Echinodermata
Characteristics of echinodermata:
- Free living exclusively marine forms.
- Adults are radially symmetrical while larvae are bilaterally symmetrical.
- Body is represented by a central disc covered by ossicles with spines called pedicellaria.
- Disc may bear extensions called arms.
- Digestive system is complete.
- A unique ambulacral or water vascular system is present.
- Tube feet are present for locomotion and respiration. Tube feet are extended and retracted by variation in hydraulic pressure of the fluid in them and contraction of their muscles.
- Nervous system has a central nerve ring with five radiating nerves.
- Reproduction is sexual. Sexes are separate. Development is indirect.
- Show very high power of regeneration.
- Tube feet are for feeding as well.
Sea Urchins
Sea urchins have 5 gonads that are located in the interambulacral region of the urchin. Each gonad has a duct rising out of it and out of the gonopore which lies in the anal region of the urchin. The urchin's gonads are surrounded my muscles and allows the urchin to squeeze gametes out of its body. The sea urchin starts to release gametes from its body during breeding season in the spring. The male ejaculates sperm while the female ejaculates eggs. Therefore, the eggs are fertilized in the open ocean when they come in contact with sperm.
The urchin larvae hatches from its eggs with 4 arms. In the weeks to follow he grows more arms until he has 8 arms (the rate at which its arms grow depends on how much plankton is consumed by the urchin). By the time the urchin has 8 arms, it begins to show mature features. Shortly after the growth of the 8th leg, spines and tubefeet protrude out of the urchin.
The urchin larvae hatches from its eggs with 4 arms. In the weeks to follow he grows more arms until he has 8 arms (the rate at which its arms grow depends on how much plankton is consumed by the urchin). By the time the urchin has 8 arms, it begins to show mature features. Shortly after the growth of the 8th leg, spines and tubefeet protrude out of the urchin.
Sea cucumbers
To reproduce, Sea cucumbers rise up on their back ends and release their gametes into the ocean (the sea cucumber raises its body up so that its gametes dont fall to sea bottom). The sea cucumber's gametes come out in a single stream from a tube within the tentacles. The reproduction system is actually a gonad consisting of tubules which empty out into this tube.
Once fertilized, the small eggs of the sea cucumber becomes quite large and yolky. The hatchlings come out as free-swimming plankton and remain this way for around 3-5 weeks before metamorphosing into a sea cucumber.
Once fertilized, the small eggs of the sea cucumber becomes quite large and yolky. The hatchlings come out as free-swimming plankton and remain this way for around 3-5 weeks before metamorphosing into a sea cucumber.
Starfish
Asexual reproduction in starfish takes place by fission or through autotomy of arms. In fission, the central disc breaks into two pieces and each portion then regenerates the missing parts. In autotomy, an arm is shed which continues to live independently as a "comet", eventually growing a new disc and further arms. Only certain genera of starfish are able to reproduce in these ways.