Phylum: Rotifers and Nematodes

Advantages of having a body cavity:

  • Space for dev. of organs and organs systems
  • Body is more flexible, adv for locomotion
  • Gut can move ind. of the body wall
  • Fluid in the cavity allows for Hydrostatic Skeleton
  • Fluid in cavity protects internal organs
  • Fluid in cavity can act as a Transport/Circulatory System

Adv. of a True Coelom=Compartments

Phylum: Rotifera

Screen Shot 2017-10-16 at 10.58.37 AM.png

“Pair of rotifers”by Wikimedia Commons under CC by 2.0

Mastax: Crushing/grinding form and grasping, predatory forms

Some rotifer species consist exclusively of females

Circulatory System: Open

Use their body cavity fluid for internal transport


Diploid females–> Envi stimuli (meiosis)–> Haploid egg production–> haploid males–>haploid sperm production–> fertilization–>diploid resting eggs–>Envi stimuli (hatching)–>Parthenogenesis

-Freshwater, filter feed

Phylum: Nematoda

Screen Shot 2017-10-16 at 11.02.36 AM.png

“C.elegans”by Wikimedia Commons under CC by 2.0


  • Mostly free-living some notorious parasites
  • Psuedocoelomate
  • Open circulatory system
  • Complete digestive tract
  • Cuticle that is molted ( Nematodes are Ecdysozoans)
  • No specialized organs for respiration or excretion
  • Cephalization
  • Mostly dioecious (different sexes)
  • Exhibit Eutely


  • a non-cellular covering of collagen
  • Permeable to water and gases
  • Free-living nematodes must live in water or moist soil
  • Shed cuticle during dev. = Ecdysis (molting)
  • The Epidermis is syncytial

-Liquid in the psuedocoel functions as an open circulatory system

-No circular muscles, sinusoidal motion

Undulatory locomotion in a nematode

  • Complete digestive tract
  • Extracellular digestion
  • No specialized organs for respiration or excretion

Reproduction and Dev.

  • Mostly dioecious, copulate with internal fertilization
  • No morphologically distinct larval stage, young emerge from eggs as miniature adults
  • Chromosome diminuation
  • Eutely- constant number of cells

C. elegans

  • Model organism for dev. bio
  • A small cluster of homeobox genes specify cell fate along the A/P axis
  • Four homeobox genes similar to the HOM/HOX gene plus an additional less related homeobox gene make up the C. elegans Hox cluster
  • They are expressed in different positions along the A/P axis
  • Expressed during embryogens

Nematodes cause elephantiasis: caused by filarial parasites

Loa loa adults can be found in subcutaneous tissues in any part of the body as well as the eye. The females produces microfilaria and the vector for the disease is a fly of the genus Chrysops







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