Gonaxia incisa Galea, 2021

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 : 413-415

Gonaxia incisa Galea , sp. nov.

Figs 1F , 5D , 9 , 15 , 16 ; Tables 2, 3

Material examined. Holotype: KANACONO, Stn. DW4670, MNHN-IK-2015-2679: a 4.5 cm high colony bearing ♂ gonothecae.— Paratype: KANACONO, Stn. DW 4670, MNHN-IK-2015-2670: many colonies, 2–6 cm high, old- er ones bearing either ♂ or ♀ gonothecae; GenBank: MZ 099700 (16S).— Additional material: KANACONO, Stn. DW 4670, MNHN-IK-2019-2061: two colony fragments, 0.9 and 2.2 cm high, both bearing presumably ♀ gono- thecae.—KANACONO, Stn. DW 4671, MNHN-IK-2015-2667: six colonies, 1.8–6.0 cm high, the five largest bear- ing either ♂ or ♀ gonothecae; GenBank: MZ 099701 (16S), MZ 099687 (18S), MZ 099671 (28S).—KANACONO, Stn. DW 4672, MNHN-IK-2015-2681: three colonies, 1.6–6.5 cm high, the two largest bearing gonothecae.—KA- NACONO, Stn. DW 4677, MNHN-IK-2019-2062: three colonies, 3.8–4.5 cm high, smallest bearing presumably ♀ gonothecae, while the two largest bear presumably ♂ gonothecae.—KANACONO, Stn. DW 4681, MNHN-IK- 2015-2680: a 5 cm high colony bearing ♂ gonothecae.—KANACONO, Stn. DW 4682, MNHN-IK-2019-2063: a 3.2 cm high colony bearing presumably ♂ gonothecae .

Etymology. From Latin incîsus, -a, -um, meaning notched or incised, to describe the shape of the adaxial, proximal part of its hydrothecae.

Description. Colonies firmly anchored to hard substrates be means of dense, rhizoid stolons; erect, up to 6 cm high, of rigid appearance, able to support themselves when out of liquid. Stems brownish, unbranched, fascicled for most of their length, proximally 2 mm thick, distal tip monosiphonic; main tube with smooth perisarc; accessory tubes tortuous, anastomosed, with wrinkled perisarc; division into internodes indistinct, but equivalents of internodes comprising three alternating hydrothecae and a short cladial apophysis given off laterally below the distalmost hydrotheca, the latter becoming axillar; an ovoid fenestra below the base of each axillar hydrotheca; stem “internodes” slightly geniculate, each cladial apophysis introducing a bend along the longitudinal axis of the stem. Cladia up to 15 mm long, straight, straw-colored, alternate along the stem, strictly coplanar, always monosiphonic, and generally unbranched; a distinct constriction at junction between cladium and the corresponding stem apophysis; cladial nodes indistinct, except for the proximal-most that is distinctly longer; equivalents of internodes short, gradually widening distally, and there bearing a hydrotheca; up to 30 hydrothecae arranged in two alternate, strictly coplanar rows. Hydrothecae similar on both stem and cladia; long, tubular, ca. 1/6 adnate to their corresponding internodes, given off at ca. 60° with their longitudinal axes; free adaxial wall distinctly notched immediately above origin from internode, then straight throughout; adnate adaxial wall thick, slightly arched, basally forming a short perisarc plug projecting abaxially into the lumen of internode; floor of hydrotheca incomplete, formed adaxially by this perisarc plug and, on the abaxial side, by an internal, upward projection of the perisarc at the origin of the abaxial hydrothecal wall; the latter with a slight proximal concavity, and straight for most of its remaining length. Hydrothecal aperture almost triangular in frontal view; margin with three, slightly raised, obtuse, triangular cusps (two latero-adaxial, one abaxial) separated by wide, shallow embayments; opercular apparatus composed of three similar triangular flaps, one adaxial and two latero-abaxial, forming a low, pointed roof when closed; hydranths with ca. 14–16 filiform tentacles surrounding a dome-shaped hypostome; abaxial caecum absent. Gonothecae borne on middle and upper parts of the stems; given off from the accessory tubes of the caulus and, consequently, adnate proximally, often forming a median, longitudinal row on both the front and back sides of the stem; when two or more accessory tubes give rise to neighboring gonothecae, the latter are shifted on alternately left and right; gonotheca tubular, tapering distally into an upwardly-bent neck region bearing distally a rounded aperture set transversely; perisarc thick and generally smooth, though distal undulations could be noted in certain gonothecae. Colonies dioecious; gonothecae sexually dimorphic, although their differences are only slight: female gonothecae appear broader and have wider apertures than their male counterparts.

Remarks. The large-sized, long, straight, tubular, barely-adnate, basally-notched hydrothecae, with free adaxial walls not adjacent proximally to the following internode, are distinctive within the genus.

Although the cladia are generally unbranched, occasional exceptions occur (as noted in sample MNHN-IK- 2015-2670): 1) a second-order cladium is given off laterally by means of a short apophysis from below one of the cladial hydrothecae; 2) an evidently aberrant secondary cladium is given off from within a cladial hydrotheca.

Bathymetric distribution. Between 290–806 m (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 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 9. Gonaxia incisa Galea, sp. nov. A. Portion of colony. B. Hydrotheca seen laterally. C. Opercular apparatus seen frontally. D. Presumably male gonothecae. E. Presumably female gonothecae. From samples MNHN-IK-2015-2670 (A–C), MNHN-IK-2015-2680 (D) and MNHN-IK-2015-2681 (E). 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).