Zygophylax africana Stechow 1923

Zygophylax africana Stechow, 1923

Plate 2 A–G

Zygophylax africana Stechow, 1923: 106–107; Stechow, 1925: 445–446, fig. 18; Millard, 1964: 15–18, fig. 4a–f; Millard, 1968: 263; Millard, 1973: 28, fig. 4b; Millard, 1975: 189–190, fig. 62a–e; Millard, 1977a: 106; Millard, 1978:199; Gravier-Bonnet, 1979: 29; Millard, 1980: 131; Hirohito, 1983: 22–24, fig. 6; Rees & Vervoort, 1987: 75; Hirohito, 1995: 136–138, fig 40 a–e; Calder & Vervoort, 1998: 28; Bouillon et al., 2006: 341; Ruthensteiner et al., 2008: 25; Altuna, 2012: 5–8, figs. 2, 3.

Zygophylax africanus Vervoort & Watson, 2003: 69. [incorrect subsequent spelling]

Type Series. Holotype—colony pieces on some substratum in alcohol (ZSM 20040731). Paratypes—slides with colony branches (ZSM 20041574; ZSM 20043579) (Ruthensteiner et al., 2008).

Type Locality. Valdivia, St. 92, North of Agulhas Bank, 33°41’S 18°00’E, Cape Town, South Africa, 178 m, 26 October 1898.

Material examined. Cape Town, South Africa, 34°23’S 18°08’E, 287 m, 18 December 1929, Det. N.H. Millard, fertile colony (ZMUC-HYD 268); Coll. Benthedi, St. S 97, Indian Ocean, Îles Glorieuses, off nothern Madagascar, 11°32’S 47°16’E, 715 m, 07 April 1977, without gonophores (RMNH-Coel. slide 250); St. FA 131, La Reunion Island, Indian Ocean, 20°52.2’S 55°05.9’E, 675–720 m, 01 September 1982, fertile colony (RMNH-Coel. slide 259); St. IIC 176, as “ Z. africana var. irregularis ”, La Reunion Islands, Indian Ocean, 21°01.7’S 55°10.6’E, 165–195 m, 08 September 1982, fertile colony (RMNH-Coel. slide 251).

Description of additional material (ZMUC-HYD 268). Stem weakly polysiphonic, without nodes and internodes; branches of first order with numerous hydrocladia, all at same plane; hydrothecae and nematothecae irregulary arranged. Hydrocladia mostly monosiphonic, some polysiphonic basally (Pl. 2A–B). Hydrothecae tubular, widening distally, adcauline wall convex, abcauline wall concave (Pl. 2C); pedicel continuous to apophysis; diaphragm thick, oblique in relation to hydrothecal long axis; renovations common (up to 6) (Pl. 2D); two rows of hydrothecae at same plane, turned to one side of the colony. Nematotheca insertion scar on hydrothecal apophysis; one or two cylindrical preserved nematothecae observed on apophysis (Pl. 2D–E). Gonosome aggregated in dense clusters into coppinia, gonothecae surrounding branch with nematophorous tubules provided nematothecae and hydrothecae (Pl. 2F); each gonothecae with two long horn-shaped projections with large oval apertures on their tips (Pl. 2G).

Measurements of additional material. Stem: distance between two subsequent hydrothecae 156–260 µm; diameter 156–312 µm; distance between subsequent hydrocladia on the same side 1.4–1.6 mm. Hydrocladia: lenght 3.3–9.6 mm; diameter at base 78–182 µm. Hydrothecae: lenght of adcauline wall from rim to diaphragm 270–300 µm / with renovations 350–370 µm; diameter at rim 90–100 µm; diameter at diaphragm 60–70 µm; length of pedicel on adcauline side 40–60 µm. Nematothecae: lenght 90–120 µm; diameter at rim 30 µm. Coppinia: maximal diameter of gonothecae 170 μm.

