Lytocarpia subtilis, Galea, 2020

Galea, Horia R., 2020, Aglaopheniid hydroids (Cnidaria: Hydrozoa: Aglaopheniidae) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program, European Journal of Taxonomy 615, pp. 1-47 : 33-38

Lytocarpia subtilis sp. nov.

urn:lsid:zoobank.org:act:F077EEF0-D13A-499A-AA86-6F8D82062D42

Figs 16B , 17 C–J

Diagnosis

Species of Lytocarpia with tall, exceedingly slender, pinnate colonies of a very delicate appearance, with lightly fascicled, unbranched stems. Division into internodes indistinct; a row of 8–17 frontal nematothecae between two successive cladial apophyses, the latter with a basal, simple, conical nematotheca, and a fronto-axillar nematotheca. Cladia widely-spaced from one another; cormidia quite long, with up to 11 intranodal septa, accommodating an elongate hydrotheca and its 3 associated nematothecae; free part of mesial nematotheca gutter shaped, borne on a prominent, basal, abaxial bulge of the hydrotheca; an adaxial, intrathecal septum projecting slightly upwards and over halfway into the hydrothecal lumen; rim with prominent, median, abaxial cusps, edges wavy. Corbula on distal end of cladium; rachis indistinctly divided; each segment with a lateral costa and a nematotheca near to its insertion point; costae with a hydrotheca with its full complement of nematothecae, as well as an additional one on dorsal side of internode; mesial nematotheca far below hydrothecal base, so as to give rise to an appendage set with lateral nematothecae.

Etymology

From the Latin ‘ subtīlis ’, meaning ‘slender’, to describe the appearance of its hydrothecae.

Material examined

Holotype

PACIFIC OCEAN • 1 upper part of colony, ca 8.5 cm long, bearing a corbula; off New Caledonia, stn DW4711 ; 22°47ʹ S, 167°24ʹ E; 335–338 m; 18 Aug. 2016; KANACONO leg.; MNHN-IK-2015-525 .

Paratype

PACIFIC OCEAN • 3 specimens (1 colony, nearly complete, ca 14.5 cm high, with hydrorhiza but missing its distalmost part, without gonosome, 1 colony fragment, ca 14.5 cm long, missing both hydrorhiza and distal part, without gonosome, and 1 colony fragment, ca 5.5 cm long, missing both its hydrorhiza and distal part, bearing a corbula); off New Caledonia, stn CP4674 ; 22°48ʹ S, 167°29ʹ E; 311– 302; 13 Aug. 2016; KANACONO leg.; MNHN-IK-2015-526 .

