Zygophylax africana Stechow 1923

Zygophylax africana Stechow, 1923

(fig. 2A–D, fig. 3A–D, table 2)

Zygophylax africana Stechow, 1923: 106.— Stechow, 1925: 445, fig. 18.— Millard, 1964: 15, fig. 4A–F.— Millard, 1973: 28, fig. 4B.— Millard, 1975: 189, fig. 62A–E.— Millard, 1977: 106.— Millard, 1978: 199.—Hirohito, 1983: 22, fig. 6a–e.— Rees & Vervoort, 1987: 75.—Hirohito, 1995: 136, fig. 40a–e.— Calder & Vervoort, 1998: 28.— Bouillon et al. 2006: 341. Zygophylax africanus: Vervoort & Watson, 2003: 69.

Material examined. INDEMARES 2010, La Gaviera Canyon (Avilés Canyon System), 28.04.2010, station DR06, 43º56.0440’N – 05º46.1390’W, 790 m, several colonies, one with a coppinia, on Madrepora oculata Linnaeus. INDEMARES 2011, La Gaviera Canyon (Avilés Canyon System), 0 4.05.2011, station DR04, 43º59.584’N – 05º43.915’W, 593 m, a small colony without gonosome on a scleractinian fragment.

Description. Colonies erect and branching, rising from a small hydrorhizal mass formed by numerous tubules. Stems polysiphonic, up to 2.5 cm high and 535 µm basal diameter, slightly flexuous. Ramification pinnate with second order branching. Side-branches up to 6.0 mm long, basally polysiphonic, given off left and right in the same plane at slightly acute angles below a cauline hydrotheca. Internodes indistinct, although slight constrictions of the perisarc occur over the axil of the hydrothecae. Second order branching following the same pattern.

Hydrothecae in two rows on stem and branches, pedicellate, borne on a short apophysis, alternatively to left and right, widely spaced and oriented frontally. Apophyses not always clearly demarcated from pedicel. Pedicels short, even or slightly undulated, sometimes moderately twisted. Hydrothecae long and tubular, thin, straight or slightly curved, with adcauline wall convex and abcauline side straight to slightly concave. Rim circular, even, faintly everted, normally with renovations. A subtle narrowing below rim sometimes occurs. Diaphragm distinct, straight or oblique, in this case with abcauline side higher.

Nematothecae short, tubular, with a small peduncle and somewhat everted rim with a few renovations; a subtle sub-marginal narrowing is sometimes present. Base flat, with rounded corners. Abundance variable, being numerous proximally in the stem of some colonies and scarce in others; 1–2 (rarely) occur typically on the hydrothecal apophyses. Others appear scattered on hydrocaulus and branches arising from secondary tubes, being normally absent on monosiphonic hydrocauli.

Gonothecae forming a compact oval coppinia 1.7 mm long and 1.2 mm wide, surrounding lower third of stem. They are adpressed for about two-thirds of their length, tapering basally, polygonal, with 4–6 sides in surface view; perisarc thick. Distal end free with short and wide neck laterally compressed (117–138 µm wide, 43–53 µm high), and two small diverging horns 214–262 µm long together, no longer than width of gonotheca (with the neck they are T-shaped). Tip of horns rounded, not sharp, curved toward basis of gonotheca. Ova (234 x 151 µm) within gonothecae. Nematophorous tubules scarce, widely spaced, short, two times longer than gonothecae, protruding up to 450 µm over them.

Remarks. Colonies examined here were small compared to those described by Millard (1975, 10 cm), but are similar to the holotype (Stechow 1923, 0.5–1.8 cm) and to those described by Hirohito (1995, 2.4 cm) from Japan. Autoepizoic hydrothecae are common in the material studied, as observed also by Millard (1973) in South African colonies.

The number of species in the genus Zygophylax Quelch, 1885 is difficult to determine, as an updated revision is lacking. While much needed, such a revision is complicated by doubts that exist about the taxonomic value of some characters widely used in descriptions of species, and gonosomes of some are still unknown (see Vervoort & Watson 2003). Rees & Vervoort (1987) and Vervoort & Watson (2003) have partially revised the taxon. The latter authors listed 51 species, with at least 13 of them having no known gonosome. Additional new species have been described since then, even in the northeastern Atlantic fauna (Z. parabiarmata Vervoort, 2006, Cape Verde Islands), and changes have been made in the status of others (Z. echinata Calder & Vervoort, 1998 synonymized with Z. sagamiensis Hirohito, 1983 by Vervoort 2006).

