Annelida Segmented Worms Characteristics of Phylum Annelida Metameric

Annelida Segmented Worms

Characteristics of Phylum Annelida • Metameric body(segmented), Bilateral symmetry • Trochophore larvae, Spiral cleavage • Paired epidermal setae (chaetae) • Closed circulatory system • Dorsal suprapharyngeal ganglia and ventral nerve cord with ganglia • Metanephridia or protonephridia

Phylum Annelida, 2 Classes • Class Polychaeta- mostly marine, head with eyes and tentacles, Parapodia with numerous setae • Class Clitellata- no parapodia, few or no setae, clitellum functions in cocoon formation • Subclass Oligochaeta- few setae, no distinct head, terrestrial and freshwater, earthworms • Subclass Hirudinea- bodies with 34 segments, posterior and anterior suckers, freshwater, marine and terrestrial, Leeches

Metamerism and Tagmatization • Segmental arrangement of body parts internally, functions in flexible support and efficient locomotion • Compartmentalization has resulted in each body part having its own excretory, nervous and circulatory structures • Coelomic spaces allows hydrostatic compartments controlled independently • Lessens impact of injury, separates injured segments

Metamerism and Tagmatization • Tagmatization- modification of regions of body for specialized functions, ex. feeding, locomotion, reproduction • Each segment contains layers of circular muscles, longitudinal muscles and some polychaetes have oblique muscles and leeches have dorsoventral muscles • Each segment can be controlled independently, muscles act as antagonistic pairs • Coelomic fluid provides hydrostatic skeleton against which muscles operate

Excretion • Annelids excrete ammonia mostly thru body wall • Excretory organs (nephridia) discharge waste and regulate water and ion balance • Protonephridia- tubule with a closed bulb at one end and the other opening outside the body, Bulb contains flagella that drives fluid thru tubule • Metanephridia- open ciliated funnel at one end of coiled tubule open to outside of body or intestine at other, coil may be dilated into a bladder and connected to capillaries

Class Polychaete • Polychaete (many hairs) mostly marine, 5 to 10 cm long • Live on ocean floor, under rocks, crevices of coral reefs, burrow in mud and sand, some construct tubes of cemented sand grains or secreted organic material • Parapodia- lateral extensions of segments with setae (bristles) projecting out, internal support of chitinous rods • Various species are capable of walking, fast crawling, or swimming

Polychaete

Polychaete with Parapodia

Chloeia Polychaete

Polychaete Head

Parapodia

Bristle Worm Needles

Polychaetes • Prostomium- anterior lobe contains eyes, antennae, palps and ciliated grooves (nuchal organs) • Peristomium- first body segment, surrounds mouth and sensory tentacles • Epidermis contains single layer of cells, secrete protective cuticle, some secrete luminescent compounds

Polychaete Feeding • Proboscis- anterior digestive tract can be everted thru the mouth • When proboscis is everted paired jaws seize prey, some have poison glands at base of jaws • Others are herbivores and scavengers, use jaws to tear food • Digestive tract consists of pharnyx (proboscis), crop, gizzard and long straight intestine

Filter Feeders • Usually lack a probocis but have other feeding structure • Fan worms- tube dwellers with funnel shaped fan (Radiole), cilia on radiole circulate water and trap food, push food towards mouth • Chaetopterus lives in U shaped burrow, secretes mucos bag to collect food. Modified parapodia on segments 14 -16 create current

Fan Worms

Fan Worms

Feather Duster worm

Plume Worm

Christmas Tree Worm

Christmas Tree worms

Christmas Tree Worms

Chaetopterus

Chaetopterus

Sensory Structures • Pair of suprapharyngeal ganglia leading to subpharangyal ganglia connected to a double ventral nerve cord, ganglia at each segment with lateral nerves • Suprapharangyal ganglia- motor and sensory functions • Subpharangeal ganglia-coordinate locomoter functions of segments • Eyes 2 to 4 pairs, nuchal organs(chemoreceptors), statocysts, palps for tactile sense

Class Clitellata • Subclass Oligochaeta- Earthworms and relatives, few or no setae • Terrestrial, freshwater and a few marine species • Known for their soil conditioning habits • Body smoothed for burrowing in soil • Swollen segments near anterior form clitellum which secretes cocoon for eggs

Earthworm Anatomy • Locomotion involves antagonism of circular and longitudinal muscles, segments bulge setae stiffen when longitudinal muscles contract, circular muscles make segments elongate and push forward • Burrowing by swallowing and compacting soil • Feed on decaying vegetation • Mouth, esophagus crop, gizzard, intestine with dorsal fold to increase surface area

Earthworm Anatomy

Earthworm Anatomy • 5 Aortic arches (hearts) push blood down dorsal blood vessel and returns by ventral vessel, blood vessels serve propulsive structures also • No well developed eyes due to subterranium lifestyle but do have photorecptor cells in skin • Dorsal blood vessel contains chloragogen tissue, acts like a liver converts ammonia to urea, converts carbohydrates into fat and glycogen

Earthworm Cross section

Earthworm Reproduction • Monecious contain two pairs of testes and one pair of ovaries, exchange sperm • Clitellum forms cocoon made of mucous and chitin material, food reserve (Albumen) and sperm and eggs secreted into cocoon and worm backs out, fertilization occurs in cocoon

Trochophore

Leeches Subclass Hirudinea • Freshwater (most), marine and terrestrial • Prey on small invertebrates or body fluids of vertebrates, specific hosts- fish, alligator and turtle, mammals • Flattened dorsoventrally and taper anteriorly Have 34 segments, anterior and posterior segments modified into suckers • Single coelomic body cavity, loss of internal compartments, circular, longitudinal and transverse muscles

Engorged Leech

Leeches • Mouth modified into extensible proboscis, or has 3 jaws • Attaches with anterior sucker, bores into host • salivary glands secrete anticoagulant (hirudin) • Muscular pharnyx pumps body fluids of prey, leech gorge themselves, increase 2 to 10 times • Attracted to temperature (mammals) or extracts of prey tissue

Marine Worms • Echiurans (spoon worms) burrow in sand, extend spoon shaped proboscis up to 2 meters long to sweep food • Siboglinids (beard worms) tube dwelling worms embedded in marine sediments, no mouth or digestive tract, nutrients enter thru skin or derived from endosymbiotic bacteria, giants live near thermal vents • Sipunculans ( peanut worms) live in mud and sand, tentacles surround mouth for feeding

Echiurans (spoon Worm)

Echiurans (spoon worms)

Siboglinids (beard worms)

Sipunculans (peanut worms)