Zygophylax millardae Rees & Vervoort 1987

Zygophylax millardae Rees & Vervoort, 1987

Plate 5 A–D; Table 3

? Zygophylax biarmata: Jarvis, 1922: 335

Zygophylax ? antipathes: Millard, 1975: 190–192, fig. 62 f–g.

Zygophylax millardae Rees & Vervoort, 1987: 86–89, fig. 14; Calder & Vervoort, 1998: 28; Vervoort & Watson, 2003: 69.

Type series. Holotype—four fragments of a colony in alcohol, without gonophores (BMNH 1984.1.1.18); Para-types—slide with a colony branch, without gonophores (RMNH-Coel. slide 16520); slide with a fertile colony branch (RMNH-Coel. 16521).

Type locality. John Murray Exp., Sta 112, Zanzibar Archipelago, Tanzania, 05°04’18’’S 39°14’12’’E, 14 January 1934, 73– 165 m.

Material examined. Paratypes—John Murray Exp., Sta 112, Zanzibar, 05°04’18’’S 39°14’13’’E, 15 January 1934, 73– 165 m (RMNH-Coel. slide 16520); John Murray Exp., Sta 112, Zanzibar, 05°04’57’’S 39°13’18’’E, 15 January 1934, 113 m (RMNH-Coel. 16521); fragmented colony in alcohol, off northern Zanzibar, Tanzania, 05°04’57’’S 39°13’18’’E, 15 January 1934 (BMNH 1984.1.1.19); slide with a colony branch, Salomon Atoll, Chagos Archipelago, Indian Ocean, 220 m (BMNH 1923.2.15.118).

Description of holotype and paratype (RMNH-Coel. slide 16521). Colony attached to substratum by flattened disk formed by stolonal tubes. Stem weakly polysiphonic up to basalmost hydrocladium; sub-opposite hydrocladia pinnately disposed along stem; some hydrocladia with axillary hydrothecae, others arising direct from stem. Hydrocladia with distinct transversal septa; upright or slightly geniculate (Pl. 5A); hydrothecae of stem and hydrocladia on conspicuous apophyses arranged in two alternate series at same plane (Pl. 5B). Hydrothecae tubular to funnel-shaped; adcauline wall convex, more pronounced at basal half; abcauline wall rectilineous; plane of aperture perpendicular to hydrothecal length axis; renovations frequent, up to 5 (Pl. 5C); diaphragm thick, rectilineous to oblique; pedicel short, rectilineous, smooth. One short cylindrical nematotheca on hydrothecal apophyses; some rare wholes observed on secondary axial tubes (Pl. 5D). No coppinia.

Measurements. Stem: distance between two subsequent hydrothecae 780–936 µm; diameter 156–416 µm; distance between subsequent hydrocladia at the same side 6.6– 3.6 mm. Hydrocladia: diameter at base 104 µm. Hydrothecae: length of adcauline wall from rim to diaphragm 350–370 μm/with renovations 450–510 μm; diameter at rim 170–180 µm; diameter at diaphragm 85–90 µm; lenght of pedicel on adcauline side 160– 121 µm. Nematothecae: lenght 70 µm; diameter at rim 50 µm.

Geographical distribution. Zanzibar, Tanzania, 73–165 m (Rees & Vervoort, 1987); Mozambique and off Natal, southern Africa, 6–110 m (Millard, 1975); Amirante Islands and Atol Providence, Seychelles, 37–183 m; Salomon Islands, Chagos Archipelago, Indian Ocean 110–219 m (Jarvis, 1922).

Remarks. Millard (1975) identified material collected in Natal and Mozambique as Zygophylax ? antipathes. However, Z. antipathes has branches arising from stem in several directions and larger hydrothecae with shorter pedicels (Rees & Vervoort, 1987).

Rees & Vervoort (1987) also studied the material identified as Z. biarmata by Jarvis (1922), concluding that it could also belong to Z. millardae. These species are similar in many trophosomal characters (geniculate pattern of hydrocladia, convex adcaulinar wall and slightly concave abcaulinar wall, developed and continuous hydrothecal pedicels, hydrothecal rim with renovations, sometimes duplicate diaphragms and tubular nematothecae on apophyses or on hydrothecal pedicel), but are differentiated mainly by the larger measurements of Z. millardae hydrothecae (Table 3). Unfortunately, Z. millardae has been described from infertile material and with trophosome characters similar to those of other species. Thus, hydrothecal dimensions (cf. Ramil & Vervoort 1992 for Z. levinseni / Z. elongata; Vervoort & Watson, 2003 for Z. antipathes / Z. rufa) are important to differentiate the species, preventing them to be synonymized.