Plakortis symbiotica, Vicente, Jan, Zea, Sven & Hill, Russell T., 2016

Vicente, Jan, Zea, Sven & Hill, Russell T., 2016, Sponge epizoism in the Caribbean and the discovery of new Plakortis and Haliclona species, and polymorphism of Xestospongia deweerdtae (Porifera), Zootaxa 4178 (2), pp. 209-233 : 215-218

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Plakortis symbiotica

sp. nov.

Plakortis symbiotica   sp. nov.

( Fig. 3 View FIGURE 3 ; Table 2 View TABLE 2 )

Plakortis   sp. 2; Vicente et al. 2014 (ecology and symbiosis).

Type material. Holotype and type locality: USNM 1254650 View Materials , basibiont of Haliclona plakophila   sp. nov., Old Buoy, La Parguera, Puerto Rico (17.9552° N, - 67.0532° W), 32 m depth, coll. Jaaziel García Hernández, October 15, 2015 GoogleMaps   . Paratype USNM 1254649 View Materials , basibiont of X. deweerdtae, Old Buoy, La Parguera   , Puerto Rico, (17.9552° N, - 67.0532° W), 32 m depth, coll. Jan Vicente, August 13, 2012 GoogleMaps   .

Specimens examined for comparison (other than those described here). Plakortis halichondrioides   : PHBH, Little San Salvador, Bahamas   , PHPR, La Parguera, Puerto Rico   .

Diagnosis. Thickly encrusting cushions with a soft irregular surface and compressible body. Found as basibiont of X. deweerdtae   but also of Haliclona plakophila   sp. nov. In Puerto Rico, both X. deweerdtae   and H. plakophila   can be found on the same individual of P. symbiotica   sp. nov. Both sponge epibionts grow as patches on the P. symbiotica   body, never fully covering the basibiont as observed in P. deweerdtaephila   , but can penetrate the basibiont body forming inner channels. Oscules are slightly elevated from the surface. Color can be dark green and dark brown in vivo and exudes a brown pigment when preserved in ethanol. Reticulated tangential ectosomal skeleton and reticulated choanosomal skeleton with lacunae present. Spicules consist of triods and diods of one size class.

Description. Thick cushions 3× 30 cm by 1–3 cm in thickness ( Fig. 3 View FIGURE 3 A). Oscules are slightly elevated measuring 0.3–1.7 cm in diameter. Oscules in preserved specimens are contracted. External and internal color is dark brown; a dark brown pigment is exuded when preserved. Surface is smooth, soft and irregular where X. deweerdtae   or H. plakophila   sp. nov. grows. Consistency is compressible, and easily torn.

Skeleton. Ectosome is a disorganized tangential reticulation of diods and triods. Multispicular tracts are not well defined but form circular meshes, 43– 73 –121 µm diameter (N=20; Fig. 3 View FIGURE 3 B). Spicules barely break the surface of the ectosome. When X. deweerdtae   or H. plakophila   sp. nov. form inner channels within the choanosome of P. symbiotica   sp. nov., the ectosome forms a barrier between the two sponge species as observed by Vicente et al. (2014, their Fig. 7 View FIGURE 7 E and F). The ectosome (60–70 µm thick) is dense and sometimes hard to distinguish from the choanosome. Subectosomal lacunae are present ( Fig. 3 View FIGURE 3 C). The choanosomal skeleton is dense but has an abundance of irregular circular meshes of varying diameters formed by a confused reticulation of diods and triods ( Fig. 3 View FIGURE 3 D).

Spicules. One size class of diods and triods. Diods are significantly sinuously bent, with a thick center. Ends are sharp and significantly bent ( Fig. 2 View FIGURE 2 E–F). Size (length x width): 72– 113.1 (±16.7)–142 µm x 2.2– 3.6 (±0.8)–5.0 µm ( Table 1). Triods are rare, Y-shaped, smooth, with sharp endings that are sometimes bent ( Fig. 2 View FIGURE 2 I): 20– 40.4 (±12.8)–71 µm long by 2.0– 3.3 (±0.7)–4.7 µm in width ( Table 1). Microrhabds, quasiamphiasters and spheres are absent.

