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57 Cards in this Set

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What are the main defining features of an animal?
nutrition, cell structure, tissues, life history, and Hox genes
What is special about animal nutrition?
Animals are multicellular eukaryotic chemoheterotrophs that ingest other organisms or organic material for energy.
What is special about animal cells?
They lack cell walls, and are instead held together by proteins like collagen, with intercellular junctions (tight junctions, desmosomes, and gap junctions) also held together by structural proteins.
What is special about animal tissues?
They have nervous and muscle tissue.
What is special about animal life histories?
Animals mainly reproduce sexually, with the diploid the dominant stage, with a small flagellated sperm fertilizing a stationary egg. After that, the zygote cleaves into a hollow 1-cell-thick bastula (sphere) of cells, after which gastrulation puts some of these cells on the inside. In addition, some animals have larval (sexually immature) stages before undergoing metamorphosis.
What is a gastrula?
A stage of eumetazoan life histories, it contains an outer cell layer called the ectoderm, an inner cell layer called the endoderm, with the blastocoel between ectoderm and endoderm, a body cavity inside the endoderm called the archenteron with a hole to the outside called the blastopore.
What is special about animal genetics?
Hox genes, only found in animals, are homeoboxes (gene-regulating genes) found in genes coding for body form development.
Describe the ancestor of the animal kingdom.
likely a colonial, flagellated protist closely related to choanoflagellates
Is the animal kingdom monophyletic or paraphyletic?
monophyletic
How many animal phyla are there?
35
What are the two trees of animal life?
The traditional tree is based on anatomy and embryology, while the newer tree is based on molecular systematics.
What are grades in phylogeny?
major branches that separate animals based on body plans
What are the first two grades in the traditional phylogenetic tree of animals?
Parazoa and Eumetazoa
What distinguishes Parazoa from Eumetazoa?
Parazoans (sponges) lack true tissues, while eumatazoans have them.
What is the second set of grades in the traditional phylogenetic tree of animals?
Radiata and Bilateria, in Eumetazoa
What distinguishes Radiata from Bilateria?
Radiata have radial symmetry (rotationally symmetric in one direction), while bilateria have dorsal (top), ventral (bottom), anterior (head) and posterior (tail) sides, as well as left and right.
What is cephalization?
an evolutionary trend in bilateria to concentrate sensory organs and often a central nervous system in the anterior end (the head)
What are most radiata mobility-wise?
sessile benthos or plankton
What is different between the embryonic development of radiata and bilateria?
Bilateria have a mesoderm, a third germ layer between ectoderm and endoderm that develops into muscles and other non-digestive organs, making them triploblastic, unlike radiata which are only diploblastic.
What phyla are in Parazoa?
just Porifera (sponges)
What phyla are in Radiata?
Cnidaria (jellies, corals, anemones) and Ctenophora (comb jellies)
What is the third set of grades in the traditional phylogenetic tree of animals?
Acoelomate, Pseudomoelomate, and Coelomate, within Bilateria
What phyla are in Acoelomates?
just Platyhelminthes (flatworms)
What defines Acoelomates?
They lack a cavity between the digestive tract and outer body wall, making their bodies solid.
What distinguishes Pseudocoelomates from Coelomates?
Coelomates have a true coelom, a body cavity completely lined with mesoderm-derived tissue, while pseudocoelomates have only part of their body cavity lined with mesoderm-derived tissue.
What phyla are in Pseudocoelomates?
Rotifera (rotifers) and Nematoda (nematodes)
What functions can a body cavity have?
cushion organs for protection, act as skeletons in forcing structure, and let organs and skin act independently
What is the fourth set of grades in the traditional phylogenetic tree of animals?
Protostomia and Deuterostomia, within Coelomates
What phyla are in Protostomia?
Mollusca (clams, snails, octopi), Annelida (segmented worms), and Arthropoda (crustaceans, insects, spiders)
What phyla are in Deuterostomia?
Echinodermata (sea stars, sea urchins) and Chordata (lancelets, tunicates, vertebrates)
What distinguishes Protostomia and Deuterostomia?
cleavage, coelom formation, and blastopore fate
How does cleavage distinguish protostomes from deuterostomes?