Description

Colony erect, unable to support itself outside liquid, exceedingly slender and delicate; arising from branched, rhizoid stolon anchoring it in sandy bottom. Stem unbranched, lightly fascicled proximally, monosiphonic for most of its length; a deeply-cut, oblique node a certain distance above its origin from hydrorhiza; below the node, a succession of large, saccate nematothecae in a row along the main tube; above the node, the stem bears widely-spaced (2.5–3 mm apart), alternate cladia, the latter borne on short (ca 70 µm) apophyses given off laterally and towards the ‘front’ of the colony, the two rows of cladia forming an acute angle; division into internodes (nodes transverse, 160–170 µm wide) inconspicuous on stem, but equivalents of internodes comprising a row of 8–17 frontal, saccate nematothecae, a lateral apophysis above them, a simple, conical nematotheca (with small, rounded, apical aperture) on the basal part of the apophysis, as well as fronto-axillar nematotheca, rather lateral to the apophysis, having the distal part shifted on to the opposite direction; all stem nematothecae, except that borne on the mamelon, with large, adaxial, gutter-shaped apertures. Cladia up to 1.8 cm long, composed of up to 21 cormidia, not distinctly demarcated by transverse nodes; each cormidium 810–860 µm long, 100–105 µm wide at node, with a hydrotheca placed some distance after its proximal node, and three associated nematothecae: one mesial and a pair of laterals; 10–11 internodal projections of the perisarc, all but two given off from the adaxial wall of the hydrotheca; hydrothecae exceedingly long (680–705 µm), slightly conical, with a basal abaxial bulge, on the top of which is mounted the free portion of the mesial nematotheca; the latter long, cylindrical, slightly concave in general outline, adnate for about ⅔ of its length, free part 120–130 µm long, with gutter-shaped aperture all the way down to the junction with the lower abaxial wall of hydrotheca, apical rim distinctly crenulated; lateral nematothecae moderately long (170–175 µm), broadly tubular, reaching the hydrothecal margin, aperture scooped out on adaxial side, abaxial rim distinctly crenulated; hydrothecal aperture 225–235 µm wide, rim with a prominent abaxial cusp with crenulated apex, ridges rather wavy, without distinct cusps; an internal septum is given off from the lower part of the adaxial wall of the theca and projects for ⅔ into the lumen. Gonosome an open corbula borne on distal ends of cladia, after a succession of 6–10 normal cormidia; corbula up to 8 mm long, tubular, with straight rachis, not distinctly divided into internodes; segments short, with an indistinct lateral apophysis bearing a costa and a saccate nematotheca (with gutter-shaped aperture) lateral to it; gonothecae lenticular, with flimsy perisarc, borne near the insertion of the costa on the rachis; costae up to 20–21 per side of the gonotheca, comprising a hydrotheca with a complete set of nematothecae, in addition to which there is an extra nematotheca on the dorsal side of the internode; mesial nematotheca far below the hydrothecal base, leaving room for the insertion of a long appendage carrying 7–11 variously arranged nematothecae on both sides.

Remarks

None of the nominal species of Lytocarpia Kirchenpauer, 1872 described so far ( Schuchert 2019) possesses such exceedingly long and slender hydrothecae. Elongate, but not slender, hydrothecae are met with in L. alata Vervoort & Watson, 2003 (original account), L. distans Allman, 1877 ( Ramil & Vervoort 1992b), M. myriophyllum (Linnaeus, 1758) ( Ramil et al. 1998) , and L. spiralis ( Totton, 1930) (dealt with in the present study, Fig. 17B ).

Distribution

Known only from off New Caledonia (present study).

Genus Macrorhynchia Kirchenpauer, 1872

Macrorhynchia phoenicea (Busk, 1852)

Figs 16 C–D, 18A

Macrorhynchia phoenicea – Di Camillo et al. 2009: 218, figs 2h–i, 6, 9.

Material examined

PACIFIC OCEAN • 1 profuse colony on gorgonian, with stems up to 10 cm high, some bearing phylactocarps; off New Caledonia, stn DW4945; 25°22ʹ S, 159°43ʹ E; 130– 108 m; 4 Sep. 2017; KANADEEP leg.; MNHN-IK-2015-510 • 1 colony, composed of a couple of stems, 2.5 and 4 cm high; off New Caledonia, stn DW4775; 23°03ʹ S, 168°17ʹ E; 140–277 m; 28 Aug. 2016; KANACONO leg.; MNHN-IK-2015-511 • 5 colonies, 2.5–3.5 cm high, of which 4 bear incipient phylactocarps; off New Caledonia, stn DW4774; 23°01ʹ S, 168°19ʹ E; 100– 90 m; 28 Aug. 2016; KANACONO leg.; MNHN-IK-2015-512 .

Comparative material

PACIFIC OCEAN • 1 complete colony, 6.5 cm high, as well as 3 fragments (1.5, 2.5 and 3.5 cm long) of Macrorhynchia disjuncta (Pictet, 1893) , all fertile; off Vanuatu, stn CP1104; 15°04ʹ S, 167°07ʹ E; 125–129 m; 7 Oct 1994; MUSORSTOM 8 leg.; MNHN-IK-2015-513.

Remarks

For a recent description of this well-known species, refer to Di Camillo et al. (2009), who also provide an extensive synonymy.

