Tardigrada Classification Essay


Scientific Name: Hypsibius dujardini
Common Name: Tardigrade (Water Bear)

Domain - Eukarya
    Kingdom - Animalia
        Phylum - Tardigrada
            Class - Eutardigrada
                Order - Parachela
                    Family - Hypsibiidae
                        Genus - Hypsibius
Species - Hypsibius dujardini

Domain Eukarya: The Hypsibius dujardini is considered to be part of the domain Eukarya because its cells have a cell membrane, nuclues, among many other organelles (Eisenhour et al 2012).

Kingdom Animalia: Members of the Kingdom Animalia are multicellular organisms that are usually heterotrophic. Also most members of the kingdom Animalia ingest their food before they digest it (Eisenhour et al 2012).

Phylum Tardigrada: Members of this phylum are hydrophilous micrometazoans (Thorp et al 2010). They also have a bilaterally symmetrical body and occupy many different extreme and varying habitats (Halberg et al 2009).

Class Eutardigraga: Differentiates from other classes of tardigrades because of the absence cuticular cephalic cirri. In short these are cirri A. This class of tardigrade primarily lives in freshwater or terrestrial environments (Thorp et al 2010).

Order Parachela: Our Tardigrade falls into the order of Parachela because of the spiral structure of the buccal tube or feeding tube. This spiral structure allows these tardigrades to store more food in their buccal tube (Thorp et al 2010).

Family Hypsibiidae: The presence of interanl and external claws together is what seperates this family of tardigrades from the other 21 families in this phylum (Thorp et al 2010).

Genus Hypsibius: The Hypsibius genus of the tardigrades are freshwater and terrestrial. Also these tardigrades have a place for the insertion of muscles stylets on the anterior part of their mouth. (Thorp et al 2010)

Species Hypsibius dujardini: The species we are studying are defined by their endomesodermal pouches, this show that these tardigrades exhibit body segmentation in their embroys before they are born. This trait is unique to these tardigrades (Thorp et al 2010).


The Cambrian fauna can now reasonably be seen as containing many taxa that lie in the stem-groups of the extant phyla. As such, these fossils suggest how both the ‘body plans’ of extant phyla were assembled, and also how various ‘minor’ phyla relate to the larger groupings of today such as the arthropods and annelids.

The various arthropod and lobopod taxa of the Cambrian faunas have been controversial and have generally been considered either as lying in the crown or (occasionally) stem groups of the euarthropods, onychophorans and tardigrades. However, phylogenetic analysis strongly suggests that many of even the most euarthropod-like taxa do not lie within the euarthropod crown-group but are more basal. Further, the commonly expressed view that Cambrian lobopods are in effect stem- or crown-group onychophorans also seems not to be well supported. Lobopods in the Cambrian appear to be diverse and not particularly closely related to one another, and certainly cannot be combined in a monophyletic clade.

Both these advances offer hope that the tardigrades (placed as the sister group to the euarthropods in many analyses of extant taxa, here collectively named the Tactopoda) may be more closely related to some of these Cambrian taxa than others. The challenge for both neontologists and palaeontologists is to refine the systematic analysis of both living and fossil taxa in order to maximise the usefulness of the (admittedly few) characters that unite tardigrades to their Cambrian forbears.

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