Invertebrates

Invertebrates

1. Cnidarians

   • Cnidarians are aquatic animals that have radial symmetry. Their cells are grouped in simple tissues. Some cnidarians have organs.
     • Characteristics
       • They have a digestive cavity
       • Cnidoblasts are found in the tentacles
       • They are all carnivores. They do not have respiratory system or an excretory system
     • Types
       • Polyps
       • Jellyfish

2. PORIFERA

   • Porifera are aquatic sessile animals that mainly live in the sea. Their bodies are eithjer asymmetrical or have a radial symmetry. They do not have true tissues or organs.
     • Characteristics
       • Their bodies are shac-shaped and have many pores.
       • They have an internal skeleton that protects them.
       • Porifera feed by using filtration
       • The perform sexual reproduction but they can perform asexual by fragmentation
     • Parts
       • Choanocytes
       • Osculum
       • Incurrent pores
       • Spicule
       • Central cavity
       • Porocytes

3. Echinoderms

   • Types
     • Echinoids
       • Echinoids, or sea urchins, are echinoderms that have globular bodies with fused plates that form a shell, and long spikes which they use to defend themselves against predators
     • Asteroideans
       • Asteroideans, or starfish, have disc-shaped bodies with arms. They usually have five arms, although some species hae more than ten
     • Holothurians
       • Holothurians, or sea cucumbers, have long bodies with no arms or spikes
   • Characteristics
     • They have a locomotive system called ambulacral system
     • The skeleton of an echinoderm is called the dermoskeleton
     • They have a complete digestive system
     • They perform sexual reproduction
   • Echinoderms are aquatic invertebrates that live in the sea. They generally have radial symmetry, which is characterised by a skeleton consisting of rigid plates under the skin

4. Molluscs

   • Molluscs are invertebrates that have soft bodies and bilateral symmetry. The majority of them aquatic, although there are a few exceptions such as snails and slugs
     • Characteristics
       • Their bodies are surrounded by a mantle that protects the internal organs
       • Many molluscs have a shell
       • Some have a defined head
       • They have a muscular foot
       • Molluscs have a complete digestive tube
       • Aquatic molluscs use gills to breathe.
       • They perform sexual reproduction
     • Types
       • Bivalves
         • Bivalves are aquatic invertebrates that have two external shells or valves
       • Gastropods
         • Gastropods are mainly aquatic invertebrates that have an external spiral-shaped shell
       • Cephalopods
         • Cephalopods are aquatic invertebrates. Their foot is next to their head. All cephalopods have an internal shell, except for octopuses

5. Worms

   • Types
     • Flatworms
       • Flatworms are the simplest animals that have bilateral symmetry and cephalisation of the nervous system. Cephalisation refers to the concentration of nerve centres in the front part of the animal's body. Flatworms have a head at the front of their bodies
         • Tapeworms
         • Planarians
     • Nematodes
       • Nematodes are worms with unsegmented cylindrical bodies
         • Their digestive syste has a mouth and an anus.
         • They perform sexual reproduction
     • Annelids
       • Annelids are worms with segmented cylindrical bodies that are divided into segments called metameres
         • They have a digestive tube
         • They breathe through gills
         • Perform sexual reproduction
   • Characteristics
     • They have a bilateral symmetry
     • They tend to live in humid climates
     • They do not have jointed appendages

6. Arthropods

   • Arthropods are the most varied and largest phylum of the Animal kingdom. MOre than 75% of all known species belong to this group. Due to their diversity, arthropods can be found in a wide range of environments.
     • Characteristics
       • They have a bilateral symmetry
       • They are protected by an exoeskeleton
       • They have segmented bodies
       • They have articulated parts consisting of appendages
       • Arthropods have a complete digestive system
       • Their nervous system and sense organs
       • They perform sexual reproduction
     • Types
       • Myriapods
         • Myriapods are terrestrial arthropods that have a pair of antennae on their heads and bodies that are divided into segments. One or two pairs of legs are found of the segments
           • Chilopoda
           • Diplopoda
       • Arachnids
         • Arachnids are terrestrial arthropods. Their bodies are divided in two parts: the cephalothorax and the abdomen. They have four pairs of legs and do not have antennae.
           • Spiders
           • Scorpions
           • Mites
       • Crustaceans
         • Crustaceans are arthropods whose bodies are divided into a cephalothorax and a abdomen. They haev two pairs of antennae and five pairs of legs on their cephalothorax. The majority of crustaceans are aquatic.
           • Have a pair of mobile eyes
           • They have non-articulated appendages
           • Some species of crustaceans are carnivorous
           • Crustaceans undergo metamorphosis
       • Insects
         • Insects are the arthropods that have a head, thorax and abdomen. They have a pair of antennae on their head and three on their thorax. Insects have one or two pairs of wings. The majority of them live on land
           • Incomplete
           • Complete