Cyclacanthia bellae Samaai & Kelly 2003

Cyclacanthia bellae (Samaai & Kelly, 2003)

(Figs. 2 F, 3A, E–F, 4A)

Latrunculia bellae Samaai & Kelly, 2003: 14, Fig. 3 C, 4D, 5D.

Holotype. BMNH 2003.1.10.1: Ryi Banks, Algoa Bay, South east South Africa.

Paratype. SAM H­ 4963: Ryi Banks, Algoa Bay, South east South Africa.

Description (modified from Samaai et al., 2003). Thinly encrusting sponge, 5 mm thick in life, surface crowded with very small conical oscules and numerous thin­lipped crater­like areolate porefields (Fig. 3A). Compressible in life, slightly felty to the touch, emerald green in life, dark chocolate brown internally and in preservative. The sponges were collected from a moderately rugged rocky bottom with patches of sand between rocks, on Ryi Banks, Algoa Bay, southeastern South Africa, at 10– 22 m. Spicules. Megas­cleres— Styles: Smooth, hastate, centrally thickened straight or slightly sinuous styles, 364 (319–400) long x 12 m wide (Fig 4A). Microscleres— Acanthose isospinodiscorhabds: The median whorl is composed of four groups of discrete spines distributed evenly around the shaft, the spines of the manubrium and apical whorl are slanted obliquely from the median whorl and the spines are orientated at different angles within each whorl. A single spike protrudes from the apex and base of the spicule, all spines are markedly acanthose, 46 (44–51) m long (Fig. 2 F).

Skeleton. Large dense swathes of megascleres, 230–250 m wide, emerge from the base of the sponge towards the upper choanosome, where they diverge to form loose brushes and a whispy polygonal reticulation of tracts c. 60–180 m wide, forming a mesh c. 230 m wide (Fig. 3 F). Interstitial megascleres and microscleres are abundant. The ectosome of tangentially arranged styles is c. 320 m thick, and is aligned by an irregular palisade of densely packed isospinodiscorhabds (Fig. 3 E).

Remarks. While Samaai et al. (2003) considered C. bellae (Samaai & Kelly) to be unique amongst South African Latrunculiidae, they did not consider the combination of characters that this species displayed to be sufficient evidence for the erection of a new genus until further species were discovered. The discovery of two additional species has now justified this action.

The isospinodiscorhabds of C. bellae (Samaai & Kelly) (Fig. 2 F) are superficially similar to the isoconicodiscorhabds of the North Atlantic latrunculid genus Sceptrella (Fig. 2 C) in that they both have whorls of discrete spines grouped in an irregular distribution around the shaft (‘furcate spines’ of Samaai & Kelly, 2002), and these microscleres are both secondarily spinose. The key difference is that in the isospinodiscorhabds of Cyclacanthia sp. nov., the subsidiary whorl is absent in all three known species. The morphology of the isospinodiscorhabds is in fact more similar to the isochiadiscorhabds of Tsitsikamma. While the mature microscleres differ considerably in their overall morphology (the microscleres of Tsitsikamma bear three regular whorls of apically spined tubercules (Fig. 2 B), the subsidiary whorl in both types of microscleres is absent, and the ontogenetic pathways of both are similar. Moreover, species in both genera have thick tracts or swathes of megascleres in addition to the typically whispy polygonal reticulation of other Latrunculiidae (Samaai & Kelly 2002; Samaai et al., 2003). The phylogenetic implications of the similarities between Cyclacanthia sp. nov. and Tsitsikamma will be considered in the final discussion of this work.

The primary character of C. bellae (Samaai & Kelly), that is diagnostic at the species level, is the overall morphology of the microsclere, the design and geometry of the spines in the various whorls on the microsclere, the degree and nature of ornamentation of the spines, and the basal choanosomal architecture (Table 1).