Notes on Invertebrate Marine Animals

Invertebrate marine animals

• Vertebrates: animals with a backbone
• Invertebrates: animals without a backbone
• There are more invertebrates than vertebrates

Porifera

• The representative groups of the phylum Porifera are sponges
• Sponges are considered as one of the structurally simplest multicellular animals, and they lack true tissues and organs.
• Sponges consist of aggregations of cells, which carry out specific functions.
• The collar cells of the sponge trap food particles
• The osculum is a large opening located on top of the sponge that allows water to escape.
• Nearly all sponges are marine
• Sponges are filter feeders because they filter food particles that are suspended in water.

Cnidarians

• Examples of cnidarians: sea anemones, corals, jellyfish.
• Cnidarians are multicellular animals that have tissue
• Cnidarians have radial symmetry.
• They have nematocysts, which are stinging structures used to capture prey.
• They lack true nerves or a brain, but they have specialized nerve cells that are interconnected.
• The nerve cells form a nerve net.
• Cnidarians occur in two different forms: polyp or medusa
• Polyp
• The mouth and tentacles are oriented upward
• Medusa
• Bell-shape with the mouth and tentacles oriented downwards
• Example: jellyfish

Ctenophora

• Comb jellies represent the phylum Ctenophora
• Comb jellies, also known as ctenophores, have radial symmetry.
• Comb jellies are similar in appearance to the cnidarians.
• However, comb jellies have eight rows of ciliary combs.

Platyhelminthes

• Tapeworms, flukes and turbellarians are Platyhelminthes,
• Platyhelminthes also known as flatworms
• Flatworms are bilaterally symmetrical and have flat backs and flat bellies.
• Flatworms have true organs and organ systems
• Flatworms have a simple central nervous system

Nemertea

• Ribbon worms represent the phylum Nemertea
• Ribbon worms have a complete digestive tract that includes a mouth and an anus
• Ribbon worms also have a closed circulatory system
• The characteristic feature of the ribbon worms is the proboscis
• The proboscis helps capture prey and it releases toxins.

Nematode

• Nematodes and roundworms represent the phylum Nematoda
• These organisms are usually found on marine sediments
• Nematodes also have hydrostatic skeleton, which helps in locomotion and support
• Hydrostatic skeleton uses water pressure against the body wall
• Muscles in the body pushes against the water fluid.

Annelida

• Annelids, or segmented worms, have segmentation
• Segmentation: the body contains a series of similar segments (compartments)
• Annelids have a coelom, which is a body cavity
• Most of the marine annelids are polychaetes

Sipuncula

• Also known as peanut worms
• Peanut worms are mostly found in shallow waters
• Peanut worms are deposit feeders

Echiura

• Echiurans are deposit feeders that have proboscis

Mollusca

• The molluscs make up the largest group of marine animals

Arthropoda

• Arthropoda are the largest phylum of animals
• Most of the marine arthropods are crustaceans, which are specialized to live in water
• Characteristics of crustaceans
• They possess two pairs of antennae, which can be for sensing the surrounding environment
• They have a calcified, chitinous exoskeleton
• They have appendages that helps in movement, attachment, mating and feeding
• Most have gills, which are used for oxygen
• Types of crustaceans
• Copepods
• These are the most abundant zooplankton
• Barnacles
• Isopods
• Decapods
• Crabs, lobsters and shrimps

Lophophorates

• Characteristics
• Has lophophore, a type of feeding structure that has a set of ciliated tentacles arranged as a horse-shoe
• They are suspension feeders
• Lack segmentation
• Types of lophophorates:
• Ectoprocta
• Bryozoans
• Phoronida
• Phoronids
• Brachiopida
• Lamp shells

Chaetognatha

• Arrow worms

Echinodermata

• Pentamerous radial symmetry
• Radial symmetry consists of 5 parts.
• Only the adult echinoderms develop radial symmetry
• Larvae are bilaterally symmetrical
• Echinoderms have an endoskeleton
• They have a unique water vascular system
• The water vascular system consists of a network of water-filled canals with tube feet as the muscular extensions
• The tube feet aids in locomotion, attachment and stimuli.
• Types of echinoderms
• Sea Stars
• Sea Urchins
• Brittle Stars
• Sea Cucumbers

Hemichordata

• Hemichordates have some of the same basic developmental characteristics of echinoderms and chordates.
• Like the chordates, hemichordates have dorsal, hollow nerve cord and gill slits
• Acorn worms are representative groups of the phylum Hemichordata
• Acorn worms are deposit feeders

Chordata

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