Placospherastra antillensis (Van, Rob W. M. 2009)
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Ordo: Hadromerida
Familia: Placospongiidae
Genus: Placospherastra
Name
Placospherastra antillensis Van, Rob W. M., 2009 – Wikispecies link – Pensoft Profile
- Placospherastra antillensis Van, Rob W. M., 2009, Zootaxa 2107: 6-11.
Materials Examined
Holotype. ZMA Por. 0 8973, Netherlands Antilles, Bonaire, Red Slave 2, 12.034 °N - 68.259 °W, 23 m, 20 -08- 1987, coll. G.J. Roebers # 202. Paratypes. ZMA Por. 0 8974, Curaçao, Blauwbaai, under rubble, 12.131 °N - 68.987 °W, 35 m, 2-1989, coll. E. Meesters & P. Willemsen; ZMA Por. 21077, Curaçao, SeaQuarium, 12.081 °N - 68.8919 °W, 25 m, 1991, coll. M. Kielman #S 64.
Additonal material (not belonging to the type series). ZMA Por. 0 8487, Bonaire, reef caves, 12–43 m, 1984, coll. D. Kobluk; ZMA Por. 13716 & 14085, Curaçao, Buoy 0, 12.124 °N - 68.974 °W, in reef caves, 01- 1999, coll. I. Wunsch; ZMA Por. 19063, Curaçao, Buoy 3, 12.136 °N - 68.97 °W, reef, 2006, coll. N. van der Hall; ZMA Por. 0 8879, U.S.Virgin Islands, St. Croix, Cane Bay, 17.7417 °N - 64.7392 °W, 1990, coll. W. Gladfelter; ZMA Por. 0 3347, Puerto Rico, off Mayaguez, 18.25 °N - 67.225 °W, dredged at 60–75 m, bottom muddy sand, 21 -02- 1963, coll. J.H. Stock.
Description
Description. Thick encrustations with Placospongia -like surface of elongated polygonal plates, separated by meandering ridges below which thin pore grooves are situated (Fig. 3 A). The system of plates and ridges is irregular and forms a maze, with few ridges entirely enclosing the plates. Size of holotype5 x2.5 cm, thickness 1–5 mm. Color in life orange, dark orange, brown-orange or more yellow; in alcohol pale yellow or off-white. Consistency hard, rough to the touch. Skeleton. Distinctly zoned similar to the skeleton of Placospongia. A dense ectosomal layer of spherasters forms the surface of the polygonal plates. These are surrounded by strong columns of tylostyles rising up from the bottom of the sponge supporting the plates and forming the sides of the meandering pore grooves, in which they also protrude slightly causing the sides of the grooves to be elevated. No clear separation or localization of a smaller and a larger category of tylostyles is apparent, but the tylostyles have a large size range (see below). Subdermal tissue between the columns with few spherasters, scattered ‘diplasters’ and densely distributed microspirasters forming a distinct fibrous layer devoid of heavy spiculation. At the bottom of the sponge a thin layer of spherasters lines the boundary with the substrate. Spicules. Tylostyles, spherasters, ‘diplasters’, microspirasters/amphiasters. Tylostyles (Fig. 2 A–B), with prominent elongated heads, often annulated beneath the tyle, in a large size range,, 162- 428.6 - 578 x 3.5- 5.4 - 8 µm. Spherasters (Fig. 2 D and part of C), globular, with short conical rays, in full-grown condition ornamented with little blunt spines in a ring around the base of the cones, 27- 28.6 - 31 µm in diameter. Diplasters (Fig. 2 E and part of C), elongated with an often one-sided constriction in the middle, with long conical rays, with crenulated surface, 14- 17.8 - 21 µm. Possibly these are juvenile forms of the spherasters, in which case, nonetheless, one would expect to find more intermediate forms. Micramphiasters, microspirasters, and related forms (Fig. 2 F and part of C), tiny, with short rhabds and composite rays, often a bit irregular in shape, 2– 4.5 µm in length. Ecology. Usually under coral rubble and in reef caves, 20–23 m; occasionally exposed in deeper locations.
Etymology
Etymology. The genus name refers to the placospongia-like aspect of the surface and to the spherasters that replace the placospongiid selenasters. The species name indicates the so far Antillean occurrence (both Lesser and Greater Antilles) of the species.
