Lytocarpia pseudoctenata

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.

urn: lsid: zoobank. org: act: F 9 BD 38 C 7 - AFF 6 - 4703 - B 6 E 4 - 3 C 11 BB 0 EFE 16 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.

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. 15 B with Totton (1930: fig. 69 a )). However, the hydrothecal apertures of A. ctenata appear more tilted forward (Totton 1930: fig. 69 a; Ralph 1961: fig. 9 b; Vervoort & Watson 2003: fig. 62 e, 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. 12 G 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. 62 j), but there is no hydrotheca associated with it, and the number and position of the nematothecae are also slightly different.

Distribution Known only from off New Caledonia (present study).

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 CP 4739; 22 ° 41 ʹ S, 167 ° 41 ʹ 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 DR 4772; 23 ° 02 ʹ S, 168 ° 21 ʹ E; 795 – 230 m; 28 Aug. 2016; KANACONO leg.; MNHN-IK- 2015 - 528.