Flatworms belong to endoparasites and live inside other animals. They move through the intestines of the host animal and live at the expense of nutrients coming from food. They do not have their own organs for getting food. Flatworms are hermaphrodites, they are both males and females at the same time. They multiply themselves, laying eggs or simply dividing in half. Flatworms have a long and flat shape. They do not have a blood circulatory system. Some of them do not even have an intestine. The length of flatworms can vary from one millimeter to 30 meters.
2. Coral Polyps
Coral polyps live in the bottom of the water mass. Most polyps have a calcareous skeleton, nervous and digestive systems, are able to hunt fish and crustaceans. However, they do not have blood. Coral polyps are immovable and look like beautiful plants. They live in warm tropical sea waters, and after their death participate in the formation of coral reefs, which consist of the skeletons of many generations of coral polyps.
With the help of tentacles, coral polyps can catch various small animals. Like plants, they can be fed by photosynthesis, carried out by unique unicellular algae, which are embedded in the structure of coral cells. These algae perceive light and form nutrients consumed by coral polyps.
The word “mollusk” is translated from Latin as “soft.” Their bodies are very soft, and they have a leg growing from the head that transformed into 8-10 developed tentacles in the process of evolution. The tentacles perform the hands’ functions.
Mollusks do not have blood. The majority of mollusks are predators, hunting for small fish, crabs, other mollusks and small marine animals.
Nautilus pompilius is the oldest species of cephalopod mollusks. Its unique feature is a spirally twisted outer shell. It is his refuge and underwater transport.
Nautilus pompilius lives at a depth of 400 meters in warm sea waters near the seashores of Australia, China, Indonesia, the Philippines. Its ancestors lived in the World Ocean more than 500 million years ago
Jellyfish is one of the first creatures on earth. The first jellyfish that appeared 600 million years ago were transparent and small. Nowadays, there are many types of jellyfish different in size and color. They consist of water for 98%, and cannot resist sea currents. At first glance, jellyfish seem sluggish, limp creatures.
Jellyfish have no blood, skeleton, and fangs, but they are called sea predators. Their numerous tentacles are poisonous. Moreover, one jellyfish has more than 20 eyes which monitor passing animals. When a prey approaches, the jellyfish strikes it with its poison, which has a paralyzing effect and pulls it to the mouth with its tentacles.
Sea sponges are the oldest and most primitive type of multicellular animals. Sea sponges can have a variety of shapes. Their length can vary from a few millimeters to 10 meters. These bright and motionless creatures look like ornamental plants. They inhabited the Earth’s water bodies 600 million years ago. Sea sponges lack internal organs, they have no muscles, blood and nervous system. They lead an immobile lifestyle. The main food for marine sponges is microorganisms. During the day, each sponge strains a huge amount of sea water to extract oxygen and the smallest parts of food from it.