Zygophylax levinseni ( Saemundsson, 1911 )

Peña Cantero, Álvaro L. & Horton, Tammy, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from bathyal and abyssal depths of the Northeast Atlantic held in the modern Discovery Collections, Zootaxa 4347 (1), pp. 1-30 : 13-14

Zygophylax levinseni ( Saemundsson, 1911)

( Fig. 5C–H )

Lictorella levinseni Saemundsson, 1911: 86 , fig. 2.

Zygophylax biarmata — Broch, 1918: 24; Kramp, 1938: 28 [not Zygophylax biarmata Billard, 1905 ]

Zygophylax elegantula Leloup, 1940: 11 , pl. 1 fig. 8; Rees & Vervoort, 1987: 78;

Zygophylax levinseni — Ramil & Vervoort, 1992: 78, figs 18a–d, 19a–f; Altuna Prados & Álvarez Claudio, 1994: 6–10, figs 3, 4; Calder & Vervoort, 1998: 35, fig. 17a–c; Schuchert, 2001: 71–72.

Zygophylax sp. Aguirrezabalaga et al., 1988: 119, figs 12a–f.

Not Zygophylax levinseni — Calder & Vervoort, 1998: 35, fig. 17a–c.

Material examined. 9752#1, several stems up to 60 mm high, on axis of dead gorgonian and S. plicatile , with coppiniae; 13881#1, several stems up to 11 mm high, on Sertularella gayi , no coppiniae.

Description. Polysiphonic stems, up to 60 mm high. Polysiphony extending almost to end of stem. Primary branches also polysiphonic. Branching alternate in more or less one plane and roughly at right angle from stem; frequently forming sub-opposite pairs of contiguous hydrocladia (however, there are two hydrothecae between pairs; less frequently only one). Branches resting on apophyses usually provided with a nematotheca ( Fig. 5E ). Stems and hydrocladia with a series of apophyses alternately arranged in two planes, making an acute angle (less frequently in approximately one plane), and giving rise to hydrothecae ( Fig. 5C ). Apophyses short and sometimes provided with a nematotheca placed on the side facing the space delimited by the alternating apophyses ( Fig. 5F ).

Hydrothecae tubular ( Fig. 5C–D ), on long pedicels, separated from them by a circular diaphragm ( Fig. 5D ). Pedicel arising from hydrocladial apophysis. Hydrotheca slightly asymmetrical (adcauline wall longer than abcauline one) and directed outwards ( Fig. 5C–D ). Adcauline wall convex; abcauline one straight or slightly concave below aperture ( Fig. 5C–D ). Maximum diameter at aperture, gradually decreasing to diaphragm. Hydrothecal aperture circular; rim smooth, slightly everted ( Fig. 5D ).

Female gonothecae densely grouped, but separated. On axis of dead gorgonian and on basal part of some stems. Gonotheca ovoid, distally with a pair of laterally curved tubes, distally facing down ( Fig. 5G ). Gonotheca with two apertures, each at the end of corresponding distal tube and facing downwards. Gonothecal wall with fine striae. Several planulae per gonotheca (up to six observed).

Measurements (in µm). Hydrotheca: height 320–400, diameter at aperture 130–180; length of pedicel 110– 200, diameter at diaphragm 80, length of apophyis 60. Nematotheca: height 60–80, diameter at aperture 30–40.

Remarks. Nematothecae on the apophyses supporting hydrothecal pedicels are always on the side facing the space delimited by the alternating hydrothecae. The presence of nematothecae is not constant; they are frequently absent, which does not seem to be caused by lost. Where there was a nematotheca, currently lost, there is a clear hole in the perisarc ( Fig. 5E ). However, in many cases there is no indication of its presence.

Ramil & Vervoort (1992) indicated that there is usually one nematotheca on each side of the hydrothecal pedicel. We have only observed one nematotheca associated with each hydrothecal apophysis, which was also found by Altuna Prados & Álvarez Claudio (1994).

Ecology and distribution. This is a deep-sea species, collected at depths from 183 to 3657 m (Vervoort 2006); the present material is from the Porcupine Seabight at depths between 863 and 1042.

Temperate Atlantic south of Iceland and sub-tropical Atlantic (Vervoort 2006).

Figures

FIGURE 5. Clytia gigantea (Hincks, 1866): A, hydrotheca; B, detail of distal part of hydrotheca showing aperture with cusps. Zygophylax levinseni (Saemundsson, 1911): C, fragment of branch showing hydrothecal arrangement; D, hydrotheca, pedicel and apophysis; E, origin of branch showing apophysis and perisarc hole left by missing nematotheca; F, nematotheca; G, gonotheca; H, nematocyst (arrow). Scale bars: 200 µm (A, C, G), 100 µm (B, D – F), 10 µm (H).