Lecture 19 Key Concepts/Terms

what did the common ancestor of mollusks look like?

the ancestor to all is some sort of unsegmented worm

visceral mass (mollusks)

contains internal organs, excretion, and reproduction

foot (mollusks)

used for locomotion

mantle (mollusks)

secretes the shell and covers the gills

cephalization in mollusks

cephalopods and gastropods have a distinct head
bivalves=no head
chitons have mouth parts but no head
mollusks have variable levels of cephalization

radula

An organ covered with teeth that mollusks use to scrape food into their mouths

mollusk reproduction

cross fertilization common in all mollusks
gastropods - internal fertilization
bivalves and many gastropods - hermaphroditic
some sea slugs and oysters can change their sex

Polyplacophora (chitons)

bodies with 8 dorsal plates
herbivorous
some have internal fertilization and internal digestion
typically live in shallow water

gastropods

snails and slugs
some free-swimming, others creep
tentacles are common
chemo or mechano-sensing eyes
the only terrestrial mollusks

bivalves (oysters, clams)

ligaments hold shells closed
most filter feed
have incurrent and excurrent syphons
sedentary adults
free-swimming larvae

incurrent and excurrent syphons

Extract small organisms form water and bring into body through incurrent syphon
Exit through excurrent syphon

cephalopods (octopus, squid, nautili)

marine predators
arms and tentacles
color changing
jet propulsion
highly intelligent

what makes an ecdysozoan?

they grow by molting
monophyletic

nematodes (roundworms)

pseudocoelomates
typically parasitic
separate sexes (not hermaphroditic)
hydrostatic skeleton

eutely

condition of a body composed of a constant number of cells or nuclei in all adult members of a species, as in rotifers, acanthocephalans, and nematodes

model organisms

organisms studied by many different researchers so they can compare their results and determine scientific principles that apply more broadly to other species
ex.) fruit flies

horsehair worms

parasites of arthropods
only 350 species
variable length
either free-living or parasitic
adults may not eat

paired appendages

arthropods and their relatives are a monophyletic group united by having what?

Water bears (tardigrades)

fleshy appendages
extremely small
can be dormant for long periods

ecdysozoan

protostome characterized by periodic molting of their exoskeleton, includes the roundworms and arthropods.

lophotrochozoans

Brachiopods
Mollusks (chitons, bivalves, gastropods and cephalopods)
Annelids

velvet worms

closely related to arthropods
terrestrial
segmented bodies
fleshy, unjointed bodies
external cuticle containing chitin
internal fertilization and egg development

what did the common ancestor of the arthropods probably look like?

a velvet worm

species richness in arthropods

arthropods are 2/3 of all species

trilobites

early arthropod that lives during the Paleozoic era
had jointed appendages

four groups of arthropods

arachnids
crustaceans
myriapods
insects

jointed appendages

head, thorax and abdomen in arthropods

exoskeletons in arthropods

from excreted chitin and protein, what muscles are
attached to, new one is grown under one that shed

molting in arthropods

new skeleton grows under the old one and the old one sheds

limitations places on organisms with exoskeletons

the organism stays small because of the exoskeleton
the exoskeleton must get thicker to be able to hold weight

arachnids

mouthparts - chelicerae
no antennae or wings
8 legs
spiders, scorpions, mites

myriapods

mouthparts - mandibles
bodies consists of head and repeated segments
some have variable tail segments
single antennae pair, no wings
centipedes and millipedes

crustaceans

mouthparts - mandibles
two pairs of antennae
5 pairs of legs, some front pairs modified into claws
shrimp, lobsters, crabs, pill bugs

insects (hexapods)

mouthparts - mandibles
bodies have three regions
one pair of antennae
6 legs
most have two pairs of wings

slugs

gastropods which look like snails without shells

snails

Gastropods

Nudibranchs

marine gastropods that lack a shell (sea slugs)

clams

Bivalve mollusks / most their life buried in sand or seafloor or riverbeds

mussles

a mollusc with a black shell that can be eaten.

oyster

marine mollusks having a rough irregular shell

scallops

Types of mollusks called bivalves. These have many eyes and can swim.

octopus

a cephalopod mollusk with eight sucker-bearing arms, a soft saclike body, strong beaklike jaws, and no internal shell

squid

Cephalopod with a pen that serves as support; can change from red to gray; some deep living ones are huge

Nautilius

cephalopod

E) B and C

This is a picture of a/an:

A) an insect
B) an arthropod
C) an arachnid
D) A and B
E) B and C

Which of the following statements about mollusks is TRUE?

A) All mollusks have radulae
B) Some mollusks, but not all, have a variation of the 3-body part plan
C) Some mollusks, but not all, show signs of cephalization
D) Digestive organs typically form a cluster called the mantle
E) Cephalopods have lost their muscular foot

C) Some mollusks, but not all, show signs of cephalization