I. Phylum Nemertea (Rhychocoela); ribbon worms



Дата24.04.2016
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Nemerteans
I. Phylum Nemertea (Rhychocoela); ribbon worms

A. 900 spp.

B. mostly benthic marine; three spp. fresh H2O in N. America & terrestrial
II. Morphology:

A. size: several mm to >20m; mostly ~20cm

B. anterior commonly pointed or spatula shaped

C. often brightly colored

D. body wall of connective tissue and thick musculature covered by epidermis.

E. epidermal cilia

F. mucus secreted by the cephalic gland

G. hydrostatic skeleton


III. Feeding:

A. carnivores

B. proboscis separate from the digestive tract.

1. rhynchocoel- houses the proboscis

2. stylet- calcareous barb

C. digestion- extracellular then intracellular


IV. Circulation & Excretion:

A. true contractile vessels lined w/ endothelium

B. protonephridia (Fig. 7-10)
V. Nervous System
VI. Reproduction & Development:

A. asexual- fragmentation

B. mostly dioecious- simple reproductive system

C. external fertilization



D. pilidium- ciliated larval phase
VII. Phylogeny- Nemerteans are believed to have shared a common ancestor with the flatworms.


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