Word Finder - zooids

definition

An organic body or cell having locomotion, as a spermatic cell or spermatozoid.

definition

An animal in one of its inferior or early stages of development, as one of the intermediate forms in alternate generation.

definition

One of the individual animals in a composite group, as of Anthozoa, Hydrozoa, and Bryozoa; — sometimes restricted to those individuals in which the mouth and digestive organs are not developed.

Associated with these males are neuter zooids, which usually possess no functional repro ductive organs, but have in I -...

Hence it is necessary to distin guishbetween,first,the"zooids," FIG.

A given stock only produces zooids of one sex.

Zooids possessing a high degree of individuality.

Zooids usually connected laterally with their neighbours.

Ctenostomata the colony is similarly constituted, a branched stolon giving off the zooids, which are not connected with one another.

In the majority of Ectoprocta there is no stolon, the zooids growing out of one another and being usually apposed so as to form continuous sheets or branches.

In the encrusting type, which is found in a large proportion of the genera, the zooids are usually in a single layer, with their orifices facing away from the substratum; but in certain species the colony becomes multilaminar by the continued superposition of new zooids over the free surfaces of the older ones, whose orifices they naturally occlude.

The zoarium may rise up into erect growths composed of a single layer of zooids, the orifices of which are all on one surface, or of two layers of zooids placed back to back, with the orifices on both sides of the fronds or plates.

In Actinia, as in all Anthozoan zooids, the coelenteron is not a simple cavity, as in a Hydroid, but is divided by a number of radial folds or curtains of soft tissue into a corresponding number of radial chambers.

The only exceptions to this structure are found in the arrested or modified zooids, which occur in many of the colonial Alcyonaria.

Such modified zooids are called siphonozooids, their function being to drive currents of fluid through the canal-systems of the colonies to which they belong.

These form a more or less complicated canal system, lined by endoderm, and communicating with the cavities of the zooids.

In the order Stolonifera the zooids spring at intervals from branching or lamellar stolons, and are usually free from one another, except at their bases, but in some cases horizontal solenia arising at various heights from the body-wall may place the more distal portions of the zooids in communication with one another.

Thus the coenenchyma forms a stem, sometimes branched, from the surface of which the free portions of the zooids project.

In the order Pseudaxonia the colonies are upright and branched, consisting of a number of short zooids whose proximal ends are imbedded in a coenenchyma containing numerous ramifying solenia and spicules.

The latter contains the proximal moieties of the zooids and numerous but separate spicules.

It owes its commercial value to the beauty of its hard red calcareous axis which in life is covered by a cortex in which the proximal moieties of the zooids are imbedded.

In the order Stelechotokea the colony consists of a stem formed by a greatlyelongated mother zooid, and the daughter zooids are borne as lateral buds on the stem.

They resemble and are closely allied to certain families of the Cornulariidae, differing from them only in mode of budding and in the disposition of the daughter zooids round a central, much-elongated mother zooid.

The prorachidial and metarachidial aspects of the rachis are sterile, but the sides or pararachides bear numerous daughter zooids of two kinds - (I) fully-formed autozooids, (2) small stunted siphonozooids.

The pinnae are formed by the elongated autozooids, whose proximal portions are fused together to form a leaf-like expansion, from the upper edge of which the distal extremities of the zooids project.

A, Zoanthid colony, showing the expanded zooids.

After division the corallites continue to grow upwards, and their zooids may remain united by a bridge of soft tissue or coenosarc. But in some cases, as they grow farther apart, this continuity is broken, each corallite has its own edge-zone, and internal continuity is also broken by the formation of dissepiments within each calicle, all organic connexion between the two zooids being eventually lost.

The lastnamed method has proved little more than that there is a remarkable similarity between the zooids of all recent corals, the differences which have been brought to light being for the most part secondary and valueless for classificatory purposes.

On the other hand, the study of the anatomy and development of the zooids has thrown much light upon the manner in which the corallum is formed, and it is now possible to infer the structure of the soft parts from a microscopical examination of the septa, theca, &c., with the result that unexpected relationships have been shown to exist between corals previously supposed to stand far apart.

Duerden has shown that in Porites the ordinary zooids possess only six couples of mesenteries arranged on the Actinian plan.

But some zooids grow to a larger size and develop a number of additional mesenteries, which arise either in the sulcar or the sulcular entocoele, much in the same manner as in Cerianthus.

The familiar lightbulb sea squirt also multiplies by budding, with the zooids remaining attached at the base to form colonies.

Sea-mat Although the sea-mat called hornwrack resembles dried seaweed it is actually a bryozoan colony of tiny animals called zooids.

The small translucent zooids (approximately 4 mm long) are budded from stolons and generally rather closely packed.

In other cnidarian species, the planula is directly produced by specialized zooids near the stem base.

Both genera are characterized by their habit of secreting a tubular gelatinoid investment, the "coenoecium," composed of a number of superposed lamellae, doubtless the result of its intermittent secretion, mainly though perhaps not exclusively, by the proboscides of the zooids.

In Cephalodiscus the coenoecium is more massive, and may contain a continuous irregular cavity in which the zooids live (Demiothecia), or may be secreted in such a way that each zooid has its own independent tube (Idiothecia, Orthoecus).