Page 342 - Introduction to Paleobiology and The Fossil Record

SPIRALIANS 2: MOLLUSKS 329

Class SCAPHOPODA
• Long, cylindrical shell, open at both ends
• Devonian to Recent

Class CEPHALOPODA

• Most advanced mollusks with head and well-developed sensory organs together with tentacles
• Cambrian (Upper) to Recent

Solenogastres
Aplacophora
(a) Visceral mass
Caudofoveata Aculifera
(guts, reproductive
organs, etc.)
Polyplacophora
Shell Anus
Mantle Mantle cavity
cavity Monoplacophora
Mouth with Palps Siphons
radula Gills Foot Bivalvia Enlarged Mantle cavity
gills
HAM
Scaphopoda
Conchifera
Mantle cavity
Gastropoda Head
Siphuncle
Cephalopoda Chambers
Mantle Tentacles
cavity Funnel surrounding
(b) Visceral mass mouth
(guts, reproductive
organs, etc.)
Solenogastres
Aplacophora
Shell Anus
Caudofoveata
Mantle
cavity Polyplacophora
Mouth with
radula Gills Foot Monoplacophora Mantle cavity
HAM Palps
Bivalvia Siphons
Enlarged Mantle cavity
gills Testaria
Scaphopoda
Gastropoda Mantle cavity
Head
Siphuncle
Cephalopoda
Chambers
Mantle Tentacles
cavity Funnel surrounding
mouth
Figure 13.1 Pseudocladograms of molluskan evolution: hypothetical archemollusk (HAM) evolution
integrated with a cladistic-type framework. Model (a) demonstrates a split into the Aculifera and
Conchifera, whereas (b) indicates a division into the Aplacophora and Testaria. (Based on Sigwart &
Sutton 2007.)