Habitat and ecology. Sponge pairs are found on vertical walls (> 30 m), shaded side of pinnacles, and in reef cave habitats. Like Plakortis deweerdtaephila   sp. nov., the new species has only been found either associated with X. deweerdtae   or H. plakophila   , never free-living ( Vicente et al. 2014). Sponge pairs have been documented from small recruits ( Fig. 3 View FIGURE 3 D in Vicente et al. 2014) and growth morphologies of sponge pairs remain stable for long periods of time (Supplementary Fig. 4 View FIGURE 4 in Vicente et al. 2014).

Distribution. Bahamas (Little Inagua) and Puerto Rico (Mona Island, La Parguera, Desecheo) ( Figure 1 View FIGURE 1 B, D).

Taxonomic remarks. As in Plakortis deweerdtaephila   sp. nov., the lack of microrhabds or quasiamphiasters in P. symbiotica   sp. nov., places it within the P. simplex   species group (see above, cf. Muricy 2011). P. symbiotica   can be distinguished from all species of this complex by its association status with either haplosclerid, as well as by color, shape, size consistency and spicule composition. For example, P. symbiotica   has an irregular surface with large oscules which sets it apart from other Plakortis   spp. in this group. Unlike P. edwarsii   , only large diods are present in P. symbiotica   that form organized ectosomal meshes without cluttering opened circular spaces. Diods are also densely packed in both the ectosome and choanosome. P. symbiotica   occasionally forms lacunae which are not present in P. da r i a e or P. insularis   .

Other than P. deweerdtaephila   , the only other species to associate with X. deweerdtae   is P. symbiotica   (but see remarks above regarding P. angulospiculatus   as basibiont of X. deweerdtae   from Belize, cf. Rützler et al. 2014). In Puerto Rico, H. plakophila   is also an epibiont of P. s y m b i o t i c a. There are several morphological differences between P. deweerdtaephila   and P. symbiotica   . For example, P. s y m b i o t i c a has only large diods with small diods absent. The large diods are significantly more bent than in P. deweerdtaephila   ( Fig. 2 View FIGURE 2 E, F). The ectosome has circular meshes with smaller diameters (43– 73 –121 µm; Fig. 3 View FIGURE 3 B) than the ectosomal circular meshes of P. deweerdtaephila   (114– 205 –329 µm; Fig. 2 View FIGURE 2 C). The ectosome is denser and harder to differentiate in cross-sections of P. symbiotica   than of P. deweerdtaephila   . Subectosomal lacunae are present but much fewer than in P. symbiotica   ; the choanosome also appears to have more circular meshes than P. symbiotica   .

As for P. deweerdtaephila   , P. symbiotica   spicules were compared with those of P. halichondrioides   by Vicente et al. (2014), and shown to be larger in the latter. Our direct comparisons with a specimen of P. halichondrioides   from Puerto Rico show that P. s y m b i o t i c a can be distinguished by having smaller spicules and like P. deweerdtaephila   spicules never cross the surface of the ectosome or the open spaces of the circular meshes. Circular meshes are therefore better defined in P. deweerdtaephila   than in P. halichondrioides   .

Phylogenetic analysis. Our phylogenetic analysis used maximum likelihood to compare partial sequences of the cytochrome b (cob) and c (cox1) genes of our new Plakortis   spp. to other homoscleromorph sponge sequences deposited in GenBank. Our analysis confirmed that P. deweerdtaephila   sp. nov. and P. symbiotica   sp. nov. are more closely related to one another than to any other homoscleromorph or Plakortis   species ( Fig. 4 View FIGURE 4 ). Sequence homology between both species was 93% for cob and 94% for cox1 and formed a clade that was supported with bootstrap values (85 and 78% respectively). On the other hand, these differences are enough to support their status as separate species, which is further supported by the morphological differences outlined above. The closest relatives of the new species were P. simplex   and P. dariae   with a 92% sequence homology for both genes. Despite having similar morphological features compared to P. e dw ard s i, this species turned out to be more closely related to P. halichondrioides   and P. angulospiculatus   in the phylogenetic analysis of both genes (Ereskovsky et al. 2013). Support values in the phylogenetic analysis for the P. symbiotica   and P. deweerdtaephila   clades suggests that the symbiotic association of these sponges with other sponges is perhaps an ancestral, and even a synapomorphic character.

Etymology. The name symbiotica   denotes the tendency of the new species to associate with X. deweerdtae   and H. plakophila   sp. nov.


Smithsonian Institution, National Museum of Natural History