The circumstance that in the sponges and the cnidaria (polyps, medusae, etc.
The Hydrozoa may be defined, therefore, as Cnidaria in which two types of individual, the polyp and the medusa, may be present, each type developed along divergent lines from the primitive actinula form.
In the development of the Hydrozoa, and indeed of the Cnidaria generally, the egg usually gives rise to an oval larva which swims about by means of a coating of cilia on the surface of the body.
The striking typical form of these pelagiccnidaria is sometimes called biradial, sometimes four-rayed and bilateral, and sometimes eight-rayed-symmetrical.
In most of thecnidaria a small stationary polyp is developed out of the ovum of the free-swimming medusa, and this polyp, in turn, generates by budding medusae, which reach sexual maturity.
The extremely delicate and soft body of these gherkin-shaped cnidaria swims slowly in the water by means of the strokes of thousands of tiny oar-blades.
The large group of the cnidaria offers a long series of evolutionary stages, from very small and simple to very large and elaborate forms.
The simplest living forms of the sponges (olynthus) and the cnidaria (hydra) only differ from this hypothetical primitive form of the gastraea by a few secondary and subsequently acquired features.
In all the larger cnidaria the body-wall becomes thicker, and is traversed by branching gastro-canals; these convey the nutritive fluid to all parts of the body.
On the other hand, the cnidaria develop into higher radial (star-shaped) persons, and the platodes into lower bilateral persons.
I began with the consideration of the simplest sponges (olynthus) and cnidaria (hydra).
Flagellated epithelium is especially found in the cnidaria and platodes; ciliated epithelium mostly in the vermalia and mollusca.
This simplest of all the cnidaria has, it is true, a crown of tentacles round its mouth.
In most of the cnidariaand many of the annelids (worm-like animals) they remain unchanged throughout life.
This we find in the lowercnidaria and worms, as well as in the more highly-developed molluscs, echinoderms, articulates, and vertebrates.
The uni-axial Gastraea became sessile, and gave rise to two stems, the Sponges and the Cnidaria (the latter all reducible to simple polyps like the hydra).
The lowest form of the Cnidariais also not far removed from the gastraeads.
The lowest Cnidaria (the hydroid polyps) also are little superior to the Gastraeads in structure.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "cnidaria" in a variety of sentences. We hope that you will now be able to make sentences using this word.
