Agelas dilatata Duchassaing & Michelotti, 1864

Parra-Velandia, Fernando J., Zea, Sven & Van Soest, Rob W. M., 2014, Reef sponges of the genus Agelas (Porifera: Demospongiae) from the Greater Caribbean, Zootaxa 3794 (3), pp. 301-343 : 316-318

Agelas dilatata Duchassaing & Michelotti, 1864

Fig. 6

Etymology from Latin, meaning to expand, to dilate.

Ectyon flabelliformis Carter, 1883 , BMNH 1884.4.14.9 only, designed as lectotype by Wiedenmayer (1977).

Agelas dilatata Duchassaing & Michelotti, 1864: 77 , pl. 14, Fig. 1 ; Assmann 2000: 38, pl. 3; Assmann et al. 2001: 363, Fig 2 ; Alcolado 2002: 61; Zea et al. 2009.

? Agelas inaequalis Pulitzer-Finali, 1986: 111 , Figs. 32, 33.

Material and distribution. Holotype lost (van Soest et al., 1983), collected at Guadeloupe. Species redescribed by Assmann et al. (2001), who designed as neotype specimen ZMA POR. 15604 (examined by us), collected at Little San Salvador, Bahamas, 26 m. The material described here (INV– POR 939, 947) was collected in the same area of the neotype.

This species seems to be restricted to the Bahamas (see also Assmann 2000; Zea et al. 2009), and the north and south coasts of Cuba ( Alcolado 2002). We consider this as a Bahamian-Greater Antilles species. Our specimens were found from 18 to 30 m in depth, abundant at 23–25 m depth.

Description. This species is normally flabellate (Fig 6A), and usually pedunculated (Fig 6C); this basic form can adopt some variations like divided flabella (Fig 6B) or cylindrical branches with flattened ends; some specimens have a half-cup shape (Fig 6F). The diameter is typically 25–50 cm, although some specimens can reach 0.8–1 m; thickness usually up to 3 cm. External colour in the areas exposed to light is orange to tan; in shaded specimens it is darker orange to brown; at the centre or the base of most specimens there are some cinnamon spots; the underside or the base are orange to orange yellow; internal colours are orange yellow to yellow. When preserved the colour becomes brownish, when dry it becomes greyish. Pinacoderm supported by tracts of spicules protruding from the main fibres; the surface is smooth and even underwater, becoming roughish when taken out of the water; subdermal channels are not apparent.

There are two different types of openings: (1) on the exposed side, abundant evenly scattered circular oscules, 4–8 mm in diameter, surrounded by a milky membranous ring (Fig 6D); the confluent exhalant channels are visible throughout the aperture; (2) on the underside, unevenly dispersed ostia, about 1–2 mm in diameter (Fig 6E). This side is usually infested with black to dark brown zoanthids. The consistency is firm but compressible, harder when dry. The choanosome is dense, with narrow channels that do not exceed 4 mm in diameter.

The skeleton is a dense reticulation of spongin fibres; the primaries are cored by 1–5 spicules per cross section, but occasionally the coring spicule tract is absent. Primaries 50–100 µm in diameter, secondaries 40–60 µm in diameter, and tertiaries 20–50 µm in diameter. Primary fibres have slightly less echinating spicules than secondary and tertiary. Although in some specimens primaries are irregular and hardly distinguishable, in others they are clear, despite absence of coring.

Spicules are straight acanthostyles with 4–7 spines per whorl; length 75–160 (108±22.2) µm, width 4–8 (6±1.1) µm and 9–18 (13±2.4) whorls per spicule. Detailed lengths, widths and average number of whorls are shown in Table 2.

Remarks. Typically found in outer reef and island slopes of the Bahamas, growing on vertical or overhanging reef walls; also in caves and other shaded environments; hardly above 15 m in depth. The tentative neotype designation by Assmann et al. (2001) was made following as close as possible the original description of Duchassaing & Michelotti (1864): “Mass widened rather flattened, reddish surface above, blackish on side, small pores almost always scattered” and the accompanying picture.

The description of Agelas inaequalis Pulitzer-Finali, 1986 fits within the variation observed by us in a wide set of specimens of A. dilatata . Thus, it is probably a junior synonym of A. dilatata , although a closer re-examination of A. inaequalis holotype is mandatory, paying special attention to the oscular morphology, skeleton fibres organization and differences between upper and lower surfaces. Dr. P.M. Alcolado (pers. comm.) suspects this could be a record of A. dispar .

Agelas flabelliformis ( Carter, 1883) , specimen BMNH 1884.4.14.9, as described by Carter himself and designated by Wiedenmayer (1977) as lectotype, belongs to A. dilatata ; its spicule length, shape and cribriform pore groups were also seen in A. dilatata specimens.

Figures

FIGURE 1. SEM images of Agelas. A) Spicules of A. conifera holotype. B) Spicules of A. clathrodes holotype. C) to D) Fibre skeleton with primary and secondary fibre echination, in A. citrina (C), A. dispar (D, curved fibres) and A. conifera (E). F) Detail of the skeleton of A. conifera showing coring spicules in a broken primary fibre. G) Detail of the skeleton of A. citrina with its long spicules.

FIGURE 2. Photographs of Agelas dispar. A) Holotype. B) Bahamas massive specimen; note clustered collared oscules, and small circular oscules. C) Barbados round lobate specimen. D) Belize. E) Jamaica. F) San Andres Island (Colombia) flabellate specimen; note the keyhole-shaped oscules. G) Rosario Islands (Colombia) lobate specimen.