Schizoplumularia helicoidalis Galea & Maggioni 2020, sp. nov.
Creators: name: Galea, Horia R.
name: Maggioni, Davide
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Hydrozoa
Leptothecata
Plumulariidae
Schizoplumularia
Schizoplumularia helicoidalis

description: Schizoplumularia helicoidalis sp. nov.
urn:lsid:zoobank.org:act: 902D24C0-DC53-4610-A3D0-80EBC01A9B09
Figs 9B, 10 B–K; Table 3
Schizoplumularia elegans Ansín Agís et al., 2016 (pro parte): 68, 72, figs 6a, 8 [non S. elegans Ansín Agís et al. 2016 (pro parte): 67, figs 6b–e, 7, (?) 9].
Diagnosis
Schizoplumularia with slender, flaccid, geniculate stem, lightly fascicled proximally, then composed of only two adjacent tubes for most of its length; tubes with scattered nematothecae along their length; at each geniculation, one tube, while diverging as a cladia-bearing branch, gives rise to an auxiliary tube running upwards along the second tube, a situation that is reversed throughout the stem; branches undivided, but each equivalent of internode with a latero-distal cladial apophysis (the latter with a mamelon and 2 axillar nematothecae) and 1–2 nematothecae on side opposite the apophysis; apophyses shifted on to the upper side of the branch; cladia heteromerously segmented into short, ahydrothecate internodes with 1 nematotheca alternating with comparatively longer hydrothecate internodes bearing a small, cup-shaped hydrotheca and its 3 associated nematothecae.
.
Etymology
From Greek ‘ ἑΛΙΚΟΕΙΔής ’, meaning ‘in the form of a helix’, to describe the arrangement of the cladiabearing branches along the stem.
Material examined
Holotype
PACIFIC OCEAN • a 15.5 cm high, sterile colony without hydrorhiza; off New Caledonia, stn DW4711; 22°47′ S, 167°24′ E; 335–338 m; 18 Aug. 2016; KANACONO leg.; MNHN-IK-2015-610.
Additional material
PACIFIC OCEAN • 1 ca 6 cm high, sterile colony, and the top part (ca 2 cm high) of a colony with immature gonothecae; off New Caledonia, stn DW4762; 23°16′ S, 168°06′ E; 810– 805 m; 26 Aug. 2016; KANACONO leg.; barcode identifier MT655152; MNHN-IK-2015-596.
Description
A 15.5 cm high colony of very delicate and flaccid appearance, detached from its hydrorhiza; stem slender, composed proximally of bundle of few tubes running parallel to each other and communicating, at intervals, through common holes in the perisarc; nematothecae scattered along their length; more distally, remainder of stem composed of only two contiguous tubes forming alternately-placed geniculations at intervals of 3.5–5.5 mm; at each geniculation, one of tubes diverges from stem at acute angle and transforms itself into cladia-bearing branch; it also gives rise simultaneously, at level of axil thus formed with its henceforth single counterpart, to another tube running upward along that counterpart, so as to ensure the obligatory presence of two adjacent tubes composing stem; at next geniculation, there is a reversal of roles played by couple of tubes: that newly-added at previous geniculation continues unaffected (skips one geniculation), while its counterpart detaches distally from stem as cladia-bearing branch; stem tubes with two parallel rows of alternately-placed nematothecae; between successive geniculations, stem acquires slight torsion, so that its cladia-bearing branches are arranged in helicoidal manner along it. Stem, branches and cladia very slender; perisarc straw colored. Cladia-bearing branches up to 2 cm long, unsegmented, but each equivalent of internode with distallyplaced cladial apophysis and 1–2 nematothecae on side opposite to apophysis (up to 6 nematothecae in two closely-set whorls found on proximalmost ‘internode’); apophyses alternate, not coplanar, but forming wide angle between two rows; axil with conical mamelon provided with rounded aperture on summit, and two nematothecae, one on each side. Cladia up to 2.5 mm long, heteromerously segmented by means of transverse nodes into alternating ahydrothecate and hydrothecate internodes; proximalmost internode ahydrothecate, slightly shorter than its subsequent counterparts, with proximal nematotheca on its upper side; ahydrothecate internodes with generally two (occasionally up to four) internal, incomplete perisarc ridges near both ends, and proximal nematotheca placed frontally; hydrothecate internodes, up to 6 per cladium, comparatively longer than their ahydrothecate counterparts, with almost centrally-placed hydrotheca and its three associated nematothecae: a mesial one and pair of laterals; up to eight internal incomplete perisarcal ridges per hydrothecate internode. Nematothecae of colony all alike: trumpet-shaped, bithalamic, lower chamber tall, upper chamber shallow, wall of the latter lowered on adaxial side. Gonothecae in axils of cladia-bearing branches; immature in material at hand; broadly piriform, tapering gradually below into an indistinct, laterally curved pedicel; distal end truncate, not fully formed.
Remarks
The present material is, with little doubt, conspecific with part of that originally assigned to S. elegans by Ansín Agís et al. (2016), as for instance the colony from SMIB 4, stn DW53 that displays a “spirallybuilt” appearance (see their fig. 6a) and “larger hydrothecae” (see their fig. 8c–d). Although these authors acknowledged that “the remaining characters are similar to the other examined colonies” of S. elegans, they refrained from separating it specifically.
However, when compared to all available specimens of S. elegans occurring in the present collections, the colony from sample MNHN-IK-2015-610 is comparatively more slender and decidedly lax, and, most importantly, displays a spiral arrangement of the hydrocladia-bearing branches around the stem; the latter is lightly fascicled for the proximal 2.5 cm of its length, while the remainder (13 cm high) is composed of only two contiguous tubes. In S. elegans, the stems are fairly fascicled for nearly their whole length, with only the very tips of the colonies being monosiphonic, and their cladia-bearing branches of both rows are strictly coplanar (compare Fig. 9A and Fig. 9B).
The material MNHN-IK-2015-596, besides displaying shorter stem internodes (and consequently more closely-set cladia-bearing branches) compared to the holotype, has similar cladia (Fig. 10 D–E). Due to the scarcity of the available specimens of S. helicoidalis sp. nov., its intraspecific variability could not be assessed properly. In order to avoid any possible identification error, these specimens are not selected as a paratype, despite one of them being provided with (immature) gonothecae.
Distribution
Known only from off New Caledonia (Ansín Agís et al. 2016; present study).
description: Published as part of Galea, Horia R. & Maggioni, Davide, 2020, Plumularioid hydroids (Cnidaria: Hydrozoa) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program, pp. 1-58 in European Journal of Taxonomy 708 on pages 19-23, DOI: 10.5852/ejt.2020.708, http://zenodo.org/record/4011061