Discussion
Remarks. With this new genus the family Placospongiidae, until recently monotypical, consists now of three genera. Placospongia Gray (1867 a) so far has six species, while Onotoa de Laubenfels (1955 b) has two species, and the new genus Placospherastra so far has one species (but see below). All three genera are closely similar in outlook and skeletal structure, making membership of a single family quite obvious, but possession of selenasters, until recently considered a strong synapomorphy for the family, is now restricted to the genus Placospongia. The two other genera lack selenasters and have instead amphinolasters (genus Onotoa) or globose spherasters (Placospherastra n. g.) in the same position, i.e. making up the surface armour. The new species was previously identified as an undescribed Placospongia, but to accommodate it within this genus would widen the defintion too far. Following the erection of Onotoa for placospongiid species with a replacement spicule type for the surface armour, it is proposed here to erect a separate genus for placospongiid sponges with yet another replacement spicule type. One could argue that this is unnecessary, since the lack of selenasters may be merely a loss, and the remaining spicules all occur in one or more true Placospongia species. Placospongia species frequently have tiny (2–3 µm diameter) spherasters lodged in the spaces among the selenasters at the surface. In Placospongia melobesioides Gray (1867 a) from Borneo, P. melobesioides sensu Arndt (1927) from Curaçao, P. intermedia Sollas (1888) from the Caribbean end of the Panama Canal, and P. cristata Boury-Esnault (1973) from Brazil, a complement of medium-sized spherasters occurs in the choanosome, looking surprisingly similar to golf balls in SEM images. In Placospongia decorticans (Hanitsch, 1895), spherasters of 16 µm diameter apparently form an extra surface armour on the outside of the layer of selenasters, which could indicate that the surface structure in P. antillensis n. g., n. sp. is induced by loss of the selenasters and the need for a replacement structure. Of the true Placospongia species, P. decorticans resembles P. antillensis n. g., n. sp. closest, sharing most spicule types. The same observations apply mutatis mutandis to differences between Placospongia and Onotoa, but the case for the latter genus is stronger since there are two species sharing the same surface spicule types. It is expected that more species lacking selenasters and having a surface armour of globose spherasters will be found to exist (see below). A further argument for keeping the new species in a genus of its own, is that the spherasters are morphologically distinct from those of P. melobesioides and P. decorticans in having an ornamentation of small spines encircling the conical rays. Possibly the term spheraster in this case does not cover homologous spicule forms. A somewhat deviating specimen (Fig. 3 B) of the new species, or possibly a representative of a second species of the new genus, is here recorded from a non-sciophilous muddy deep water habitat off the west coast of Puerto Rico (ZMA Por. 0 3347, details listed above). The sponge is seemingly branching, with branches 6 cm long and 0.5–1 cm in diameter, but cross section of the branches showed that the centre is formed by dead bryozoan material, indicating that the sponge is encrusting. Color was given as vermillion by the original collector, in alcohol it is yellow-brown. A striking feature are the white striated grooves separating the polygonal plates, which are much wider (4–5 mm) than in the sciophilous specimens described above (Fig. 3 B). The spicules are generally similar to those of the sciophilous specimens, but sizes of tylostyles (up to 600x 10–12 µm) and spherasters (32–40 µm) are on the upper side of the range or exceeding those of the type and paratypes. In spite of this and in spite of the unusual live color, for the time being the specimen is treated as a somewhat extreme specimen of the new species. Four other species of Placospongiidae were recorded from the Central West Atlantic: Placospongia carinata (Bowerbank, 1858), P. melobesioides Gray (1867 a), P. intermedia Sollas (1888) and P. cristata Boury-Esnault (1973).
Description
(1986) (including citation of Lehnert & van Soest, 1998), Rua et al. (2006), and unpublished specimens from the ZMA collection mentioned above = Placospongia sp. 1 (not: P. carinata (Bowerbank, 1858) (2) Placospongia melobesioides sensu Schmidt (1870), Arndt (1927), de Laubenfels (1936 a), González-Farías (1989) =? P. cristata Boury-Esnault (1973) (not: P. melobesioides Gray, 1867 a) (3) Placospongia cristata Boury-Esnault (1973) = valid species, see also above. (4) Placospongia melobesioides sensu Mothes et al. (2006) = Placospongia sp. 2 (not: P. melobesioides Gray, 1867 a) (5) Placospongia intermedia sensu de Laubenfels (1936 b) = Placospongia sp. 3 (not: P. intermedia Sollas, 1888) (6) Placospherastra antillensis n. g., n. sp. = valid species. Scott & Barnes (2005) performed sequence analysis of a world-wide set of Placospongia specimens, not further identified to species. Their conclusions were that more genetic differentiation is found than would be expected if there were only two or three cosmopolitan ‘species’. Our critical comparison of spicule sizes and types appear to support the conclusions of the genetic research. Several hadromerid species possessing tylostyles and spherasters occur in the Central West Atlantic. For completeness sake we present an overview to demonstrate they are not conspecific with our new species. Paratimea galaxa de Laubenfels (1936 a) from Florida differs in lacking the surface plates and possessing tornotes in addition to the tylostyles and the spherasters. Columnitis squamata, also from Florida, as described by Schmidt (1870) reminds of our new species in having polygonal surface ornamentation, but redescription by Sarà & Bavestrello (1996), made it clear that this is a tethyid genus and species (after previously having been assigned to the synonymy of Timea by de Laubenfels, 1936 a) showing little in common with our new species. The definition of the new genus resembles that given by de Laubenfels (1936 a) for the genus Kotimea, with type species Hymedesmia moorei Carter (1880, from the Gulf of Mannaar, India). The precise affinity of Carter’s species with tylostyles and spherasters remains undecided because the type material is lost. There are no indications in Carter’s description that the surface would have had armoured placospongiid plates. Rützler (2002 b) assigned Kotimea to the synonymy of Timea Gray (1867 b). A second species assigned to Kotimea, Hymeraphia spiniglobata Carter (1879) is a Diplastrella, while Kotimea tethya de Laubenfels (1954) is a Timea.
Taxon Treatment
- Van, Rob W. M.; 2009: New sciophilous sponges from the Caribbean (Porifera: Demospongiae), Zootaxa 2107: 6-11. doi
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