ANNELIDA

• Annelida: a large phylum that comprises the segmented worms, which include earthworms, lugworms, ragworms, and leeches.
• Annelida are sometimes called "segmented worms"
• annelida are bilateral symmetry
• annelida have metameric body which means that the body is made up of many cells that are joined together by a network of fibers
• annelida respire through their body surface
• annelida have a well-developed circulatory and digestive system.
• annelida's body contains hemoglobin, which gives them a red color.
• annelida have a heart
• annelida's body are Coelomate and triploblastic
• coelomate means a body cavity that is enclosed by a membrane
• Triploblastic:

  Ectoderm is the epidermis

  Mesoderm is the dermis (muscle)

  Endoderm is the hypodermis
• mesoderm are the middle layer of the embryo and give rise to the muscles, bones, and connective tissue
• endoderm are the cells that form the lining of the digestive system and the respiratory system
• ectoderm are the outer layer of cells that form the epidermis
• 1/2 Movement

  ❑ Setae

  ✓ Are bristle-like structures attached to the body wall.

  ✓ Provide traction for movement and help anchor the worm in the substrate.

  ✓ They vary in number, size, and arrangement depending on the species and habitat.
• 2/2 Movement

  ❑ Parapodia

  ✓ Many annelids possess paired, paddle-like appendages along the body segments.

  ✓ They are equipped with setae and can be used for swimming, burrowing, crawling, or even gas exchange.

  ✓ They are especially well-developed in polychaete annelids, which are primarily marine worms.
• Specialized Excretory Organs

  ❑ Nephridia

  ✓ Responsible for removing metabolic wastes and maintaining osmotic balance.
• Closed Circulatory System

  ❑ Blood is confined to vessels and does not directly bathe the tissues.

  ❑ The circulatory system consists of blood vessels and a pumping organ called the heart, which propels blood through the body.
• 1/3 Nervous System

  ❑ Ganglia and Nerve Cords

  ✓ A ladder-like nervous system consisting of a pair of ventral nerve cords that run along the length of the body, one on each side.

  ✓ The nerve cords are interconnected by transverse nerves and ganglia, or nerve clusters, located in each body segment.

  ✓ The ganglia serve as local processing centers for sensory and motor information.
• 2/3 Nervous System

  ❑ Prostomium

  ✓ A distinct head region which lies in front of the mouth.

  ✓ The prostomium may bear sensory organs such as eyes, antennae, and palps.
• 3/3 Nervous System

  ❑ Peristomium

  ✓ The first body segment behind the prostomium and typically surrounds the mouth.
• Reproductive Organ

  ❑ Clitellum

  ✓ Smooth midpiece that is present at sexual maturity Secretes mucous during reproduction.
• Sexual Reproduction (Internal Fertilization)

  • Earthworms are hermaphroditic.

  • However, they still require a mate for sexual reproduction.

  • Earthworms typically locate potential mates through chemical cues released in their mucus trails or by physically encountering another worm
• Asexual Reproduction (regeneration)

  ❑Many annelids have remarkable powers of regeneration.

  ❑They can replace lost parts, and some species have break points that allow worms to sever themselves when a predator grabs them.

  ❑Lost segments are later regenerated.

  ❑Some polychaetes reproduce asexually by budding or by transverse fission