Schizoplumularia helicoidalis, Galea & Maggioni, 2020

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, European Journal of Taxonomy 708, pp. 1-58 : 19-23

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).

Figures

Fig. 9. A. Schizoplumularia elegans Ansín Agís et al., 2016, colony from sample MNHN-IK-2015-548. — B. Schizoplumularia helicoidalis sp. nov., holotype colony, MNHN-IK-2015-610. Scale bar: 2 cm.

Fig. 10 (opposite page). A. Schizoplumularia elegans Ansín Agís et al., 2016, monosiphonic portion of a branch with proximal part of a cladium, from sample MNHN-IK-2015-548. — B–K. Schizoplumularia helicoidalis sp. nov., portion of stem showing fate of component tubes (B); portion of branch with five successive cladial apophyses and proximal part of a cladium (C); portions of cladia from material other than the holotype (D–E); detail of cladial apophysis (F); cladial internode with hydrotheca and its associated nematothecae (G); nematothecae of stem (H) and of cladial intersegment in adaxial (I) and lateral (J) views; gonotheca from material not belonging to the type (K); B–C, F–J from the holotype, MNHN-IK-2015-610; D–E, K from sample MNHN-IK-2015-596. Scale bars: A, C–E = 300 µm; B = 1 mm; F–K = 100 µm