Lecture 19: Animals Pt. 2

Question 1

what did the common ancestor to mollusks look like?

Answer 1

-an unsegmented, marine worm

Question 2

visceral mass on a mollusk

Answer 2

-it holds the organs, what you can eat

Question 3

foot on a mollusk

Answer 3

• muscular, for locomotion or anchoring
• can be used for food capture and can also excrete mucus
• in cephalopods, its been divided into tentacles

Question 4

mantle on a mollusk

Answer 4

• thickened sheet of skin that covers respiratory organs and creates shell
• mollusks have them even if they don’t have a shell

Question 5

cephalization in the mollusks

Answer 5

-some have very pronounced heads, some have no heads at all (so varying levels of cephalization)

Question 6

radula

Answer 6

• specialized mouthparts, scrape stuff off of rocks to eat

- some have been modified into drills to bore through others shells

Question 7

mollusk reproduction

Answer 7

• many are hermaphroditic, and some have different sexes but can change sex
• land ones often use external fertilization
• marine ones often use external fertilization

Question 8

polyplacophora

Answer 8

• aka chitons
• -herbivorous
• typically live in shallow waters (inter-tidal zones)
• most use external fertilization, some use internal and some even develop their embryos internally

Question 9

gastropods

Answer 9

types: snails, nudibranchs, and slugs
- some creep along and others free swim
- tentacles are common (used for eyes and chemo-/mechano- sensing).
- most are marine

Question 10

bivalves

Answer 10

• marine and freshwater
• ligament holds shell closed and most filter feed
• have in-current (brings stuff in) and ex-current (water and gametes out) syphons
• free swimming larvae, external fertilization
• types: mussels, oysters, scallops, clams

Question 11

cephalopods

Answer 11

• exclusively marine
• active predators
• they have arms and tentacles
• are coloring changing and use jet propulsion
• are highly intelligent and have a highly developed nervous system/eyes
• types: octopus, squid, nautilus

Question 12

what makes an ecdysozoan?

Answer 12

• they grow by molting

- monophyletic

Question 13

molting

Answer 13

-have a hard outer covering (aka exoskeleton)

Question 14

nematodes

Answer 14

• aka roundworms
• species rich, pseudocoelomates
• typically parasitic and have separate sexes
• hydrostatic skeleton and can also be active predators -have complete guts and are covered by a protective cuticle (which they shed 4 times)
• have lateral muscles and are eutley
• types: hookworms, pinworms

Question 15

eutley

Answer 15

-adult has a fixed number of cells, makes it nice for us to study them and then compare it to other organisms

Question 16

model organisms

Answer 16

-define the way we study a certain topic or field

Question 17

horsehair worms

Answer 17

• ecdysozoan
• larvae and adults are very different and they range widely in length
• almost all are freshwater and the adults have no mouth and a non-functioning gut
• we think they may only feed as larvae.

Question 18

water bears

Answer 18

• extremely small and live on sand/water film on plants

- can remain dormant for a very long time and ecdysozoan

Question 19

onychophorans

Answer 19

• aka velvet worms
• completely terrestrial (only one)
• closely related to arthropods
• have segments and are unjointed
• external cuticle contains chitin
• have internal fertilization and egg development
• ancestor to arthropods probably looked like it

Question 20

species richness in arthropods

Answer 20

-2/3rds of all species on Earth are arthropods (and most of those are insects)

Question 21

trilobites

Answer 21

• had jointed appendages and heavy exoskeletons

- they were fossilized which lets us see this (also had heads)

Question 22

jointed appendages and body segments in arthropods

Answer 22

body segmented into head, thorax, abdomen

-body plans are dominated by jointed appendages which is good bc they can extend and retract

Question 23

exoskeleton in arthropods

Answer 23

• have them, made from excreted chitin and protein (it’s what the muscles are attached to)
• they then grow a new skeleton under the old one. -the Exoskeleton has to get thicker as the muscles get bigger, that’s why they stay relatively small

Question 24

molting in the arthropods

Answer 24

-old skeleton pops open, arthropod puffs itself up to make the new exoskeleton harder, but he’s very vulnerable at this point so he goes into hiding

Question 25

4 groups of arthropods

Answer 25

• arachnids
• myriapods
• crustaceans
• insect

Question 26

arachnids

Answer 26

• have chelicerae as mouth parts, four pairs of legs

- types: ticks, spiders, scorpians

Question 27

myriapods

Answer 27

• mouth parts are mandibles
• bodies consist of head and one pair of antennae and repeated segments
• types: centipedes (one pair of legs on each segment), millipedes (some segments have 2 pairs of legs)

Question 28

Crustacean

Answer 28

• mouth parts are mandibles
• 2 pairs of antennae
• fertilized eggs stay attached to female body
• three part bodies
• types: Shrimp, lobster, crab

Question 29

insects

Answer 29

• mouth parts are mandibles
• bodies have three regions (1 pair of antennae, 3 pairs of legs, very successful!) -types: grasshopper, pill bug, fly, dragonfly