Genus Schizoplumularia n. gen.

(Fig. 1)

Diagnosis. Plumulariid hydroids having an erect, polysiphonic, branched or unbranched main axis lacking apophyses and hydrocladia except at proximal end, main axis geniculate, at least in younger parts of colony. Tubes of main axis giving rise to ultimate branches, equivalent to hydrocauli. Primary axial tube at base of main axis with apophyses and hydrocladia, giving rise to secondary axial tubes before diverging laterally from main axis to form first ultimate branch (proximalmost hydrocaulus of colony). As with primary axial tube, secondary axial tubes giving rise to new secondary axial tubes before diverging laterally from main axis, and so on; apophyses and hydrocladia absent on all axial tubes beyond the primary one. Hydrorhiza where known a root-like mass of intertwining tubules adhering to sandy sediment. Ultimate branches equivalent in morphology to hydrocauli of Plumularia in being monosiphonic, unbranched, and divided into internodes with varied numbers of alternate apophyses bearing hydrocladia. Hydrocladia unbranched, borne only on ultimate branches and at base of primary axial tube, divided into homomerously or heteromerously segmented internodes. Hydrothecate internodes of hydrocladia each with a hydrotheca, a pair of lateral nematothecae, and one or more median inferior nematothecae. Ahydrothecate internodes of hydrocladia, when present, with one or more median nematothecae each. Hydrothecae occurring only on hydrocladia, uniseriate, small, cup-shaped, adnate to internode, margin smooth. Nematothecae conical, bithalamic, movable.

Gonophores presumably fixed sporosacs. Gonothecae solitary, pyriform, arising from apophyses on ultimate branches (hydrocauli), unprotected by phylactocarps or nematothecae; aperture terminal, round, closed by an operculum.

Type species: Schizoplumularia vervoorti n. sp., designated herein.

Remarks. In species of Schizoplumularia, unlike those of any other genus in the family Plumulariidae, hydrocauli arise alternately and laterally from a polysiphonic, branched or unbranched main axis. The proximalmost hydrocaulus of the colony is formed by divergence of the primary axial tube from the polysiphonic main axis. While still constituting part of the main axis, the primary axial tube bears apophyses and hydrocladia. All other hydrocauli of the colony are formed by divergence from the main axis of secondary axial tubes that originated distal to the original primary axial tube, and none of these subsequent and more distal axial tubes have apophyses and hydrocladia while confluent with other tubes of main axis. Once curving away from main axis, secondary axial tubes become monosiphonic hydrocauli that are much as in the genus Plumularia Lamarck, 1816, with hydrocladia given off from alternate and lateral apophyses.

Colony morphology is reminiscent of P. insignis, P. abietina and P. insignis var. gracilis (= Plumularia billardi nom. nov.) described and figured by Allman (1883) and Billard (1913). An examination of type material showed that this similarity is only superficial and that all three species belong to the genus Plumularia.

Etymology. The generic name Schizoplumularia is derived from a combination of the Latinized form of the Greek word-forming element skhizein (split, separate), refering to the independent origins of the ultimate branches of the colony, and the generic name Plumularia Lamarck, 1816, applied to a group with which the new taxon shows affinities. The gender of the name is feminine.