Biology: Hydra Characteristics

Study Notes

Body Structure

Hydra is a freshwater solitary animal with a cylindrical body (2-20 mm in length)
It has a basal disc for attachment and a free oral cone (hypostome) bearing the mouth
The mouth is situated on a conical hypostome encircled by 6-10 hollow filiform tentacles in one cycle
The tentacles are provided with nematocysts

Reproductive System

Gonads appear as buds on the side of the body stalk
Several testes arise on the sides of the upper third of the body near the oral end
One ovary is present near the basal disc
Lateral buds may be present by asexual reproduction

Nematocysts

There are four kinds of nematocysts in Hydra: penetrants, volvents, small stereoline glutinants, and large streptoline glutinants
Each type of nematocyst has a specific function: defense, catching prey, and food collection
Nematocysts respond only to mechanical stimuli

Body Wall

The body wall of Hydra viridis is diploblastic, consisting of an outer ectoderm (epidermis) and inner endoderm
The ectoderm and endoderm are separated by a thin structureless jelly-like mesogloea
The body wall encloses a digestive cavity (coelenteron) that extends into the tentacles

Ectoderm and Endoderm

Ectoderm cells are musculo-epithelial, interstitial, nematoblast, sensory, nerve, mucous cells, and germ cells
Endoderm cells are musculo-nutritive, interstitial, sensory, nerve (less developed cells), glandular or secretory cells, and few mucous cells around the mouth
Musculo-epithelial cells have longitudinal muscle fibres that contract to shorten or bend the body
Musculo-nutritive cells have circular muscle fibres that contract to narrow and elongate the body

Nutrition and Digestion

Hydra is carnivorous, feeding on freshwater microorganisms, small crustaceans, and insect larvae
Food is digested extracellularly by secreting proteolytic enzymes from the glandular cells of the endodermal layer
Nutritive muscle cells engulf small fragments of food, forming food vacuoles and undergoing intracellular digestion
The products of digestion are absorbed by the nutritive cells and circulated by cellular diffusion

Respiration and Excretion

Respiration and excretion take place by diffusion

Locomotion

Hydra is essentially sessile and lives attached to the substratum by a sticky secretion
It can move from one place to another by gliding, walking, somersaulting, and floating
Walking is the most common method of locomotion, using the adhesive threads of the small glutinant nematocysts

Description

This quiz covers the physical characteristics and features of Hydra, a freshwater solitary animal. Learn about its body structure, tentacles, and reproductive organs. Test your knowledge of Hydra's biology!