Features Shared by Nematoda With Related Groups


       Nematodes share a basic worm-like appearance with most other worms of different phyla.  Segmentation is what differentiates Annelida from Nematoda.  The difference between phylum Platyhelminthes and Nematoda is evident in their respective names; flatworms and roundworms.

        Nematodes share the pseudocoelom with rotifers and horsehair worms of the phyla Rotifera and Nematomorpha.  Horsehair worms Rotifers are very common aquatic animals distinguishable by their cilia crowned head and "wheel-like" appearance during cilia motion (Raven et al. 747).  More information on rotifers can be found here.     

        The feature of a pseudocoelom (a partial body cavity) is important in that it represents an intermediate step between total absence of a body cavity in unicellular organisms to a true coelom in more complex organisms.  Recently, however, features like the pseudocoelom have been questioned when used to group organisms together.  The nematode had previously been placed in the group Aschelminthes, which included the phyla Rotifera, Gastrotricha, Kinorhyncha, Priapulida and Nematomorpha (Poinar Jr. 19).

      Similarly, the cuticle is a structure that is present in arthropods and other ecdysozoans, a group in which nematodes are now generally placed.  The cuticle of the nematode is a rigid structure that must be shed before further growth can occur.  This process of molting is considered to be a link between nematodes and arthropods (Waggoner et al. 2004).  Moreover, the cuticle is often used to resolve phylogenetic issues within the phylum Nematoda.  However, according to Wilfrida Decraemer and her colleagues, the cuticle may have arisen independently within the phylum and cannot necessarily be used to determine relationships between very closely linked nematodes (Decraemer et al.  465).

      Finally, along with rotifers and tardigrades, Nematodes are able to undergo a process known as cryptobiosis where normal life processes and functions are suspended during periods of environmental instability and inhospitability (Waggoner et al. 2004)




Evolution & Phylogenetic Relationships

Features Shared by Nematodes with Related Groups

Features Unique to Nematodes

World Distribution of Roundworms

Nematode Habitat Use

Energy/Modes of Nutrition

Ecological Roles of Nematodes

Impacts on Human Society

References Page