Plate 1 A–F; Table 1, 2
Zygophylax? geniculata Millard, 1968: 264-266, fig 3; Millard, 1975: 195–197, fig. 64 [ non Zygophylax geniculata ( Clarke, 1894)].
Type series. Holotype—eleven small fragments of a colony, without gonophores (ZMUC-HYD 270).
Type locality. Off Cape Peninsula, South Africa, 34°23’S; 18°08’ E, 287 m.
Material examined. Holotype—Fragments of colony, 18 December 1929, Coll. T. Mortensen Exp. 1929, St. 58, 287 m, 34°23’S 18°08’E, South Africa, Det. N.H. Millard as “ Zygophylax? geniculata ” ( ZMUC-HYD 270).
Description. Small fragments of a colony, up to 50 mm high. Stem most polysiphonic composed by main and parallel secondary axial tubes with some nematothecae, terminal portion of stem monosiphonic bearing nodes and internodes. Branches up to second order, sub-opposite hydrocladia with axillary hydrothecae, branching off stem at angles of 70–80°; nodes irregularly distributed marking rectilineous internodes with a slight constriction above axillary hydrotheca, each bearing one to three hydrothecae. Hydrothecae of stem and hydrocladia free, biserially arranged, slightly turned into frontal direction placed on conspicuous apophyses (Pl. 1A), two hydrothecae between each pair of hydrocladia, some hyrothecae placed at proximal portion of stem. Hydrothecae tubular, narrowing basally, slightly swollen at median region, consequently adcauline and abcauline walls slightly convex; rim smooth, plane of aperture perpendicular to hydrothecal long axis; 1–2 renovations common (Pl. 1D); diaphragm thick, oblique to rectilineous, with large circular hydropore; pedicel on distinct apophyses, long, with 2–8 segments (Pl. 1B–D). Nematothecae tubular, on hydrothecal apophyses and on secondary axial tubes, rim smooth; pedicel with 4–15 segments (Pl. 1E–F). No gonophores present.
Measurements. Stem: distance between two subsequent hydrotheca 338–468 µm; diameter 104–1,482 µm; distance between subsequent hydrocladia on the same side 2.2–2.6 mm. Hydrocladia: length 3.0– 9.1 mm; diameter at base 104 µm. Hydrothecae: lenght of adcauline wall from rim to diaphragm 250–290 µm; lenght from base budding of the axis to rim 450–660 µm; diameter at rim 120 µm; diameter at diaphragm 60–80 µm; lenght of pedicel on adcauline side 190–370 µm; diameter at apophysis 60 µm. Nematothecae: lenght 120–290 µm; diameter at rim 50 µm.
Etimology. The specific name was given in honour of Dr Naomi A. H. Millard, one of the founders of the Zoological Society of South Africa and of the Zoologica Africana Journal (now African Zoology), for her numerous contributions to the study of hydroids, especially in southern Africa and adjacent oceans.
Geographical distribution. West Off Cape Peninsula, South Africa.
Remarks. The lack of gonothecae in the descriptions of new species has historically caused taxonomic difficulties within the genus, such as for Zygophylax pinnata ( Sars, 1874) and Zygophylax brownei Billard, 1924 ( cf. Schuchert, 2000). However, trophosomes may present unique and diagnostic characters, like in Zygophylax recta Jarvis, 1922, Zygophylax tottoni Rees & Vervoort, 1987, Zygophylax binemathophorata Vervoort & Watson, 2003 and Zygophylax kakaiba Campos et al., 2016. The uniqueness of a trophosomal character supports the description of this new species.
Zygophylax naomiae sp. nov. may be distinguished from all other species of the genus by the strong pattern of annulations of the hydrothecae pedicels (2–8 segments) and nematothecae (4–15 segments), with no equivalents within Zygophylax. Annulated pedicels are largely used in the taxonomy of many taxa, both in leptothecates ( e.g., Campanulariidae, cf. Cunha et al., 2017), and anthoathecates ( e.g., Eudendriidae, cf. Marques et al., 2000; Puce et al., 2005).
The annulation pattern of the nematothecal pedicels of Z. naomiae sp. nov. is unique within the genus. This pattern shall not be confused with the bilobed or trilobate aspect presented by the nematothecae of some species, such as Zygophylax cervicornis ( Nutting, 1905) ( e.g., Vervoort & Watson, 2003) and Zygophylax curvitheca Stechow, 1913 (NMS 1959.33.305), associated to renovations of nematotheca and consisting of subtle sinuosities of the perisarc, not forming segments.
The pedicels of Z. stechowi, a species only recorded for its type locality (Sagami Bay, Japan; see Jaderholm, 1919), are somewhat similar, but they have a smaller number of annulations (up 4) that are not well demarcated, being related to the regenerative processes of the colony ( Table 1). Moreover, the nematothecae of Z. stechowi are short and rounded, with smooth pedicels [ Hirohito, 1995; corroborated by the examination of the type material UP- STY 2133, Table 1, and additional material ZMA 5144 ( 70 µm length; 50 µm diameter at rim)], and located at the proximal half of the hydrothecal pedicel, whereas those of Z. naomiae sp. nov. are located at the apophysis.
Annulations at the hydrothecal pedicels are also described for Zygophylax unilateralis Totton, 1930, a species distinguished by the curved shape of the hydrothecal walls and by the hydrothecae turned all to one of the facies of the colony. Besides, we observed that the holotype BMNH 29.10.28.77 has a variation of this character, with pedicels completely smooth, or slightly wrinkled, or ringed only proximally, or even ringed to almost all of its extension. This variation may suggest that the different patterns of annulations could be associated with processes of regeneration of the colonies and their hydrothecae. Anyhow, the segments of Z. naomiae sp. nov. are better defined and demarcated than those of Z. stechowi and Z. unilateralis.
Millard (1968, 1975) studied the type material of Z. naomiae sp. nov. and assigned that to Zygophylax? geniculata, not confirming the identification due to the lack of fertile materials. Although Z. geniculata may have rings at the hydrotecal pedicels, the annulation is not always present (like observed in the type material MCZ-CNID 2283). Also, hydrothecae of Z. geniculata are distinctly oriented to different planes of the colony whereas those of Z. naomiae sp. nov. are arranged at the same plane, and the nematothecae of Z. geniculata are rare on secondary axial tubes and hydrothecal pedicels. Millard (1975) also pointed out that the specimen presently described had similarities with Zygophylax bifurcata Billard, 1942, because of its bifurcated hydrocladia and the shape of the nematothecae, but the dimensions of the hydrothecae of Z. naomiae sp. nov. are larger ( Table 1).
Millard (1968) considered the presence of segments in the specimen ZMUC-HYD 270 associated with the process of colony regeneration. We disagree with this hypothesis because of the high frequency of segmented pedicels in hydrothecae and nematothecae and for its strong segmentation, distinct from the wrinkled perisarc commonly found in regenerative pedicels/hydroids. A comparison of the main morphological structures and measurements of Zygophylax naomiae sp. nov. with related congeners are detailed in Table 1 and Table 2, respectively.
gophylax geniculata ( Clarke, 1894), and Zygophylax bifurcata Billard, 1942 (in μm).