Zygophylax crozetensis Millard 1977

Zygophylax crozetensis Millard, 1977

Plate 3 A–D

Zygophylax crozetensis Millard, 1977b: 3, 15–18, fig. 4; Millard, 1979: 140; Van Praët, 1979: 883–884, fig. 24; Rees & Vervoort, 1987: 85; Calder & Vervoort, 1998: 28; Vervoort & Watson, 2003: 69.

Type Series. Holotype—fertile colony in alcohol (MNHN H.01577). Paratype—fertile colony in alcohol (SAM- H2779); three slides with fertile colony branches (3 RMNH-Coel. slides 114).

Type Locality. “Marion Dufresne” Sta. 26/64-B, Orques Channel, Crozet Island, Indian Ocean, 46°24.8’ S 51°59.1’ E, 180 m.

Material examined. Paratype—Coll. Marion Dufresne, Sta. 26/64-B, 46°21.8’S, 51°52.1’E, 180 m, 20 April 1974, fertile colony (3 RMNH-Coel. slides 114).

Description of paratype. Stem polysiphonic composed by several secondary axial tubes along all extension, decreasing number distally; stem and hydrocladia with distinct apophyses budding off obliquely upwards in relation to main axis, in several planes (Pl. 3A); variable number of free hydrothecae between each pair of sub-opposite hydrocladia. Hydrocladia rectilineous attached to stem without apophysis, arising at angles 65°–70° in relation to stem; few irregular nodes/internodes observed, slightly oblique on main axial tube and on distal region of hydrocladia; some hydrocladia covered by secondary tubes with nematothecae and scar at insertion; weakly polysiphonic at proximal region, stem monosiphonic distally. Hydrothecae tubular, adcauline wall slightly convex, abcauline wall slightly concave (Pl. 3B); rim without renovations; diaphragm as thickened oblique perisarcal ring; pedicel from smooth to wrinkled at different degrees, sometimes with distinct annulations (Pl. 3B–C). Nematothecae pedicellated, on hydrothecal apophysis and secondary axial tubes, cylindrical to tubular, with constriction on proximal third (Pl. 3D); nematotheca on hydrothecal apophysis long, surpassing level of hydrothecal diaphragm. Gonosome aggregated into coppinia, thin gonothecae in dense clusters, distal part with free tubular processes pointing obliquely upwards, each process with one elliptical aperture; nematophorous tubules projecting among gonothecae with nematothecae and hydrothecae.

Measurements. Stem: diameter 140–590 µm; distance between subsequent hydrocladia at same side 1.1–2.3 mm. Hydrocladia: lenght 2.9–7.8 mm; diameter at base 170–250 µm. Hydrothecae: length of adcauline wall from rim to diaphragm 330–740 µm; diameter at rim 150 µm; diameter at diaphragm 90 µm; lenght of pedicel on adcauline wall 80–150 µm; diameter at apophysis 70–100 µm. Nematothecae: lenght 110–120 µm; diameter at rim 50–60 µm.

Geographical distribution. Only known from the type locality.

Remarks. Unfortunately, we did not study the entire colony of the type material of Z. crozentensis because it was not found in the collection of the MNHN (Paris, France), even though holotype and paratype were listed for that collection (Van Praët, 1979). The paratype specimens deposited in the South African Museum (SAM) were also not available for loan. However, we had access to permanent slides of the paratype deposited in the RMNH.

Millard (1977b) described Z. crozetensis with hydrotecae similar to many congeners, especially Z. africana, from which it differs by its totally adnate gonothecae while in Z. africana the gonothecae are not entirely fused. Mil- lard (1977b) emphasizes that many species of Zygophylax from the southern hemisphere have similar trophosomes, but different gonosomes. Indeed, Z. crozetensis have similar hydrothecae to its congeners, but their trophosome differ by the irregular pattern of hydrocladia around the colony axis.

The hydrothecae of the non-fascicled hydrocladia of Z. crozetensis are arranged alternate and on a single plane, whereas those of the fascicled branches are in many directions. The multiplanar pattern is similar to that of Zygophylax armata (Ritchie, 1907) from the South Atlantic, specially comparing to its polysiphonic axis. Another similar character between these two species is the coppinia formed by densely aggregated gonothecae with pointed projections at their distal ends. In contrast, Z. crozetensis is characterized by some of its hydrotecal pedicels being wrinkled at different degrees, while in the same colony some pedicels of the monosiphonic regions of the hydrocladia are totally smooth, as observed in the specimen RMNH-Coel. slide 114. Although Millard (1977b) did not cite this feature in the original description of the species, she represented one of the pedicels of the type material wrinkled with a strong proximal constriction. On a highly polysiphonic region in the specimen RMNH-Coel. slide 114, the most proximal third of the stem had numerous, long and well wrinkled pedicels, many without hydrothecae due to the bad state of conservation of the material.

Zygophylax crozetensis also resembles Z. sagamiensis in the coppinia and the wrinkled pattern of some hydrothecal pedicels, but the hydrothecae of the latter are arranged in one plane and either oriented to one side (cf. RMNH-Coel. slide 5352) or both sides of the colony (Hirohito, 1995).