From your observations draw a detailed labeled diagram that illustrates the life cycle of Obelia.
A cylindrical projection, the manubrium, hangs from the middle of the subumbrellar surface. The planula swims freely for a brief period and settles down on some submerged substratum by one end. ii.
A thin sheet of endodermal lamella, presumably formed by the fusion of an upper and a lower layer of endoderm, lie between the radial canals and between the ex- and subumbrellar layers of ectoderm. 1. Cnidocytes are formed continuously in the bulb and migrate to the tentacles. 10. or gonozooids. 6. The tentacles and the hypostome bear cnidocytes. A circlet of about twenty-four tentacles are present around the hypos tame.
contrast with scyphomedusae, into the coelenteron. 14, 20.15) 6. They are dioecious—testes and ovaries are borne by separate individuals. A hydro-medusa (Fig.20.14) is a solitary and free-swimming modified zooid. 20. Most laboratories, however, will provide commercially prepared wholemount slides. 3. The asexual generation is dependent on, and is alternated by the sexual generation. The hydrula sends out lateral buds and, by a repetition of this process, it is converted into a complex obelia colony. Medusae buds are unisexual and free- living at maturity. 11. Each branch consists of a granular coenosarc made of two cell layers enclosing the coelenteron and surrounded by a thin transparent horny perisarc. The larva can swim from place to place with the help of cilia and, being aided by water current, it can travel a long distance.
At the distal end a conical projection the hypostome or- manubrium, bearing a mouth is present (20.13). 2.
By repeated branching of the simple polyps colony is formed. By invagination the blastula is converted into an oval, ciliated planula larva. 12.
Marginal sense organs, statocysts or lithocysts are eight in number and attached at regular intervals on the subumbrellar side to the bulbs of the tentacles. The tentacles are solid, each containing a core of vacuolated endodermal cells covered by ectoderm. Then examine the Obelia medusa w.m. 2.
7.
1.
A typical medusa consists of a bowl- shaped gelatinous disc or umbrella, the concave surface of which is described as sub-umbrella and the outer convex surface as ex-umbrella. Each medusa bears only four gonads situated on the subumbrellar surface, one on the middle of the course of each radial canal. From gastric cavity four gastro dermal canals radiate to the margins of the bell. The planula consists of an outer layer of ciliated ectoderm and an inner mass of endoderm cells enclosing a space, the rudiment of coelenteron. The tentacles are solid with a core of endoderm cells surrounded by a layer of ectodermal cells. The space between the two layers is filled with a mass of interstitial cells which become differentiated into ova or sperms, as the case may be. 4. The mouth leads to a small, central, rounded or quadrangular chamber known as gastric cavity or stomach. 3. 12. Obelia is representative of typical hydrozoan morphology and possesses a life cycle in which polyp and medusa are of approximately equal importance. The interstitial cells are mainly accumulated at the bulbs or vesicles of tentacles and give rise to cnidocytes of only one type.
These are medusae, tiny jellyfish (larger jellyfish may or may not be a medusa stage). 7. The medusa stage of the jellyfish reproduce sexually.
The whole canal system is lined by endoderm cells, continued, at the lip of the mouth, into the surface ectoderm. Both exumbrellar and subumbrellar surfaces of medusa are covered by ectoderm cells. 3. Examine the slide labeled Hydra nematocysts. 3. 6. The manubrium contains a mouth as its tip, … b. Blastostyles. 4. 11.
At the proximal end, the zooid is continuous with the coenosare. a. Polyps or gastro zooids (vegetative zooids).
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