Invertabrate zoology

Sipunculans, echiuroids, and priapulids were grouped together in a phylum called Gephyrea.
The Gephyrea were thought to represent a link between annelids and holothuroids. Most
zoologists consider these three groups to be separate phyla with little direct relationship to
each other. Nevertheless, the Zoological Record retained the concept until 1950, and the
Gephyrea is still retained by some zoologists. How are these three groups similar, and how
could they possibly be considered related to the annelids and holothuroids? Why do you think
most systematists separate the phyla, and to what extent should they be separated?
2. The origin of the chordates is one of the most obscure, and, accordingly, controversial
argument in metazoan systematics. The position of the hemichordates is especially notorious.
Some argue that they are no closer to the chordates than they are, say, to the echinoderms.
Some scientists propose that they share features in common with both the Chordata and the
Echinodermata. To what extent do the hemichordates represent a link between echinoderms
and the chordates? How might you derive a chordate from an echinoderm via a hemichordate?
Choose one of the two following questions (33 points).
3. The Bryozoa is the only phylum in which all members are colonial. What are the
morphological and demographic consequences of coloniality in this group, and how have these
consequences influenced the distribution and abundance of bryozoans? How have these colonies
coped with predation, competition, and various environmental stresses that go along with being a
colonial animal?
4. The Lophophorates comprise 3 (or 4 depending on sources), major phyla that were all united
based on the morphological feature of a lophophore, cell division patterns, formation of the
blastopore, and cell fate. Recently, modern molecular data has shown that these phyla do not
necessarily group together, nor are they closely related on one another. Give evidence of
whether you support the ideas that the lophophore and other developmental features are
synapomorphic characteristics that group these phyla together, or is a result of convergent
evolution among all or some of the phyla.
Choose one of the two following questions +
5. The presence/absence of a coelom (at least at some point during the life cycle), type of cell
division, blastopore formation, and cleavage patters are considered to be traditional features of
a number of invertebrate phyla. In recent years, the usefulness of these criteria as a unifying
feature for metazoan evolution has been questioned on several grounds. Discuss the values and
dangers of using any or all of these morphological characters as well as molecular data, as
systematic characters for the evolution of all invertebrate taxa.
6. The fossil record provides enormous amounts of information regarding the evolution of
various metazoan taxa. In particular, echinoderms have an extensive fossil record, with many
key morphological features still evident in extant taxa. What are the pros and cons of using
morphological features derived from this form of data, and why or why not is this information
valuable to taxonomists when comparing extinct versus extant taxa such as the Crinoids?
And the final question:
7. What is Nish’s favorite invertebrate

 
ORDER THIS ESSAY HERE NOW AND GET A DISCOUNT !!!