Gonaxia solenoscyphoides 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 : 418-420

Gonaxia solenoscyphoides Galea , sp. nov.

Figs 1J , 14–16 ; Tables 2, 3

Material examined. Holotype: KANACONO, Stn. DW4742, MNHN-IK-2019-2065: a colony, 6.3 cm high, bearing presumably ♀ gonothecae.— Paratype: KANACONO, Stn. DW 4743, MNHN-IK-2015-2665: two colonies, 9.5 and 13.5 cm high, former sterile, latter bearing gonothecae; GenBank : MZ 099710 (16S) , MZ 099690 (18S) , MZ 099674 (28S).—Additional material: KANACONO, Stn. DW4785, MNHN-IK-2019-2066: one colony, 15.5 cm high, with remains of a few gonothecae.

Etymology. The specific epithet is a combination of the words Solenoscyphus , a hydroid genus ( Galea 2015: 7), and the Greek suffix εἶΔΟΣ, meaning resembling, to illustrate the morphological similarities of the new species with members of that genus.

Description. Colonies in the examined material reaching as much as 15.5 cm high; very rigid, arising from what appears to be the remains of a rhizoid stolon firmly anchoring them to hard substrates. Stems generally simple in appearance, strongly fascicled, up to 5 mm thick basally, grading to monosiphonic distally, perisarc brown; accessory tubes anastomosed, with wrinkled perisarc; main tube with smooth perisarc, longitudinal axis slightly geniculate, division into internodes indistinct, although equivalents of internodes composed of three alternating hydrothecae and a latero-distal apophysis below the distalmost hydrotheca, the latter becoming axillar; an elongated, vertical fenestra below the base of axillar hydrothecae. Cladia alternate along the stem in two coplanar rows, up to 20 mm long, generally unbranched, straight, bearing a succession of up to 25 very short internodes; nodes indistinct, except at junction between a cladium and its corresponding stem apophysis, marked by a distinct constriction. Stem and cladial hydrothecae alike, arranged in two alternate, coplanar rows; large-sized, long, tubular, free from the internode for ca. 2/3 their length; free adaxial wall straight or nearly so; abaxial wall slightly convex proximally, then straight for most of its length; adnate adaxial wall arched downwards, almost meeting an internal perisarc projection given off nearly horizontally from the origin of abaxial wall, thus leaving only a short passage for the hydranth into the hydrothecal lumen; thecal margin with eroded, indistinct cusps, producing an even rim, often renovated, renovations closely-set; closing apparatus lost in all specimens. Hydranths generally highly contracted near bases of hydrothecae; small compared to the size of the thecae, body columnar, without abaxial caecum, bearing distally a whorl of 16–18 filiform tenacles encircling a dome-shaped hypostome. Gonothecae arising from secondary tubes of the stem; arranged in a row on front and back sides of the colony, confluent with one another; when multiple accessory tubes produce neighboring gonothecae, the latter are shifted on laterally along the longitudinal axis of the stem. Gonothecae thick-walled, flask-shaped, adnate for more than half their length, free part gradually tapering distally, aperture transversely-set, large, circular, closed by rounded, deciduous operculum; gonothecae presumably female in the material at hand.

Remarks. As suggested by the specific epithet, sterile specimens of this hydroid are indistinguishable morphologically from members of the genus Solenoscyphus Galea, 2015 . Only the presence of gonothecae along the caulus, as noted in material MNHN-IK-2015-2665, vouches for their belonging to the genus Gonaxia Vervoort, 1993 .

Hydrothecae of G. solenoscyphoides Galea , sp. nov. are the largest within the genus. Only G. robusta Vervoort, 1993 has morphologically-similar hydrothecae, but their size is about 60% that of the new species [total depth 800–815 µm vs. 1255–1450 µm, abaxial wall 725–760 µm vs. 1080–1225 µm, free adaxial wall 560–590 µm vs. 890–1060 µm, maximum width 260–280 µm vs. 465–490 µm, diameter at rim 235–260 µm vs. 395–415 µm; measurements of the cladial hydrothecae of G. robusta are taken from Vervoort (1993: Table 21)].

Cauli of this species, as long as they appear from this rather scarce material at hand, are generally unbranched; however, one colony from sample MNHN-IK-2015-2665 possesses a stump (devoid of cladia) on the proximal part of its stem. The other colony, for its part, has a cladium bearing several second-order cladia, similarly to the stem; the original cladium, in addition, bears along its axis a few gonothecae derived from the caulus.

Bathymetric distribution. Between 290–403 m (present study).

G. bulbifera 0.8 ±

0.4

G. crassicaulis 6.0 ± 0.8 ±

1.0 0.4

G. crusgalli 4.9 ± 1.7 ± N.C.

0.9 0.5

G. elegans 6.0 ± 4.1 ± 4.6 ± 0.0 ±

1.0 0.8 0.8 0.0

G. errans 8.3 ± 8.3 ± 8.1 ± 9.5 ± 0.4 ±

1.2 1.2 1.2 1.2 0.2

G. incisa 10.3 ± 8.8 ± 8.3 ± 9.1 ± 8.0 ± 0.0 ±

1.3 1.1 1.1 1.2 1.1 0.0

G. cf. intermedia 5.1 ± 5.0 ± 5.0 ± 6.4 ± 10.1 ± 10.0 ± N.C.

0.9 0.9 0.9 1.0 1.3 1.3

G. perplexa 5.2 ± 4.8 ± 4.9 ± 6.2 ± 8.9 ± 9.6 ± 4.5 ± 0.2 ±

0.9 0.9 0.9 1.0 1.2 1.2 0.8 0.2

G. sinuosa 7.5 ± 3.0 ± 2.3 ± 5.7 ± 8.5 ± 8.7 ± 5.7 ± 6.6 ± 0.4 ±

1.1 0.7 0.6 0.9 1.2 1.1 1.0 1.0 0.2

G. solenoscy- 10.2 ± 8.0 ± 7.7 ± 8.7 ± 7.2 ± 4.0 ± 10.8 ± 8.4 ± 8.3 ± N.C.

phoides 1.3 1.1 1.2 1.2 1.1 0.8 1.3 1.2 1.2

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 14. Gonaxia solenoscyphoides Galea, sp. nov. A. Portion of colony. B. Hydrotheca seen laterally. C. Female gonotheca seen laterally. All from sample MNHN-IK-2019-2065. Scale bars: B = 300 µm; A, C = 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).