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Phylogenetic tree of the animals
Transcript of Phylogenetic tree of the animals
Unicellular organism exist as single cells or if colonial, cell differentiation is minimal. Protozoans comprise several uncellular phyla that are not included within the Kingdom Metazoa (All other "invertebrate" phyla in this course are within the Kingdom Metazoa). While many other organism are unicellular, at least one group of protozoans is thought to have given rise to metazoans. Protozoans are not a monophyletic group (e.g. Choanoflagellata and metazoans have a more recent common ancestor than other protists), so they are perhaps best defined as "eukaryotes that aren't plant, animal, or fungus."
Phyla of uncertain
Diploblasts/Radiata are phyla with two well
organized tissue layers and are radially symetrical.
There is conflicting evidence on whether this is
a monophyletic group.
Morphological studies have traditionally considered the diploblast/radiata phyla as a paraphyletic group (with cnidarians more closely related to triploblast/bilateria phlya than to poriferans). However molecular studies suggest the cnidarians, poriferans, and ctenophores may be monophyletic, though this may be an artifact of computer analysis of molecular data know as 'long branch attraction (Garey and Schmidt-Rhaesa,1998). In any case, molecular data suggest that the Metazoa as a whole are a monophyletic group (Schutze, et al. 1998).
Metazoans are the kingdom of animals, hence they are:
* Motile at some stage of its lifecycle
* Diploid organisms with development proceeding via a blastula
Triploblasts/Bilateria are phyla with three well-organized tissue layers and are bilaterally symetrical.
This grouping (clade) of platyhelminthes, rotifers, and lophotrochozaa is based primarily on molecular similarities. The name "Spiralia" has been used to refer to this clade based on the presence of spiral cleavage during early development in many of its members. However, spiral cleavage occurs in some taxa not included in this group (e.g. some crustaceans), and does not occur in some within this clade (e.g. the Phoronids).
"Platyzoa" is a proposed name for the group of phyla that include Platyhelminthes and Rotifers, but the name implies a morphology (i.e. "flat") that is not representative of all organisms in this grouping (e.g. Rotifers). Molecular evidence supports this grouping.
Gnathifera share a similar, complex jaw structure (and supported by molecular evidence)
Syndermata possess a cuticle but do not molt (previously considered related to nematodes and the related minor phya). Rotifers and acanthocephlans are considered related because both possess a syncytial epidermis and a peculiar stiffening network of protein fibers (and is supported by molecular evidence)
Cycloneuralians have brains that encircle the pharynx like a collar. Cycloneuralia also share a loss of locomotory cilia
Cephalorhyncha have have a spiny proboscis which can be everted (turned inside out) to gather food using the spines
Lophotrochozoa comes from the names of the two major animal groups included: the Lophophorata and the Trochozoa. Some phylogenetic schemes include rotifers, platyhelminthes, and related pyhla in the Lophotrochozoa group.
Lophophorata possess a lophophore, a crown-shaped (circular or U) feeding appendage surrounding the mouth and bearing hollow (coelomic cavity) tentacles. Water is pulled down the center of the lophophore and this circulation is used for food-gathering and gas exchange. Anus lies outside of ring of tentacles.
Trochozoa share trochophore larval stage. Trochophore lava have two bands of cilia around the middle; at the "top" is a cluster of longer flagellae.
Ecdysozoans build a cuticle, an outer layer of organic material that functions as its skeleton and is flexible enough to function as joints where this layer is thin. Many members of this group regularly shed their cuticle, a process called ecdysis.
Panarthropoda share molting cuticle (as in other ecdysozoans), a repetition of paired limbs, and hemocoel. Molecular data also support a close relationship among the three phyla in this group.
Deuterstomes are characterized by:
-the mouth not derived from the blastopore
-radial indeterminate cleavage
-enterocoelous coelom formation
-dipleurula-like larval stage
Molecular evidence supports this grouping, though some evidence suggests that Xenoturbellida may basal deuterstomes or even basal metazoans.
Why study Inverts?
What is phylogeny?
Problems with the traditional phylogeny of animals
Why has it been so difficult to construct a phylogeny?
'Tools' to resolve this phylogeny
What does invertebrate phylogeny reveal about evolution and ecology?
Lectures by phylum
Click on link below lecture title name to go to the lecture outline
Click on link below phylum name to go to the lecture outline for that phylum
(How can we make sense of all this biodiversity?)
Recent studies suggest the Phylum Porifera may
be paraphyletic. See: