Plumularia fragilia, Watson, 2012

Watson, Jeanette E., 2012, Some hydroids (Hydrozoa: Hydroidolina) from Dampier, Western Australia: annotated list with description of two new species., Memoirs of Museum Victoria 69, pp. 355-363 : 360

Plumularia fragilia sp. nov.

Figure 4A–D

Material examined. Holotype, WAM Z31846 , One infertile stem on Lytocarpia delicatula ( Busk, 1852) ; microslide, malinol mounted.

Description. Hydrorhiza a tubular creeping stolon. Stems pinnate, slender, to 13 mm long, monosiphonic, proximal hydrocauline segment long, straight, athecate, following internodes long, cylindrical, nodes transverse, distinct, a slight tumescence below each node.

Hydrocladia distal on cauline internode, alternate, position not quite planar. Apophysis smooth, directed upward at an angle of about 45° to hydrocaulus, abcauline apophysial wall contiguous with cauline internode, adcauline wall concave with three deep septa, distal node transverse.

Hydrocladia with two or three hydrothecae, cylindrical, narrow, beginning with a proximal athecate internode with transverse proximal and oblique distal node, usually with indistinct internal supplementary proximal and distal septa. First athecate internode followed by alternate hydrothecate and athecate internodes; athecate internodes variable in length, sometimes much longer than hydrothecate internode; hydrothecate internode long, straight with almost transverse distal node; nodes often with one or two internal septa.

Hydrotheca seated about halfway along internode, small, deep bowl–shaped, abcauline wall weakly concave to straight, adcauline wall weakly convex, completely adnate to internode, floor of hydrotheca transverse to hydrocladial axis, margin circular, oblique to hydrocladial axis, rim everted.

Nematothecae all of same shape and similar in size, bithalamic, moveable, slender conical, base long, cup wider than deep, margin circular, not excavated. One median nematotheca about halfway along athecate internode, one median inferior on hydrothecate internode well below base of hydrotheca, bases of twin laterals inserted just below hydrothecal margin; one or two nematothecae on cauline internode, standing out from internode, one about one third distance up internode from apophysis, the other two thirds distance up internode and on same side as hydrocladium, two nematothecae in axil, a bun–shaped hydrostatic pore at base of axillar nematothecae.

Colony colourless (preserved material), perisarc thin.

Figures

Figure 4A–E. A. Plumularia fragilia sp. nov., holotype colony. B, stem internodes and alternate hydrocladia. C, proximal part of hydrocladium and apophysis with axial nematothecae. D, hydrocladium with athecate and thecate internodes. E. Plumularia bedoti. Distal part of hydrocladium with developing anastomose. F. Lytocarpia delicatula. Two hydrocladial hydrothecae. Scale bar, mm: A 10. B, 1.0. C–F, 0.2