Upload
ann-marshall
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
Molluscs & Annelids
Zoology LS2014, Donald Winslow
3 March 2008,
Following Hickman, et al., 2008
Ch. 16 (pp 332-344, 346-357)
Ch. 17 (pp 363-378)
Molluscs & Annelids
• Protostome
• Spiral cleavage
• Mosaic development
• Eucoelomate
• Schizocoelous coelom formation
• Many have trochophore larvae
Phylum Mollusca
• Coelom usually only around heart
• Unsegmented with organ systems
• Trochophore & veliger larvae in many
• Gills (ctenidia) or lung
• Circulatory system usually open
• Variation in body size
• Mantle, mantle cavity, shell, foot, head
Molluscan characteristics
• Radula & odontophore
• Visceral mass
• Surface epithelium, cilia & mucous glands
• Metanephridic kidneys (drain from coelom)– Empty liquid waste into mantle cavity
• Usually nerve ring & paired ganglia
• Mostly dioecious
Phylum Mollusca
• Classes Caudofoveata & Solenogastres
• Class Monoplacophora—one shell plate
• Class Polyplacophora—8 shell plates
• Class Scaphopoda—tusk shells
• Class Gastropoda—snails & slugs
• Class Bivalvia—clams, mussels, etc.
• Class Cephalopoda—squid, octopus, etc.
Class Gastropoda
• Snails w/ coiled or uncoiled shells
• Slugs w/ no shells
• Pulmonate land snails & slugs
• Marine nudibranchs (no shell, “sea slugs”)
• Poisonous cone shells
• Conchs, whelks, limpets, abalones
Class Bivalvia
• Clams, scallops, mussels, oysters
• Zebra mussels, shipworms, giant clams
Class Cephalopoda
• Giant squid
• Cuttlefish
• Octopus
• Chambered nautilus
Phylum Annelida
Developmental characteristics
• Spiral cleavage & mosaic development
• Protostome
• Eucoelomate
• Schizocoelous coelom formation
• Segmentation (metamerism)– External rings called annuli– Few differences between segments
Morphological characteristics
• Bilateral symmetry
• Chitinous setae (bristles)
• Parapodia in Class Polychaeta
• Cerebral ganglia
• 2 ventral nerve cords with giant axons
• Ganglia & lateral branches in each segment
Specialization of annelid head
• Tactile organs
• Taste buds
• Statocysts
• Photoreceptors
Annelid circulatory system
• Closed
• Dorsal blood vessel pumps blood
• Aortic arches control blood flow
• Ventral blood vessel
• Respiration by skin, gills, or parapodia
Digestion and excretion
• Complete digestive tract
• Unsegmented digestive tract
• Nephridia in each segment remove waste from blood.
Reproduction of annelids
• Complete regeneration when injured
• Monoecious or dioecious sex
• Trochophore larvae in some taxa
• Budding in some taxa
Sections of annelid body
• Prostomium (“head”)
• Somites (“body”)
• Pygidium (“tail”)
Annelid coelom
• Septa divide coelom and separate segments.
• Fluid in coelom provides hydrostatic pressure for “hydrostatic skeleton”.
• Epidermis secretes cuticle.
• Peritoneum (visceral & parietal)
• Mesenteries (dorsal & ventral)
Phylum Annelida
• Class Polychaeta– Mostly marine– Some tube-dwelling– Mostly dioecious (separate sexes)
• Class Oligochaeta– Earthworms and other terrestrial & freshwater
species
• Class Hirudinida—leeches and relatives
Examples of polychaetes
• Nereis
• Eunice viridis—Samoan palolo worm
• Featherduster worms
• Chaeopterus
Earthworms
• Mix, aerate, hydrate, & fertilize soil
• React to many stimuli, learn
• Hermaphroditic, testes, ovaries
• Seminal vesicles, oviducts, seminal receptacles
• Clitellum, fertilization in cocoon
• Freshwater oligochaetes with gills
Leeches
• Ectoparasitic
• Anterior & posterior suckers
• Medicinal uses