Hincksella immersa Galea, 2019

Galea, Horia R. & Schuchert, Peter, 2019, Some thecate hydroids (Cnidaria: Hydrozoa) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program, European Journal of Taxonomy 562, pp. 1-70 : 15-18

Hincksella immersa Galea , sp. nov.

urn:lsid:zoobank.org:act:20EE4072-852E-492F-869A-80E120C82AE5

Figs 6A , 7 A–F; Table 3

Diagnosis

Colonies erect, regularly-pinnate; stems lightly fascicled, divided by indistinct transverse nodes; each equivalent of internode with a proximal apophysis and its axillary hydrotheca, two alternate hydrothecae above, and a second, distal apophysis together with its axillar hydrotheca. Cladia alternate, coplanar, separated from corresponding apophyses by transverse nodes; division into internodes indistinct; each equivalent of internode relatively short, provided with a hydrotheca distally. Hydrothecae cup-shaped, relatively shallow, almost completely adnate. Gonothecae given off from below the bases of cladial hydrothecae; ovoid, laterally flattened, tapering below, apically rounded.

Etymology

From the Latin ‘ immergo, -si, -sum, -ĕre ’, meaning ‘immersed’, to depict the condition of its hydrothecae.

Material examined

Holotype PACIFIC OCEAN • a 3.8 cm high broken in middle, bearing numerous gonothecae on cladia; off New Caledonia, stn DW4768; 23°25′ S, 168°01′ E; 180–210 m; 27 Aug. 2016; KANACONO leg.; a portion of cladium was used for DNA extraction, DNA1367; voucher MHNG-INVE-120801; barcode identifier MK073091; MNHN-IK-2015-390 .

Paratype PACIFIC OCEAN • a colony without gonothecae, 4.3 cm high; off New Caledonia, stn DW1712; 23°22′ S, 168°03′ E; 180–250 m; 26 Jun. 2001; NORFOLK 1 leg.; MNHN-IK-2015-392 .

Description

Colonies erect, up to 4.3 cm high, arising from root-like hydrorhiza strongly anchoring the colony to its substrate. Stems simple, fascicled for most of their length, grading to monosiphonic distally; perisarc thick, brownish; division into internodes indistinct; equivalents of internodes with quite regular structure, composed of a proximal apophysis supporting a cladium and its associated axillar hydrotheca, two alternate hydrothecae above, and a second, distal cladial apophysis given off on opposite side, together with its associated axillar hydrotheca; occasionally three instead of only two alternate hydrothecae intervene between the proximal and distal cladial apophyses. Cladia alternate, coplanar, borne on short stem apophyses separated from their 1 st internodes by distinct oblique nodes; cladia distant of 2.5–3 mm on each side; division by nodes indistinct, but each equivalent of internode relatively short, widening abruptly distally to accommodate a hydrotheca; internodes collinear. Hydrothecae alternate, in two parallel, coplanar rows; cup-shaped, deeply immersed into their corresponding internodes, leaving only a short portion of their adaxial wall free; abaxial wall straight to slightly convex, adnate adaxial wall distinctly curved, forming large perisarc plug basally; there is no complete base for the hydrotheca, as the abaxial wall invaginates basally for only a limited extent at junction between the hydrothecal lumen and internode; aperture circular, rim smooth. Gonothecae inserted slightly laterally under the bases of cladial hydrothecae; saccular, flattened ‘dorso-ventrally’, tapering basally into indistinct pedicel, distally rounded; no distinct aperture.

Remarks

This species, through its colony structure and origin of gonothecae, comes close to the type species of the genus, H. sibogae Billard, 1918 . It is distinguished from it through its comparatively shorter internodes, and much immersed hydrothecae (compare Fig. 7 A–E and 7K–L).

According to the present concept ( Bouillon et al. 2006), the genus Hincksella Billard, 1918 includes not only species forming pinnate colonies, but also congeners with simple, unbranched stems. Among the former category, H. alternans (Allman, 1888) gives rise to gonothecae from within the hydrothecal lumina, while H. formosa (Fewkes, 1881) , the present new species, as well as H. sibogae produce external gonothecae. As for H. indiana Millard, 1967 , a species with so-far undescribed gonothecae, it could instead belong to Staurotheca Allman, 1888 .

Conversely, among the species with simple stems, H. cornuta Galea, 2015 ( Galea 2015a) , H. cylindrica ( Bale, 1888) ( Preker & Lawn 2010) , H. neocaledonica Galea, 2015 (see below) and H. pusilla (Ritchie, 1910) ( Galea 2015b) give rise to their gonothecae from within their hydrothecae. The latter also produces stolonal gonothecae ( Hirohito 1969, as Cyclonia pusilla ). As for the remaining four species, viz. H. corrugata Millard, 1958 , H. projecta (Fraser, 1938) , H. rigida (Fraser, 1938) and H. similis Galea, 2015 , their gonothecae have not yet been described.

Owing to the above-mentioned features, it is likely that the genus Hincksella is polyphyletic. The 16S tree, indeed, shows that the four included species of Hincksella do not group into a common clade (see Fig. 20 and the ‘Molecular study’ section) and are rather scattered.

Distribution

Only known from off New Caledonia (present study).

Figures

Fig. 6. A. Hincksella immersa Galea, sp. nov., holotype colony, MNHN-IK-2015-390. — B. Hincksella sibogae Billard, 1918, one colony from sample MNHN-IL-2015-391. — C–F. Synthecium hians Millard, 1957, one colony from sample MNHN-IK-2015-494 (C) and detail of its fascicled base (D); individual stems diverging from common base (E) and fertile stem (F), both from sample MNHN-IK-2015-486. — G–H. Synthecium rectangulatum Galea, sp. nov., holotype colony (G) and gonothecae on proximal parts of the stems (H), both from sample MNHN-IK-2015-485. Scale bars: A–B, D–E = 1 cm; C, G = 2 cm; F, H = 5 mm.

Fig. 7. A–F. Hincksella immersa Galea, sp. nov., portion of stem with three cladia (A), four hydrothecae (B–E) showing varied degree of immersion, portion of cladium with gonothecae (F), all from sample MNHN-IK-2015-390. — G–J.? Hincksella neocaledonica Galea, 2015, portion of stem with three hydrothecae (G), immature gonotheca in frontal (H) and lateral (I) views, all from sample MNHN- IK-2015-384; fully-formed gonotheca (J) from sample MNHN-IK-2015-385. — K–L. Hincksella sibogae Billard, 1918, portion of colony showing branching pattern (K), three hydrothecae (L), all from sample MNHN-IK-2015-391. Scale bars: A, K = 1 mm; B–J, L = 500 µm.

Fig. 20 (opposite page). 16S maximum likelihood phylogenetic tree of selected Leptothecata species obtained with PhyML(GTR+G+I model) and based on 622 aligned basepair positions of the mitochondrial 16S gene. Node-support values are bootstrap values of 100 pseudoreplicates (shown only if> 70%). Species treated in this study are in bold. Some family clades with sufficient bootstrap support discussed in the present study are highlighted in blue boxes. N.B.: Two species names were not used as given in GenBank (FJFJ550462 and FN424141), and the reasons are given in the Material and methods section.