Phylum Annelida True Coelomates with true body segmentation. Different segments can have different organs or perform different functions. There are around 12,000 species of annelids.

Annelids are characterized by 3 principal features: 1- Repeated Segments Excretory and locomotory organs are repeated every segment. The fluid in each segment creates a hydrostatic skeleton.

2- Specialized Segments The anterior segments are specialized and contain sensory organs. A well developed cerebral ganglion is located in an anterior segment.

Materials and information does pass between segments. There is a closed circulatory system. A ventral nerve cord connects the ganglia in each segment with the cerebral ganglion. The basic body plan is a digestive tract located within the coelom. 3- Connections

Digestive Tract has several portions: Pharynx  esophagus  crop  gizzard  intestine Annelids use circular muscles and their hydrostatic skeleton for movement. Most annelids have segments that possess SETAE, bristle-like hairs used for locomotion Each segment has a pair of nephridia used to excrete wastes.

Class Oligochaeta Includes earthworms and some aquatic worms. Earthworms have fewer setae than polychaetes, and no head region or parapodia. They do not possess eyes, but do have many sensory mechanisms.

Class Oligochaeta - the common Earthworm

Earthworm Locomotion/Muscular System

Digestive System of an Earthworm

Circulatory, Nervous, and Reproductive Systems

Origin of the Kidney – the Nephridia

Clitellum – what’s it for? A glandular swelling that secretes the cocoon that will contain the fertilized eggs, that will of course, grow into new worms

Class Polychaeta Marine annelids called bristleworms. Polychaetes have segments that possess many setae. They possess a well developed head with specialized sense organs. Each segment has a pair of fleshy appendages called PARAPODIA.

All annelids have a structure called the CLITELLUM that secretes a cocoon that is specialized to receive eggs. Earthworms are hermaphroditic, meaning they have both gonads. Why might this be?

Ewwwwwwwwwwwwwwwwwwwwwwwww! Ah, but they are sooooooo in love, don’t you think?

Class Hirudinea Leeches – parasites . Are hermaphroditic and produce a clitellum. Have suckers at one or both ends for attachment. Produce a chemical in saliva called HIRUDIN, which is an anti- coagulant Most leeches have no setae.

Leech Anatomy 101 Mmmm – lunch!

Leeches Used in Medicine Successful reattachment of severed ear, as blood continued to flow and carry nutrients to the damaged region

Ready to Suffer? AssiGnment 1.Your Lab drawings of the Clam are due. 2.SR/KT on 27.1 on Mollusks was due Friday. 3.Hwk = 27.2 Annelids – SR/KT 4.Annelid Dissection is Tomorrow, bring you lab book!