Gonaxia scalariformis Vervoort, 1993

Galea, Horia R., 2016, Notes on some sertulariid hydroids (Cnidaria: Hydrozoa) from the tropical western Pacific, with descriptions of nine new species, European Journal of Taxonomy 218, pp. 1-52 : 19-20

Gonaxia scalariformis Vervoort, 1993

Figs 5 C–G, 6F–R

Gonaxia scalariformis Vervoort, 1993: 173 , figs 31b, 32, 33c–d, 35a.

Material examined

BIOCAL: Stn. DW46, three colonies (#1–3) slightly differing in the size of their hydrothecae: colony #1 is 3.5 cm high, devoid of its hydrorhiza, and bears two female gonothecae (MNHN-IK-2012-16539), colony #2 is 2.8 cm high, devoid of its hydrorhiza, and bears three female gonothecae (MNHN- IK-2012-16540), and colony #3 is 2.2 cm high and broken in two parts, the basal one exhibiting remnants of hydrorhiza; both parts bear five male gonothecae each (MNHN-IK-2012-16541); Stn. DW66, a 1.6 cm high colony devoid of both its hydrorhiza and apical part, with two abortive gonothecae (MNHN- IK-2012-16542); Stn. CP69, a 1.4 cm high colony devoid of its distalmost part, with a single female gonotheca (MNHN-IK-2012-16543).

NORFOLK 1: Stn. DW1699, a 1.7 cm high colony devoid of both its hydrorhiza and upper part, bearing two female gonothecae (MNHN-IK-2012-16544).

Remarks

All available specimens have lightly fascicled stems basally, and none is ramified. Although the arrangement and general shape of the hydrothecae perfectly match the description of the holotype, noticeable variations in size could be observed. Thus, the colony #3 from sample BIOCAL, Stn. DW46 has the slenderest hydrothecae, while those from NORFOLK 1, Stn. DW1699 are the widest ones. In the sample from BIOCAL, Stn. DW66, incipient antero-dorsal diverticuli are seen in most hydrothecae ( Fig. 5F ). Gonothecae of both sexes are present in the available material. Although they conform to the original description, the male gonothecae in the colony #3 from BIOCAL, Stn. DW46 are arranged on both anterior and posterior sides of the stem, and some exhibit bifid ( Fig. 6M) or trifid apices. The female gonothecae from BIOCAL, Stn. DW66 are likely abortive, as they originate from within the hydrothecae ( Fig. 6 N–O); in addition, they are not fully formed, as their distal ends are missing; their sex is indeterminate. The female gonothecae from NORFOLK 1, Stn. DW1699 ( Fig. 6 Q–R) are the longest with respect to those present in the other samples.

Geographical distribution

New Caledonia and Norfolk Ridge ( Vervoort 1993; present study).

Figures

Fig. 5. ― A–B. Gonaxia nova sp. nov. (MUSORSTOM 8, Stn. CP1083). A. Distalmost, monosiphonic part of a colony. B. Portion of stem with basal part of a cladium. ― C–G. Gonaxia scalariformis Vervoort, 1993, portions of stems and basal parts of cladia from BIOCAL, Stn. DW46 (C = colony #1; D = colony #2; E = colony #3), Stn. DW66 (F), and NORFOLK 1, Stn. DW1699 (G), showing discrete differences in shape and size. ― H. Gonaxia aff. similis Vervoort, 1993 (MUSORSTOM 6, Stn. DW423), portion of stem with cladium. Scale bars: A = 1 mm; B–H = 500 µm.