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 : 361-362

Measurements of Plumularia fragilia , (µm)

Hydrorhiza, width 40–56

Stem internode length 264–320 width at node 56–64

Hydrocladium apophysis, adcauline length 36–48 first athecate internode length 84–120 succeeding athecate internodes, length 220–260 thecate internode, length 248–284 width at node 24–36 Remarks. Plumularia fragilia is a very small species. It closely resembles but is somewhat smaller than Plumularia setacea recorded from Darwin by Watson (2000). Stems are flaccid out of fluid. Cauline nematothecae may be absent leaving no scars on the internode

Descriptions of Plumularia mossambicae Millard, 1975 , P. Antonbruuni Millard, 1967 , P. strobilophora Billard 1913 and P. orientalis Billard, 1911 were compared with Plumularia fragilia . P. mossambicae is larger in dimensions, lacks cauline nematothecae, the abcauline hydrothecal wall is straight, and the margin is not everted. Millard’s figure of P. antonbruni shows differences in structure and is also larger in all dimensions than P. fragilia . P. strobilophora is closer in overall dimensions, but the hydrothecae are more bowl– shaped and have no marginal eversion. While P. orientalis also has an outrolled margin, its dimensions are larger than P. fragilia .

Etymology. The species is named to describe the fragility of the colony.