Gonaxia crassicaulis 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 : 407-410

Gonaxia crassicaulis Vervoort, 1993

Figs 1B , 4 , 5A–B , 6A–E , 15 , 16 ; Table 3

Gonaxia crassicaulis Vervoort, 1993: 145 , figs 18C–D, 19A–B.— Galea, 2016: 11 , fig. 4A.

Material examined. KANACONO, Stn. DW 4743, MNHN-IK-2019-2087: a 6.3 cm high colony, with groups of ♀ gonothecae; GenBank: MZ 099693 (16S).—KANACONO, Stn. DW 4763, MNHN-IK-2019-2089: two colonies, 4.2 and 6.1 cm high, smallest bearing a ♂ gonotheca, largest sterile.—KANACONO, Stn. DW 4764, MNHN-IK- 2019-2088: three colonies, 6.0– 7.8 cm high, one sterile, one bearing ♂ gonothecae, and one bearing ♀ gonothecae; GenBank: MZ 099694 (16S).—KANACONO, Stn. DW 4768, MNHN-IK-2019-2076: a 5.7 cm high colony bearing ♂ gonothecae .

Remarks. Although the cladia are generally unbranched, a case of branching occurs in sample MNHN-IK- 2019-2076. Second-order cladia are given off from two primary cladia, pointing in front and the back side of the colony; in one case, the secondary cladium is given off from a site near the base of a hydrotheca, while in the other case, it is given off from near the axil formed between the free and fused parts of the adaxial wall of another hydrotheca.

Some intraspecific variations occur in this species, and they rely in the size of the free part of the hydrothecae, and the length of internodes (compare Figs 4A and 4B ).

In this species, the coenosarc lies in an inner gutter of perisarc built up on one side (“anterior” or “posterior”) of the longitudinal axis of the stem/cladia ( Fig. 6E ); occasionally, the coenosarc passes from one side to the other, and the inner gutter is then formed on the opposite side. Vervoort’s (1993: figs 19A–B) and Galea’s (2016: fig. 4A) illustrations show that side of the colony to which the gutter of perisarc is confined.

Another feature of this species, not elucidated by Vervoort (1993: 146) but highlighted by Galea (2016: 13), is the distinctive U-shaped hydrothecal floor, when the hydrothecae are seen frontally. In lateral view, the insertion of lateral walls of hydrotheca into the corresponding internode adopts a convex shape ( Figs 4C and 6A ), forming two diverticula, one in front, and the other on the backside of the hydrotheca, particularly noticeable when the hydrotheca is seen frontally ( Fig. 6C ). In a cross-section of the internode at the lowest level of the hydrothecal floor, a narrow, drop-shaped hydropore can be seen ( Fig. 6D ).

Female gonothecae ( Figs 4D , 5A ), not previously described, occur in one colony from sample MNHN-IK- 2019-2087. Similar in shape to their male counterparts ( Figs 4E , 5B ), about 3.2 mm long and 1160 µm wide, they have comparatively wider (ca. 425 µm) apertures. In this material, they arise from the main tube of the stem, in the vicinity of an axillar hydrotheca.

Bathymetric distribution. Between 160–650 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 5. Gonothecae of several species of Gonaxia dealt with herein: G. crassicaulis Vervoort, 1993 (A: female, B: male), G. elegans Vervoort, 1993 (C), G. incisa Galea, sp. nov. (D), G. perplexa Vervoort, 1993 (E), G. sinuosa Vervoort, 1993 (F). Scale bar: 5 mm.

FIGURE 6. A–E. Gonaxia crassicaulis Vervoort, 1993 (continued). A. Hydrotheca seen laterally. B. Opercular apparatus in frontal view. C. Cross section of a hydrotheca seen frontally, to show lateral diverticula. D. Cross section through a cladial internode at the level of the hydrothecal floor, showing the hydropore. E. Cross section through the middle part of a cladial internode to show the unilateral gutter of perisarc to which the coenosarc is confined. F, G. Gonaxia crusgalli Vervoort, 1993. Hydrotheca in lateral (F) and frontal (G) aspects. From samples MNHN-IK-2019-2088 (A–E) and MNHN-IK-2019-2678 (F, G). Scale bar: A–G = 300 µm.

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).