phylum: annelida

phylum: annelida

1. approximately 16500 species

2. range between 100 um and 3 m in length

3. live in marine, freshwater and damp terrestrial habitats

4. has serial homology / metamerism - the body rings look the same but they may perform different functions

5. complete gut

6. closed circulatory system

7. some protonephridia but mainly metanephridia

   • The nephridium (plural nephridia) is an invertebrate organ which occurs in pairs and performs a function similar to the vertebrate kidney. Nephridia remove metabolic wastes from an animal's body. They are present in many different invertebrate lines.
     • Protonephridia. A protonephridium (proto = "first") is a network of dead-end tubules lacking internal openings found in the phyla Platyhelminthes, Nemertea and Rotifera. The ends are called flame cells (if ciliated) or solenocytes (if flagellated); they function in osmoregulation and ionoregulation, respectively.
     • A metanephridium (meta = "after") is a type of excretory gland found in many types of invertebrates such as annelids, arthropods and molluscs. (In molluscs it is known as the Bojanus organ.)

8. trochophore larva in some marine species

   • trochophore: the planktonic larva of certain invertebrates, including some molluscs and polychaete worms, having a roughly spherical body, a band of cilia, and a spinning motion.

9. class 1: polychaeta

   • = many setae
   • sand, tube and clam worms
   • 25 orders, 87 families - most primitive members of the phylum
   • almost all marine, few freshwater species and 2 terrestrial species - some symbiotic
   • errantia (active) - mainly homonomous
     • nereidae, syllidae, phyllodocidae, tomopteridae
   • sedentaria (static) - mainly heteronomous
     • terebellidae, sabellidae, serpulidae, arenicolidae
   • palps + antennae (tentacles) on prostomium
   • cirri (tentacular) on peristomium
   • Setae (or chetae) most often on parapodia
   • Parapodia biramous → notopodium (dorsal) neuropodium (ventral)
   • Parapodia operated by diagonal muscles, supported by acicula (chitinous rods) often modified as gills, pseudolegs, tentacles etc.
   • Movement and feeding
     • Fast-crawling predators → undulating movements: coelomic hydrostatic pressure + long. Muscles; evertable pharynx armed with jaws
     • Slow-crawling carnivores → strong parapodia, no undulation; ambushed prey sucked or grasped into mouth
     • Burrowers (deposit-feeders)→ loss of inter- segmental septa, or perforated septa: coelomic fluid can move + very reduced parapodia
     • Tube dwellers (filter-feeders) → soft body, reduction of parapodia and muscles CaCO3 secreted by pair of peristomial glands: collar
     • Free-swimmers (predators or filter-feeders) → parapodia modified as paddles, body laterally expanded
   • Myzostomida: aberrant Order → symbiotic/parasitic ► live on arms of crinoids & other echinoderms ► some within gut or body cavity of host – parasites

10. class 2: clitellata

    • = clitellum (saddle) bearing
    • subclass 1: oligochaeta - few setae
      • 3 orders, 25 families, 6000 species
      • Mainly terrestrial, some freshwater sp & few marine sp
      • Brooded or encapsulated embryos that develop directly to juveniles
      • Head appendages strongly reduced in size & number
      • Clitellum: thick sleeve encircling worm’s body 3 types of gland cells: mucus (copulation); egg capsule (cocoon) material; albumin (food) inside embryo
      • Terrestrial species: pores (with sphincter) connecting coelomic fluid to outside → moist film
      • Burrowing → peristalsis + chaetal anchoring
      • Feeding deposit feeders, detritivores, few predators (evertable pharynx)
    • subclass 2: hiudinoidea - leeches or blood-suckers
      • 3 orders, 14 families, 500 species
      • Mainly freshwater & marine sp & few semi- terrestrial
      • Body heteronomous, chaete few or absent
      • One posterior + 1 anterior sucker
      • Fixed number of segments (34 in true leeches)
      • Coelom reduced to interconnected channels → no septa
      • Thick dermal connective tissue layer beneath epidermis
      • Body divisible into 5 regions: 1) anterior (eyes, mouth + sucker); 2) pre-clittellar; 3) clitellar (visible only during reproductive period); 4) post-clitellar (central); 5) posterior (sucker)
      • Hermaphroditic
      • Embryo undergoes direct development
      • Locomotion → surface- dwellers, inchworm-type of movements (2-anchor points)
      • Feeding → mostly ectoparasites (blood-suckers → anti-coagulant hirudin); many free-living predators; some scavengers (dead animals)
    • No parapodia; chetae greatly reduced or absent
    • Hermaphroditic with clitellum (secretory organ for reproduction)
    • Homonomous body, except clitellum area

11. general body plan

    • metameric, triploblastic, coelomate and bilateria
    • elongated body - cylindrical (earthworms) or dorsally and ventrally flattened (leeches)
    • head - prostomium + peristomium (mouth)
    • terminal post-segmental pygidium - anus
    • segmentation: external rings, annuli + internal coelomic compartments separated by intersegmental septa
      • similar segments throughout = homonomous
      • segments specialized = heteronomous