Pachastrella pacoi Van Soest, Meesters & Becking, 2014

Van, Rob W. M., 2017, Sponges of the Guyana Shelf, Zootaxa 1, pp. 1-225 : 100-101

Pachastrella pacoi Van Soest, Meesters & Becking, 2014

Figures 61 a–f

Pachastrella abyssi ; Van Soest & Stentoft 1988: 34, pl. V figs 3–6, text-fig. 15 (Not: Schmidt, 1870: 64, pl. VI fig. 4) Pachastrella pacoi Van Soest et al., 2014: 407 , figs 4a–d, 5a–g

Material examined. RMNH Por. 9786, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 51, 7.6833°N 57.0333°W, depth 98 m, bottom calcareous sand, 30 August 1970 .

Description. Irregular shaped, thickly flattened fragment ( Fig. 61 a), 12 x 8 x 3–4 cm, dark red–brown in alcohol, with rough surface, encrusted with vermetids, serpulids and sponges. No apparent oscules. Consistency hard.

Skeleton. At the surface the skeleton consists of a dense, approximately 150 µm thick, layer of microrhabds. The choanosomal skeleton consists of thin bundles and single oxeas running at right angles to the surface, with inbetween a confused mass of triaenes and microscleres.

Spicules. ( Figs 61 b–f) Oxeas, plagiotriaenes, amphiasters, microrhabds, microrhabdose streptasters (sensu Cárdenas & Rapp 2012).

Oxeas ( Figs 61 b,b1), or occasional stylotes, smooth, slightly curved, sharply pointed, in a large size range, 1.800– 2117 – 3000 mm x 17 – 27.0 –51 µm.

(Small fusiform oxeas, not shown, 210–300 x 6–11 µm, are present as usual, but these are suspected to be from encrusting sponges).

Plagiotriaenes ( Figs 61 c), short-shafted to calthrops-like, quite variable in size, cladomes 61– 221 –350, cladi 30– 171 –280 x 6 – 22.8 –31 µm. No dichotriaenes or spicules with bifid ends were found.

Amphiasters ( Fig. 61 d), quite uniform in shape and size, with usually 10–12 thin, strongly spined rays, 13– 14.2 –15 µm.

Microrhabds/microstrongyles ( Figs 61 e,e1,e2), densely spined with conical or sharp-ending spines, variable in length and thickness, not clearly divisible in shape and size categories, (smaller ( Fig. 61 e) 12–15 µm, middle sized ( Fig. 61 e1) 16–18 µm, larger ( Fig. 61 e2) 22–28 µm), overall 12– 16.6 – 28 x 2 – 3.8 –6 µm.

Microhabdose streptasters ( Figs 61 f,f1), somewhat similar to microrhabds but longer and thinner, with the spines crowned with sharp smaller spines ( Fig. 61 f1), 32– 36.1 – 41 x 1 – 1.3 –1.5 µm (these microscleres are termed ‘thin long microrhabds with complicated spines’ in the description of the holotype).

Distribution and ecology. Guyana Shelf, Bonaire, Barbados, 98–232 m ( Guyana Shelf 98 m).

Remarks. Although the body shape of the present specimen deviates rather strongly from the cup-shaped habit of the type and Barbados specimens, the spiculation is quite similar. The fragment likely does not properly reflect the shape of the specimen.

P. pacoi is part of a complex of species including P. monilifera Schmidt, 1868 and P. abyssi (see discussion in Cárdenas & Rapp 2012), distinguished on small details of spiculation. It remains to be demonstrated what the phylogenetic status of the species exactly is.

Puerto Rican Pachastrella dilifera De Laubenfels, 1934 (p. 1) is quite dissimilar to P. pacoi (and also P. abyssi ), by possessing acanthomicroxeas and both amphiasters/metasters and spirasters. Re-examination of a slide made from the holotype USNM 22331 revealed that P. dilifera should be reassigned to the genus Poecillastra .

Figures

FIGURE 61. Pachastrella pacoi Van Soest, Meesters & Becking, 2014, a, habitus of RMNH Por. 9786 (scale bar = 1 cm), b – f, SEM images of spicules, b, oxea, b 1, details of b, c, larger and smaller short-shafted plagiotriaenes, d, amphiaster, e, small microrhabd, e 1, intermediate microrhabd, e 2, large microrhabd, f, microrhabdose streptasters, f 1, detail of f.