Notes on some sertulariid hydroids (Cnidaria: Hydrozoa) from the tropical western Pacific, with descriptions of nine new species Author Galea, Horia R. text European Journal of Taxonomy 2016 2016-08-02 218 1 52 journal article 21896 10.5852/ejt.2016.218 cba502b0-cc06-4252-94f1-3eda754e8183 2118-9773 3840195 A4D7AA38-D18F-4604-A5E0-D965637BD9F8 Gonaxia plumularioides sp. nov. urn:lsid:zoobank.org:act: 6A07FF84-EAA6-4AE6-8755-B450B17A28EB Fig. 4 G–J; Table 2 Diagnosis Gonaxia with slender, fascicled, branched or unbranched stems; cladia monosiphonic. Equivalents of internodes composed of a proximal hydrocladial apophysis and its associated axillary hydrotheca, two alternate hydrothecae above, and a second, distal hydrocladial apophysis and its associated hydrotheca. Hydrothecae tubular, slightly curved up- and outwards, comparatively slender and more immersed on stem than on cladia. Gonothecae unknown. Etymology From the Latin plūma , meaning feather, and the Greek εἶδΟς , meaning likeness, with reference to their plumose appearance, recalling the branching pattern displayed by some hydroids belonging to the superfamily Plumularioidea . Material examined Holotype BIOCAL: Stn. CP34, a 2.8 cm high, distal fragment of a branch or a stem, itself branched twice, sterile (MNHN-IK-2012-16535). Paratype BIOCAL: Stn. CP34, a 7.7 cm high, unbranched colony devoid of its hydrorhiza, as well as a 1 cm high fragment corresponding to the distalmost part of a colony; both are sterile (MNHN-IK-2012-16536). Description Colonies attaining at least 8 cm high, composed of either simple or ramified stems of slender appearance, despite being fascicled; accessory tubes on both “frontal” and “dorsal” sides of stems; the latter uniformly grading to monosiphonic distally. Side branches, when present, arising only in “frontal” aspect of the stem or higher order branches; up to 2 nd order branching observed. Division into internodes indistinct, but equivalents of internodes composed of the regular sequence: a first, basal apophysis ( 60–90 µm long) and its associated axillar hydrotheca, two additional, alternate hydrothecae above, and a second axillar apophysis with its associated hydrotheca. Following internode with same sequence, but its proximal apophysis on side opposite to the distal apophysis of preceding internode. Cladia leaving axis at 75–80° from upper part of stem or branches; two successive cladia on same side of stem are distant of 2200–2310 µm ; strictly monosiphonic, alternate, up to 1 cm long, comprising a succession of up to 23 alternate hydrothecae. Division into internodes indistinct; equivalent of first cladial internode comparatively longer ( 580–705 µm ) than subsequent ones ( 480–515 µm ); internodes short, accommodating a single hydrotheca distally. Hydrothecae widely spaced on stem ( 570–740 µm ), less so on cladia ( 470–530 µm ); tubular, slightly curving up- and outwards, free part angled at 50° to the axis of internode; stem hydrothecae slightly shifted on frontally; the two rows of cladial hydrothecae coplanar; less than half adnate on cladia, but considerably immersed into the stem internodes; free adaxial side nearly straight, adnate counterpart curved, ending basally in perisarc peg; abaxial side convex, with inflexion point in middle; aperture with three low cusps separated by shallow embayments; opercular apparatus lost. Gonothecae unknown. Table 2. Measurements (in µm) of hydrothecae of Gonaxia plumularioides sp. nov. and G. nova sp. nov.

G. plumularioides sp. nov.			G. nova sp. nov.
Caulinar hydrotheca	Axillar hydrotheca	Cladial hydrotheca	Caulinar hydrotheca	Axillar hydrotheca	Cladial hydrotheca
Free adaxial side	85–125	75–140	180–210	555–575	565–630	580–615
Adnate adaxial side	355–380	360–440	315–350	220–245	175–220	175–205
Abaxial side	315–345	195–245	395–440	600–630	505–575	620–665
Maximum width	110–125	125–145	195–205	260–270	270–290	250–260
Diameter at rim	80–90	80–95	160–170	160–165	150–185	165–175

Remarks The branching pattern of the stems of G. plumularioides sp. nov. resembles that seen in some plumularioid hydroids that build three-dimensional colonies (e.g., Macrorhynchia philippina Kirchenpauer, 1872 , M. allmani (Nutting, 1900) , Plumularia spiralis Billard, 1911 , etc.), and is consequently different from that observed in its congeners (e.g., G. amphorifera , G. sinuosa , G. nova sp. nov. , see description below), which generally build planar colonies. The regular structure of the stem internodes is also peculiar, and is only occasionally observed in the material assigned herein to G. errans , a species known for its inconstant structure of the stem ( Vervoort 1993 ). The shape of the hydrocladial hydrothecae resembles that of other congeners: 1) G. complexa Vervoort, 1993 , but in this species the hydrothecae have an exceedingly long part free from internode; 2) G. elegans , but its hydrothecae have a conspicuously straight axis instead of being convex (compare Fig. 4C and 4H ); 3) G. errans , whose hydrothecae have, however, a much longer free part (compare Fig. 4F with Fig. 4H ); 4) G. intercalata Vervoort & Watson, 2003 , but its hydrothecae are huge compared to those of the new species; 5) G. stricta Vervoort, 1993 , but here the hydrothecae have a much longer free part, and the cladial internodes are marked by internal, oblique perisarcal thickenings ( Vervoort 1993 ); 6) G. tasmanica Watson & Vervoort, 2001 , but its hydrothecae are comparatively larger. Geographical distribution New Caledonia .