Annelids, Mollusks and
Arthropods
Announcements
•There will be a quiz next lab that covers materials from
annelids and echinoderms.
•Assignment for this lab include page77, 78,79, 80 and 81
This lab.
•definitions
•Mollusks
•Annelids
•Arthropods
•Dissection of formaline-fixed earthworm and squid
•Examination of Grasshoppers,Crayfish
Phylogeny of protostome matazoans
Annelides
Mollusks
Arthropods
Closed vascular system
Trochophore larva lost
Mantle
Jointed appendage
Veliger larva
Exoskeleton
Radula
Metamerism
Trochphore larva
schizocoelom
Protostome mode of developement
Assumed ancestral character:bilateral symmetry, mouth and anus
Definitions
* Protostome (Schizocoelomate):
multicellular metazoans with a coelom formed by
splitting in the mesoderm layer
*Trochophore:
ciliated larval stage
*Metamerism:
body segmentation. Coelom in each segment is separated
from the other.Segmentation allow better control of body
movement and function.
*Serially homologous
structures share a common origin through segmental
duplication.
Definitions
*Mantle:
skirt-like epidermal enlargement that surround the
viscera and is responsible for synthesis of the shell
* Radula:
tongue-like structure formed by a belt of tissue covered
with chitinous teeth.
*Setae:
chitinous bristles on each segment used for burrowing.
*Jointed exoskeleton:
hard chitinous plates separated by flexible membranes
Annelids, Mollusks and
Arthropods
* Grouped together b/c they evolved three shared derived
characters
1- Trochophore larva
2- Schizocoelom
3- protostome mode of development
Mollusks
* They evolved
1- mantle
2- veliger larva (certain type of trochophore)
3- radula
*They feed on algae using the radula and exchange gases
using gills
*The foot (ventral mass of muscle) is used for locomotion
Radula
heart of a clam
mantle
Mollusks
They include
1-Polyplacophora (chitons)
-no distinct head
-8 shell plates
-large foot
2-Gastropoda (snails)
-distinct head
-spiral shell
-U-shaped gut
3-Bivalvia (clams, oysters)
- two parts shell
-filter feeders
Mollusks
4-Cephalopoda(octopus, squid)
-adapted for free swimming (jet propulsion of water)
-muscular mantle
-foot modified into multiple arms
(8 in case of octopus and 8+2 tentacles in squid)
-horny parrot-like beak adapted for predation
-squid eyes are analogous to vertebrate eyes
- the pen is a chitineous structure homologous to the
exoskeleton of the arthropods and anologous to the
notochord of vertebrates
Annelids
*they are
-metameric scchizocoels
-nerves, muscles, nephridial tubes
and blood vessels are serially
homologous
-closed vascular system
-appendages on each segment include
parapodia and/or setae
-well developed digestive system(crop,gizzard,
stomach and intestine)
-gas exchange through body surface
Annelids
They include
1-Polychaeta (marine fanworms)
2-Oligochaeta(earthworms)
3-Hirudinea(leeches)
-lost setae and move by
undulatory swimming
- it has some therapeutic indications
(venous congestion to areas with
good arterial supply)
Arthropods
* They are
-metameric schizocoel
-segmentation is less regular(fused or lost)
-lost trochophore larval stage
-modification of the appendages (sensing, collection of
food, grinding food, defense, transfer of gametes or
aeration
-ancestral open vascular system
-jointed exoskeleton
-complex gas exchange organs
-serially homologous appendages
Arthropods
* They include
1-Chelicerata (spider, mites and ticks)
-chelicerae
-cephalothorax and abdomen
2-Crustacea (lobsters, crayfish and crabs)
-aquatic
-2 pairs of antennae
-use mandibles to crush food
-gills
-head, thorax and abdomen
-biramous appendages
Arthropods
3-Uniramia (insects)
-unbranched appendages
-mouth with pair mandible and two pairs of maxillae
-pair of antennae
-branching gas-filled tubes
-head, thorax and abdomen
What should I do
1- dissect formaline fixed earthworm
2- dissect fresh squid
3- clams and grasshoppers also available
4-demo (live earthworm, leeches, hissing roaches)
5-Sonoran arthropod studies institute cart (bug cart)