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Taxon
Synthecium patulum (Busk, 1852)
Nomenclature
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Family: SyntheciidaeGenus: Synthecium
SUMMARY
Stems up to 50 mm high, occasionally with secondary branching; hydrorhiza tubular, reptant, perisarc of stems and hydrocladia fairly thick. Proximal ahydrocladiate stem segment variable in length, some stems with hydrocladia extending almost to base; stem internodes long with one or two pairs of opposite hydrothecae near middle of internode, node a constriction in perisarc.
Hydrocladia up to 12 mm long, opposite, given off at an angle of 45°- 50° to stem from distal end of internode. Hydrocladial hydrothecae paired, distal on internode, not conjoined; internode somewhat constricted proximally, expanding to base of hydrothecae; hydrothecae of first one or two pairs on internode a little displaced relative to one another.
Hydrotheca tubular, expanding a little distally, perisarc smooth, adcauline wall almost straight proximally, gently convex distally, free part about one quarter total length of wall, base rounded with a small plug of perisarc; abcauline wall proximally tumescent, becoming concave to margin. Margin tilted upwards at an angle of 45° - 60° to hydrocladial axis, strongly sinuate, rim moderately everted, sometimes replicated several times. Hydranth small with about 10 tentacles.
Two kinds of nematocysts present:
- Small ?mastigophores in tentacles, 9 µm long.
- Large isorhizas 45-50 x 12-13 µm, tubule up to 500 µm long and 1 µm diameter, armed throughout with spirals of short bristles; in hydranth and scattered throughout coenosarc.
Colonies dioecious, gonotheca arising on a long pedicel from deep within hydrotheca on stem and proximal parts of hydrocladia; male gonotheca long, straight to curved, elliptical, and flattened in frontal aspect; narrow in side view with up to eight deep, irregular corrugations fading proximally, corrugations shallower in frontal view, perisarc very thick; orifice circular, small, on a very short neck sealed by a plug of tissue. Female gonothecae on different stems from male, lenticular, shorter than male, with five or six irregular corrugations, orifice small, circular, on a short neck, sealed by a plug of tissue; gonophore one large or two small ova covered by a thick gelatinous pellicle, almost filling gonothecal cavity.