ALCYONELLA (diminutive of Alcyonium), a genus of animals belonging to the Fresh-Water Polyzoa, or Aecidian Zoophytes. The species of this genus were originally regarded as plants. They are composed of a fleshy sponge-like mass, which consists of vertical, aggregated, membranaceous tubes, which open on the surface. In these tubes the polypes are seated, which are ascidian ; the mouth is encircled with a single series of filiform teutacula, which, like those of the whole family, are depressed or incomplete on one side. The eggs are contained in the tubes, and are coriaceous and smooth.
The most common species is the A. Staynoruni of Lamouroux, which is commonly found in stagnant waters, especially when they contain iron in solution. The polype-mass of this species is a sponge-like substance, somewhat elastic, of a blackish green colour, and is more or lege apparently porous. It is composed of tubes which rise
from the base to the surface, and are connected together by a firm transparent gelatinous substance. The walls of the tubes are composed of a thin pellucid colourless membrane, through which the ova in their interior can be easily seen. The ova are very numerous, although the animal itself is comparatively rare, abounding at one season, and almost absent at another, in the same pond.
This animal was originally described by Trembley in 1741, and although he was perfectly aware of its nature at that early period, it has been often described since both as a plant and a sponge. One of the best modern accounts is that of Mr. T. P. Tealc, in the first volume of the Transactions of the Leeds Philosophical and Literary Society.' (Johnston, Brigsh Zoophytes.)