Schizoplumularia geniculata, Agís, José Ansín, Ramil, Fran & Calder, Dale R., 2016

Agís, José Ansín, Ramil, Fran & Calder, Dale R., 2016, One new genus and three new species of plumulariid hydroids (Cnidaria, Hydrozoa, Plumulariidae) from the western Pacific Ocean, with a re-examination of Plumularia insignis Allman, 1883 and related taxa, Zootaxa 4169 (1), pp. 57-86 : 64-67

Schizoplumularia geniculata n. sp.

( Figs 4‒5 ; Table 3)

Material examined. North New Caledonia. BATHUS 4, stn CP 906, 19º01'S, 163º15'E, 339‒350 m, 04-VIII-1994: one colony 45 mm high with one immature gonotheca, holotype ( MNHN-IK-2012-16602).

Etymology. The specific name geniculata refers to the bent or geniculate habitus of the hydrocauli in the colony.

Distribution. This species is known only from the type locality, North New Caledonia, at a depth between 339‒ 350 m.

Description. Hydrorhiza comprising a small tuft of perisarcal fibres given off from base of colony. Main axis erect, polysiphonic, geniculate. Along basal 27 mm of main axis, primary axial tube giving rise to alternate apophyses and hydrocladia arranged in same plane. Beyond 27 mm from base of colony, primary axial tube curving away from main axis and becoming initial branch (hydrocaulus) of colony. Remaining branches (hydrocauli) given off alternately to left and right of main axis, originating from secondary axial tubes having apophyses and hydrocladia only when tube curves away from main axis to form a typical hydrocaulus. Distal part of colony with main axis comprising a few accessory axial tubes; new secondary axial tubes arising in axils of each hydrocaulus, extending along and adhering to preceding secondary axial tube, then diverging from main axis to create a new hydrocaulus, as in Schizoplumularia vervoorti n. sp. Hydrocauli monosiphonic, divided into internodes by oblique nodes visible only towards apical end. Each internode with one or two apophyses and one to three nematothecae between two consecutive apophyses. Apophyses arranged alternately left and right in one plane in older parts of branches; younger parts with apophyses occurring left and right but almost in a single frontal row; each apophysis with a well developed mamelon on upper surface and with two axillary nematothecae, an extra distal nematotheca appearing on some apophyses; one perisarcal ring often present near node. Hydrocladia heteromerously segmented, beginning with a short ahydrothecate internode having one nematotheca on basal part and two internal perisarcal rings near proximal and distal ends; nematotheca of first internode sometimes lost. Remainder of hydrocladia divided into alternating hydrothecate and ahydrothecate internodes by oblique nodes. Each hydrothecate internode bearing a hydrotheca and three nematothecae: one mesial inferior on an elevation, and two laterals located on short apophyses. Hydrothecae tubular, deep, narrowing towards base, adcauline wall fully adnate, abcauline wall slightly sinuous with basal half slightly convex and distal half slightly concave; hydrothecal rim smooth, circular, slightly tilted toward abcauline wall. Ahydrothecate internodes each with one nematotheca on an elevation along basal third. All nematothecae movable, bithalamic, conical; mesial inferior nematotheca with adcauline wall of upper chamber somewhat deeper than usual and emarginated. Internodes with two perisarcal rings, one at each end, sometimes an additional thickening appearing below, behind or above hydrotheca.

One immature gonotheca observed springing from a hydrocladial apophysis; walls pyriform, widening to depressed distal end.

Remarks. Hydrothecae of this species are similar in morphology to those in hydroids described by Billard (1913) as Plumularia insignis var. conjuncta (= Plumularia conjuncta Billard, 1913 ), but it is impossible to reach a well-founded conclusion about the relationship of the two forms. Although the ramification pattern remains unknown in P. conjuncta , other characters differentiate it from our material. Ultimate branches or hydrocauli (equivalent to the type material of Billard’s species) in Schizoplumularia geniculata n. sp. are divided into cauline internodes by oblique nodes, each one carrying one or two apophyses, whereas they are undivided in P. conjuncta . In addition, hydrocladia were heteromerously segmented in our colonies, with the intermediate internodes always clearly separated by oblique nodes from hydrothecate internodes. Separation between hydrothecate and ahydrothecate internodes is weak or absent in P. conjuncta . Both hydrothecate internodes and hydrothecae are smaller in Schizoplumularia geniculata n. sp. ( Table 8).

BALTHUS stn CP 906

Height of colony (in mm) 43 First hydrocladial internode, length 90‒100 Length hydrothecate hydrocladial internodes 390‒460 Length ahydrothecate hydrocladial internodes 140‒180 Diameter at node 40‒50 Hydrotheca

Length abcauline wall 160‒190 Length adcauline wall 185‒210 Diameter at rim 85‒90 Mesial nematotheca, length 50‒60 Diameter at rim 25‒30 Lateral nematotheca, length 70‒90 Diameter at rim 30‒35 Gonotheca, length 170* Greatest diameter 150*

* The gonotheca is probably immature.

Figures

FIGURE 4. Schizoplumularia geniculata n. sp. A ‒ D, holotype (BATHUS 4, stn CP 906); A, habit of colony; B, detail of branch; C, internode of distal part; D, immature gonotheca. Scales: a, 1 cm. b ‒ d, 0.1 mm.

FIGURE 5. Schizoplumularia geniculata n. sp. A ‒ E, holotype (BATHUS 4, stn CP 906); A, basal part of a hydrocladium of main axis; B, proximalmost internode of a hydrocladium, lateral view; C, internode from distal part of a hydrocladium, lateral view; D, internode, lateral view; E, apophysis. Scales: a ‒ e, 0.1 mm.