Latrunculia (Latrunculia) apicalis Ridley and Dendy. The 1886

Latrunculia (Latrunculia) apicalis Ridley and Dendy, 1886

(Figs 1C, 2, 3B, 4B; Tables 2 & 3)

Latrunculia apicalis Ridley and Dendy, 1886: 492; 1887: 239, PL. XLIV FIG. 4, PL. XLV FIGS 9A–C [in part]

Holotype material. BMNH 1887.5.2.88, ethanol preserved sample (a wet, dark deep chocolate brown subsample of specimen, 2 x 10 x 10 cm was examined) and microscope­slides, Kerguelen, off Christmas Harbour, January 29, 1874; depth 126 m, Challenger Expedition.

Description. Massive, semispherical sponge, 6 x 7.5 x 8 cm diameter, with broad base and convex upper surface (Fig. 3B). Surface smooth but sandpapery to the touch, with volcano­ and cylindrical­shaped oscules, 6 mm high, and truncate mammiform areolate porefields 2 x 2 mm in diameter. Ectosome thick, leathery, not separable from underlying choanosome. Colour in life dark brown, in preservative pale yellow.

Skeleton. The choanosomal skeleton is a very irregular polygonal­meshed reticulation formed by wispy tracts of smooth styles (Fig. 4B). These tracts range in width from 91–136 µm thick, forming meshes that are 230 µm wide. Towards the surface the spicules tend to be vertically arranged. The surface of the ectosome consists of an erect layer of aciculodiscorhabds. Beneath the discorhabds in the ectosome is a thick paratangential layer of densely interlocking megascleres, approximately 730 µm wide.

Spicules. Megascleres: styles are smooth, centrally thickened, fusiform and slightly sinuous 406 (382–436) x 16 (16) m, n=20. Microscleres (Fig. 1C): aciculodiscorhabds, basal whorl closely associated with the manubrium, followed by a smooth slender cylindrical shaft 11 m long and 5 m wide. The median whorl is circular, broad, flat and horizontally arrange, 25 m in diameter, being the largest of the four whorls. The median whorl is divided into three distinct segments each possessing 7–8 denticulate margins or spines. The subsidiary whorl is 20 m in diameter, and divided into three discrete segments each with six denticulate margins or spines. The spines of the apical whorl are slanted upwards and not divided into segments, so that whorls ends in a crown­like tuft of acute spined projections. Projecting beyond the apical whorl is a smooth slender, fusiform acicula (apical projection) ~ 46 m long. The base of the acicula is armoured with two horizontally arranged whorls of spines that are followed by the smooth slender acicula. Anisodiscorhabd length, 74 (53–83) m, n=20.

Substratum, depth range, and ecology. Found on sandy and muddy environments at a depth of 126.

Geographic distribution (Fig. 2). Kerguelen Islands.

Remarks. Ridley and Dendy (1886) first described this species in a preliminary report of the Challenger Expedition. The most characteristic feature of this species (and from which the specific name has been derived), is the apical prolongation (acicula) of the aciculodiscorhabd. Ridley and Dendy (1887) described two specimens under the name Latrunculia apicalis from the same geographical area and although they indicated various slight differences between the two specimens, they considered both to be species of Latrunculia apicalis as stated by them…"we have, during the course of our description, indicated various slight differences between the specimens from the two localities, but there is nothing to justify us in separating them specifically". In their description however, Ridley and Dendy (1887) failed to mention that one of their specimens (from station 320) possessed two types of anisodiscorhabds.

After examining the two specimens in question BMNH 1887.5.2.88 (Type) and BMNH 1887.5.2.84a (Type), the latter (BMNH 1887.5.2.84a) is considered a species of Latrunculia biformis Kirkpatrick (see below on this species) (Table 2 & 3). BMNH 1887.5.2.88 (Type) differs from BMNH 1887.5.2.84a in that the surface of the ectosome is lined with an erect layer of single aciculodiscorhabds and a multitude of oscules and areolate porefields. Although there is a great variability in the length of the acicula of the aciculodiscorhabd within BMNH 1887.5.2.88 (Latrunculia apicalis), all possess an extended smooth acicula, indicating that only one type of anisodiscorhabd is present within this species. The ontogeny of the developing spicule also conforms to that described by Dendy (1921). Latrunculia apicalis has not been recorded since from the same or any other locality