noun
definition
A jellyfish; specifically , a non-polyp form of individual cnidarians, consisting of a gelatinous umbrella-shaped bell and trailing tentacles.
Examples of medusae in a Sentence
To establish the exact relationship it is necessary not only to breed but to rear the medusa, which cannot always be done in 1 In some cases hydroids have been reared in aquaria from ova of medusae, but these hydroids have not yet been found in the sea (Browne [Io a]).
Naked- cation is seen when the eyed Medusae.
A, colony of but grow in all planes Lar;B and C, young and adult medusae.
The sub-umbrella invariably shows a velum as an inwardly projecting ridge or rim at its margin, within the circle .of tentacles; hence the medusae of this sub-class are termed craspedote.
In contrast with the polyp, the longitudinal muscle-system is entirely ectodermal, there being no endodermal muscles in craspedote medusae.
Further, two distinct types of otocyst can be recognized in the Hydro medusae; that of the Leptolinae, in which the entire organ is ectodermal, concrement-cells and all, and the organ is not a tentaculocyst; and that of the Trachylinae, in which the organ is a tentaculocyst, and the concrement-cells are endodermal, derived from the endoderm of the modified tentacle, while the rest of the organ is ectodermal.
Moreover, all the medusae budded from a given hydroid colony are either male or female, so that even the non-sexual polyp must be considered to have a latent sex.
It has been shown above that polyps are budded only from polyps and that the medusae may be budded either from polyps or from medusae.
Normally the medusae are liberated in quite an immature state; they swim away, feed, grow and become adult mature el individuals.
In some cases both free medusae and gonophores may be produced from the same hydroid colony.
This is the case in Syncoryne mirabilis (Allman [1], p. 278) and in Campanularia volubilis; in the latter, free medusae are produced in summer, gonophores in winter (Duplessis [14]).
Again in Pennaria, the male medusae are set free st.c, Statocyst containing the minute cyst.
As medusae are known to bud medusae from the radial canals there is nothing impossible in Aliman's theory, but it cannot be said to have; received satisfactory proof.
It is convenient to distinguish buds that give rise to polyps from those that form medusae.
Hence the budding of medusae exemplifies very clearly a common phenomenon in development, a phylogenetic series of events completely dislocated in the ontogenetic time-sequence.
B, The lower layer forms a solid G,H, Formation of the medusae.
Hence the Trachylinae are termed " hypogenetic " medusae to contrast them with the metagenetic Leptolinae.
In Cunina parasitica, however, the ovum develops into an actinula, which buds actinulae as before, but only the daughter-actinulae develop into medusae, while the original, parent-actinula dies off; here, therefore, larval budding has led to a true alternation of generations.
For the most part, polyp and medusa have been regarded as modifications of a common type, a view supported by the existence, among Scyphomedusae (q.v.), of sessile polyp-like medusae (Lucernaria, &c.).
Leuckart in 1848 compared medusae in general terms to flattened polyps.
Mechnikov considered the plate thus formed at the base of the polyp as equivalent to the umbrella, and the body of the polyp as equivalent to the manubrium, of the medusa; on this view the marginal tentacles almost invariably present in medusae are new formations, and the tentacles of the polyp are represented in the medusa by the oral arms which may occur round the mouth, and which sometimes, e.g.
In some cases, any polyp of the colony may bud medusae; in other cases, only certain polyps, the blastostyles, have this power.
Until quite recently the hydroids (Gymnoblastea) and the medusae (Anthomedusae) have been classified separately, since the connexion between them was insufficiently known.
Trophosome encrusting with hydranths of Bougainvillea-type, polyps differentiated into blastostyles, gastrozoids and dactylozoids; gonosome free medusae or gonophores.
The typical genus is the well-known hydroid Podocoryne, budding the medusa known as Dysmorphosa; Thamnostylus, Cytaeis, &c., are other medusae with unknown hydroids.
Trophosome, polyps with two whorls of tentacles, the lower filiform, the upper capitate; gonosome, free medusae, with tentacles solid and branched.
Trophosome, polyps with a single whorl of capitate tentacles; gonosome, free medusae, with ten tacles branched, solid.
Corymorphidae (including the medusa-family Hybocodonidae).--, Trophosome solitary polyps, with two whorls of tentacles; gonosome, free medusae or gonophores.
Turris produces free medusae.
Trophosome (only known in one genus), polyps with two tentacles forming a creeping colony; gonosome, free medusae with four, six or more radial canals, giving off one or more lateral branches which run to the margin of the umbrella, with the stomach produced into four, six or more lobes, upon which the gonads are developed; the mouth with four lips or with a folded margin; the tentacles simple, arranged evenly round the margin of the umbrella.
It buds medusae, which, however, are as yet only known in an immature condition (C. Mereschkowsky [41]).
The medusae, on the other hand, have the tentacles in four tufts of (in the buds) five each, and thus resemble the medusae of the family Margelidae.
It is quite possible that some of these medusae will be found to be truly hypogenetic, that is to say, with a life-cycle secondarily simplified by suppression of metagenesis.
The gonosome consists of free medusae in Milleporidae, which are budded from the apex of a dactylozoid in Millepora murrayi, but in other species from the coenosarcal canals.
Medusae with sense-organs represented by otocysts derived from modified tentacles (tentaculocysts), containing otoliths of endodermal origin, and innervated from the ex-umbral nerve-ring.
This order, containing the typical oceanic medusae, is divided into two sub-orders.
The actinula, when free, may multiply by larval budding, but in all cases both the original actinula and all its descendants become converted into medusae, so that there is no alter nation of generations.
The buds become medusae by the direct method of budding described above.
Of doubtful position, but commonly referred to the Trachylinae, are the two genera of fresh-water medusae, Limnocodium and Limnocnida.
It is a re markable fact that all specimens of Limnocodium hitherto seen have been males; it may be inferred from this either that only one polypstock has been introduced into Europe, from which all the medusae seen hitherto have been budded, or perhaps that the female medusa is a sessile gonophore, as in Pennaria.
It buds medusae from the margin of the mouth in May and June, and in August and September the gonads' are formed in the place where the buds arose.
Both these medusae have sense-organs of a peculiar type, which are said to contain an endodermal axis like the sense-organs of Trachylinae, but the fact has recently been called in question for FIG.
In this connexion must be mentioned, finally, the medusae budded from the fresh-water polyp Microhydra.
In view of the great resemblance between Microhydra and the polyp of Limnocodium, it might be expected that the medusae to which they give origin would also be similar.
As yet, however, the medusa of Microhydra has only been seen in an immature condition, but it shows some well-marked differences from Limnocodium, especially in the structure of the tentacles, which furnish useful characters for distinguishing species amongst medusae.
Gonostyles, appendages which produce by budding medusae or gonophores, like the blastostyles of a hydroid colony.
In their most primitive form they are seen in Velella as " gonosiphons," which possess mouths like the ordinary sterile siphons and bud free medusae.
They show every transition between free medusae and sporosacs, as already described for hydroid colonies.
Thus in Velella free medusae are produced, which have been described as an independent genus of medusae, Chrysomitra.
In other types the medusae may be set G, Cavity of the large central and a " trachea.