1 Phylum Mollusca: stuff to know • Important morphologic features (hard parts only) • Classification: – Subphyla; classes; subclasses within Class Cephalopoda • Molluscan phylogeny • Ammonoid suture types • Pelecypod genera: – Pecten, Inoceramus, Gryphaea, Exogyra
32
Embed
1 Phylum Mollusca: stuff to know Important morphologic features (hard parts only) Classification: –Subphyla; classes; subclasses within Class Cephalopoda.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Phylum Mollusca:stuff to know
• Important morphologic features (hard parts only)• Classification:
– Subphyla; classes; subclasses within Class Cephalopoda
• Size ranges from microscopic (snails) up to 18m (giant squids)
• Inhabit marine, freshwater and terrestrial environments
• Aquatic types may be benthonic, planktonic, nektonic, even flying (squids)
3
Phylum overview (cont.)• Mollusks are extremely diverse, so there are few features
common to all representatives– Free-living metazoans– Dorsal calcareous exoskeleton – Muscular foot for locomotion– Visceral mass with major organ systems– Mantle cavity with gills (digestive and reproductive systems
open into mantle cavity)– Radula (rasping structure in mouth)– Head with mouth (maybe also tentacles and eyes)– Mantle (tissue layer) that surrounds soft parts and secretes shell
4
“typical” mollusk
radula
5
Phylum overview (cont.)
• Phylum originated in Early Cambrian (earlier?) from a flatworm ancestor– All major classes and subclasses originated by
Middle Ordovician– Only one major class has become extinct
(Rostroconchia)
• Shells:– mostly univalved or bivalved, aragonitic,
multilayered, with growth lines and muscle scars
6
Mollusk shell and musculature
7
Classification
S u bp h ylu m A m p h ine u ra(in c lu d e s C h ito n s)
C a m b ria n -H o lo ce ne
C la ss M o n op la cop h o raC a m b ria n -H o lo ce ne
C la ss G a s tro p o daC a m b ria n -H o lo ce ne
Subcla ss Nau tiloide a(Late Ca m brian-H olocene )
Subclass A m m onoide a(Devonian-Cretaceous )
Subcla ss Co leoide a(Devonian-H olocene; m o stly Jurassic )
C la ss C e ph a lop o daC a m b ria n -H o lo ce ne
S u b p hylu m C yrtoso m aC a m b ria n -H o lo ce ne
C la ss R o s tro co n ch iaC a m bria n -P e rm ian
C la ss S cap h op o daO rd o v ic ia n -H o lo ce ne
C la ss P e le cyp o daC a m b ria n -H o lo ce ne
S u b ph ylu m D iaso m aC a m b ria n -H o lo ce ne
P h ylu m M o llu sca
8
Phylogeny of molluscan classes
9
Monoplacophorans
• Cap-shaped to helical shell; bilateral symmetry; soft parts not twisted; paired muscles; apex of shell points anteriorly and overhangs head
• Important because ancestral to most other mollusks
• Only group of organisms to be described hypothetically before being discovered, AND to be known as fossils before live specimens were found
10
Monoplacophorans
Bellerophon
11
Monoplacophorans
• Most important group is bellerophontids– Cambrian-Early Triassic– Resemble gastropods– Very common in Late Permian of Tethyan
region (e.g., “Bellerophon Limestone”)
12
Gastropods
• Characterized by torsion of soft anatomy
• Head and foot regions combined or closely associated
• External shell usually coiled in a corkscrew helix
13
Gastropod anatomy
14
Gastropod shell terminology
• Apex (earliest part)
• Aperture (opening for head-foot)
• Operculum (cap)
• Whorl (coil of 360°)
• Suture (contact between adjoining whorls)
• Siphonal canal (opening for inhalent siphon)
15
Gastropodshells
16
Cephalopods• Class includes Nautilus, squids, octopuses, extinct
ammonoids• Highly evolved nervous system (cephalization;
eyes)• Carnivorous and capable of swimming (nektonic)
(up to 70 km/hour)• Foot and head closely associated (indistinguishable
in some)—hence the name: kephalus + poda • Possess hyponome (funnel for jet propulsion) and
arms or tentacles
17
Cephalopods
• Shelled forms possess gas-filled chambers
• Buoyancy is controlled by (1) poise adaptation of the shell (shell form) and (2) adding or subtracting fluid from chambers by the siphuncle
• Most living forms possess an ink sac
• Exclusively marine
18
Nautilus soft anatomy(shell not shown)
19
Cephalopod shell morphology• Chambered shell is divided into living chamber
and phragmocone• Chambers separated by septa• Suture is junction of septum with the outer shell
wall• Siphuncle = tube with blood vessels, nerves and
mantle that extends from animal back through phragmocone (usually ventral)– Septal foramen = hole through which siphuncle passes– Septal neck = projection of septum surrounding
siphuncle
20
Cephalopod shell morphology
21
Siphuncleterminology
22
Cephalopod sutures
• If suture is fluted, saddles point toward aperture and lobes point toward apex– Orthoceratitic = unfluted or with broadly undulating
lobes and saddles (Cambrian-Holocene)– Goniatitic = distinct lobes and saddles that are