Phylum Annelida

http://shapeoflife.org/video/annelids-powerful-and-capable-worms

Phylum Annelida From the Latin Annellus a “little ring”. Segmented body Metamere – segment in the body Setae Small hair-like structures Absent in leeches Coelom divided by septa Separating tissue 4

Phylum Annelida The segments of an annelids body are separated by internal walls called septa. Most of these segments are the same but a few are modified to perform special functions such a photoreceptors, antennae, etc. 5

Metamerism Septa Pygidium Prostomium Peristomium

Phylum Annelida Annelids range in size from the Giant Earthworms, of which Michrochaetus rappi (Michrochaetus michrochaetus) is the largest average length of 1.36 m (54 ins) and a record breaking specimen has been recorded that measured 6.7 metres (22 ft) in length, it was 2cm (0.8 ins) in diametre. The smallest Annelid known to science is Chaetogaster annandalai full grown at 0.5 mm (0.02 ins).

General Annelid Anatomy

Body Plan Cylindrical Bilateral symmetry True coelom Annelids are the first major phyla showing segmentation (metamerism) which is advantageous to movement, safety, and tagmatization

Feeding Annelids have a complete digestive system The digestive tract is a long tube from the mouth to the anus. Their system contains mouth, pharynx, esophagus, crop, gizzard, intestine and anus They have a pharynx which is used to grind up the larger particles of food. 10

Feeding Some annelids are carnivorous. Carnivorous annelids can extend the pharynx through the mouth. These have two or more sharp jaws attached to it which are used to catch its prey. In earthworms the pharynx acts like a pump pulling in soil and detritus through the mouth and forcing it into the gut. In parasitic annelids the pharynx is used to suck blood from the host. Some aquatic annelids are filter feeders and use fan-like structures to catch food particles.

Respiration Aquatic annelids breathe through gills. Many annelids take in oxygen and give off carbon dioxide through their skin. The skin must stay moist for this type of gas exchange to occur. Terrestrial annelids secrete a thin protective coat called a cuticle to hold moisture around them. 12

Circulatory System Annelids usually have a closed circulatory system with two blood vessels running the length of the body. In earthworms there are several ring vessels connected to these blood vessels in the anterior part of the worm. The ring vessels are muscular and contract in rhythm so they are sometimes referred to as hearts. They do help pump blood through the system. In other annelids the blood is moved around by the worms movements. 13

Closed Circulatory System 14

Excretion Solid waste is removed through the anus while waste resulting from cellular activity is removed by a pair of nephridia in each segment of the body. 15

Nervous System Annelids have a well developed nervous system. Sense organs are most developed in the free-living marine annelids. They often have sensory tentacles, photoreceptors, two or more eyes, and statocysts. 16

Nervous System cont’d A statocyst is an organ used to detect gravity while they are in the water. Many other annelids have simpler sensory systems like the earthworm. They rely only on cells in their skin to sense their environment. 17

Nervous System Fig. 17.15 18 18

Movement Annelids have two major groups of muscles they use to move. Longitudinal muscles run from the front to the rear. These make the worm shorter when they are contracted. The other group runs in circles around the worm. When they are contracted they make the worm skinnier. These two muscle groups are used together to help the worm wiggle forward. 19

Movement

Setae – help in movement

Reproduction Most annelids reproduce sexually but a few can reproduce by budding. Oligochaetes are hermaphroditic and during copulation they line up facing in the opposite direction The clitellum secretes a mucous that holds the worms in place Later, the clitellum acts as a cocoon where the fertilized egg develops 22

Earthworm Reproduction 23

Palolo worm spawning.

Trochophore larva Apical tuft Stomach Ciliary band Mouth Anus

Annelid development

Classification Class Polychaeta (many hairs) Class Oligochaeta (few hairs) Class Hirudinae (leeches)

Class Polychaeta Many setae Parapodia = “paired feet” Characterized by paired paddle-like appendages on the segments. The appendages are tipped with bristles that help the move about. They live in the ocean, usually around reefs. 28

Fig. 17.3 29 29

Class Polychaeta Parapodium Head Tentacle 30

Polychaete Worm Predatory Jaw Tentacle Everted pharynx Palp Eye Cirrus Parapodium 31 31

Nereis 32

Class Polychaeta Fireworm 33

Sedentary Polychaete Lugworm Fig. 17.5 34 34

Fig. 17.4 35 35

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Pelagic* Polychaete *Drift in the open ocean 37

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Class Oligochaeta Few setae have bristles but they are much shorter and help the earthworm burrow through the soil. Clitellum No parapodia Monoecious Both male and female parts 41

Earthworms play an important role in soil fertility Return nutrients to soil by decomposing dead leaves and organic matter Burrowing allows air and water to penetrate to roots Tunnels loosen soil so roots can grow more easily “intestines of the earth” -Aristotle 42

Lumbricus terrestris - earthworm Enrich soil Exceedingly important in soil creation, particularly in temperate areas. Without them, agriculture and perhaps the whole of human society as we know it would never have evolved. 43

External Structures of an Earthworm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. External Structures of an Earthworm

The Anatomy of an Earthworm Section 27-3 Anus Clitellum Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel Ganglion Brain Mouth Dorsal blood vessel Crop Gizzard Body segments Setae

Fig. 17.12c

Body wall Epithelium Circular muscle Longitudinal muscle

Class Hirudinea - Leeches No setae Anterior & posterior sucker Most live in fresh water Feed Invertebrates Body fluids Blood

Class Hirudinea Usually no more than 6 cm in length but some tropical species can reach 30 cm. After they attach to a host they release a substance called hirudin into the wound. This keeps the blood from clotting. A leech can take in up to 10 times its weight in blood during a single feeding. 49

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Fig. 17.21

PARASITIC SEGMENTED WORMS LEECHES Medical uses

Man vs. Wild - Leeches

Annelid Annelid 3 Annelid 4

Dirty Jobs worm grunting http://dsc.discovery.com/tv-shows/dirty-jobs/videos/worm-grunter.htm

Dirty Jobs – Bloodworms

Video! Annelida (Leech Therapy) Caution! If you don’t like leeches, you won’t like this news clip. http://www.youtube.com/watch?v=bYeqPvv5s_E Copyright © 2010 Ryan P. Murphy

Video Link! Leeches NOVA podcast http://www.youtube.com/watch?v=cKUAroimQrk