Aspiculophora madinina, Ruiz & Muricy & Lage & Domingos & Chenesseau & Pérez, 2017

ASPICULOPHORA MADININA View in CoL SP. NOV.

FIGS 5 View Figure 5 , 6 View Figure 6

Diagnosis: Plakinidae without spicules, well-developed mesohyl with a thick collagen layer and without subectosomal cavities. Generally brown, but also cream to white. Smooth and ‘grooved’ surface. Jelly-like consistency. Leuconoid aquiferous system and aphodal choanocyte chambers. High abundance of prokaryotic symbionts.

Holotype: MNHN DJV180 , Rocher du Diamant at 12 m depth, La Martinique (14 ° 26.5 0 N, 61 ° 03.083 0 W). Collector: T. Perez, 13 June 2011.

+, Presence;, absence; HMA, high microbial abundance; LMA, low microbial abundance; NA, data not available (modified from Muricy et al., 1999). Paratype 1: MNHN DJV181 , Tintamare, Les Arches at 10 m depth, Saint Martin (18 ° 07.588 0 N, 62 ° 58.248 0 W). Collector: C. Ruiz, 26 May 2015 .

Paratype 2: MNHN DJV182 , Grotte Cathedrale at 16 m depth, Anse Bertrand, La Guadeloupe (16 ° 27.740 0 N, 061 ° 31.837 0 W). Collector: C. Ruiz, 29 May 2015 .

Other specimens examined

150514- MT6 -TP1, Grotte Chauve-Souris at 7 m depth, Anse Noire , La Martinique (14 ° 32.024 0 N, 61 ° 05.278 0 W). Collector : T. Perez, 14 May 2015 .

150517-SV1-CR14, Bat Cave at 8 m depth, Bucament Bay, Saint Vincent (13 ° 11.275 0 N, 61 ° 16.174 0 W). Collector C. Ruiz, 17 May 2015.

150523-GU1-CR7, Cave north-west of Les Saintes at 8 m depth, Les Saintes, La Guadeloupe (15 ° 52.984 0 N, 61 ° 34.25 0 W). Collector: C. Ruiz & T. Perez, 23 May 2015 .

131206- MT3 -AE2, Grotte Couleur, Pointe Burgos at 12 m depth, Anse d’Arlet, La Martinique (14 ° 29.752 0 N, 61 ° 05.407 0 W). Collector: A. Ereskovsky, 6 December 2013 .

150527-SN5-TP5, Basses Espagnoles at 10 m depth, Saint Martin (18 ° 07.821 0 N, 63 ° 00.270 0 W). Collector: T. Perez, 27 May 2015 .

150528-AG3-CR1, Little Scrub at 15 m depth, Anguilla (18 ° 17.903 0 N, 62 ° 57.294 0 W). Collector C. Ruiz, 28 May 2015.

150530-GU6-TP7, Grotte Amedien at 12 m depth, La Guadeloupe (16 ° 30.033 0 N, 061 ° 28.774 0 W). Collector: T. Perez, 30 May 2015 .

Etymology: The genus name reflects the absence of skeleton: from Latin a (= without) spiculum (= spearhead, arrowhead) phora (= bearing). The species name, madinina , refers to the amerindian name, ‘Flower Island’, of La Martinique Island, which is the first island of the Caribbean Sea where this aspiculate Plakinidae was found.

Description: Aspiculophora madinina has mainly a cushion shape, measuring 2 – 15 cm in diameter by 2 – 5 cm high, but sometimes it can be found hanging down, with prominent oscules surrounded by a thin membranous collar ( Fig. 5A View Figure 5 ). The colour in vivo is mainly brown, occasionally yellow to cream ( Fig. 5A View Figure 5 ). Brown specimens produce a dark exudate in contact with alcohol. The consistency is soft, almost gelatinous. The surface is smooth and grooved. Oscules are circular, 1 – 2 mm in diameter with an elevated rim.

Soft tissue organization: The ectosome is 6 – 15 lm. The aquiferous system is leuconoid with inhalant/ exhalant canals about 30 – 100 lm wide. A dense collagen fibril layer, about 8 lm in thickness, surrounds the exhalant canals. Some specimens also exhibit a thicker collagenous layer, about 1 mm, between the ectosome and the basal part of the sponge, where very few cells or prokaryotes are found ( Fig. 5B View Figure 5 ). Choanocyte chambers (18 – 36 lm in diameter) are spherical and aphodal.

Cytology: The choanocytes are cylindrical to spherical, 4 – 7 lm wide and 6 – 7 lm high. Their nucleus, 2 lm in diameter, is spherical and in apical position ( Fig. 6A, B View Figure 6 ). Their cytoplasm is not dense, often with one to three phagosomes and microgranular inclusions of about 1.5 lm in diameter. These inclusions are also observed in endopinacocytes ( Fig. 6C View Figure 6 ). The exo- and endopinacocytes are flattened, 15 – 20 lm long and 7 – 11 lm wide. Only one type of vacuolar cell is present and restricted to the ectosomal region, sometimes in aggregates, always close to exhalant canals ( Fig. 6C View Figure 6 ). This spherical cell, 9 – 13 lm in diameter, has a nucleus of 3 – 4 lm and harbours between two and ten vacuoles. Few archaeocytes were observed, with an irregular form and a nucleus of about 2 lm in diameter.

