or gonozooids. It is a branched, fixed colony (Fig 20.12).
Obelia has a simple nerve net with no brain or ganglia. 7. The life cycle usually includes both polyp and medusa generations (Fig A) but may be entirely polyp (Fig B) or entirely medusa (Fig C). 1. When the gonads are ripe, ectodermal covering ruptures and the germ cells are shed in water. 2. 7. 2. 11. pic source Cnidaria (Overview) - ... 474 x 609 jpeg 59kB. Obelia is representative of typical hydrozoan morphology and possesses a life cycle in which polyp and medusa are.Hydrozoa MorphologyHydra Anatomy Answer Key. The muscles coordinate the snake-like swimming movements of the medusa. 8. 20. The vertical branches towards the base are further branched and all the branches end in zooids. Near the bulbs the ectoderm has pigment granules and nerve cells called ocelli. A.E. It can be recognised by having a thin, flat umbrella, with only a rudimentary velum, and four sac-like gonads located on the middle of radial canals. The velum is composed of a double layer of ectoderm enclosing a ring canal and a strip of narrow mesoglea in between the canal and ectoderm. The whole canal system is lined by endoderm cells, continued, at the lip of the mouth, into the surface ectoderm. The Hydra's tentacles are hollow, tubular extensions of these three layers.
Barrel-shaped and responsible for the nutrition of the colony. Pitman (pub).
One medusa bears either four testes or four ovaries close to the four radial canals. This genus is a hydrozoan that exhibits alternation of generations—attached polyp and free-swimming medusa. The medusae die soon after liberating the gametes. A. , or ball of cells several cell layers thick, The hydroid colony possesses a double nerve net similar to that in, . The planula swims freely for a brief period and settles down on some submerged substratum by one end. For example, the hydrozoan genus Obelia appears to have independently re-evolved a medusa life-stage, with solid tentacles as opposed to the hollow form typical of hydromedusa . Content Guidelines 2. 6. A number of small buds—the medusae buds develop on the walls of the blastostyle.
Hydrozoa is a diverse taxon of about species of mostly marine cnidarians. This website includes study notes, research papers, essays, articles and other allied information submitted by visitors like YOU. The tubes that make up the hydrorhiza and hydrocauli contain an inner cylinder, (shown as orange in the coloured picture) surrounded by a hollow outer cylinder, , which is a chitinous sheath that acts as an exoskeleton supporting the colony. The gonads mature after the medusae escape from the gonotheca. c. Medusae buds. At maturity, small umbrella-like me dusae buds get detached from the blastostyle and escape to the sea water through an aperture at the free end of the gonotheca. 2. . Each branch consists of a granular coenosarc made of two cell layers enclosing the coelenteron and surrounded by a thin transparent horny perisarc. pic source Explore Animal Diversi... 500 x 350 jpeg 30kB. The life cycle of Obelia has two stages; motile medusa and sessile polyp. 3. 12. A cylindrical projection, the manubrium, hangs from the middle of the subumbrellar surface. A statocyst is a tiny, circular, closed vesicle lined with ectoderm and filled with a fluid containing calcareous granules called otoliths. At the proximal end, the zooid is continuous with the coenosare. The planula consists of an outer layer of ciliated ectoderm and an inner mass of endoderm cells enclosing a space, the rudiment of coelenteron. 1. 3. Umbrella-like reproductive zooids bearing gonads, enclosed in a gonotheca. 13. 4. 7 thoughts on “ Hydrozoa diagram ” Wd4ity says: 22.02.2019 at 10:23. Welcome to NotesOnZoology.com! At maturity, small umbrella-like me dusae buds get detached from the blastostyle and escape to the sea water through an aperture at the free end of the gonotheca. A circlet of about twenty-four tentacles are present around the hypos tame.
1. A.E. The life cycle usually includes both polyp and medusa generations (Fig A) but may be entirely polyp (Fig B) or entirely medusa (Fig C). 20.12, 20.16). The small branched hydroid colony is found attached to rocks, stones, shells of animals or on large seaweeds and appears like a delicate whitish or light brownish fur-like growth. The gelatinous mesoglea form the main bulk of the body and contains certain non-cellular fibres. Disclaimer Copyright, Zoology Notes | Exclusive Notes on Zoology for Students, Life Cycle of Aurelia (With Diagram) | Phylum Cnidaria, Difference Between Obelia and Aurelia | Phylum Cnidaria, Structure of Aurelia (With Diagram) | Phylum Cnidaria. a. Polyps or gastro zooids (vegetative zooids). A square mouth is present, at the apex of the manubrium. 5. The germ cells originate in the ectoderm of the manubrium quite early when the medusa itself remains attached to the blastostyle. 3. A hydro-medusa (Fig.20.14) is a solitary and free-swimming modified zooid. The outer nerve ring processes signals from the statocysts, the inner nerve ring, . 1. The four gonads are shown in yellow, the statocysts in red. From the edge of bell numerous small solid tentacles hang downwards. They are dioecious—testes and ovaries are borne by separate individuals. Since sexes are separate, these are either testes or ovaries. Computer model of a hydrozoan medusa of the Obelia type. 5. The existence of different types of individual.
Each gonad (testis or ovary) is an ovoid, knob-like body; it has an outer covering of ectoderm, continuous with that of the sub-umbrella, and an inner lining of endoderm continuous with that of the radial canal (Figs. 5. Mercedes Benz 4.5 Ignition Wiring Diagram With Xr 700, Led Headlight On Kenworth W900 Wiring Diagram, Starter Relays Wiring Diagram Harley 03 Road Glide. 2. (stinging structures located in cells called nematoblasts, nematocytes, cnidoblasts or cnidocytes). 6. Cnidocytes are formed continuously in the bulb and migrate to the tentacles.
Each medusa bears only four gonads situated on the subumbrellar surface, one on the middle of the course of each radial canal.
2. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. 5. These are a few in number and restricted to the basal end of the hydrocaulus. 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. Pitman (pub). The tentacles have swollen bases of accumulated interstitial cells, called vesicles or bulbs. Both polyp and medusa forms are diploid, whereas their gametes are haploid. Club- shaped zooids, bearing the medusae buds. pic source Department of Zoology ... 400 x 497 jpeg 60kB. 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. The hydrula sends out lateral buds and, by a repetition of this process, it is converted into a complex obelia colony. 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.
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