1. The Animal Clade Extant
Platyhelminthes
acoelomates
Arthropoda
Annelida
Mollusca
protostomia
Nematoda
Rotifera
pseudo-coelomates
Hemichordata
Echinodermata
Porifera
parazoa
Cnidaria
Chordata
deuterostomia
coelomates
radiata
This cladogram omits several smaller animal phyla!
bilateria
eumetazoa (true tissues)
loss of chloroplast, colonial organization
Ancestral Choanoflagellate

2. Domain Eukarya Kingdom Animalia Phylum Mollusca
Animals
Domain Eukarya
Kingdom Animalia
Phylum Mollusca
35,000 species making this the second-largest phylum of Animalia

3. Polyplacophora: chitons
The most-primitive mollusc has 8 valves (plates) protecting its soft tissues beneath. The chiton foot attaches to rocks and the animal uses its radula to scrape organic material from the rock surfaces.

4. After working hard to remove the “suck rock” organism from the rock,
the ventral surface of the chiton shows the obvious mollusc features.
gills
foot
mouth
(radula inside)

5. The chiton has multiple eyes. Some are just light-sensitive spots.
The primary eyes are of a lens-type. Many chiton species lack eyes.

6. This cartoon shows a longitudinal slice of a chiton with the three principal parts: foot (locomotion or attachment), visceral mass (internal organs), and mantle (secretes valves).
dorsal aorta
gonad
heart
valve plates
pericardial cavity
(coelom)
hemocoel
ventricle
radula
auricle
mantle
mouth
anus
foot
digestive gland
stomach
nephridium
nephridiopore
ventral nerve cord
(not shown)
gonopore

7. As for all other molluscs, chitons use a radula to scrape their food from environmental surfaces. Below is a radula removed from a chiton mouth.

8. Gastropoda: snails and relatives (slugs)
Snails have a single spiral-shaped valve (univalve)
Slugs and nudibranchs have lost this feature.
shell
optical tentacle
eye
foot
gonopore
sensory tentacles

9. And now for a look inside our gastropod mollusc…
Trochophore larva:
And now for a look inside our gastropod mollusc…
Veliger larva:
The shell obviously provides a hard covering for the visceral mass.
The snail shown here is a pulmonate, with a vascularized mantle cavity serving as a lung. Vascularizing this led to loss of the gills in most gastropods.
The gastropods, are clearly hermaphroditic, and some are self-fertile.

10. This is a slug, its mantle is reduced to a “saddle” and does not secrete a shell. The other features of the snail are all present.
optical tentacles
sensory tentacles
mantle
foot
skirt

11. Here is the longitudinal section of an optical tentacle.
The eye of the slug is a lens-type eye.
1. digitate ganglion
2. collar cell
3. olfactory nerve
4. tentacle retractor muscle
5. lateral processed cell
6. lateral oval cell
7. optic nerve
8. accessory retina
9. lens
10. retina
retinal cell:
11. microvilli
12. pigment cell
13. light sensitive cell

12. Here is a micrograph of a longitudinal section of a snail eye
The tentacle has all of the optical, sensory, and neural parts we expect for vision.
The tentacle has all of the sensory, and neural parts we expect for chemical sensation too.
The sensory tentacles have these features too.
olfactory
ganglion
nerve
lens
retina
optic
nerve

13. The slug shows the pneumostome in the mantle for breathing.
foot
mantle
optical tentacles
skirt
sensory tentacles

14. These two slugs are showing mating behavior.
The slugs are dangling on a slime thread and grip each other with their feet.
The slugs evert their reproductive organs out through the gonopore.
The organs unite and spermatophores are exchanged.
Sperm are stored in a spermatheca for a week or more. Syngamy and deposition of zygotes occurs later.

15. This group includes the clams, oysters, mussels, and scallops.
Bivalva: bivalves
This group includes the clams, oysters, mussels, and scallops.
Their body is typical mollusc too, but with two hinged valves (shells)
graphics/jpegs/aopercu.jpg

16. Adductor muscles to hold the valves together.
Here is a cartoon of a lateral view of the foot, visceral mass and mantle
Adductor muscles to hold the valves together.
Bivalves have gills rather than lungs.
Their incurrent siphons take in plankton lodging in mucus.
The mucus laden particles gather on the gills (palps) and enter the mouth.
The mouth lacks the radula.

17. The foot can push a bivalve through sediments.
This cartoon is shows a plane of section perpendiular to the previous one.
hinge and ligament
The foot can push a bivalve through sediments.
The food-trapping gills are used for gas exchange.
The heart pumps the blood into the hemocoel bathing the tissues. It goes through the gills for gas exchange. The blood then returns to the heart.
shell
heart
nephridium
intestine
mantle
gonad
gills
foot
Nephridia cleanse the blood of nitrogenous waste.

18. Here are three different molluscs
Here are three different molluscs. Between the valves of the bivales the mantle fringe is quite visible. With the valves ajar, the bivalve can carry out its filter feeding. If you swim nearby, the bivalve adductor muscles snap the valves shut.

19. How does the bivalve know you are swimming by? Eyes!

20. Here are close-ups of the bivalve eye and a cartoon of its structure.
This gives the impression of being somewhat intermediate between a lens-type and a pinhole-type eye.

21. Tridacna crocea Gymnodinium microadriaticum

22. Cephalopoda: the chambered nautilus, squid, and octopus
The nautilus has gastropod features
operculum
eye
valve
tentacles

23. Advantage: simple, detailed
Disadvantage: low light collection
Pinhole eye of Nautilus
retina
pinhole

24. Smaller arms surround the mouth
This Caribbean reef squid is small. The giant squid is the largest invertebrate animal known…17 meters long…2 tons!
fin
mantle
chromatophores
eye
Smaller arms surround the mouth
Two grasping tentacles

25. Between the tentacles part of the beak is shown.
Contrary to the filename, this is a Humboldt squid. It is certainly large, but is not the giant squid.
Between the tentacles part of the beak is shown.
The eyes face the man’s knee and elbow.
The mantle is in his lap and the fin is over his shoulder.

26. The squid eye is a lens-based eye, rather than a pinhole eye.
The squid eye is a lens-based eye, rather than a pinhole eye.
Is this cartoon correct, based upon your dissection of the squid in class?
retina
lens
Advantage: collects more light

27. Another cephalopod is the octopus.
It obviously has eight tentacles surrounding the mouth…no, duh!
This one is obviously swimming.

28. Here is another swimming octopus
Here is another swimming octopus. The idea of cephalopod (head-foot) is shown nicely here. Behind one tentacle the siphon is showing the basis for jet-action locomotion among cephalopods.

29. What kind of eye does an octopus have?
What kind of eye does an octopus have?
Squid eye
Note: I am fairly certain that the animal shown above on the right is a squid, rather than an octopus:

31. gastropod
bivalve