Brachyrhynchus acutus Artois & Schockaert

Artois, Tom, Willems, Wim, Reygel, Patrick & Schockaert, Ernest, 2013, Brachyrhynchus n. gen. n. sp., a new genus of Polycystididae Graff, 1905 (Rhabdocoela: Kalyptorhynchia), with the description of three new species from the Mediterranean and the Indian Ocean, Zootaxa 3635 (2), pp. 127-136 : 132

Brachyrhynchus acutus Artois & Schockaert n. sp.

( Figs 1 A, 3B, 4A)

Localities. Italy, Sardinia, Stintino, Punta Negra, 40°57’11.6”N 8°13’43.2”E, on algae from rocks, partially shaded, at 0.5 m, 19 August 1994 (TYPE LOCALITY); same locality, coarse-grained sand with pebbles, 25 March 2010.

Studied material. Three animals studied alive and mounted, one designated holotype (SMNH, no. 7835), the other two deposited as voucher specimens (HU, nos VI.1.40–VI.1.41). Three serially-sectioned specimens, also deposited as voucher specimens (HU, nos VI.1.42–VI.1.44).

Etymology. The species name refers to the sharp-ending main stylet. Acutus (Lat.) : sharp ending, pointed.

Description. In behaviour, habitus and internal organisation ( Fig. 1 A), this species is almost identical to B. triplostylis n. sp. (see above). The main differences are found in the shape and dimensions of the hard parts of the male system. Animals are about 0.7 mm long (measured on whole mounts).

The prostate stylet of B. acutus n. sp. is 107–111 µm long (x = 109 µm; n = 3) ( Figs 1 A; 3B; 4A: pst), slightly curved and ends in a sharp point. The first accessory stylet ( Figs 1 A; 3B; 4A: ast1), connected to the larger of the two accessory glandular vesicles ( Fig. 1 A: av1), is 103–111 µm long (n = 2; one of the specimens could not be measured). The shape of this stylet does not differ from the first accessory stylet in B. triplostylis n. sp. The second accessory stylet ( Figs 1 A; 3B; 4A: ast2), is 81–86 µm long (x = 83 µm; n = 3) and is also of the same shape as the corresponding stylet in B. triplostylis n. sp. This accessory stylet is connected to the smaller accessory glandular vesicle ( Fig. 1 A: av2). The stylet ratios (same symbols as in the description of B. triplostylis n. sp.) are α = 98–104% (n= 2), β = 76–77% (x = 76%; n = 3) and γ = 73–84 % (n = 2).

Diagnosis. Species of Brachyrhynchus with a sharply-ending prostate stylet type IV, 107–111 mm long. Accessory stylets 103–111µm and 81–86µm long. Stylet ratios (symbols: see description): α=98–104%, β=76–77% and γ=73–84%.

Figures

FIGURE 1. Brachyrhynchus acutus n. sp. (A) Habitus of a live specimen. Brachyrhynchus triplostylis n. sp. (B) Atrial organs (from a live specimen). (C) Sagittal reconstruction of the genital system, combined from the two serially-sectioned specimens (from the right hand side).