Gonaxia errans Vervoort, 1993

Galea, Horia R. & Maggioni, Davide, 2021, An integrative study of some species of Gonaxia Vervoort, 1993 from off New Caledonia, with the establishment of Gonaxiidae as a new family of thecate hydroids (Cnidaria: Hydrozoa), Zootaxa 5004 (3), pp. 401-429 : 410-412

Gonaxia errans Vervoort, 1993

Figs 1E , 7 , 8 , 15 , 16 ; Table 3

Gonaxia errans Vervoort, 1993: 154 , figs 23A–D, 24A–C.

Gonaxia cf. errans — Galea, 2016: 13 , fig. 4E–F.

Gonaxia plumularioides Galea, 2016: 14 , fig. 4G–J, syn. nov.

Material examined. KANACONO, Stn. CP4675, MNHN-IK-2015-2668: a 8.5 cm high, sterile, unbranched colony; GenBank: MZ 099698 (16S), MZ 099685 (18S).—KANACONO, Stn. DW4786, MNHN-IK-2019-2059: two unbranched colonies, 8 and 12.7 cm high, both sterile; GenBank: MZ 099699 (16S).— KANACONO, Stn. DW4668, MNHN-IK-2015-2677: two branched colonies, of which one is ca. 13 cm high, devoid of its basal part, but bearing a couple of mature gonothecae, and a second, sterile colony, originally ca. 13.5 cm high, now broken into three pieces.—KANACONO, Stn. DW4670, MNHN-IK-2015-2673: a branched colony, 6.3 cm high, and two fragments, 2 and 3 cm high, all sterile.—KANACONO, Stn. DW4715, MNHN-IK-2015-2676: a branched colony, ca. 15 cm high, bearing a few incipient gonothecae whose sex could not be ascertained.—KANACONO, Stn. DW4748, MNHN-IK-2015-2674: a branched, sterile colony, 9 cm high.—KANACONO, Stn. DW4786, MNHN- IK-2015-2672: many branched colonies up to 25 cm high, some bearing incipient gonothecae whose sexes could not be ascertained; GenBank: MZ 099705 (16S) (colony A); MZ 099706 (16S), MZ 099686 (18S), MZ 099670 (28S) (colony B).—KANADEEP 2, Stn. CP5109, MNHN-IK-2015-2675: upper portion of a branched colony, 5.5 cm high, sterile.

Remarks. As noted earlier by Galea (2016: 14), the branching pattern of the stems is peculiar in this species: although the nodes are indistinct, each equivalent of internode is composed of four alternating hydrothecae, of which the proximal- and the distalmost become axillar through the insertion of two cladial apophyses given off on opposite sides ( Galea 2016: Fig. 4E ). The account of Vervoort (1993: 154), however, is misleading in stating that “zero to three hydrothecae [occur] between two successive apophyses”, suggesting that either one, two or three hydrothecae could be present. Nevertheless, the branching pattern observed both earlier ( Galea 2016) and presently proved always regular.

Among the genus, only the stems of G. errans and G. plumularioides Galea, 2016 share the same division into internodes. Besides the occurrence of several simply pinnate colonies ( Fig. 1E ), the material studied herein comprises well-developed, lofty (up to 25 cm high) colonies ( Fig. 7 ), much taller than those on which both the holo- and paratype (2.8 and 7.7 cm high, respectively) of G. plumularioides were based upon. Concomitantly, it is realized that the latter merely represents the fully-grown stage of G. errans , a hydroid previously known based on young, unbranched colonies, not exceeding a few centimeters in height ( Vervoort 1993: 154; Galea 2016: 13). Consequently, G. plumularioides is assigned to the synonymy of G. errans . The largest colonies met with herein provide additional, crucial data on the general aspect of this hydroid, granting a comprehensive understanding of its morphology.

A strongly reticulated hydrorhiza, firmly anchoring the colony to a hard substrate, gives rise to a fascicled (though rather slender, not exceeding 3 mm in width), strongly geniculate stem forming, at regular intervals (6–10 mm), up to 6.5 cm long, spirally-arranged cladia-bearing branches. In the largest colonies, some lower cladia-bearing branches may branch again twice. Along the stem and on the proximal parts of cladia-bearing branches, all cladia are shed, although most axial hydrothecae still protrude from the fascicle of auxiliary tubes. The cladia are up to 17 mm long and comprise an alternation of up to 24 hydrothecate internodes, not delimited by distinct nodes.

Although the microscopical structure of the trophosome was described thoroughly earlier ( Galea 2016: 14), the so far unknown gonothecae are present in a number of samples, although fully-formed ones are only met with in sample MNHN-IK-2015-2677. These originate from below the bases of axillar hydrothecae of the cladia-bearing branches ( Fig. 8A ), and are broadly club-shaped ( Fig. 8D ), provided with 6–7 prominent, longitudinal ridges ( Fig. 8E ), ca. 2.8 mm long and 770 µm wide; their ca. 350 µm wide aperture is at the top of a truncate summit, irregularly rounded in shape and apparently closed by a flimsy, deciduous operculum.

Bathymetric distribution. Between 350–1508 m ( Vervoort 1993; Galea 2016; present study).

Figures

FIGURE 1. Species of Gonaxia dealt with in this study: G. bulbifera Vervoort, 1993 (A), G. crassicaulis Vervoort, 1993 (B), G. crusgalli Vervoort, 1993 (C), G. elegans Vervoort, 1993 (D), G. errans Vervoort, 1993 (E, unbranched form), G. incisa Galea, sp. nov. (F), G. cf. intermedia Vervoort, 1993 (G), G. perplexa Vervoort, 1993 (H), G. sinuosa Vervoort, 1993 (I), G. solenoscyphoides Galea, sp. nov. (J). Scale bar: 1 cm.

FIGURE 4. Gonaxia crassicaulis Vervoort, 1993 (part). A–B. Portions of colonies. C. Hydrotheca. D, E. Female (D) and male (E) gonothecae. From samples MNHN-IK-2019-2087 (A, C, D) and MNHN-IK-2019-2088 (B, E). Scale bars: C = 300 µm; A, B, D, E = 1 mm.

FIGURE 7. Gonaxia errans Vervoort, 1993, two fully-developed colonies from Stn. DW4786. Scale bar: 3 cm.

FIGURE 8. Gonaxia errans Vervoort, 1993.A. Portion of fertile colony. B. Two successive hydrothecae seen laterally. C. Opercular apparatus seen frontally. D, E. Gonotheca in lateral (D) and apical (E) views. From sample MNHN-IK-2015-2677. Scale bars: B, C = 300 µm; A, D, E = 1 mm.

FIGURE 15. Phylogenetic hypothesis for Gonaxia species based on a 16S dataset. Numbers at nodes show maximum likelihood bootstrap values, Bayesian posterior probabilities, and maximum parsimony bootstrap values, respectively.

FIGURE 16. Phylogenetic hypothesis for the position of the Gonaxiidae Maggioni, fam. nov. within Macrocolonia, based on a multi-locus dataset. Numbers at nodes show maximum likelihood bootstrap values, Bayesian posterior probabilities, and maximum parsimony bootstrap values, respectively, and are shown only when at least two analyses demonstrated high support (> 0.9 for Bayesian posterior probabilities and> 75 for bootstrap values).