1. MOLLUSCA II
Bivalves
Cephalopods

2. Bivalves
Shells indicative of life habit/environment – good eco indicators,
Live in all marine habitats except anoxic.
Invaded fresh water by mid Paleozoic.
Species tend to be long-lived – little biostrat use.
Ancestor (limpet-like) developed hinged shell, lost head, sense organs, radula.
First appear in Cambrian
Survive P/T extinction and came to dominate (due to predation & infaunal habit?)
Survive K/T extinction with little effect (except rudists & inoceramids)
Survive all following extinctions

3. Plane of Symmetry runs between valves
Plane of Symmetry runs between valves. Standard orientation is hinge at top.
Body consists of mantle, adductor muscles, foot, gills, digestive system.
No diductor muscles – use ligament as spring

4. Shell interior contains muscle scars, pallial line (attachment line of mantle), pallial sinus (notch marking siphon)
Also see teeth and sockets at hinge
Externally
beak – usually points forward prosogyral (can be opisthogyral)
ligamental groove or resilifer – for ligament

5. Gills used for respiration and filter feeding.
Gill Types
Protobranch – primitive
Filibranch – W-folded gill sheets
Eulamellibranch – folded gills with cross partitions
Septibranch – divide mantle cavity

6. Teeth and Sockets
None
Taxodont (Arca)
Schizodont
Dysodont
Isodont
Heterodont
Pachydont
Desmodont

7. Taxonomy based on gills, hinge structure
Class Bivalvia
Subclass Protobranchia
Order Nuculoidea – (Palaeotaxodonta) nut clams
Order Solemyoidea - (Cryptodonta) awning clams
Subclass Pteriomorpha – (Filibranchia)
Order Arcoida – taxodont ark shells & bittersweet clams
Order Mytiloida – dysodont, unequal muscles
Order Pterioidia – scallops, oysters, inoceramids, unequal muscles or 1 muscle, reduced foot
Subclass Heterodonta – (Eulamellibranchia)
Order Veneroida – “clams”, tridacna, razor, tellines, cockles
Order Myoida – boring clams and ship-worms
Order Hippuritoida – rudists
Subclass Paleoheterodonta
Order Modiomorpha – Paleozoic, heterodont
Order Unionoidia – fresh water heterodonts
Order Trigoniodia – Paleoz-Mesoz schizodont
Subclass Anomalodesmata
Order Pholadomyoida – burrowing/boring desmodont

8. epifaunal suspension
byssus attached
boring infaunal susp.
infaunal
nonsiphonate
suspension
siphonate
carnivore
siphonate susp
infaunal
deposit
feeders
infaunal
mucus tube
feeder
siphonate deposit

9. For burrowing bivalves shell shape related to burrowing
deep = smooth thin shells
shallow – thick ornamented shells
discoidal, bladed, cylindrical shells = faster
divaricate surface pattern = rapid
deep pallial sinus = long siphon = deep burrow
Swimming bivalves = large umbonal angle, monomyarian
Byssally attached = byssal sinus
Cemented = asymmetrical shells
Lots of convergence

11. Evolution
Early Cambrian – Taxodont nut clams – probably descended from early rostroconch
Early Ordovician – great radiation, most subclasses and orders found, not very diverse. Occupied nearshore habitats and muddy substrates
Post P/Tr increased due to predation and ability to burrow and siphons
Free-swimming scallops appeared in Triassic
Free-living forms in Mesozoic: Gryphaea, Exogyra, Inoceramus, Rudists

14. CEPHALOPODS
Most intelligent of the molluscs (possibly of all invertebrates)
Dominant predators throughout most of Paleozoic.
Extremely useful for biostratigraphy in Dev-Cretaceous

15. Physiology based on modern Nautilus
Body – 38 tentacles surrounding mouth, horny beak in center
Pair of well developed eyes.
Hood covers body when retracted
Mantle cavity contains gills, water can be expelled through hyponome for jet action
Shell consists of body chamber and phragmocone. Chambers (camerae) closed by septa (suture is line of join of septa with outer shell, only visible on steinkern)
Siphuncle extends through septa and connects body with camerae – controls
fluid/bouyancy

16. Taxonomy
Class Cephalopoda
Subclass Nautiloidea – living Nautilus, orthocone, crytocone, involute coiled forms simple sutures
Subclass Endoceratoidea – Paleozoic orthocones, huge siphuncle on ventral, endocone deposits O-Sil
Subclass Actinoceratoidea – Paleozoic orthocones, septa w necks around siphuncle, siphuncular deposits O-Carb
Subclass Bactritoidea – Dev -Tr orthocones w globular protoconch, ancestors to Ammonites
Subclass Ammonoidea – Dev-K, Goniatite, Ceratite, Ammonite sutures
Subclass Coleoidea – lower Carb-R, squids, octopi, cuttlefish, belemnites

18. Endoceratoidea
Nautiloidea
Bactritoidea
Actinoceratoidea
Ammonoidea
Coleoidea

19. Coiling shapes

20. Suture Complexity
Buttressing
Ion exchange
Muscle attachment

21. Bouyancy solutions
B. Endoceratoidea
C. Actinoceratoidea
D. Liquid retention
E. Cameral deposits
G. Shed chambers

22. Variations on the basic Ammonite
Some bizzare forms thought to be “racial senescence”.
Good examples of iterative evolution.
“Haeckel’s Law”