The genus has received considerable attention in Europe and nearby areas (Ramil & Vervoort 1992a; Altuna Prados & Álvarez Claudio 1994; Vervoort 2006), with nine species reported in the ERMS area after updating (Table 3). Of these, only two (Zygophylax parabiarmata and Z. sagamiensis) have gonothecae fused as in material studied here, with the latter recently recorded from continental Europe (Moura et al. 2012a, no description available). Colonies of Z. parabiarmata differ from material studied here, and their gonothecae have a unique terminal round aperture (Vervoort 2006).

Trophosomes of Zygophylax africana and Z. sagamiensis are almost identical in size and shape (Table 2). In describing Z. sagamiensis, Calder & Vervoort (1998, as Z. echinata sp. nov.) mentioned as main differences between the two species the distal end of the gonothecae —a unique spine (or horn) in Z. sagamiensis, two horns in Z. africana —, and the shape of the hydrothecae, which widen distally in Z. sagamiensis and are tubular in Z. africana. In the La Gaviera Canyon colonies, hydrothecae are tubular. In descriptions of Z. africana only one nematotheca is mentioned on the apophyses (Stechow 1923; Millard 1964; Hirohito 1983, 1995), although Millard (1975) reported ‘normally one on each hydrothecal apophyses’, without mentioning other alternatives. Colonies studied here have one, and exceptionally two (fig. 3A). This character, together with the different morphology of the gonothecal horns (described as longer and with sharp tips) and the absence of anastomoses, distinguish these colonies from those of other regions. Such differences cannot be justification for proposing a new species, given that in other better-known species of the family, such as Cryptolaria pectinata (Allman, 1888), development of the horns is very variable.

Millard (1964) noticed the great similarity between coppiniae of Zygophylax africana and Cryptolaria pectinata. Both species have fused gonothecae with a distal neck and two diverging horns. However, according to Stechow (1925) and Millard (1975), C. pectinata is also capable of forming gonothecae with a unique distal projection (see Ralph 1958), although it is not clear if both types of gonothecae (one-horned and two-horned) occur together in the same coppinia. Stechow (1925) attributed variability in the number of horns on gonothecae of C. pectinata to differences between male (one horn) and female (two horns) colonies, although that conclusion has not been confirmed (Millard 1975).

One-horned gonothecae of Cryptolaria pectinata and Zygophylax sagamiensis are similar (see Hirohito 1983; Calder & Vervoort 1998, as Zygophylax echinata). Moreover, Z. sagamiensis and Z. africana differ mainly in gonosomal characters (one-horned gonothecae in the former, two-horned in the latter). If colonies of C. pectinata conceivably have one and two-horned gonothecae (perhaps male and female), could Z. africana and Z. sagamiensis be the male and female colonies of a single species given that their main difference is the number of horns on their gonothecae? Millard (1964, 1975) stated that in Z. africana gonothecae of both sexes are identical and two-horned (but occur in different colonies). In Z. sagamiensis, one-horned gonothecae are male (Hirohito 1983, 1995), or of undetermined sex (Calder & Vervoort 1998, as Z. echinata sp. nov.; Watson 2003; Vervoort 2006), and apparently, its female gonothecae have not been described. Given that gonothecae are polygonal as in Z. africana (Hirohito 1995; Vervoort 2006), but also cylindrical (Watson 2003), there is meaningful variability. For this reason, a description of the female gonosome of Z. sagamiensis and an evaluation of the shape of the gonothecae as a taxonomic character are needed to establish the status of both species of Zygophylax.

Distribution. Zygophylax africana is evidently a rare species. While it has been mentioned in several papers, original records of it are few. It was first described from South African coasts (Stechow 1923, 178 m depth; Millard 1964, 1975, 137– 364 m depth), and is also known from Japan (Hirohito 1983, 1995, 50–103 m depth).

The species was dredged from a depth of 593–790 m in La Gaviera Canyon (Avilés Canyon System). This is the deepest record of the species, the northernmost record in the Atlantic Ocean, and the first time that it has been collected within the European and ERMS area.