Symbiotic prokaryotes: This sponge can be considered as an HMA sponge. Five morphotypes were distinguished based on their morphological traits. All prokaryotes are randomly dispersed and occupy most of the mesohyl ( Fig. 6B – D View Figure 6 ). The first morphotype corresponds to an abundant ovoid cell (2 – 3 lm long; 1 – 1.5 lm wide), with a clear membrane about 0.1 lm wide. The second morphotype, also abundant in the sponge mesohyl, has a rod form (1.5 lm long; 0.5 lm wide). The third morphotype has an irregular ovoid form (1.5 – 2.0 lm long; 1 lm wide), with a dense cytoplasm and one to three external vacuoles in contact with the cells’ outer membrane. The fourth morphotype is a spherical cell, with a dense periplasm, of about 1 lm in diameter. The fifth morphotype is a small spherical cell of about 0.1 lm in diameter. This morphotype was sometimes observed in groups of three to five cells in a row ( Fig. 6D View Figure 6 ).

Ecology: Aspiculophora madinina sp. nov. is a sciaphilous species, living on vertical walls of semi-dark and dark caves or under overhangs. It was recorded between 5 and 50 m depth.

Taxonomic remarks

Aspiculophora madinina sp. nov. is a homoscleromorph sponge without skeleton and with a high content of collagen, providing a jelly-like consistency. As yet, massive forms such as this have not been reported in the aspiculate Oscarellidae . On the other hand, this species could be a Plakortis without spicules because most of its representatives occur as massive or globular forms. There is one report of such a Plakortis without spicules in the Caribbean Sponge Guide ( Zea, Henkel & Pawlik, 2014), but the taxonomic affiliation to Plakortis was based only on the external morphology and the pungent smell of some specimens. It is difficult to compare the cytological characteristics of a putative new species with other Plakinidae , because of the lack of data at this level of biological organization. Indeed, traditional taxonomy has placed most attention on the skeletal description of this family, even if skeletal differences are poorly detectable in many species. Some other characters such as a leuconoid aquiferous system, eurypylous choanocyte chambers, well-developed mesohyl and subectosomal cavities are not sufficiently diagnostic, as they can be present or absent among Plakina , Plakortis and Plakinastrella species. We thus believe that more thorough cytological investigations of Plakortis , Plakinastrella and Corticium might help in resolving a good number of taxonomic questions in this family.

The new genus is proposed because of the singularity of its CO1 sequences positioning the new species among the Plakinidae , near the base of this clade, but outside all previously known genera.

Moreover, we believe that its internal organization, with a thick collagen layer surrounding the inhalant canals and within the mesohyl, is unique among Homoscleromorpha.

DNA ANALYSIS OF STUDIED SPECIES

GenBank accession numbers for all sequences in this study are presented in Table 3. The two families of Homoscleromorpha are well supported in the phylogenetic reconstructions ( Figs 7 – 9 View Figure 7 View Figure 8 View Figure 9 ). With the Folmer partition ( Fig. 7 View Figure 7 ), Corticium appears as a monophyletic taxon of Plakinidae . Plakortis seems to be paraphyletic, a first clade being composed of Plakortis angulospiculatus ( Carter, 1879) and the type species P. simplex Schulze, 1880 , while a second clade clusters P. albicans Cruz-Barraza & Carballo, 2005 with two Plakinastrella species. In this representation lacking a sequence of the type species, Plakina appears as a poorly supported monophyletic group ( Fig. 7 View Figure 7 ), with two clades (bootstrap values of 312/47), one with P. crypta Muricy, Boury-Esnault, Bezac & Vacelet, 1998 , P. monolopha and P. muricyae Cruz-Barraza, Vega & Carballo, 2014 closely related, and the other comprising three specimens of P. nathaliae , P. trilopha , P. jani and P. kanaky .

The second phylogenetic tree using the I3-M11 CO1 fragment ( Fig. 8 View Figure 8 ) supports three monophyletic genera among Plakinidae , Aspiculophora , Plakinastrella and Plakortis . In this analysis Plakina is paraphyletic, P. monolopha (type species) forming a highly supported clade with C. candelabrum Schmidt, 1862 , a second group containing P. arletensis sp. nov. and P. jani , and a third with P. crypta and P. trilopha .

The third phylogenetic tree was made by concatenating all available sequences ( Fig. 9 View Figure 9 ). Because of missing data for one of the two fragments, the alignment contains several gaps and the concatenated tree appears less robust than the two-first representations of the inter-specific relationships among Homoscleromorpha. However, the topology of this third tree is quite congruent with the previous ones. In this representation, Aspiculophora forms a separate clade within the Plakinidae . Also, Plakina seems paraphyletic with two different clades, the first one grouping P. arletensis sp. nov. with P. kanaky , P. jani , P. trilopha and P. nathaliae , whereas the second one, containing the type species P. monolopha , P. muryciae and P. crypta , is related to Corticium , which seems monophyletic. Plakortis also appears paraphyletic, a first clade grouping the type species P. simplex , P. halichondroides and P. angulospiculatus , and a second clade containing P. albicans , Plakinastrella onkodes and an undetermined Plakinastrella . Finally, a separate clade containing five specimens of Plakinastrella also makes this genus paraphyletic in this phylogenetic representation.