BIOL 1030 – TOPIC 11 LECTURE NOTES Topic 11: Introduction to Bilateria, Protostomes, and Lophotrochozoans (Ch.
33)
I. Bilateria (clade)
A. have bilateral symmetry at some point in their life cycle
B. all are triploblastic
C. all the rest of the animal phyla that we will cover are in this group
D. traditional taxonomy note:
1. were once generally divided into acoelomates, pseudocoelomates, and coelomates
2. acoelomates and pseudocoelomates sometimes called lower bilateria
3. however, based on molecular evidence (sequencing of ribosomal RNA genes) it appears that
grouping into acoelomate, pseudocoelomate, and coelomate bilateria produces polyphyletic
groups, so we do not use it anymore
4. even so, the traditional taxonomy is so firmly entrenched that it is worth knowing about
E. Most members of Bilateria fall into one of two large clades, Deuterostomia (deuterostomes) and
Protostomia (protostomes)
F. we will cover one exception to the two main clades: arrow worms
II. Phylum Chaetognatha (arrow worms) [clade]
A. ~70 living species; abundant predators in marine plankton
B. coelomate
C. translucent
D. centimeter size range
E. arrow shape with head, trunk, and tail segments and septa between these
F. large eyes and powerful jaws in some
G. date back to 500 MYA in fossil record
III. Protostomia (clade)
1 of 2 BIOL 1030 – TOPIC 11 LECTURE NOTES A. most have spiral, determinate cleavage; coelom form from splits within mesoderm; and blastopore
become mouth
B. made up of two “sister taxa”: Ecdysozoa (molting) and Lophotrochozoa (non-molting)
IV. Lophotrochozoa (clade)
A. grow by extending the size of their skeletons; do not molt
B. group is unified mostly by genetic similarities and lack of molting
C. name comes from two things found in some animals in the group
1. lophophore
• feeding structure of ciliated tentacles with coelom within them
• found in three phyla: Ectoprocta, Brachiopoda, and Phoronida
2. trochophore
• larva with a ring of cilia around its middle
• used for swimming and feeding
• found in many lophotrochozoan phyla, such as Annelida and Mollusca
D. clade includes the following phyla that we will cover:
1. Ectoprocta (or Bryozoa; clade)
2. Platyhelminthes (clade?)
3. Rotifera (clade)
4. Annelida (clade)
5. Nemertea (clade)
6. Brachiopoda (clade?)
7. Phoronida (clade)
8. Mollusca (clade)
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