Gonaxia constricta (Totton 1930)
- Dataset
- Second records and redescriptions of two rare thecate hydroids (Cnidaria: Hydrozoa) from the southwestern Pacific
- Rank
- SPECIES
Classification
- kingdom
- Animalia
- phylum
- Cnidaria
- class
- Hydrozoa
- order
- Leptothecata
- family
- Sertulariidae
- genus
- Gonaxia
- species
- Gonaxia constricta
description
Description. Colony erect, ca. 9 cm high, of flaccid appearance, unable to support itself when out of liquid (Fig. 7); basally, there are remains of a branched, rhizoid stolon apparently firmly attached to a hard substrate. Stem unbranched, weakly fascicled in its proximal 3 cm, then monosiphonic towards the distal tip. Division into internodes almost indistinct, but equivalents of internodes long, slightly geniculate, bearing distally a hydrotheca. Although minor irregularities occur here and there, the stem is composed of successive modules comprising four alternating hydrothecae of which the proximal- and the distalmost ones become axillar through the insertion of two cladial apophyses given off on opposite sides (Fig. 8 A). Cladia borne on short lateral apophyses of the stem, given off from below the axillar hydrothecae (Fig. 8 B); distally, an oblique node; cladia up to 2 cm long, composed of up to 20 hydrothecate internodes; nodes almost indistinct, except for an inconspicuous notch on side where the hydrotheca becomes free from the corresponding internode, a situation also noted in the stem; first cladial internode comparatively longer than subsequent ones, and delimited by a distinct adaxial notch from its corresponding stem apophysis (Fig. 8 A, B); regular internodes moderately long, distinctly geniculate, each bearing a hydrotheca distally (Fig. 8 A). Hydrothecae similar on stem and cladia; tubular, with straight axes (Fig. 8 C), except for the axillar hydrothecae of the stem that are distinctly curved upwards (Fig. 8 B); regular hydrothecae with longitudinal axes forming angles of 80 – 90 ° with the internodes above; hydrothecae adnate for about 1 / 4 their length to the corresponding internodes; ab- and adaxial walls straight; hydrothecal base not closed laterally, but composed of two intrathecal projections of the perisarc: one given off from the end of adnate adaxial wall, while the other projects some distance above into the hydrothecal lumen from the proximal end of abaxial wall; second ridge projects distinctly upwards in regular hydrothecae (Fig. 8 C), and downwards in their axillar counterparts (Fig. 8 B); hydrothecal aperture distal, set transversely; margin composed of three triangular cusps (one adaxial, two latero-abaxial) separated by broad, rounded embayments; aperture broadly triangular in frontal view, closed by three triangular flaps (two latero-adaxial, one abaxial) forming a low roof (Fig. 8 D). Hydranths preserved in some hydrothecae, but very contracted, provided with 14 – 16 filiform tentacles. Gonothecae absent. Perisarc straw colored, hydranths white in this ethanol-preserved material.
description
Figs 7 – 8; Table 2
discussion
Remarks. The branching pattern of the stem was inaccurately described in earlier accounts. On one hand, Totton (1930: 181) stated that G. constricta is a “ branched species […] with regularly alternate pinnae. Separating each alternating pair of pinnae is a pair of alternating hydrothecae, and in the axil of each pinna a hydrotheca ”. On the other hand, Vervoort (1993: 140) noted that “ between two successive hydrocladia there are two free hydrothecae, in addition there is an axillary hydrotheca at base of each hydrocladium ”. Nevertheless, the present material shows a combination of both accounts: although the nodes are indistinct, the stem is composed of successive modules of four alternating hydrothecae, of which the proximal- and distalmost ones become axillar upon the insertion of two cladial apophyses given off on opposite sides; with a few minor exceptions, the arrangement of cladia in conserved at each following module (Fig. 8 A). A similar branching pattern is only met with in G. errans Vervoort, 1993 [Galea (2016: 14, fig. 4 E, as G. cf. errans; 2016: 15, fig. 4 G, as G. plumularioides Galea, 2016); Galea & Maggioni (2021: 411, fig. 8 A)]. The gonothecae of this species still have to be discovered.
distribution
Distribution. Off Three Kings Island [Totton (1930, as Symplectoscyphus constrictus)], off New Caledonia (present study). Occurs at depths between 549 – 1087 m [Totton (1930) and present study, respectively].
materials_examined
Material examined. MNHN-IK- 2019 - 2090, KANADEEP 2, Stn. CP 5095, off southern New Caledonia, Capucine Bassin, 23 ° 38 ’ S, 167 ° 53.1 ’ E, 29 Sep 2019, 1087 – 1081 m, a ca. 9 cm high, sterile colony.
Name
- Synonyms
- Symplectoscyphus constrictus Totton 1930
- Homonyms
- Gonaxia constricta (Totton 1930)