Sigmaxinella cearense Salani & Lotufo & Hajdu 2006, sp. nov.

Sigmaxinella cearense sp. nov.

Figs. 2, 3, 4

Holotype. MNRJ 8687, Parque Estadual Marinho da Pedra da Risca do Meio (ca. 03°34'399 S-38°22'840 W, off Fortaleza, State of Ceará, Brazil) 23m depth, flat sandstone reef, coll. E. Hajdu, 15.vii.2004.

Diagnosis. Sigmaxinella cearense sp.nov. is the only Sigmaxinella in the Atlantic Ocean, and the only species in the genus with absence of raphides/microxea. Further, it still is the only species with a single category of styles as megascleres (mean length 435µm, mean width 12µm), and sigmas (mean length 21µm).

Description. The single specimen collected is 105mm high and 65mm in maximum diameter. Its live colour was yellow, which turned into beige after preservation in 70% ethanol. It has the form of a short bush on top of a narrow peduncle, 20mm across, with a wider base, 50mm in diameter (Fig. 2). The bushy part is composed of six main, slightly fusiform branches which run parallel to the main axis of the sponge. The tallest of these branches is 55mm long, the smallest, 40mm long. Each branch is composed by a collection of smaller, coalescent, secondary branchlets. The overall aspect of the bush is rather spiny, due to the erect-oblique, conulose or spatuliferous projections which abound at the surface of the branchlets. Similar but shorter projections are also found on the peduncle and base. Consistency is hard but compressible and elastic. Oscules were not clearly seen, but small (1–2mm diameter) apertures occur here and there, some of which might be oscules.

Skeleton. Ectosomal architecture unspecialized, made by the slightly divergent terminations of ascending choanosomal spiculo fibres. Isolated spicules are frequent, spread in a criss-crossed fashion, some of which may pierce the surface up to 300µm (Fig. 3A). Sigmas are abundant in the choanosome, in between the spiculo fibres. Choanosomal skeleton axially compressed. Axial skeleton only slightly visible in longitudinal sections of the spatuliferous projections, ca. 350µm across, composed of ramifying, multispicular tracts of styles coated by abundant spongin. The overall pattern is plumo-reticulate. From this central axis, multispicular, slightly plumose, slightly echinated tracts of styles run towards the surface. The axial skeleton in the peduncle bears in transverse section, a much denser, reticulate arrangement of ascending spiculo-fibres (mostly around 200µm thick, but up to 625µm in diameter), coated by a much stouter layer of spongin (Fig. 3B, longitudinal section), when compared to the spatuliferous projections. In spite of the abundant spaces spread in between these thick spongin coated spiculo fibres, the arrangement is quite firm and rather hard and friable when sectioned. Sigmas are common, but not so much as in the spatuliferous projections.

Spicules (Table 1): Megascleres — Styles (Fig. 4A), smooth, mostly slightly bent just below the middle portion, equally thick on most of its length, but tapering very gradually to a sharp point (Fig. 4B), 320- 434.9 - 764µm long (S.D. 78.4µm) and 2.6- 12.1 - 15µm thick. They are mostly around 400µm long, with a very few spicules reaching over 500µm in length.

Microscleres. Sigmas (Fig. 4C), variably slender, smooth along the wider curve in its shaft, abruptly bent, with sharp apices, 15- 21.2 - 25µm. Both terminations bear a few barblike, Paresperella - type spines on their outer edge.

to be continued.

Ecology and distribution. The single specimen was collected from a small horizontal crevice, with its upper part fully exposed to light. Five ophiuroids are still in place within the bushy part of the sponge. The species is probably rare, as only a single specimen was found in four dives. The area is characterized by warm waters year round, but strong swell may occur when winds blow stronger (August – January, Silva et al., 2002). During this time the abundant sand deposited on top and around the sandstone reefs may be suspended in the water column and increase stress for sponges, which are common occurrences on beach worn debris, at nearby beaches.

Etymology. “Cearense” is the name of those born in the state of Ceará. The species’ name, cearense, is a name in apposition.

Remarks. Table 1 compares the spicule measurements, collecting locality and depth of occurrence of all 12 known species of Sigmaxinella including the new species. It is a compilation of data presented by Hooper (1984), in addition to data from Carter (1883, 1885), Kirkpatrick (1903) and Brøndsted (1924). Sigmaxinella ramosa, from SE Australia, is most similar to the new species in its spicule set. Both possessing a single category of style and sigmas of comparable dimensions. Important points of distinction are the much stouter megascleres, and much smaller sigmas in the Australian species, as well as its possession of raphides. Sigmaxinella dendroides, another SE Australian species, is also close to the Brazilian species as far as spicule dimensions are concerned. That species, nevertheless, has two categories of sigmas, and possesses microxeas. The overall external morphology also sets all these species apart. Sigmaxinella ramosa has a digitiform, ramose shape with compressed, tapering branches; Sigmaxinella dendroides has cylindrical, dichotomous branches, disposed mostly in a single plane; and the new species has a pedunculate bushy form, with slightly fusiform branches which frequently anastomose. Other species in the genus have markedly distinct external morphologies as well as spicule dimensions.

From a biogeographic perspective, the most diverse areas for Sigmaxinella are the waters surrounding Australia and New Zealand (Hajdu & Van Soest, 2002). The occurrences of species in the Gulf of Aden and South Africa are nearly as unlikely as the new finding reported here from the south western Atlantic, representing a widely disjunct distribution of the genus across the entire Indian Ocean. There are no records for any Southeast Asian locality, the Indian subcontinent or any of the many archipelagoes in the Indian Ocean. Curiously, the species which appears morphologically the closest to the new Atlantic species described here occurs in SE Australia, which supports a transpacific track (Sluys, 1994) for the colonization of the South Atlantic Ocean (around Cape Horn), rather than a colonization via the shorter Agulhas track (around Cape of Good Hope).

Alternatively, as already pointed out by Hajdu & Van Soest (2002), the recognition of Sigmaxinella depends on the value attached to the axial condensation of its skeleton as a synapomorphic trait. It is quite conceivable that the genus may be polyphyletic, with axial condensations arising independently several times in its history. In this scenario, S. cearense sp. nov. would most likely be closer to Tropical western Atlantic species of Biemna, than to species currently assigned to Sigmaxinella, all of which occurring on widely distant areas of the globe. Mothes et al. (2004) described Biemna microacanthosigma from northern Brazil, which at first glance would appear as a likely sister-species. Nevertheless, the terminations of the sigmas in this species are more rugose than properly acanthose. The species bears also microxea and raphides, as well as styles in a much narrower size range (418–494µm length), which render it quite distinct from S. cearense sp. nov. The barb-like spines on the outer margin of the new species reported here are similar to those seen on Mycale (Paresperella) Dendy, 1905 (Van Soest & Hajdu, 2002), which could be suggestive of the need for a necessarily much broader review of the Mycalina classification.