Rhabderemia itajai, Oliveira & Hajdu, 2005

Oliveira, Maíra V. & Hajdu, Eduardo, 2005, Taxonomy of Rhabderemia Topsent, 1890 collected from the southeastern Brazilian continental shelf and slope by Programme REVIZEE (Rhabderemiidae, Poecilosclerida, Demospongiae), with the description of two new species, Zootaxa 844 (1), pp. 1-12 : 7-9

Rhabderemia itajai sp. nov. ( Fig. 5 )

Material studied. Holotype: MNRJ 3177 , station 6786, 27°28.700´S – 47°09.660´W, off Itajaí (Santa Catarina State), 380m depth, collected by N. Oc. Prof. W. Besnard, 19 January 1998.

Diagnosis. Rhabderemia itajai sp. nov. is the only species in the genus with rhabdostyles which are never smaller than 300µm, next to microstyles always smaller than 70µm and small spirosigmata always smaller than 10µm.

Description. The holotype is composed of nineteen fragments, the largest of which measures 33 x 27 x 13 mm (length x width x thickness — Fig. 5. a ). It is massive with a flexible consistency. Surface is microhispid, uneven with scattered oscules (0,5mm in diameter). Light ­ brown colored in alcohol.

Skeleton. Ectossomal skeleton composed of brushes of rhabdostyles originating from terminating ascending choanosomal bundles. A crust of embedded sediment is visible in parts. Rhabdostyles barely protrude beyond the surface (ca. 150 m at most). Choanosomal skeleton plumose to plumo­reticulate, made of straight, ascending bundles of rhabdostyles from which other such megascleres may project at right angles. Aquiferous channels (up to 150 m in diameter) are visible all over the choanosome, although not in large numbers. Microscleres occur in great numbers all over the sponge, but not nearly as densely as in R. besnardi sp. nov. ( Fig. 5. b ).

Spicules. Megascleres: Rhabdostyles ( Fig. 5. c ) – large, robust, with a smooth and well marked base and heavily spined shaft, with sharp thorns; 302 – 412,9 – 488µm in length, by 16 – 20,3 – 24µm thick. Microscleres: Microstyles ( Figs. 5. d, 5. e ); 34 – 51,2 – 68µm in length, by 1 – 1,5 – 2µm thick. Small spirosigmata – ( Figs. 5. f, 5. g ); 5 – 6,4 – 9µm in largest diameter.

Ecology. Collected on soft sediment.

Etymology. The species is named after the city of Itajai, used as a name in apposition, in front of which it was collected.

Remarks. Rhabderemia itajai sp. nov. is set apart from all other species in the genus by a combination of morphological traits. Van Soest & Hooper (1993) conducted a taxonomic revision of Rhabderemia , in which a total of seven species appear to have a set of spicule categories comparable to that of the new species, viz. one category of rhabdostyles, one of microstyles and one of small spirosigmata. These are R. antarctica Van Soest & Hooper, 1993 ; R. gallica Van Soest & Hooper, 1993 ; R. indica Dendy, 1905 ; R. profunda Boury­Esnault et al, 1994; R. spirophora (Burton, 1931) ; R. stellata Bergquist, 1961 and R. topsenti Van Soest & Hooper, 1993 . Further, R. uruguaiensis , as described here, can be added to these. The new species difers from all these, but for R. profunda , by its considerably larger rhabdostyles (302–488µm long in the new species, as opposed to 202–265µm in R. antarctica , 54–178µm in R. gallica , 211–263µm in R. indica , 240–286µm in R. spirophora , 200–356µm in R. stellata , 145–315µm in R. topsenti and 92–429µm in R. uruguaiensis ). R. profunda appears to be the closest relative to the new species, from which it differs by its still larger rhabdostyles (411–620µm long) with a subterminal swelling, its larger microstyles (77–135µm long vs. 34–68µm in the new species) and small spirosigmata (9,5–15µm long vs. 5–9µm in the new species). If subjectivity in the establishment of size categories is accounted for by further considering those species which are reported to have two size categories of either spicule category present in the new species, another eight need to be considered, viz. R. acanthostyla Thomas, 1968 ; R. africana ; R. bistylifera ; R. burtoni Van Soest & Hooper, 1993 ; R. forcipula (Lévi and Lévi, 1989) ; R. minutula (Carter, 1876) ; R. prolifera Annandale, 1915 and R. uruguaiensis (sensu Van Soest & Hooper, 1993). All of these have considerably smaller rhabdostyles (reaching a maximum lenght of 352µm in R. minutula ), apart from R. forcipula and R. uruguaiensis (up to 381µm and up to 429µm long, respectively). The new species differs from R. forcipula by the latter’s much longer microstyles (150–171µm), and from R. uruguaiensis by the latter’s possession of rhabdostyles that can be as small as 98µm long (as opposed to rhabdostyles always larger than 300µm in the new species). The new species appears thus well differentiated from other congeners.

Figures

FIGURE 5. Rhabderemia itajai sp. nov. (A) Preserved specimen; (B) Skeleton arrangement; (C) Rhabdostyle; (D) Microstyles; (E) Spined base of microstyles; (F) Microstyles and a small spirosigmata; (G) Small spirosigma; (H) Small spirosigma. Scale bars: A, 1,0cm; B, 100µm; C, 100µm; D, F, 10µm; E, G, H, 1µm.