho:Choanocyte; end: Endopinacocyte; vc: part of a vacuolar cell.