The Invertebrates – Annelid Worms
Phylum Annelida (e.g. earthworms & leaches):
Diverse group of segmented worms
Marine, freshwater, and terrestrial environments
Polychaetes, Oligochaetes and Hirudinea
About 15,000 known species
Body metamerically segmented
Body wall with outer circular and inner longitudinal muscle layers
Outer transparent moist cuticle secreted by epithelium
Chitinous setae, often present on fleshy appendages called
parapodia
Coelom well developed and divided by septa
Coelomic fluid supplies turgidity and functions as hydrostatic
skeleton
Blood system closed and segmentally arranged, with respiratory
pigments (e.g. haemoglobin)
Digestive system complete and not metamerically arranged
Respiratory gas exchange through skin, gills, or parapodia
Excretory system typically a pair of nephridia for each metamere
, Closed circulatory system:
Nervous system with a double ventral nerve cord and a pair of
ganglia with lateral nerves in each metamere
Brain is a pair of dorsal cerebral ganglia with connectives to cord
Sensory system of tactile organs, taste buds, photoreceptor cells,
and eyes with lenses (in some)
Hermaphroditic or separate sexes, asexual reproduction by budding
in some
Main annelid groups:
Polycheata (e.g. ragworms) – many chaetae. Paraphyletic.
Oligochaeta (e.g. earthworms) – few chaetae
Hirudinea (e.g. leaches) – probably a group within the oligochaetes,
really
Class Polychaeta:
The polychaetes is the largest class, 10.000 species, most marine
A well-differentiated head with specialised sense organs
Paired, paddle like appendages (parapodia) on most segments
Sexes are separate, hatch into a planktonic larva, which later
metamorphoses into a juvenile annelid
Example: Nereis (the ragworm)
Life habits:
Errant (free moving) e.g. Nereis and Aphrodite (sea mouse)
Sedentary, burrowers e.g. Arenicola (lugworm)
Sedentary, tube formers: a) Filter feeders e.g. Sabella. Serpulid, b)
Nutrition from endoymbiotic bacteria e.g. Riftia pachyptila
Tube-living annelids:
Tube-living, deposit-feeding annelids
Phylum Annelida (e.g. earthworms & leaches):
Diverse group of segmented worms
Marine, freshwater, and terrestrial environments
Polychaetes, Oligochaetes and Hirudinea
About 15,000 known species
Body metamerically segmented
Body wall with outer circular and inner longitudinal muscle layers
Outer transparent moist cuticle secreted by epithelium
Chitinous setae, often present on fleshy appendages called
parapodia
Coelom well developed and divided by septa
Coelomic fluid supplies turgidity and functions as hydrostatic
skeleton
Blood system closed and segmentally arranged, with respiratory
pigments (e.g. haemoglobin)
Digestive system complete and not metamerically arranged
Respiratory gas exchange through skin, gills, or parapodia
Excretory system typically a pair of nephridia for each metamere
, Closed circulatory system:
Nervous system with a double ventral nerve cord and a pair of
ganglia with lateral nerves in each metamere
Brain is a pair of dorsal cerebral ganglia with connectives to cord
Sensory system of tactile organs, taste buds, photoreceptor cells,
and eyes with lenses (in some)
Hermaphroditic or separate sexes, asexual reproduction by budding
in some
Main annelid groups:
Polycheata (e.g. ragworms) – many chaetae. Paraphyletic.
Oligochaeta (e.g. earthworms) – few chaetae
Hirudinea (e.g. leaches) – probably a group within the oligochaetes,
really
Class Polychaeta:
The polychaetes is the largest class, 10.000 species, most marine
A well-differentiated head with specialised sense organs
Paired, paddle like appendages (parapodia) on most segments
Sexes are separate, hatch into a planktonic larva, which later
metamorphoses into a juvenile annelid
Example: Nereis (the ragworm)
Life habits:
Errant (free moving) e.g. Nereis and Aphrodite (sea mouse)
Sedentary, burrowers e.g. Arenicola (lugworm)
Sedentary, tube formers: a) Filter feeders e.g. Sabella. Serpulid, b)
Nutrition from endoymbiotic bacteria e.g. Riftia pachyptila
Tube-living annelids:
Tube-living, deposit-feeding annelids
