These hydroids form, by their rootstalks, a firm, chitinous coating on shells and stones, and esp.
They in turn produce the eggs from which the hydroids are developed.
The group of hydroidsto which the fresh-water hydras belong.
Note: These hydroids usually form tufts of delicate tubes, and both gonophores and hydranths are naked.
Defn: A division of hydroids comprising those which have the hydranths in thecæ and the gonophores in capsules.
Defn: A kind of gonophore produced by hydroids of the genus Gonothyræa.
Defn: Any species of Sertularia, or of Sertularidæ, a family of hydroids having branched chitinous stems and simple sessile hydrothecæ.
Defn: Permanently attached; -- said of the gonophores of certainhydroids which never became detached.
Defn: A minute soft filamentary process springing from the surface of certain hydroids and sponges.
Defn: A genus of delicate branching hydroids having small sessile hydrothecæ along the sides of the branches.
The zooids or hydranths of marine hydroids are sometimes called hydras.
Defn: One of a peculiar kind of cups, or calicles, found upon hydroids of the family Plumularidæ.
Defn: The group of hydroids to which the fresh-water hydras belong.
Defn: The hard outer covering of hydroids and other marine animals; the perisarc.
A genus of delicate branching hydroids having small sessile hydrothecæ along the sides of the branches.
Permanently attached; - - said of the gonophores of certain hydroidswhich never became detached.
It is found in deep water attached to shells, and in tide-pools, where it grows chiefly on /Sertularia/ and other hydroids and on slender red algae.
Hydroids and polyzoans are often gathered and preserved as seaweeds.
The most abundant of all the hydroids on the northeast coast is this species, which is found in profusion upon /Fucus/ and other seaweeds, and mingled with them upon the rocks.
This species is found on the New England coast creeping over hydroids and ascidians.
Many medusae cannot be referred with certainty to the hydroids from which they sprang, and the medusa-buds of many of the hydroids have not been noted.
Hydroids are colonies of associated animals living a communal life.
Hydroids are particularly interesting as exemplifying the close resemblance that may exist in outward appearance between animal and vegetable life and as illustrations of communal life and of the alternation of generation.
The reported cases of luminosity among marine algae are now known to be due to hydroids or unicellular organisms living on the alga.
Indeed, similar hydroidsof salt water are often taken and dried by unscientific collectors under the impression that they are feathery seaweeds.
Such is the general natural history of the group; but the oceanic hydroids have developed a vast variety of forms, and, with increased breadth of life, have added many interesting features and habits.
The Sertularians form another group of Hydroids closely allied to the Campanularians, though differing from them in the arrangement of the sterile Hydrae upon the stem.
Among the Tubularians, on the contrary, the communities are usually composed of a small number of comparatively large individuals; and indeed theseHydroids may even grow singly, as in the case of the Hybocodon (Fig.
To the Hydroids belong the Campanularians, the Sertularians, and the Tubularians.
They are especially interesting with reference to the history of Hydroids in general, because they were among the first of these animals in whom the true relation between the different phases of their existence was discovered.
Transverse section of a branch, showing pits, a a a a, of the largeHydroids with the horizontal floors.
Many of these Sertularian Hydroids assume the most graceful forms, hanging like long pendent streamers from the Laminaria, or in other instances resembling miniature trees.
Allman thus describes[79] the process in Laomedea, as representing the Hydroids (Pl.
The Tubularian Hydroidsare the subject of an exhaustive and admirably illustrated monograph by Prof.
The bodies or polypes of hydroids which exercise nutritive functions.
The few cases of an “improvement” of morphogenetic acts in hydroids described by myself are too isolated at present to be more than mere problems (*Arch.
There are other Hydroids giving rise to Medusae buds, from which, however, the Medusae do not separate to begin a new life, but wither on the Hydroid stock, after having come to maturity and dropped their eggs.
It is true that the Hydroids live along the shore, and may be reared in tanks without difficulty; but they are small, and would be often taken for sea-weeds by those ignorant of their true structure.
For this reason they are divided into two Orders,--the Hydroids and the Discophorae.
This group of Hydroids retains the name of Coryne; and the Medusa born from it, Sarsia, has received, as I have said, the name of the distinguished investigator to whose labors we owe much of our present knowledge of these animals.
Protohydra occurs in oyster-banks and Monobrachium also grows on the shells of bivalves, and both these hydroids probably fish in the currents produced by the lamellibranchs.
Until quite recently the hydroids (Gymnoblastea) and the medusae (Anthomedusae) have been classified separately, since the connexion between them was insufficiently known.
Two of the commonest British hydroids belong to this family, Obelia and Clytia.
The interspaces between the tubes are filled up by a solid mass of lime, consisting chiefly of calcium carbonate, which replaces the chitinous perisarc of ordinary hydroids and forms a stony corallum or coenosteum (fig.
Other hydroids are Garveia, Bimeria, Eudendrium and Heterocordyle, with gonophores, and Dicoryne with peculiar sporosacs.
Hallez [22] has recently shown that hydroids hitherto regarded as distinct species are only forms of the same species grown under different conditions.
The laws of budding in hydroids have been worked out in an interesting manner by H.
Doubtful families, or forms difficult to classify, are: Pteronemidae, Medusae of Cladonemid type, with hydroids for the most part unknown.
Thus from the original planula three appendages are, as it were, budded off, while the planula itself mostly gives rise to coenosarc, just as in some hydroids the planula is converted chiefly into hydrorhiza.
A genus of delicate branching hydroids having small sessile hydrothec\'91 along the sides of the branches.
A genus of hydroids having large, naked, flowerlike hydranths at the summits of long, slender, usually simple, stems.
A division ofhydroids comprising those which have the hydranths in thec\'91 and the gonophores in capsules.
These hydroids usually form tufts of delicate tubes, and both gonophores and hydranths are naked.
Permanently attached; -- said of the gonophores of certain hydroids which never became detached.
A minute soft filamentary process springing from the surface of certain hydroids and sponges.
The hard outer covering of hydroids and other marine animals; the perisarc.
Part of this is sandy beach which after a heavy tide would often be covered by the laminæ and holdfasts of Macrocystis and other kelps, to which hydroids were generally attached.
Such production undoubtedly takes place, not only in Hydroids and Phanerogams, but in many other instances.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "hydroids" in a variety of sentences. We hope that you will now be able to make sentences using this word.
