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They develop by spiral mosaic cleavage
make a coelom by schizocoely
share a trochophore as the ancestral larval form.

Phyla include:

Members of phylum Annelida

Segmented worms living in marine, freshwater, and moist terrestrial habitats.

Marine bristle worms, leeches, and the familiar earthworms belong to this group.

15000 Species

Class Polychaeta

mostlly marine segmented worms; parapodia

Annelida Nervous System

Nervous system with a double ventral nerve cord and a pair of ganglia with lateral nerves in each segment

Brain a pair of dorsal cerebral ganglia with connectives to ventral nerve cord.

Where do Annelids Live

Marine, freshwater and terrestrial

Annelid Symmetry

Body bilaterally symmetical
often with distinct head.
metameric which means they have multiple speciallized segments.

Annelid Cell Type


Annelid Coelom

Coelom (Schizocoel) well developed and divided by septa, except in leeches; coelomic fluid functions as hydrostatic skeleton.

Annelid Digestive System

Digestive system is complete and not segmentally arranged.

Annelid Body

Epithelium secretes outer transparent moist cuticle.

Body wall with outer circular and inner longitudinal muscle.

Annelid Senses

Sensory system of tactile organs, taste buds, statocysts, photoreceptors cells, and eyes with lenses

specialization of head region into differentiated organs, such as tentacles, palps, and eyespots of polycaetes.

Annelid Reproduction

Asexual reproduction by fission and fragmentation

Capable of complete regeneration.

Annelid Sexs

Hermaphroditic or separate sexes

larvae are trochophore type

asexual reproduction by budding in some.

spiral cleavage and mosaic development

Annelid Excretory

Excretory system typically a pair of nephridia for each segment

Nephridia remove waste from blood as well as from coelom.

Annelid Gas Exchange

Respritory gas exchange through skin, gills, or parapodia.

Annelid Circulatory System

Circulatory system closed with muscular blood vessels and aortic arches for pumping blood, segmentally arranged

respiratory pigments often present

amebocytes in blood plasma.

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