13 April 2016
HMNH Exhibit on Arthropod Diversity
For this segment of the lab, we will take advantage of the side-by-side layout and the enormous arthropod diversity presented here. As you explore the exhibit, consider the following questions – which will also be useful as a review/study guide for the final exam. Discuss in small groups.
• In what ways is the wall phylogeny of the arthropods in strong or potential disagreement with our current understanding of arthropod relationships?
• Describe the tagmosis of the major arthropod clades – i.e., into how many regions is the body divided, and what is the name and major function of each tagma in this clade? For crustaceans, you may choose a decapod as your “idealized” form.
1 Lab 9: Tardigrada, Onychophora OEB 51
• Which of the major arthropod clades are well adapted to land, and how do they differ in their adaptations to terrestriality with respect to aquatic ones? Consider respiratory, locomotory and excretory systems. Are there groups that were more successful on land than others? Why?
• Distinguish between biramous and uniramous limbs in theoretical terms, and give specific real examples of each. What, functionally, is the utility of a biramous appendage? Why do few terrestrial arthropods possess biramous appendages?
2 Lab 9: Tardigrada, Onychophora OEB 51
• Compare the anterior segments of the major arthropod groups and explain their homology. Also describe the relationship between the three anterior-most pairs of ganglia and the appendages they innervate in each group.
• How is growth in an organism with ecdysis? Is it a continuous process?
3 Lab 9: Tardigrada, Onychophora OEB 51 Tardigrada Water bears are divided in to two main groups: Eutardigrada and Heterotardigrada. Today we have live specimens of both groups! (Courtesy of Dennis Persson, postdoc at the Giribet Lab) Choose one species and start by looking at them moving under the dissecting scope. Then pipette CHOOSE ONE one specimen out and make a wet mount to look closer at its anatomy (clay feet not necessary, but might help to change the position of the animal).
• Echiniscus testudo, an orange Heterotardigrade • Hypsibius dujardini, a transparent Eutardigrade
Make an illustration of the entire animal, showing the regionalization of the gut, the position of the mouth and anus, and whatever internal anatomy is visible. Use the 100x lens with immersion oil (ask for it) to get a good view of the oral stylet and the claws, and draw. Exchange slides with a classmate to take a quick look at differences between the two groups.
4 Lab 9: Tardigrada, Onychophora OEB 51 Onychophora We have several preserved specimens of Onychophora from both the family Peripatidae and the family Peripatopsidae. One of these families has body pigment insoluble in ethanol – can you guess which? CHOOSE ONE
Choose one species and draw the external morphology. Orient the specimen to get a good ventral view of the head, and distinguish the antennae, the slime-spitting oral papillae, the jaws and the first pair of legs. What are the openings in the posterior end?