Plumularia billardi, 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 : 79-81

Plumularia billardi nom. nov.

( Figs 13‒14 ; Table 7)

Plumularia insignis var. gracilis Billard, 1913: 47 , fig. 41, pl. III, figs. 29‒30; Bedot, 1921: 28; Van Praët, 1979: 925.

Material examined. Plumularia insignis var. gracilis , Syntype material: ZMA.COEL.P.4052. Type locality, in part: Siboga Expedition Stn 159, 0º59.1’S, 129º48.8’E, 411 m, 16-08-1899: five fragments, 15–140 mm, some with gonothecae; also one colony, 93 mm high, in two fragments, without gonothecae.

ZMA.COEL.P.5234. Type locality, in part: Siboga Expedition Stn 262, 5º53.8’S, 132º48.8’E. 560 m: five fragments, probably of same colony, 5–90 mm high, without gonothecae.

MNHN-IK-2012-16032. Type locality, in part: Siboga Expedition Stn 159, 0º59.1’S, 129º48.8’E, 411 m, 16- 08-1899, one slide: L.1283, two monosiphonic fragments, 4 mm and 9 mm long, smaller one with three gonothecae.

Etymology. The specific name billardi honours Dr Armand Eugène Billard (1871–1942), who first described this species (as Plumularia insignis var. gracilis ).

Distribution. Plumularia billardi is known only from two localities in Indonesian waters (type localities), at depths of 411 and 560 m.

Description. Hydrorhiza a tuft of perisarcal fibres given off from base of colony. Colony branched, main axis polysiphonic proximally, becoming monosiphonic distally. Main tube with several nematothecae, up to 12, between two consecutive apophyses; not divided into segments; internal perisarcal rings lacking; apophyses arising from main tube, disposed alternately left and right; each apophysis with two axillary nematothecae and one mamelon on distal part; hydrocladia pinnately arranged. Lateral branches given off from main tube, arising from tubular apophyses located in axil of a thickened hydrocladial apophysis with a missing hydrocladium (fig. 13B, arrow); these apophyses with one axillar nematotheca. Branches composed of a succession of internodes separated by slightly oblique nodes; basal internodes with two or rarely three apophyses, distal ones normally with only one. Nematothecae four below first apophysis, with two others between consecutive apophyses, these sometimes displaced to posterior side of branch. Basal internodes lacking perisarcal rings, or with one at each end; number of perisarcal rings increasing towards distal part, with up to 12 per internode. Apophyses of branches alternately directed left and right, more or less in the same plane in basal parts and frontally directed distally. Hydrocladia of main axis and branches identical in structure; each hydrocladium with a proximalmost ahydrothecate internode; this first internode with one proximal nematotheca on a small elevation, and with two perisarcal rings, one at each end; remainder of hydrocladium a succession of hydrothecate and ahydrothecate internodes separated by oblique nodes. Hydrothecate internodes each with one hydrotheca and three nematothecae: one mesial inferior and two laterals. Hydrotheca deep, with adcauline wall fully adnate; abcauline wall straight; hydrothecal rim smooth, perpendicular to hydrocladial axis. Mesial inferior nematotheca on small elevation, not reaching base of hydrotheca; lateral nematothecae on small apophysis, arising below hydrothecal margin, extending well beyond orifice. Ahydrothecate internodes with one proximal nematotheca, borne on a small elevation. All nematothecae bithalamic, movable, with adcauline wall of distal chamber lowered. Perisarcal thickenings in internodes decidedly varied in number. Observed morphological variations mainly including number of apophyses, and number and disposition of nematothecae per axial and branch internodes; these related to processes of regeneration following damage.

Gonothecae elongated, tubular, with a distal circular aperture; arising from apophyses.

ZMA.COEL.P.4052

Hydrothecate internode, length 540‒560 Ahydrothecate internode, length 140‒170 Diameter at node 60‒70 Hydrotheca

Abcauline wall, length 250‒300 Adcauline wall, length 220‒290 Diameter at rim 110‒140 Mesial nematotheca, length 70‒80 Diameter at rim 30‒40 Lateral nematotheca, length 70‒80 Diameter at rim 30‒40 Gonotheca, length 1300‒1570 Maximum diameter 350‒400

Remarks. The trophosome of Plumularia insignis var. gracilis Billard, 1913 resembles that of P. insignis Allman, 1883 , but its gonosome differs in morphology. In P. insignis var. gracilis , the gonothecal aperture is circular in shape and apical in position, whereas that of P. insignis is semicircular and oriented laterally. Moreover, gonothecae of the two differ in size, with those of P. insignis var. gracilis being considerably smaller. The ramification pattern of this morphotype, with lateral branches arising from the axil of hydrocladial apophyses, also seems quite peculiar. In addition, the type localities of the two morphotypes are decidedly different both geographically and environmentally, with P. i n s i g ni s var. gracilis being from tropical waters of Indonesia and P. insignis from Prince Edward Island ( South Africa ) in the cold subantarctic region.

We therefore consider the hydroid described as P. insignis var. gracilis to be a different species from P. insignis . The binomen Plumularia gracilis cannot be applied to Billard’s species because that name is an invalid junior homonym of Plumularia gracilis Murray, 1860 [= Hydrallmania franciscana (Trask, 1857) ], Plumularia gracilis Clarke, 1879 [= Plumularia clarkei Nutting, 1900 = Halopteris clarkei (Nutting, 1900) ], and Plumularia gracilis (Fraser, 1948) [= Nemertesia gracilis (Fraser, 1948) ]. Instead, Plumularia billardi is proposed as a replacement name for the species.

Figures

FIGURE 13. Plumularia billardi nom. nov. Syntype material of Plumularia insignis var. gracilis Billard, 1913; A: colony (after Billard 1913). B: fragment of axis with an axillary apophysis with the basal part of a lateral branch with a hydrocladium; note the point of insertion of a hydrocladium on stem (arrow). Scale a: 1 cm. b: 0.1 mm.

FIGURE 14. Plumularia billardi nom. nov. Syntype material of Plumularia insignis var. gracilis Billard, 1913; A: fragment of a hydrocladium with two hydrothecate and two ahydrothecate internodes. B: last hydrothecate segment of a hydrocladium. C: hydrotheca from the middle part of a hydrocladium. D: distalmost hydrotheca of a hydrocladium. E: gonotheca. Scales a ‒ e: 0.1 mm.