Hydra: Morphology, Histology, Nutrition, and Reproduction
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| hydra diagram |
Introduction
In this post, you will learn about Hydra, including its morphology, histology, nutrition, reproduction, and importance in a simple and exam-oriented way.
Classification
Phylum: Cnidaria
Class: Hydrozoa
Genus: Hydra
Habit and Habitat
Hydra is a solitary and sessile freshwater organism. It is commonly found in ponds, lakes, and slow-moving streams. It attaches to aquatic plants, stones, or other substrates using its basal disc. Although sessile, Hydra can move slowly when required.
External Morphology
Hydra has a cylindrical, tubular body showing radial symmetry.
Main Parts:
- Basal disc (foot): Helps in attachment
- Body column: Main cylindrical region
- Hypostome: Conical elevation at the oral end
- Mouth: Present at the tip of hypostome
- Tentacles: Several long, slender projections (usually 6–10, but variable)
Tentacles contain cnidocytes, which have nematocysts (stinging capsules) used for capturing prey and defense.
Body Wall (Histology)
Hydra is diploblastic, consisting of two germ layers:
Layers and Functions:
Epidermis (Ectoderm) – Protection, movement, and presence of cnidocytes
Gastrodermis (Endoderm) – Digestion and enzyme secretion
Mesoglea – Thin, non-cellular layer providing support
Gastrovascular Cavity
The central cavity, also called coelenteron, performs multiple functions:
- Digestion
- Circulation of nutrients
- Gas exchange
Hydra has a single opening (mouth) used for both ingestion and egestion.
Nutrition
Hydra shows carnivorous holozoic nutrition.
Steps of Nutrition:
- Capture: Tentacles immobilize prey using nematocysts
- Ingestion: Prey is taken into the mouth
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Digestion:
- Extracellular digestion in the cavity
- Intracellular digestion inside cells
- Absorption: Nutrients are distributed throughout the body
- Egestion: Undigested food is expelled through the mouth
Respiration and Excretion
Respiration: Occurs by simple diffusion through the body surface
Excretion: Waste products (mainly ammonia) diffuse out directly
Nervous System
Hydra has a primitive nerve net without a central nervous system.
- Nerve cells are distributed throughout the body
- Allows simple responses to stimuli
Reproduction
Hydra reproduces both asexually and sexually.
Asexual Reproduction (Budding)
- Most common method
- A small bud develops on the body wall
- It grows and detaches to form a new individual
Sexual Reproduction
- Occurs under unfavorable conditions
- Hydra may be monoecious (hermaphrodite) or dioecious, depending on species
- Produces gametes; fertilization leads to zygote formation
Regeneration
Hydra has a remarkable ability to regenerate lost body parts. Even small fragments can develop into complete individuals. This makes Hydra important in developmental biology.
Locomotion
Although mainly sessile, Hydra can move by:
- Looping (somersaulting)
- Gliding using basal disc
Identification Features
- Cylindrical body with radial symmetry
- Tentacles surrounding the mouth
- Presence of nematocysts
- Diploblastic organization
- High regenerative capacity
Importance
- Used as a model organism in regeneration and stem cell research
- Helps in understanding early animal evolution
- Useful in ecological studies of freshwater ecosystems
Why Important for Exams
- Frequently asked in Class 11 Biology exams
- Important for NEET basic concepts
- Common topic in practicals and viva
Viva Questions
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What type of symmetry does Hydra show?
Answer: Radial symmetry
Explanation: Body parts are arranged around a central axis -
What are nematocysts?
Answer: Stinging structures used for defense and prey capture
Explanation: Present inside cnidocytes -
How does Hydra reproduce asexually?
Answer: By budding
Explanation: A bud grows and detaches to form a new Hydra -
Why is Hydra important in research?
Answer: Due to its regenerative ability and simple organization
Explanation: It helps in studying development and cell differentiation
MCQs
Which cell in Hydra is responsible for stinging?
(a) Interstitial cell
(b) Nerve cell
(c) Cnidocyte
(d) Gland cell
Answer: (c)
Explanation: Cnidocytes contain nematocysts used for stinging
Hydra belongs to which phylum?
(a) Porifera
(b) Cnidaria
(c) Annelida
(d) Arthropoda
Answer: (b)
Explanation: Hydra is a cnidarian animal
What type of body organization is seen in Hydra?
(a) Triploblastic
(b) Diploblastic
(c) Acoelomate
(d) Bilateral
Answer: (b)
Explanation: Hydra has two germ layers
Hydra reproduces asexually by:
(a) Binary fission
(b) Budding
(c) Fragmentation
(d) Spore formation
Answer: (b)
Explanation: Budding is the most common method
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