Schuchert (2003) noted striking resemblances between the hydrothecae of Aglaophenia disjuncta Pictet, 1893 , a hydroid with a so far unknown gonosome, and those of the present species, and questioned their possible conspecificity. A few well-preserved, fertile specimens, undoubtedly assignable to Pictet’s species, occur in material from off Vanuatu gathered during the MUSORSTOM 8 Expedition. Their appearance ( Fig. 16D ) immediately distinguishes them from typical colonies of M. phoenicea ( Fig. 16C ), in being more delicate, with a less rigid and straw-colored perisarc, with more distant and comparatively longer cladia, with longer cormidia and slightly larger hydrothecae.

Stems of the species described by Pictet (1893) are lightly fascicled and scarcely branched, as for instance with one branch occurring in the tallest (6.5 cm high) specimen available. The stem and side branches are transversely divided into moderately long internodes, each bearing a cladial apophysis and 3 nematothecae, two large and one reduced: one at the base of the apophysis, a second axillar, and a short, conical theca on a mamelon ( Fig. 18B ). The large nematothecae are half adnate to the internode and possess a small, rounded aperture projecting laterally, as well as a large, broadly ovoid aperture behind. The proximal parts of the stem and branches are devoid of cladia, bear a row of large nematothecae with a conical distal half and have one of their apertures pointing upwards, while the other is comparatively larger and situated behind. The characteristic shape of the hydrothecae is depicted in Fig. 18C . The gonosome is typical of Macrorhynchia , and replaces a normal cladium, not forming pseudo-corbulae, but isolated phylactocarps; the proximalmost internode is a normal cormidium, on the distal part of which is inserted a long appendage with pinnate appearance resuting from the presence of (often) opposite pairs of exceedingly long nematothecae with two apertures: one small, apical, the other ovoid, at the base of the nematotheca. Occasionally, a few additional nematothecae in a row are to be found on the outer side of the phylactocarp. The gonothecae are large and lenticular, with flimsy perisarc, and are borne near the base of the appendage, amongst the proximalmost nematothecae.

Distribution

Widespread in the tropical parts of the Indian and southern Pacific oceans ( Di Camillo et al. 2009).

Figures

Fig. 16. A. Lytocarpia cf. spiralis (Totton, 1930), colony from sample MNHN-IK-2015-546. — B. Lytocarpia subtilis sp. nov., colony and corbula (insert) from sample MNHN-IK-2015-525 (holotype). — C–D. Macrorhynchia phoenicea (Busk, 1852) (C), from sample MNHN-IK-2015-512, compared to M. disjuncta (Pictet, 1893) (D), from sample MNHN-IK-2015-513. — E–G. Macrorhynchia spiralis sp. nov., colonies from samples MNHN-IK-2015-519 (E, holotype) and MNHN-IK-2015-520 (F, one paratype), and medusoid gonophore (G) from former sample. Scale bars: A = 3 cm; B–F = 1 cm; B (insert) = 1 mm; G = 100 µm.

Fig. 17. A–B. Lytocarpia cf. spiralis (Totton, 1930), portion of stem (A) and hydrotheca (B), from sample MNHN-IK-2015-546. — C–J. Lytocarpia subtilis sp. nov. C. Portion of stem. D–I. Lateral view of a hydrotheca (D), with details of its basal (E) and distal (F) parts; hydrotheca seen apically (G), and variation in the shape of its margin seen frontally (H) and laterally (I). J. Portion of corbula rachis with costa and gonotheca. From samples MNHN-IK-2015-525 (C, E–G) and MNHN-IK-2015-526 (D, H–J). Scale bars: A = 300 µm; B, D–F, J = 200 µm; C = 1 mm; G–I = 100 µm.

Fig. 18. A. Macrorhynchia phoenicea (Busk, 1852), hydrotheca from sample MNHN-IK-2015-510. — B–D. Macrorhynchia disjuncta (Pictet, 1893), portion of stem (B), hydrotheca (C) and phylactocarp with gonotheca (D) from sample MNHN-IK-2015-513. Scale bars: A–C = 200 µm; D = 500 µm.