Test Practical on Prawn/Crayfish, Crab, and Woodlouse.
Test Practical on Prawn/Crayfish, Crab, and Woodlouse.
SPECIMEN: FRESHLY PRESERVED PRAWN OR CRAYFISH.
Habitat:
- Rivers or Swamps
- Ponds
- Lakes
Feeding habit
- Herbivorous and Detritivorous. (feeds on green weeds and dead organic matter)
Respiratory structure:
- Gills
Biological classification;
Phylum Arthropoda
Reasons:
- Presence of chitinous exoskeleton
- Metameric segmentation
- Presence of jointed appendages attached to each segment.
- Bilaterally symmetrical
- Triploblastic coelomate
- Open circulation (haemocilic)
- Undergo moulting.
Class Crustacea
Reasons
- Presence of two pairs of antennae
- Presence of two stalked eyes
- Presence of carapace
- Presence of five pairs of walking legs on the cephalothorax
- Presence of cephalothorax and abdomen
Observable characteristics
- Two stalked eyes
- Two pairs of antennae
- Presence of cephalothorax and abdomen
- Presence of carapace
Describe briefly observable features on the Cephalothorax
- Covered and protected by the carapace
- Rostrum at the anterior end
- A pair of stalked compound eyes (raised on stalks) for a wider vision
- Five pairs of legs, the first pair modified into (clawed) chela
- Two pairs of antennae
- The first pair is shorter and is called antennules, and the second pair is larger
Observable features and their functions
- Body is divided into the cephalothorax and the abdomen
- Carapace covers the cephalothorax for the protection of the cephalothorax
- The abdomen is made up of six segments; the first five each have a pair of swimmerets, also called pleopods
- The six abdominal segments bear the tail fin consisting of the uropod and telson
- Pleopods/swimmerets for Swimming Attachment of eggs in females, and also protects the young ones
- Chela have claws for defence and to grab prey.
- Tail fin consisting of uropod and telson for swimming backwards, protects eggs and young ones
- Uropod for swimming backwards
- Stalked eyes enable vision in all directions
- The first pair of antennae is shorter (antennule) and is branched and sensitive to touch, smell, and balance
- The second pair of antennae is sensitive to touch only
- Maxillipedes in the cephalothorax are used for feeding: Chopping food and passing it to the mouth
- Rostrum for defence against predators
Observable Adaptive Features of the Specimen
- It has swimmerets for swimming
- It has stalked compound eyes for vision
- The cephalothorax is protected by a carapace
- It has a hard, chalky, chitinous exoskeleton for the protection of its internal organs.
- The carapace extends to form a saw-like rostrum, which is used for defence.
- At the base of the walking legs are feathery gills for breathing.
- It has a pair of tail plates (Telson), which help propulsion backwards through the water.
- The first pair of walking legs, the cheliped, has been modified into pincers for feeding and defence.
Economic importance
- Source of food
- Source of protein and calcium
- Source of income
Observable Adaptations for Swimming.
- Tail fin for swimming/ uropod for swimming backwards
- Swimmerets/pleopods for swimming
- Streamlined body for easy movement
- Antennule for balancing
SPECIMEN: FRESHLY PRESERVED CRAB.
Habitat:
- Rocky intertidal zone (shore),
- Sandy shore,
- Pond,
- Swamp,
- Lake,
- River
The mode of nutrition is holozoic (Carnivorous and Detritivorous), and uses gills for gaseous exchange.
Sensory features are antennae and stalked eyes with detachable claws and a flat body to escape predators.
The pair of detachable claws is also used for defence.
Biological classification
Phylum Arthropoda
Reasons:
- Presence of a chitinous exoskeleton
- Metameric segmentation
- Presence of jointed appendages attached to each segment.
- Bilaterally symmetrical
- Triploblastic coelomate
- Open circulation (haemocilic)
- Undergo moulting.
Class Crustacea
Reasons;
- Presence of cephalothorax and abdomen
- Has a thick exoskeleton called a carapace
- Five pairs of walking legs on the cephalothorax
- Two pairs of antennae, one pair being larger than the other
- They have a pair of compound eyes raised on a stalk
Observable Adaptive Features of the Crab to Its Habitat
- Possession of powerful chelipeds for seizing food
- Presence of an exoskeleton carapace to prevent desiccation
- Presence of gills for gaseous exchange
- Possession of lung-like tissue for the absorption of atmospheric oxygen
- Pointed legs end in pointed claws to burrow into mud
- Setae on the leg to trap water to avoid desiccation
- Body fluid is isotonic with seawater to prevent loss of body fluids by osmosis
- Stalked eyes enable vision in all directions
Observable characteristics
- Two stalked eyes
- Two pairs of antennae
- Presence of cephalothorax and abdomen
- Presence of abdominal appendages
Observable Adaptive Characteristics of the Crab to Escape Danger
- Detachable claw
- Stalked eyes to provide vision in all directions
- Antennae for sensitivity
- Flat body to pass through narrow rocks
- Carapace for mechanical protection
- Legs for fast movement
- Chela has claws for defence and grabbing prey
- Last pair of legs for swimming
- Pleopod for swimming
Observable External Features Common to Crabs and Snails
- Calcareous shell
- Eyes raised
- Eyes can be withdrawn
- Gills
- Two pairs of sensory structures on the head
Observable Differences Between Crab and Snail
| CRAB | SNAIL |
| Flat body | Conical body |
| Possess compound eyes | Possess simple eyes |
| No distinct head | Distinct or prominent head |
| Bilaterally symmetrical | Asymmetrical |
| The entire body is hard. | Soft body |
| Presence of claws | Absence of claws |
| Possess legs | Absent legs. |
External feature common in crabs and bony fish
- Eyes
- Mouth
- Bilateral symmetry
Observable Differences Between Crab and Bony Fish.
| CRAB | BONY FISH |
| The tail is absent. | Tail is present |
| No operculum | Operculum present |
| Presence of legs | Absence of legs |
| Absent of fins | Presence of fins |
| Compound eyes | Simple eyes |
| Presence of antennae | Antennae absent |
| Dorsoventrally flattened | Laterally flattened. |
| Stalked eyes | Eyes are not stalked. |
| Possess carapace | Absence of carapace |
| Scales absent | Scales present |
| Absence of lateral line | Presence of lateral lines. |
| Head fused | Distinct head |
Evolutionary relationship between snail, crab and fish: Presence of gills
SPECIMEN: Freshly preserved woodlouse
Habitats:
- Moist decaying Wood
- Soil
They are Detritivorous
Scientific classification
Phylum Arthropoda
Reasons:
- Presence of a chitinous exoskeleton
- Metameric segmentation
- Presence of jointed appendages attached to each segment.
- Bilaterally symmetrical
- Triploblastic coelomate
- Open circulation (haemocilic)
- Undergo moulting.
Class Crustacea
Reasons:
- Presence of cephalothorax and abdomen
- Has a thick exoskeleton called a carapace
- Five pairs of walking legs on the cephalothorax
- Two pairs of antennae, one pair being larger than the other
- They have a pair of compound eyes raised on a stalk
Economic importance of woodlice
- Aeration by burrowing in the soil
- Increase the humus content of the soil by feeding on plant matter
- Serve as food for other organisms, such as poultry.
Adaptation of the woodlouse to its habitat.
- Flat body to creep under litter.
- Colour for camouflage.
