BIO2231 Lecture Notes - Lecture 7: Cephalopod, Prosobranchia, Antalis
30 May 2018
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Phylum Mollusca: Snails, bivalves, chitons, squid, octopuses
• Bilateral, triploblastic coelomate (body cavity completely surrounded by mesoderm), organ
system level
• Marine, freshwater, terrestial
• Coelom is secondarily reduced in size and importance, forming only the pericardial cavity
surrounding heart, gonads and nephridia.
• Most have hemocoel which is part of open circulatory system
• Anus in mantle cavity
• Trocophore larva
• Three regions: head-foot; locomotion and retracting body into shell, muscular, relatively fast
- visceral mass; contains organ systems devoted to digestion,
reproduction and excretion (carried dorsal to head-foot)
- mantle; fleshy tissue attached to visceral mass and secretes a shell
• Head is poorly defined, retractable
• Between visceral mass and mantle is the mantle cavity; contains gills (ctenidia) or lung and
openings to excretory, digestive, reproductive system.
• Nervous system; ring around esophagus, nerve cords, ganglia
• Skirt (mantle edge); sensory and secretory
• Shell is made up of calcium carbonate and protein (secreted by mantle edge), lined by mantle,
three layers; periostracum (organic), prismatic (calcium carbonate), nacreous (mother of pearl,
on top of mantle), protects visceral mass
• 2nd largest phylum
• Buccal cavity contains Radula; tongue-like structure, chitinous belt of rasping teeth, overlies a
fleshy tongue-like structure supported by a cartilaginous odontophore
• Excretory system; pair of metanephridia , pericardial fluid (coelomic)
• Lungs in pulmonate snails (secondary gills)
• Most Dioecious, some hermaphroditic
• Blood supplied from heart
• Coiling of shell is independent of torsion
• The shell of a mollusc, when present, is secreted by the mantle and is lined by it. Typically there
are three layers. The periostracum is the outer horny plate, composed of conchoilin, which is a
resistant protein. It helps protect the underlying calcareous layers from erosion by boring
organisms. It is secreted by a fold of the mantle edge, and growth occurs only at the margin of
the shell. The middle layer, the ostracum, is composed of densely packed prisms of calcium
carbonate laid down in a protein matrix. It is secreted by the glandular margin of the mantle,
and increase in shell size occurs at the shell margin as the animal grows. The inner layer of the
shell, the hypostracum, is composed of a calcium carbonate sheet laid down over a thin protein
matrix. This layer is secreted continuously by the mantle surface, so that it becomes thicker
during the life of the anima
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Class Polyplacophora
-Chitons
~550 species
-most primitive
-all marine (rocky intertidal)
-not very mobile
-herbivores (algae)
-shell consists of 8 overlapping
plates
-Many gills in pallial groove
-mantle (usually called girdle) is
very tough
-head is indistinct
-lack eyes and tentacles
-spicules In skirt/mantle (extra
protective layer, glue onto
rocks)
-osphradia; chemoreceptive
- On each side of the broad
ventral foot and lying between
the foot and the mantle is a
row of gills suspended from the
roof of the mantle cavity in
chitons. Water enters the
grooves anteriorly, flows across
the gills and leaves posteriorly,
thus bringing a continuous
supply of oxygen to the gills
Ischnochiton
Class Gastropoda
Subclass Prosobranchia
- marine limpets, whelk
-mostly marine, terrestrial
-only class to show torsion
(twisting of larval stage so
mantle cavity faces anteriorly)
-leaf-like ctenidia
-operculum (lid) to close
Patelloidea Haliotis
Dicathais Cellana
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Visceral mass; contains organ systems devoted to digestion, reproduction and excretion (carried dorsal to head-foot) The periostracum is the outer horny plate, composed of conchoilin, which is a resistant protein. It helps protect the underlying calcareous layers from erosion by boring organisms. It is secreted by a fold of the mantle edge, and growth occurs only at the margin of the shell. The middle layer, the ostracum, is composed of densely packed prisms of calcium carbonate laid down in a protein matrix. It is secreted by the glandular margin of the mantle, and increase in shell size occurs at the shell margin as the animal grows. The inner layer of the shell, the hypostracum, is composed of a calcium carbonate sheet laid down over a thin protein matrix. This layer is secreted continuously by the mantle surface, so that it becomes thicker during the life of the anima. Spicules in skirt/mantle (extra protective layer, glue onto rocks)