Geographical distribution. Bay of Biscay, Iberian Peninsula, 593–790 m (Altuna, 2012); Cape Town and Agulhas Bank, South Africa, 137–363 m (Stechow, 1923; Millard, 1964, 1975); La Reunion Island 165–195 m (present study); Izu-Niijima and Sagami Bay, Japan, 50–103 m (Hirohito 1983, 1995).

Remarks. There are many citations to the species in the literature, but Z. africana is basically known from a few records composing a disjunct distribution, viz. South Africa (Millard, 1975), Japan (Hirohito 1995), and Iberian Peninsula (Altuna, 2012). Herein we add a record for the Indian Ocean (RMNH-Coel. slide 251). Unfortunately, the type series of Z. africana could not be accessed.

Stechow (1923) described Z. africana, comparing that with Zygophylax valdiviae Stechow, 1923 and Z. convallaria (Allman, 1877). Among these species, Z. convallaria presents larger and sigmoid hydrothecae with the adcaulinar wall more sinuous, nematothecae more elongated, gonothecae not adnate with short projections of the distal end, as we observed in the specimens ROMIZ B1921 and USNM 52473. On the other hand, Z. valdiviae has smaller dimensions than Z. africana, with more rectilineous walls of hydrothecae (Stechow, 1925). Unfortunately, Z. valdiviae is only known from the original description based on material lacking gonosome (Stechow, 1923). Zygophylax africana was also described from infertile material (Stechow, 1923, 1925), but its gonosome was subsequently described (Millard, 1964, 1975; Hirohito, 1983), being similar to the coppinia of the specimen ZMUC-HYD 268 studied by us.

Rees & Vervoort (1987) remarked about the affinities between Z. africana and Cryptolaria Busk, 1857, with apedicellate hydrotheca, based on the secondary axial tubes of the stem and hydrocladia extending over the pedicels of hydrothecae. Subsequently, Millard (1964) suggested that both Cryptolaria and Zygophylax should be united. However, this character is variable and related to the stage of development of the colony—young colonies have fewer secondary axial tubes on all planes of the colony resulting in non-immersed hydrothecae. This is clear in the specimen ZMUC-HYD 268, with monosiphonic hydrocladia and few polysiphonic stem and ramifications, resulting in few immersed hydrothecae with conspicuous pedicel.

Zygophylax sagamiensis Hirohito, 1983 is also a species with similar trophosome to that of Z. africana, what can be seen by some previous misidentifications (e.g., Ritchie, 1911; Watson, 1973). The shape and size of the hydrothecae of Z. africana and Z. sagamiensis are indeed similar, hindering the identification of infertile specimens, but the gonosomes are distinct, with gonothecae with two projections oriented to opposite directions in Z. africana and only one projection in Z. sagamiensis (Hirohito, 1995; Vervoort, 2006). In addition, the gonothecae of Z. sagamiensis are completely adnate to each other, and only the tubular processes are free, presenting a polygonal aspect on a superior view, whereas those of Z. africana have the most distal third of the gonothecae completely free. Nevertheless, in one gonotheca of the specimen Z. sagamiensis (RMNH-Coel. slide 5352), we observed two projections horn-shaped of equal size, contrary to the pattern of the majority of the gonothecae of the same colony in which the pattern with only one projection dominates. However, this pattern might be a small intraspecific variation.

The apical tubular processes of the gonothecae of Z. africana are usually elongated in South Africa (Millard, 1964, 1975; ZMUC-HYD 268). However, specimens from the Bay of Biscay have gonothecae with shorter and thicker projections, suggested to be a variable intraspecific character (Altuna, 2012). Gonothecae with two apical projections in opposite directions are present in other species of the genus Zygophylax, such as Z. convallaria, Z. bifurcata, Zygophylax levinseni (Saemundsson, 1911), Zygophylax curvitheca Stechow, 1913, among others, but the degree of proximity between the gonothecae, and the size and curvature of the projections are variable among them.