HYDRA DEFINITION FREE

The cell contains a sac-like nematocyst and a layer of specially contractile cytoplasm with distinct nucleus. This type of cellular unit constitutes a very important component of the ectoderm. Each kind of cell performs definite and specific functions in co-operation with each other for the individual as a whole. In Hydra cellular differentiation is associated with the physiological division of labour. In addition to the power of contractility common to both the layers, the ectoderm is mainly protective and the endoderm is primarily nutritive in function.īoth the layers are constituted of several cell-types, destined to perform diverse physiological functions (Fig. The outer layer is known as the ectoderm and the inner layer is known as the endoderm.

The body of Hydra is composed of two cellular layers with a thin non-cellular mesoglea (Fig. Structure and Function of the Different Cellular Units of Hydra : During breeding season the mature individuals possess many male gonads or testes and usually one female gonad or ovary. In most cases, the fairly grown individuals bear buds located at the specific budding zone of the body, i.e., the region of the body column just below the middle of the body. The mouth leads into the coelenteron which occupies the interior of the body and is also continuous with the slender cavities of the tentacles. Tentacles are totally absent in Protohydra. The usual number of tentacles is six but it may vary from four to eleven in some cases. The base of the hypostome is surrounded by a number of tentacles.

HYDRA DEFINITION FREE

The opposite end (the oral or distal end) is free and possesses the opening of the mouth, situated at the summit of a conical elevation called the hypostome or manubrium. This end of the body is named as the foot or basal disc which is used as a structure for attachment to the substratum and it aids in locomotion as well. The lower end of the tubular body is closed and this side is designated as the aboral or proximal end. The body is extremely contractile and the length varies from 10 to 30 mm. Hydra has a slender tubular body and exhibits distinct radial symmetry (Fig. Hydra exists only in polyp form (monomorphic) and the phenomenon of metagenesis or alternation of generation is totally absent. All the forms of hydra are built on same basic pattern and the following description will give an idea on the biology of hydra in general. This species harbours symbiotic algae Zoochlorella in the endodermal cells which render the colour of the body green.Ĭertain parasites are recorded in hydra, namely Hydramoeba hydroxena and few ciliates, Kerona pediculus and Trichodina pediculus. Another form of hydra which needs mentioning here is Chlorohydra viridissima (formerly known as Hydra viridis). Pelmatohydra oligactis has a comparatively slender body and the length of the tentacles exceeds three to four times the length of the body column. The phase orientalis of Hydra vulgaris is the commonest variety present in the neighbouring ponds of Kolkata. The common Indian species is the Hydra vulgaris (formerly known as Hydra grisea) and the Pelmatohydra oligacitis (formerly called as Hydra fusca).

Hydra definition