Phylum Annelida the segmented worms

The Higher Animals - two lineages Higher animals have a coelom and a mouth/anus The infolded blastopore of the forming gastrula can become either a mouth or anus If it becomes: a mouth -> called protostomes anus -> deuterostomes

blastopore

True Coelom Peritoneum (from mesoderm) lines the body wall and all organs- Totally enclosed by mesoderm.

WHAT ARE THE BENEFITS OF DEVELOPING A COELOM?

the ‘solid’ mesoderm of lower animals becomes inefficient as body size increased Body cavity = fluid + space for specialized organs needed in circulation of waste / food

Segmentation Repeated body units (seperated by septum) with similar structures Permits specialization of units

Annelid Diversity Class – Oligochaeta (earth worms) Oligo = Few Chaeta = Bristles Movement – circular and longitudinal muscles work together to produce “inching” wave-like movement called peristalsis – chitinous bristles (setae) on each segment help to anchor worm in soil

Feeding – Eat soil / decayed matter – Muscular pharynx sucks food through mouth then pushes it down to the esophagus and crop (storage) to a grinding organ (gizzard) then onto the intestine. – Blood transports nutrients digested in intestine – Wastes pass out anus – *** MPECGI ***

Closed Circulatory System Simple diffusion does not work for large animals. Anterior muscular vessels (Aortic Arches) act as ‘hearts’ (5 Pairs) Blood carries nutrients and gases through closed vessels to capillary beds No lungs; gases diffuse across moist skin

Excretory System Paired nephridea pass through septum (partition) into posterior segment. Waste out pore.

Nervous System dorsal, anterior ganglion (primitive brain) Ventral nerve cord; nerves to each segment Can sense chemicals, light, touch

Reproductive System Hermaphroditic, but reproduce by copulation Clitellum has gland cells which secrete cocoon to protect developing eggs

Class - Polychaeta Many-bristles Marine worms Each segment has parapodia (side-feet) – movement / gas exchange

Class - Hirudinea Leeches parasites who bite into skin to feed Can fast for up to one year

Questions 1.What is the significance of MPECGI ? 2.What is the function of the clitellum? 3.What function do cetea/bristles? Explain. 4.For each class give a member: Hirudinea : Oligochaeta Polychaeta