Aglaopheniid hydroids (Cnidaria: Hydrozoa: Aglaopheniidae) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program Author Galea, Horia R. text European Journal of Taxonomy 2020 2020-03-13 615 1 47 journal article 10.5852/ejt.2020.615 b2465730-6237-4a14-a98d-7fd2d1096cb0 3711000 637FC87F-13B5-4B32-BC52-11A9B30ECF1D Lytocarpia pseudoctenata sp. nov. urn:lsid:zoobank.org:act: F9BD38C7-AFF6-4703-B6E4-3C11BB0EFE16 Figs 12 G–H, 15 Diagnosis Species of Lytocarpia with tall, slender, pinnate colonies of delicate appearance. Stems unbranched, slightly fascicled, with long internodes provided with a frontal row of 4–10 nematothecae, a lateral apophysis supporting a cladium and its conical nematotheca, as well as with a fronto-axillar nematotheca. Cladia fairly distant from one another, shifted on to the anterior side of the colony. Cormidia short, with up to 7 intranodal ridges; hydrothecae strongly S-shaped, with ad- and abaxial ridges projecting far into their lumina; mesial nematotheca adnate for ¾ its length, free part projecting upwards, not reaching hydrothecal margin; the latter with strong, median, abaxial cusps and edges with 3 pairs of additional cusps, the 2 nd being comparatively more developed. Corbula on distal end of a hydrocladium, after a sequence of 5–18 normal cormidia; rachis geniculate, segments with a costal apophysis and a nematotheca lateral to it; costae forked, with a hydrotheca (devoid of its lateral nematothecae) in middle and appendages with successive pairs of opposite to subopposite nematothecae; gonothecae lenticular, flimsy, arising from the base of costal apophyses. Etymology The specific name indicates obvious resemblances with Aglaophenia ctenata ( Totton, 1930 ) . Material examined Holotype PACIFIC OCEAN • 1 colony , ca 14 cm high, hydrorhiza missing, bearing 3 corbulae; off New Caledonia , stn CP4739 ; 22°41ʹ S , 167°41ʹ E ; 393– 358 m ; 22 Aug. 2016 ; KANACONO leg.; MNHN-IK-2015-527 . Paratype PACIFIC OCEAN • 1 colony fragment , 2.2 cm long, with one gonotheca in middle part; off New Caledonia , stn DR4772 ; 23°02ʹ S , 168°21ʹ E ; 795– 230 m ; 28 Aug. 2016 ; KANACONO leg.; MNHN-IK-2015-528 . Description Undamaged colonies reaching more than 14 cm high; erect, slender and of delicate appearance, unable to support themselves when out of liquid, though perisarc rather thick throughout the colony; hydrorhiza not seen; stems lightly fascicled, composed of several superimposed auxiliary tubes, each adhering to the dorsal side of the preceding one, not forming a beam around the main tube, but rather resulting in a laterally-flattened structure; a notable deeply-cut, oblique node some distance above the origin from hydrorhiza, passing through all cauline tubes at a time; occasional oblique nodes sporadically along the remainder of stem; division into additional internodes not always distinct, though transverse nodes ( 170–180 µm wide) are more noticeable in the younger parts of the stem, where the perisarc is thinner; each internode 2–4 mm long, comprising a frontal row of 4–10 saccate nematothecae (with gutter-shaped, adaxial apertures), a short (ca 60 µm ) cladial apophysis above carrying basally a conical nematotheca (with small, rounded, apical aperture), as well as an elbow nematotheca (also with guttershaped aperture) lateral to the insertion of apophysis on the internode (fronto-axillar). Basalmost cladia broken off, but arrangement alternate along the longest portion of the stem; up to 3.7 cm long, the two rows shifted on to the anterior side of the colony so as to form an acute angle; cladia fairly distant from one another in each row; divided into rather short ( 585–600 µm ) internodes by means of transverse nodes ( 145–150 µm wide), each comprising a hydrotheca and its three associated nematothecae: one mesial and a pair of laterals; hydrotheca 525–540 µm deep, strongly S-shaped, with 2 internal septa, one adaxial arising a short distance above the base, and one abaxial given off a certain distance below the aperture from the abaxial wall, both septa protruding at least into the middle of the hydrothecal lumen; internodes with a number of incomplete internal septa: 2 abaxial and up to 5 on their adaxial side; mesial nematotheca long, tubular, adnate for more than ¾ its length, leaving only a short ( 100–115 µm ) portion free, provided with a gutter-shaped aperture along its whole free length; lateral nematothecae tubular, 215–220 µm long, aperture with rim deeply-scooped adaxially; hydrothecal margin with a prominent, rounded, abaxial cusp, continued on each side by three broad, triangular cusps, the second being the most developed. Gonosome an open corbula borne on a hydrocladium after a sequence of 5–18 normal cormidia; rachis slightly geniculate, divided into very short internodes (by means of transverse nodes), each bearing a costal apophysis and an elbow nematotheca lateral to it; costa separated from apophysis by transverse node; costa forked, with a basal hydrotheca (lateral nematothecae lost) in middle; mesial nematotheca situated far below the hydrothecal base, so as to accommodate the insertion of the ‘anterior’ arm, comprising 5–6 pairs of opposite to subopposite nematothecae; a nematotheca on the back of the hydrotheca, above which is inserted the ‘posterior’ arm, comprising 7–8 opposite to subopposite nematothecae; proximalmost costa of a corbula with the mesial nematotheca immediately below the hydrothecal base, not giving rise to the “anterior” arm set with nematothecae; all nematothecae elongated, with deeply-scooped adaxial margins. Gonothecae lenticular, with flimsy perisarc, arising from the base of the costal apophyses. Remarks None of the nominal species of Lytocarpia described so far ( Schuchert 2019 ) possesses simultaneously two (ab- and adaxial) strongly-developed internal septa, creating such a distinctive, S-shaped appearance of their hydrothecae, as L. pseudoctenata sp. nov. The new species shows striking resemblances with Aglaophenia ctenata ( Totton, 1930 ) with respect to the morphology of both hydrothecae and some components of the gonosome. Indeed, hydrothecae of both are borne on short internodes, are strongly S-shaped and possess two intrathecal ridges, one abaxial, the other adaxial, projecting halfway across their lumina (compare Fig. 15B with Totton (1930 : fig. 69a)). However, the hydrothecal apertures of A. ctenata appear more tilted forward ( Totton 1930 : fig. 69a; Ralph 1961 : fig. 9b; Vervoort & Watson 2003 : fig. 62e, g–i). Although both species possess similarly long cladia, those of A. ctenata are ‘tightly packed’ (compare image ‘a’ from the frontispiece of Vervoort & Watson (2003) with Fig. 12G herein). Its stem internodes possess “one terminal apophysis with a pair of opposite nematothecae at their base and one or two nematothecae on the proximal part […]. No mamelon has been observed […]” ( Vervoort & Watson 2003 ). As with the gonohydrocladium of L. pseudoctenata sp. nov. , that of A. ctenata also appears bifid ( Vervoort & Watson 2003 : fig. 62j), but there is no hydrotheca associated with it, and the number and position of the nematothecae are also slightly different. Fig. 15. Lytocarpia pseudoctenata sp. nov. A . Portion of stem. B–D . Hydrotheca (B) and details of its basal (C) and distal (D) parts, all seen laterally. E–F . Portion of the rachis of corbula, and costa with gonotheca (F). From samples MNHN-IK-2015-527 (C–D) and MNHN-IK-2015-528 (A–B, E–F). Scale bars: A, F = 500 µm; B–E = 200 µm. Distribution Known only from off New Caledonia (present study).