Some thecate hydroids (Cnidaria: Hydrozoa) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program Author Galea, Horia R. Author Schuchert, Peter text European Journal of Taxonomy 2019 2019-10-04 562 1 70 journal article 25305 10.5852/ejt.2019.562 f6af87ae-7f5c-482a-8437-cba6bdcf88f5 3474305 6567F621-7A92-4D1A-8902-A1E76325AF94 Dynamena opposita Galea , sp. nov. urn:lsid:zoobank.org:act: 375154A7-28FA-4897-A522-362AA994DDA1 Figs 10A , 11 ; Table 6 Diagnosis Stems simple, monosiphonic, bearing pinnately-arranged hydrocladia in opposite pairs. Division into internodes irregular; each internode with a pair of indistinct apophyses supporting cladia and their associated axillary hydrothecae, as well as 0–3 pairs of hydrothecae below. Cladia divided into more or less regular internodes comprising 0–3 pairs of opposite hydrothecae. Hydrothecae tubular, deeply immersed into internode, not contiguous, aperture facing outwards, provided with two lateral, triangular cusps. Gonothecae unknown. Fig. 10.A . Dynamena opposita Galea , sp.nov. ,holotype colony, MNHN-IK-2015-470. —B . Hydrallmania clavaformis Galea , sp. nov. , holotype colony, MNHN-IK-2015-404. — C . Sertularella leiocarpoides Vervoort, 1993 , one colony from sample MNHN-IK-2015-420. — D . Sertularella novaecaledoniae Vervoort, 1993 , colony from sample MNHN-IK-2015-424. — E . Sertularella aff. sinensis Jäderholm, 1896 , one colony from sample MNHN-IK-2015-418. — F . Sertularella tronconica Galea, 2016 , colony from sample MNHN-IK-2015-419. Scale bars: A–B, D–E = 1 cm; C = 2 cm; F = 5 mm. Etymology From the Latin ‘ oppŏsĭtŭs, -a, -um ’, meaning ‘opposite’, to illustrate the relative position of the two rows of stem apophyses supporting the cladia. Material examined Holotype PACIFIC OCEAN • a 3.8 cm high colony without gonothecae, detached from substrate, with mostly only the perisarc left; off New Caledonia , stn DW4735; 22°40′ S , 167°40′ E ; 233– 195 m ; 22 Aug. 2016 ; KANACONO leg.; MNHN-IK-2015-470. Description Colony erect, 3.8 cm high, stiff when out of liquid, arising from creeping, branching hydrorhiza; stem monosiphonic, unbranched, composed of a short ( 3.5 mm long), athecate, basal part above the origin from stolon, and a much longer, distal thecate and cladiate part; the latter divided into irregular internodes by means of transverse constrictions of the perisarc; each internode long, composed distally of a pair of axillar hydrothecae above the insertion of two opposite cladia, as well as 0–3 pairs of hydrothecae below; hydrothecae opposite and distant from each one within a pair. No distinct stem apophyses supporting the cladia; successive pairs of cladia distant of 1.5–4 mm , depending of the number of intervening pairs of hydrothecae; cladia up to 1.3 cm long and comprising up to 16 pairs of successive hydrothecae; divided by transverse nodes, occasionally indistinct, into rather irregular internodes, generally comprising a single pair of hydrothecae distally, although 2–3 of these may occur elsewhere; first, proximal most internode comparatively longer than subsequent ones. Hydrothecae in strictly opposite pairs, not contiguous, though much closer to one another compared with their cauline counterparts; almost tubular, gently curving outwards, deeply immersed into the corresponding internode, leaving 1/6-1/7 of their adaxial wall free; the latter consequently short and distinctly concave; adnate adaxial wall concave; abaxial wall slightly curved outwards, especially distally; margin thickened, provided with two conspicuous, lateral, triangular cusps with rounded tips; opercular apparatus lost. Hydranths badly-preserved, presence of an abaxial gastric diverticulum could not be ascertained. Gonothecae absent. Perisarc of the colony thick and brown. Fig. 11. Dynamena opposita Galea , sp. nov. A–B . Distal part of colony showing branching pattern (A), cladial internode with pair of hydrothecae (B). Scale bars: A = 1 mm; B = 500 µm. Table 6. Measurements of Dynamena opposita Galea , sp. nov. , in µm.

Internodes
- cauline, diameter at node	210–405
- 1st cladial, length	860–1310
- ordinary cladial, length	590–870
- cladia, diameter at node	100–195
Hydrotheca
- free adaxial wall	75–100
- adnate adaxial wall	435–465
- abaxial wall	325–340
- diameter at rim	135–140

Remarks According to Galea & Ferry (2015: 230–231 , table 2), only two nominal species of Dynamena described so far form pinnate colonies with opposite cladia, namely D. anceps (Fraser, 1938) and D. japonica Stechow, 1920 . Through the courtesy of D. Geiger of the Santa Barbara Museum of Natural History (SBMNH), CA, USA , one of us (H.R.G.) was able to see several macrophotographs of the lecto- and one of the paralectotypes of D. anceps , demonstrating that it is a much slenderer species, with hydrothecae free from their corresponding internodes for a much longer portion than in D. opposite sp. nov. Unlike the new species, D. japonica is a large hydroid (colonies reaching as much as 20 cm in height), with thick and brown perisarc ( Hirohito 1995 ), with cladia separated by 2–8 pairs of hydrothecae, the latter being closely approximated on both stems and cladia ( Hirohito 1995 ; Stechow 1913 , as Thuiaria articulata (Pallas, 1766) ; Park & Rho 1986 , as T. articulate ). In addition, its hydrothecae are bigger, having notably a wider rim ( Hirohito 1995 ). Distribution Only known from off New Caledonia (present study). Genus Geminella Billard, 1925