Annelid

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Gen. char. of Annelids

1. Segmentation

-Body segment marked by circular groove (annuli)

-Repitition organ (metamere)

-Septa seperate segment

2. Setae

-Tiny chitinous bristle

-Absent in leeches

-Short setae anchor segment in earthworm- prevent it frm slipping bckwrd

-Long setae help aquatic worm swim

2. Body wall

-Head composed o prostomium n perstonium

-Terminan portion (pygidium)

-Head n pygidium not metamere

-Strong circular n longitudinal muscle underlies body wall

4. Coelom

-Forms by schizocoely

5. Hydrostatic skeleton

-Ceolom filled w fluid serve as hydro. skele.

-Fluid vol. remain constant

-Longitudinal muscle (shorten,expand)

-Circular muscle (narrow,lengthen)

-Peristalsis (allow eficient burrowing)

-Undulatory (swimming annelid)

Class Polychaeta

-Largest class o annelids

-More specialized o sensory organ than in cilliates

-Tolerate wide range o salinity

-Warmer region have more frshwater polyc.

-Some live in crevices,tube/pelagic

-Importance in marine food chain

-Well-differentiated head w sense organ

-No clitellum

-Many setae arranged in bundle o parapodia

-Sedentary : tube-living

-Errant : free-moving,burrow,crawl

*Nutrition

-Polyc have foregut,midgut,hindgut

-Foregut (stomeduem,pharynx,anterior,esophagus lined w cuticle

-Midgut derived frm mesoderm (secrete enzyme n absorb nutrient)

-Short hinddgut derived frm ectoderm n leads to anus

*Circulation n Respiration

-Parapodia n gills for gaseous exchnge

-others use body surface

-In nereis

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