Plumularia flabellum Allman, 1883

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 : 77-79

Plumularia flabellum Allman, 1883

( Fig. 12 ; Table 6)

Plumularia flabellum Allman, 1883: 19 , pl. I, figs 1‒4; Stechow, 1 923: 225. Plumularia insignis flabellum: Billard, 1908: 759 .

Plumularia insignis var. flabellum: Billard, 1910: 34 , fig. 15; Van Praët, 1979: 925.

Material examined. Plumularia flabellum : fragments of type material at the Museum national d’Histoire naturelle, Paris , Challenger Expedition, Marion Island ( South Africa), 91–137 m, 26-12-1883, MNHN-IK-2012- 16034, two slides:

L. 1251. Two hydrocladia.

L. 1282. Fragment 15 mm long, polysiphonic over basal half; nematothecae on secondary tubes.

Distribution. Plumularia flabellum is known only from its type locality of Marion Island ( South Africa), at depths between 91 and 137 m.

Description. Fragment polysiphonic along basal part. Main tube segmented, with internodes separated by transverse nodes; each axial internode with two apophyses bearing hydrocladia, one in mid-region and another just under distal node, and two nematothecae, one just above basal node and another above first apophysis. Apophyses alternately directed right and left, arising only from main tube; each apophysis with one well-developed mamelon on upper surface, and with 3–4 nematothecae: two axillary and one or two distal to mamelon; one perisarcal ring occurring near node. Hydrocladia with proximalmost internode ahydrothecate, bearing one nematotheca on a small elevation towards base; perisarcal rings sometimes visible, with one basal and other distal; rest of hydrocladium comprising a succession of hydrothecate and ahydrothecate internodes. Hydrothecate internodes with one hydrotheca and three nematothecae: one mesial inferior and two laterals. Hydrotheca cup-shaped; adcauline wall fully adnate; abcauline wall straight; hydrothecal margin smooth, circular, perpendicular to hydrocladial axis. Mesial inferior nematotheca on a small elevation, reaching and sometimes surpassing hydrothecal base. Lateral nematothecae on a small apophysis placed below hydrothecal margin, extending well beyond orifice. Mesial and lateral nematothecae with a slightly scooped distal chamber. Number of perisarcal rings variable, with a maximum of six; on distal parts, rings may be absent or not visible. Ahydrothecate internodes with one nematotheca on basal part, arising from a small elevation; perisarcal thickenings two, with one at each end. All nematothecae bithalamic, movable. Nematothecae of apophyses larger than those of hydrocladial internodes.

L.1251 First hydrocladial internode, length 160‒180 Diameter at node 80‒100 Hydrothecate internode, length 410‒460 Ahydrothecate internode, length 140‒170 Diameter at node 70‒100 Hydrotheca

Abcauline wall, length 200‒220 Adcauline wall, length 150‒190 Diameter at rim 160‒180 Mesial nematotheca, length 80‒100 Diameter at rim 50 Lateral nematotheca, length 100‒110 Diameter at rim 50‒60 Remarks. Plumularia flabellum Allman, 1883 differs from P. insignis Allman, 1883 mainly in colony morphology, being dense and pinnately ramified and with primary and secondary branches disposed in the same plane (Allman 1883: Pl. 1 fig. 1). In P. insignis , colonies have a polysiphonic main stem, with single branches given off in all directions around the central axis (Allman 1883: Pl. 1 fig. 1). Moreover, hydrocladial internodes are shorter in P. flabellum , and hydrothecae are smaller. For these reasons we consider P. flabellum to be a valid species, distinct from P. insignis .

The structure of the colony clearly differs from that of Schizoplumularia n. gen.

Figures

FIGURE 12. Plumularia flabellum Allman, 1883. Type material; A: colony (after Allman 1883). B: fragment of axis with an apophysis and proximalmost internode of a hydrocladium. C: part of a hydrocladium, with detail of one hydrothecate and two ahydrothecate internodes. Scales a, 1 cm. b ‒ c: 0.1 mm.