Zyzzyzus parvula ( Hickson & Gravely, 1907 )

Soto, Joan J. & Peña, Álvaro L., 2019, Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica), Zootaxa 4570 (1), pp. 1-78: 17

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Zyzzyzus parvula ( Hickson & Gravely, 1907 )


Zyzzyzus parvula ( Hickson & Gravely, 1907) 

( Fig. 5View FIGURE 5 a–h)

Material examined. ANT XVII /3: 111-9, numerous polyps, up to 45 mm high, on E. generale  , H. interpolatum  , Sc. unifurcata  and T. longstaffi  , with mature gonophores; 111-18, a single polyp, c. 1 mm high, on Lafoea dumosa ( Fleming, 1820)  .

Remarks. As also mentioned by Svoboda & Stepanjants (2001), many juveniles have been observed sharing substrate with adults, pointing to a gregarious habit, and putatively restricted dispersal capabilities. Juvenile specimens, especially the youngest ones, have slightly capitate aboral tentacles ( Fig. 5aView FIGURE 5), which is in agreement with the genus diagnoses by Campos et al. (2007).

Originally described from the Ross Sea as Lampra parvula Hickson & Gravely, 1907  , the species has had a complicated taxonomical history, being re-allocated in several genera, even belonging to different families. It was considered as Corymorpha  by Stepanjants (1972), and later re-allocated in Lampra  by Stepanjants & Svoboda (1999). Svoboda & Stepanjants (2001) included it in the reestablished genus Monocaulus  . Nowadays, after the revision of the genus Zyzzyzus  by Campos et al. (2007), included within Tubulariidae  , the species is considered as a member of this genus ( Schuchert 2018).

Svoboda & Stepanjants (2001) re-described the syntypes of Z. parvula  and provided a detailed account on new material from the Weddell Sea. However, the authors pointed out, based on in situ photographs from the Weddell Sea ( Svoboda & Stepanjants 2001:57), that living specimens are white, but reddish-orange after preservation. We disagree with that assumption. In situ photographs by Brueggeman (1998) referable to Z. parvula  show deep-red to brown polyps, with a pale-orange basal section, coloration similar to that found in preserved specimens. Therefore, those white specimens mentioned by Svoboda & Stepanjants (2001) could actually correspond to an undescribed species. Material examined here entirely agrees with the description given by Svoboda & Stepanjants (2001), as well as with the original description by Hickson & Gravely (1907). Unfortunately previous authors did not provide any information about the type and size of the nematocysts. Given that the present study constitutes the first account on the cnidome, it would be necessary to compare present data with the type series and the material studied by Svoboda & Stepanjants (2001) to put in order the existent information on the species.

Cnidome comprising small stenoteles [range 10.0–11.5 x 8.0–9.5 µm, mean 10.9±0.4 x 8.8±0.4 µm (n=19)], large stenoteles [range 15.0–16.0 x 10.0–10.5 µm, mean 15.4±0.4 x 10.1±0.2 µm (n=14)] and desmonemes [range 6.0–6.5 x 5.0–6.0 µm, mean 6.2±0.2 x 5.9±0.3 µm (n=15)].

Ecology and distribution. Previously reported at depths from 3 ( Stepanjants 1979, as Corymorpha parvula  ) to 440 m ( Svoboda & Stepanjants 2001, as Monocaulus parvula  ); present material from 62 to 105 m. Species with circum-Antarctic distribution ( Stepanjants 1979).