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Animal Diversity—Part I
Introduction
Animals are a monophyletic group within the domain Eukarya. It is a morphologically diverse
group, composed of between 10 and 50 million species divided into at least 34 major lineages
(phyla). However, all animals share some common properties: they are heterotrophic,
multicellular, and actively motile at some point in their lifecycle.
Lab Organization
Body Plans
One fundamental way that animals can be categorized is by reference to their body plan, the
basic features of it’s structural and functional design. There are four major elements to the body
plan—the number of tissue layers (if any); the type of body symmetry (if any); presence/absence
of a fluid-filled body cavity; and the developmental patterns in the early embryo. One set of
stations in today’s lab will inform you about the different combinations of these features that
define the major groups of animals we will study in this course.
Functional Morphology
Another way to study animals is to focus on how their body form helps them to accomplish
basic life functions. The area of functional morphology evaluates the features or organisms with
reference to specific challenges of the environment. Key challenges for all animals include
respiration, feeding, locomotion/attachment, and reproduction. A second set of stations in today’s
lab will inform you about the myriad ways that animals have met these challenges over
evolutionary time.
Evolutionary Relationships
Because all animals are descended from a common ancestor, it is useful to organize the
diversity of animal groups using a phylogeny. By now you should expect that morphological
evidence does not always correspond to evolutionary relationships revealed by analysis of
molecular data. The attached phylogeny of some major animal groups on p. 2 can be found in
your text (Fig. 33.2). Some stations will look at this phylogeny in greater detail, explaining some of
the traits that are used to define the major groups, and asking you to hypothesize where you
would place additional important features.
Basal metazoan phyla
Because animals are quite diverse, we will not have time to investigate all 34 or so phyla of
animals. Instead, we will concentrate on a subset of phyla that illustrate the major evolutionary
lineages and key innovations in the Animalia. Today’s lab will emphasize the basal animals:
Phylum Porifera, Phylum Cnidaria, and Phylum Ctenophora. Stations will cover each of these
groups in superficial detail, highlighting some of their key features, including any
synapomorphies.
Lab Write Up
Your lab write up should include notes on the information at each station, as well as your
answers to any questions found in the station notes. You should also include relevant sketches or
diagrams to help you learn and remember the key concepts of today’s lab.
Finally, you should begin to record information about the basal animal phyla in the summary
table of animal features attached (pp. 3–4). Use this as a study aid for both lecture and lab, and
bring it with you next week as well. You will continue to work on this table during next week’s
laboratory session.
Phylum
Porifera
Cnidaria
Ctenophora
Platyhelminthes
Annelida
Mollusca
Nematoda
Arthropoda
Echinodermata
Chordata
Tissue layers
Symmetry
Body Cavity
Development
Body Support
Respiration
Locomotion/
Attachment
Feeding Mode
Reproduction
Unique traits
(synapomorphies)