With exceptions, protostomes undergo spiral cleavage, in which smaller cells are put in the grooves between larger cells, and determinate cleavage, when every cell in early stages is vital to proper development. Meanwhile, deuterostomes undergo radial cleavage, in which the planes of cell division are parallel or perpendicular to an axis, and indeterminate cleavage, which means that each cell of small embryos has the ability to develop into a fully-formed individual, making identical twins and stem cells possible.
How does coelom formation distinguish protostomes from deuterostomes?
In the gastrula stage, protostomes show schizocoelous development, in which separate masses of mesoderm form the coelom, while deuterostomes show enterocoelous development, in which the coelom-forming mesoderm is initially attached to the archenteron.
How does the fate of the blastopore distinguish protostomes from deuterostomes?
The blastopore becomes the mouth of protostomes and the anus of deuterostomes, while another cavity forms to serve the other purpose.
In general, how does molecular systematics establish phylogenies?
It establishes clades, which are monophyletic divisions of organisms more closely related to each other than to anything else. It does this by looking for unique monomer sequences in genes and their products (polypeptides).
What is the phylogenetic tree of animals based on?
small subunit ribosomal RNA, supported by the Hox genes that have been sequenced
What do the two phylogenetic trees of animals share?
The deepest branches (Parazoa-Eumetazoa and Radiata-Bilateria) agree, and the deuterostome clade is monophyletic in both.
What are the main ways the two phylogenetic trees differ?
the existence of two main protostome clades, relocation of the acoelomates and pseudocoelomates into Protostomia, and assignment of the Lophophorate phyla.
What are the two clades in Protostomia in the molecular systematics phylogenetic tree?
Lophotrochozoa and Ecdysozoa
Why are annelids more closely related to mollusks rather than arthropods in the molecular systematics phylogenetic tree?
Besides the molecular data, both go through a trochophore larva stage.
What animals are in Ecdysozoa?
nematodes, arthropods, and any other protostomes that secrete exoskeletons, getting bigger and bigger (the shedding of old ones is called ecdysis)
What are the lophophorate phyla?
Bryozoa (bryozoans), Phoronida (phoronids), and Brachipoda (brachiopods)
Where are the lophophorates phylogenetically?
They share some characteristics with deuterostomes and protostomes, but molecular data indicates they are protostomes in Lophotrochozoa.
Where does Lophotrochozoa get its name?
by sticking the lophophorates and trochophore larva together
When did the animal phyla arise?
between 565 and 525 million years ago, in the late Precambrian and early Cambrian
What is the period before the Cambrian?
the Ediacaran period, named for the Ediacara Hills in Australia
What evidences suggest a date much earlier than the Cambrian for the diversification of animals?
Paleontologists have found what could be burrows of animals in rock that's 1.1 billion years old, and molecular systematics agrees.
What animal forms are found in Ediacaran rock?
animals similar to cnidarians or hydras, soft-bellied mollusks, and burrows and tracks made by worms
What is the Cambrian explosion?
the sudden appearance of nearly all major animal body plans in Cambrian rocks between 543 and 525 million years ago
Where has the Cambrian explosion been documented?
Burgess Shale, British Columbia; Greenland and Yunnan, China which are more than 10 million years earlier
Are the fossils found in Cambrian rock more often classified as extinct or extant?
extant
What are the three main hypotheses for why the Cambrian explosion happened?
ecological, geologic, or genetic causes
How could ecological causes have resulted in the Cambrian explosion?
Predator-prey relationships developed, leading to greater selective pressures and diversification.
How could geological causes have resulted in the Cambrian explosion?
Atmospheric concentration of oxygen (for example) reached a high enough level to support active metabolism by animals.
How could genetic causes have resulted in the Cambrian explosion?
Hox genes allowed the diversity in morphology at the embryonic level (evo-devo).
What does molecular data have to say about the Cambrian explosion?
Since the lophotrochozoans, ecdysozoans, and deuterostomes each have difficult-to-resolve molecular relationships (they all branched out at once), the Cambrian explosion was really three explosions, one for each of those clades.
Did any additional phylum-level animal evolution go on after the Cambrian explosion?
No, but changes did occur within phyla.