Figure 32.8 Animal phylogeny based on sequencing of SSU-rRNA
Polychaetes Representative Annelids Oligochaetes Marine worms Hirudineans Terrestrial & aquatic Leeches - Aquatic & terrestrial
Annelid Circulatory, Respiratory & Excretory Organs Closed Circulatory System Parapodia: Gill-like function Polychaete Nephridia Excretion & selective resorbtion of water & salts Oligochaete
Closed Circulatory System Parapodia: Gill-like function Polychaete Oligochaete
Nephridia Excretion of nitrogenous wastes Excretion & selective resorbtion of water & salts
Annelid Reproduction & Development Polycheates: Indirect Development Oligochaetes: Direct Development Trochophore larva Clitellum Key feature of Lophotrochozoa (from Brusca & Brusca, 1990) (from Hickman & Roberts, 1995)
Figure 33.23x External anatomy of an earthworm Clitellum
Copulating Earthworms (Hermaphrodites)
Phylogeny of Annelid Worms* To Mollusks Polychaeta Oligochaeta Hirudinea Parapodia Elaboration of a complex head with tentacles & palps Complex gut with typhlosole Fixed reprod. system (permanent gonads) Hermaphroditic Direct development (loss of trochophore larva) Clitellum complex Body surface subdivided by superficial annuli Body with fixed number of segments (34) Reduction of coelom and internal partitions Body develops suckers Loss of setae Parasitism METAMERISM (ancestral annelid) Paired epidermal setae Annelid head (prostomium) Trochophore larva Separate sexes (gonochoristic = dioecious) No permanent gonads Marine * simplified form Brusca & Brusca, 1990)
Mollusca clams snails slugs squids octopuses nudibranchs
Adaptive Radiations Triggered by invasion of new habitat, adoption of a new nitch, or by Key Innovation.
Primitive Molluscan Body Plan Unsegmented, coelomate Coelom limited to small spaces around nephridia, heart, and intestine Principal body cavity is a hemocoel (open circulatory system) Large, well-defined muscular foot Head and foot ventrally Viscera concentrated dorsally Body covered by a thick epidermal organ - Mantle Mantle cavity houses the ctenidia, osphradia, nephridiopores, gonopores, and anus Mantle secretes shell Buccal region has a radula Trochophore larva Chambered heart Reduced coelom Shell Preoral tentacles Mantle 2 gills Posterior mantle cavity Radula Muscular foot
Body wall, shell and mantle
Body plan of five classes
Mollusca: Radula Feeding Mechanism Drilling carnivore Herbivore Secondary reduction or loss in Cephalopods & Bivalves
Another innovation Counter current gas exchange Ciliary gill
Molluscs: Nervous & Organization Slow crawlers - varied diets Primitive ladder-like nervous system (polyplacophran) No spinal ganglia Gastropod nervous system Cephalopod brain Active predators Pelecypod nervous system Stationary filter feeders Squid: giant axons
Creeping Varied diets Jet-propelled Armed predators Living fossils Burrowing Filter feeders Reign of Ammonites Benthic creepers Algae feeders Aplacophora Worm-like burrowers Detritus feeders (Modified from Hickman & Roberts, 1995)
Anatomy of aplacophorans Worm-like, burrowing or epibenthic Shell-less Radula present Small mantle cavity with gills Similar to ancestral group
Figure 33.17 A chiton Polyplacophora
Dorsal shell plates Polyplacophora Body Plan Mantle extends along side foot Multiple gills in groove Chiton
Figure 33.19 Gastropods: Nudibranchs (top left and right), terrestrial snail (bottom left), deer cowrie (bottom right)
Class Gastropoda, subclass Prosobranchia P. 611)
Gastropod body plan
TORSION (from Hickman & Roberts, 1995)
COILING
The majority of gastropods are herbivores, rasping off particles of algae. Others are scavengers or predators. Prying Drilled bivalve Harpoon radula Conus swallowing a fish
Subclass - Prosobranchia Basal group
Subclass Opisthobranchia Sea butterfly Sea slug - nudibranch Anal gill Sea slug Sea hare (Aplysia)