Phylum Annelida- the segmented worms

Phylum Annelida-Constrained body plan

hydrostatic skeleton

Muscles surround ______which function as

coelom, which
functions as a hydrostatic
skeleton

Mesenteries

hold blood vessels
and gut in place and divide each
coelomic cavity in 2 halves

Septa

separate coelomic cavities between segments

segment is thin

Circular muscles contracted

Segment is fat

Longitudinal muscles contracted

Class Polychaeta

Tube-dwelling (Sedentaria)
species often have complex
structures for filter-feeding

Class Polychaeta-
parapodia

Bear paired outgrowths of body wall

Hydrothermal vent worms

-Class Polychaeta
-Adults lack a mouth

-symbiotic (mutualistic): anaerobic bacteria that live in their
trophosome

trophosome

Remnant gut called filled with bacteria

Bacteria in trophosome are

chemoautotrophic (they use the energy from the oxidation of hydrogen sulfide (HS- ) to fix CO2 and form sugar.)

Annelids Clade

Clade Clitellata

Annelids within the Clitellata
have a

clitellum
c

clitellum

a band of
secretory cells in the
epidermis involved in mucus
secretion during reproduction

Annelids in this clade lack

parapods and have few or no chaetae (setae).
They are hermaphroditic and have
yolky eggs with direct development.

Class Oligochaeta

many terrestrial and freshwater
species, including earthworms

Class Hirudinea

the leeches, found in all habitats, including terrestrial

Bristles and function

(=chaetae, setae) used for locomotion or burrowing