Question

Expandable mollusca Arthropoda Annelida nematoda Platyhelminthes

Answer 1

Platyhelminthes

•The phylum Platyhelminthes are dorsoventrally flattened and have a definite anterior and posterior end giving them bilateral symmetry.
•Their bodies are solid so they are said to be acoelomate. Some flatworms are parasites, while others are free-living carnivores or scavengers. •Examples of parasitic flatworms are flukes and tapeworms.
•Flatworms also have only a mouth for both food and wastes. (Two way digestive tract somewhat similar to Cnidarians)
•Their nervous system is composed of a nerve net and sometimes light-sensitive eyespots; however with no central control, it isn't able to react to touch only in the area where it was touched but rather will contract all over.
•Specialized flame cells help get rid of wastes.
Nematoda (Roundworms)

• The phylum Nematoda are the roundworms such as pinworms, heartworms and hookworms.
• Roundworms are cylindrical in shape, tapered at both ends, and vary in length from being microscopic to 20 inches long.
• Roundworms are pseudocoelomate having a body cavity that is not completely lined. The body cavity or pseudocoel serves as a hydrostatic skeleton against which muscles can contract.
• Unlike flatworms, roundworms have a complete gut. This means that they have a one-way digestive tract with a gut that begins with a mouth and ends with an anus. Therefore, they are usually able to digest food.
• Roundworms have no blood or heart. Nutrients are distributed by a non-blood fluid which is not pumped but flows freely in the body cavity.
• Most roundworms are parasites and are found in all habitats.
• They are bilaterally symmetrical and unsegmented.

Annelids (segmented worms)

Earthworm, leech, sandworms

• The phylum Annelida are the segmented worms and are abundant in all habitats.
• External segments are characterized by ringlike structures called metameres along the body, and corresponding internal segments are called septa.
• Segmentation gives worms more flexibility in movement. Also, if one segment is damaged, it isn't usually fatal to the animal because their organs are duplicated in other segments.
• Annelids have a tube within-a-tube body plan known as a coelom which is fully lined and contains the body organs. The coelom runs from the mouth to the anus.
• Annelids have bilateral symmetry, and a well-developed brain and diverse sense organs showing cephalization.

Phylum Mollusca.

• Many members of this phylum have durable limestone shells and are found in all habitats.Members of this group are economically important as sources of human food, pearl and shell production, crop & flower damage, destruction to submerged wooden structures, and intermediate hosts for some parasitic diseases.
• The giant squid and giant clam are the two largest invertebrates.
• Mollusks have bilateral symmetry and a visceral mass containing their body organs.
• Mollusks also have a muscular foot for movement which can be modified into arms or tentacles in some species

Phylum Arthropoda


• The members of the phylum Arthropoda all have jointed appendages.
• In fact, the word "arthropod" means jointed leg. There are more species of arthropods than any other phylum.

• All arthropods have 3 distinct features that make them recognizable as arthropods.
• A segmented body jointed appendages such as legs, antenna, and mouthparts.a hard exoskeleton which is usually composed of substance called chitin (as they develop, arthropods go through periodic ecdysis or molting as they shed or molt their exoskeleton)
• Arthropods have
specialized body segments (head, thorax, cephalothorax, & abdomen)jointed appendages such as legs, antenna, and mouthparts.an open circulatory system (blood is pumped out of blood vessels into the body)