This document summarizes key characteristics of invertebrate phyla including molluscs, annelids, and arthropods. Molluscs are bilaterally symmetrical, coelomate animals with a mantle and muscular foot. They include gastropods, bivalves, and cephalopods. Annelids are also bilaterally symmetrical and coelomate, having setae that assist with movement. Examples include earthworms. Arthropods discussed include bean beetles, which lay eggs on beans that hatch into larvae in a few days before pupating and emerging as adults. An experiment is designed to test whether female beetles discriminate between bean types when laying eggs.

1.  From last week

2.  Invertebrates: No
backbone
 Acoelomates and
coelomates today

3.  Bilateral symmetry
 Three germ layers
 Organs
 Acoelomates
 Incomplete digestive system (one opening)
 Cephalization (concentration of sensory organs
and nerves in head)
 Some are hemaphrodites; Some are parasitic
 Planaria: Organ systems ladder-like
Advantage?

5.  Taenia pisiformism (view slides)

6.  Bilaterally symmetrical
 Three germ layers
 Cephalization
 Coelomate
 Mostly marine
◦ Some freshwater and terrestrial
 Visceral mass: includes internal organs
 Mantle: thin tissue
◦ Secretes shell in some molluscs
 Muscular foot for locomotion

7.  Gastropods: snails, slugs, nudibranchs
 Chitons
 Cephalopods: octopuses, squid
 Bivalves: oysters, mussels
 Today:
◦ Dissect a clam
◦ Dissect a squid
◦ Compare

10.  Segmented worms
 3 germ layers
 Bilateral symmetry
 Coelomates
 Cephalization
 Include leeches, earthworms
and marine worms
 Have setae to assist in
movement (bristles)
 Earthworms have clitellum for
reproduction
 Today: view earthworm model
◦ No dissection

12.  Phylum Arthropoda
 Herbivorous pests that live 1-2 weeks as adults
 Lay single eggs that change into larvae several
days later
 Larvae burrow into bean and pupate
 Emerge 24-36 hours later

13. Eggs on a bean

14.  Do female bean beetles discriminate between
types of beans when choosing a place to lay
eggs?
◦ Design your own experiment
◦ Collect results next week
 We will use a Chi Square to analyze our data
◦ Used to test an alternative hypothesis (Ha) vs. a null
hypothesis (Ho)
 Ha: There is a difference
 Ho: There is no difference

15.  Statistical test to test our hypothesis
 Test based on differences between the
observed results and the expected values
(based on null hypothesis)
 The formula for X2 is as follows:
◦ o is the observed frequency
◦ e is the frequency expected under the null
hypothesis of no difference between groups.

16.  20 snails
 2 sediments: mud and sand
Null hypothesis: There is no difference in
sediment preference for this species of snail.
 Expected results: 10 in mud, 10 in sand
 Actual results: 13 in mud, 7 in sand

17. Mud Sand
Observed 13 7
Expected 10 10
• Now you compare your experimental value (1.8)
to a critical chi2 value.

18.  Degrees of Freedom: the number of
independent cases
◦ (number of rows-1)(number of columns-1)
◦ (2-1)(2-1)=1 degree of freedom
 p level: level at which the given statistic is
on the border between rejecting or not the
null hypothesis
◦ Probability that values outside this set level are
due to chance sampling errors rather than real
differences
 Use p=0.05
◦ At p=0.05 you are 95% sure your results are real

19.  If test>critical
value @ p level,
reject null
hypothesis
 If test<critical
value @ alpha
level, fail to
reject null
hypothesis

20.  Week 1:
◦ Design your experiment
 Work first in your groups. Then we will come together as a class to
determine a final procedure
◦ Things to consider:
 How many beetles?
 How many different types of beans?
 Beetles were raised on mung beans
 How many beans of each type?
 How many replicates?
 Week 2
◦ Record results
◦ Compile class data
◦ Statistical analyses using class data
◦ Discuss lab report