Rhynchozoon undetermined

Rhynchozoon sp. (Fig. 12.1–5) ? Rhynchozoon tubulosum: Hayward 1988a: 336, pl. XIV, figs (a)–(b), non Mucronella (?) tubulosa Hincks, 1880b. Material examined. SMF 40795 (St. 283 KU; Fig. 12.1–4), SMF 40809 (St. 283 KU; Fig. 12.5). Description. Colony encrusting, multiserial, uni- to multilamellar; second layer originating from colony centre through frontal budding (Fig. 12.1–2). Zooids arranged quincuncially, separated by broad and distinct furrows. Septula inside vertical walls monoporous, circular (Fig. 12.3). Ancestrula not observed, overgrown by frontally budded autozooids (Fig. 12.2). Autozooids hexagonal, 274–411 μm (ẋ = 351 ± 33 µm; CV = 9; N = 25 on 2 specimens) long by 243–339 μm (ẋ = 291 ± 29 µm; CV = 10; N = 25 on 2 specimens) wide (Fig. 12.3). Frontal shield strongly convex, smooth, pierced by 6–10 elliptical areolar pores at the margins, and occasionally one additional pore between areolar pores and lateral side of orifice. Orifice subterminal, 81–111 μm (ẋ = 98 ± 8 µm; CV = 9; N = 20 on 2 specimens) long by 100–118 μm (ẋ = 110 ± 5 µm; CV = 5; N = 20 on 2 specimens) wide; anter subcircular to slightly transversely elliptical, surrounded by 15–20 small denticles, separated by pair of low, abraded condyles from broad and shallow sinus (Fig. 12.4). Suboral mucro usually pointed, circular to kidney-shaped, occasionally swollen and bearing an avicularium. One or two conical processes occasionally developed lateral to the orifice, circular to longitudinally elliptical (Fig. 12.2). Oral spine bases variable in number, usually two but occasionally reduced to one or completely absent, distolateral to the orifice (Fig. 12.3). Ovicells not observed. Avicularia monomorphic, adventitious, single, infrequently developed on swollen suboral mucro proximolateral to the orifice, bilaterally symmetrical, acuminate, 93–108 μm (ẋ = 103 ± 8 µm; CV = 8; N = 3 on 2 specimens) long by 55–63 μm (ẋ = 59 ± 4 µm; CV = 7; N = 3 on 2 specimens) wide (Fig. 12.5). Avicularian aperture proximally located, longitudinally elliptical, occupying most of avicularian frontal; crossbar complete, at about one-fourth the avicularian length. Rostrum acute, strongly elevated, laterally directed. Kenozooids not observed. Remarks. Rhynchozoon is a diverse genus, with at least six species reported from the Red Sea (Ostrovsky et al. 2011, and references therein), and five species reported from Mauritius (Hayward 1988a), excluding Rhynchozoon tubulosum (Hincks, 1880b), which is discussed below. Rhynchozoon sp. is distinguished from all these species by the presence of usually two oral spine bases and a very shallow, broad orificial sinus (Fig. 12.4). In some early astogenetic zooids, three oral spine bases may be present. Avicularia are occasionally observed proximolateral to the orifice on the suboral mucro, although they are frequently broken off (Fig. 12.3). The two studied colonies are young and exhibit limited secondary calcification. Unfortunately, no ovicells are present in the available material; therefore, the species is retained in open nomenclature. Amui & Kaselowsky (2006) reported Rhynchozoon haha Hayward, 1988a from the Bab-el-Mandeb Strait (St. 230 KD1 of R.V. Meteor expedition 5/2 “MINDIK”). Originally described from Mauritius, this species differs from Rhynchozoon sp. in lacking oral spine bases and in possessing large, triangular frontal avicularia. Another potentially relevant species is Rhynchozoon tubulosum, as illustrated by Hayward (1988a, pl. XIV, figs (a)–(b)) from Mauritius. While this species also has two oral spines, it differs in having a slightly narrower orificial sinus. As noted by Ryland & Hayward (1992, p. 296), the Mauritian specimens figured by Hayward (1988a) are not conspecific with Rhynchozoon tubulosum as originally described by Hincks (1880b) from Australia, but instead likely represent a distinct, undescribed species of Rhynchozoon. It is therefore possible that Rhynchozoon tubulosum sensu Hayward (1988a) is conspecific with Rhynchozoon sp.