4. * SOFT-BODIED - LEATHERY COVERING.
* RADIALLY SYMMETRICAL,
* THEY HAVE TENTACLES AROUND THEIR MOUTH AND
ROWS OF TUBE FEET ON THEIR UPPER AND LOWER
SURFACES.
*UNLIKE OTHER ECHINODERMS, SEA CUCUMBERS ARE
LONG AND HAVE A WORMLIKE SHAPE.
EXTERNAL FEATURES
5. TUBE FEET: TUBE FEET ARE HOLLOW, MUSCULAR
PROJECTIONS THAT ARE USED IN LOCOMOTION.
MOUTH: FOR FEEDING.
ANUS: REMOVES WASTE OUT OF THE BODY
TENTACLES: FEEDING OR FOOD CAPTURE
CUVARIAN TUBE
EXTERNAL FEATURES
6. REPRODUCTION
* SEXUAL AND ASEXUAL REPRODUCTION. SEXUAL
REPRODUCTION
FEMALES RELEASE EGGS INTO THE WATER WHICH
GETS FERTILIZED WHEN THEY COME INTO CONTACT
WITH SPERM THAT M ALES HAVE RELEASED.
(EXTERNAL FERTILIZATION)
AFTER FERTILIZATION THEY DEVELOP TO A
PLANKTONIC LARVAL STAGE. AFTER A 3-5 WEEK
PERIOD FLOATING IN THE PLANKTON, THE LARVAE
SETTLE TO THE SEA BOTTOM WHERE IT BECOMES AN
ADULT
LIFE CYCLE
7. •
AFTER FERTILIZATION, YOUNG SEA CUCUMBERS
FIRST DEVELOP INTO LARVAE THAT CAN SWIM
AROUND USING CILIA.
THE LARVAL STAGE IS SPENT IN A PLANKTONIC
FORM DRIFTING WITH THE CURRENT.
W HEN THEY HAVE DEVELOPED THEY SINK TO THE
SEA BED TO START AN ADULT LIFE.
DEVELOPMENT
8. ASEXUALLY REPRODUCE BY DIVIDING INTO TWO
HALVES, WITH EACH HALF REGENERATING THE
MISSING ORGANS IN A FEW MONTHS.
LIFE CYCLE
radially symmetrical, which allows them to sense food, predators, and other things in their environment from all directions. *They are cylindrical
ANTENNAE
The long segmented appendages located behind the eyestalk. These allow the crab to interact with its environment by touch, smell & taste.
LEGS
There are ten legs (five pairs) including pincers.
Walking legs (three pairs of sharply pointed walking legs): Used for movement; crabs are capable of walking forward but usually they walk sideways.
Fourth pair of leg: modified as flat swimming paddles.
CARAPACE:
The shell covering the body part which provides rigidity and protection. It is also the part of exoskeleton (hard outer covering) that covers head and thorax (center) of the crab.
PINCERS:
First pair of legs that carries the large claw which is used for defense & obtaining food.
EYES:
Visual organs mounted on the end of eyestalks. The eyestalks contain cells that release hormones that inhibit moulting
MOUTH:
Opening to the digestive system, located between the antennae. The mouth contains jaws that hold and push food into the esophagus.
Shore crabs feed primarily on invertebrates such as molluscs, clams, crustaceans and worms, but they eat practically anything they can get a hold of, including the remains of dead organisms. Their voracious appetites have lead to the regional decline of several species.
Reproduction & growth
The sexes are normally separate in crustaceans.
Eggs are laid by the female they are glued to the soft abdomen of the mother.
Males release sperm packets using modified appendages. Females hold sperm packets until fertilization.
Eggs are fertilized externally. Females carry fertilized eggs under abdomen until hatching.
The larvae are planktonic and spend up to two weeks metamorphosing into the adult
form.
Once they settle to the bottom they must quickly find a tiny, empty snail shell to live
in or they will perish.
