Gonaxia nova, Galea, 2016

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 : 16-19

Gonaxia nova sp. nov.

urn:lsid:zoobank.org:act:6C6AA611-2E5C-40B9-9502-31888388A7E9

Figs 5 A–B, 6A–E; Table 2

Diagnosis

Gonaxia with either branched or unbranched, rigid, fascicled stems arising from disc-shaped hydrorhiza. Internodes slightly geniculate, comprising a latero-distal cladial apophysis with its associated hydrotheca, and two alternate hydrothecae below. Cladia alternate, composed of moderately long, geniculate internodes. Hydrothecae arranged at a wide angle to the stem; long, tubular, slightly arcuate, tumid proximally, distally tubular, adnate for ¼ their length. Gonothecae originating on both sides of the stem from below axillar hydrothecae; adnate for about half their length; erect portion tubular, ending in rather long neck region bearing the aperture distally.

Etymology

From the Latin novus, -a, -um (and the Grek νέΟς), meaning new, indicating that we are dealing with a new, undescribed species.

Material examined

Holotype

MUSORSTOM 8: Stn. CP1083, a 4.2 cm high, unbranched colony bearing male gonothecae (MNHN- IK-2012-16537).

Paratypes

MUSORSTOM 8: Stn. CP1083, eight colonies or fragments with branched or unbranched stems, of which four bear female gonothecae and range between 2.6 and 5.0 cm in height, while the remaining four bear male gonothecae and range between 2.8 and 3.9 cm in height (MNHN-IK-2012-16538).

Description

Colonies composed of branched or unbranched, thick, rigid,fascicled stems arising from rhizoid hydrorhiza firmly attached to substrate. Nodes inconspicuous, even in the monosiphonic parts, but equivalents of internodes 1580–2000 µm long, slightly geniculate, composed of a latero-distal hydrocladial apophysis with its associated hydrotheca, and two additional, alternate hydrothecae below. Hydrocladia strictly monosiphonic, arranged at approximately right angles to the stem; up to 1.2 cm long, nodes indistinct (60–70 µm wide); equivalents of internodes moderately long, geniculate, each carrying a hydrotheca distally; first internode comparatively longer (1020–1240 µm) than subsequent ones (590–760 µm); up to 20 hydrothecae per cladium. Hydrothecae long, tubular, facing outwards at nearly right angles to their corresponding internodes; slightly tumid basally, walls parallel distally; adnate for about ¼ th their length; free adaxial side slightly convex proximally, then straight; abaxial wall with noticeable convexity in middle; aperture triangular in frontal view; margin with three conspicuous cusps (two latero-adaxial and one abaxial) separated by rather deep embayments; operculum composed of three triangular flaps forming a low roof. Gonothecae on both sides of the stem, originating from below axillar hydrothecae; about half adnate, strongly appressed proximally to the stem; distal half erect, tubular, ending in moderately long, tronconical collar, bearing the aperture distally (small in male, Fig. 6E; comparatively larger in female, Fig. 6D); perisarc of abaxial wall of fused part finely and densely striated ( Fig. 6 E–F); individual gonothecae either solitary (towards apex of stem) or fused together through auxiliary tubes given off from one or both ends of their adnate parts; in highly polysiphonic parts of stem, adnate parts of gonothecae obscured by apposition of auxiliary tubes; length of adnate part 1250–1340 µm (³) and 1720–1970 µm (♀), and of free part 1540–1910 µm (³) and 1640–1720 µm (♀); width of free part 565–590 µm (³) and 620–690 µm (♀); length of neck region 260–365 µm (³) and 165–245 µ (♀); diameter at aperture 90–105 µm (³) and 245–260 µm (♀).

Remarks

The hydrothecae of this species resemble those of several congeners: 1) G. bulbifera Vervoort, 1993 , but this species has proportionally smaller hydro- and gonothecae (about two times smaller), its hydrothecal axes are straight instead of being curved, its caulinar apophyses are conspicuously inflated, and its cladial internodes are collinear instead of being slightly geniculate; 2) G. elegans , but in this species the hydrothecae are much more closely-set, and the cladial internodes are strictly collinear (compare Fig. 5B with Fig. 4B ); 3) G. perplexa Vervoort, 1993 , but in this species the hydrothecae are more approximated and have straight axes, and the gonothecae are nearly fully adnate, their bodies being likely fused to each other, and their apertures are characteristically shifted outward from the stem; 4–7) G. complexa Vervoort, 1993 , G. persimilis Vervoort, 1993 , G. similis , and G. scalariformis , but these species are immediately distinguished through their free gonothecae, originating perpendicularly to the stems; 8) G. stricta Vervoort, 1993 , but in this species the hydrothecae have straight axes and they are more approximated on cladia.

Geographical distribution

Vanuatu.

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.

Fig. 4. ― A. Gonaxia crassicaulis Vervoort, 1993 (MUSORSTOM 4, Stn. DW205), portion of cladium. ― B–D. Gonaxia elegans Vervoort, 1993 (BATHUS 3, Stn. DW809). B. Portion of stem and basal part of a cladium. C. Two consecutive internodes with their hydrothecae. D. Portion of stem with male gonothecae. ― E–F. Gonaxia cf. errans Vervoort, 1993 (BATHUS 2, Stn. CP737). E. Distalmost portion of stem with basal parts of four hydrocladia. F. Two consecutive cladial internodes with their hydrothecae. ― G–J. Gonaxia plumularioides sp. nov. (BIOCAL, Stn. CP34). G. Distalmost part of a stem, showing the structure of internodes. H. Two consecutive cladial internodes with their hydrothecae. I. Stem hydrotheca. J. Axillar hydrotheca. Scale bars: A–B, D–E, G = 1 mm; C, F, H–J = 300 µm.