Systematic Implications of Euphysa ruthae n. sp. (Athecata: Corymorphidae), a Psammophilic Solitary Hydroid with Unusual Morphogenesis

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Abstract
E. ruthae sp. nov. is described from the San Juan Island region, Washington, USA. It is found commonly in infralittoral coarse sands at several locales, its size and field distribution suggesting that it is a member of the mesopsammic meiofauna. As is characteristic for Euphysa hydroids, E. ruthae is solitary and possesses an elongated hydrocaulus with a mucoid sheath, moniliform aboral tentacles and basal papillae. E. ruthae shares the unusual property of polarity reversal in bud formation with 3 other species of Euphysa. The buds of E. ruthae are unique in that they combine morphogenetic features of gonophores with those of asexual bud formation. Bud morphogenesis has similiarities to actinula morphogenesis in the closely related Tubularoidea. Each basal papilla contains a simple, terminal statocyst that apparently is homologous with that of Corymorpha palma, suggesting a synapomorphy that links the genera Euphysa, Corymorpha and perhaps Vannucia. Comparison with other interstitial hydroids suggests that certain features may have special adaptive value.

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