The Molluscs Flashcards
one of the largest and most diverse phyla in the animal kingdom, with over 100 000 extant species and about 70 000 fossil species
phylum
Mollusca
the Latin word
mollia, means?
Soft
which alludes to the typically soft bodies of Molluscs
True or False
phylum Mollusca contains
several taxa that are extremely dissimilar looking.
True
What forms a mantle, which secretes calcareous spicules or one or more shells
Dorsal epithelium
cuticular band of teeth in the esophagus, used for feeding
radula
tho not present in bivalves
ventral body wall muscles develop into a….
locomotory or clinging foot
How many described living species?
100,000
How many fossils species
70,000
True or False
the molluscan body plan probably the most malleable in the animal kingdom
True
Dissimilar-looking organisms
thin, outer organic layer
Periostracum
thick, calcareous middle layer
Prismatic layer
thin, innermost calcareous layer
Nacreous layer
Both the organic and inorganic components of the shell are secreted by specialized tissue
known as
Mantle
How are pearls formed
a grain of sand, parasite, or other foreign particle becomes trapped between the mantle
and the shell’s inner surface
usually houses the comblike molluscan gills
serves as the exit site for the excretory, digestive, and reproductive systems
Mantle Cavity
comblike molluscan gills are known as
Ctenidia (G: comb)
True or False
A Ctenidium (gill) may have a purely respiratory function or collection and sorting of food particles
True
A chemoreceptor/tactile receptor generally
located adjacent to the ctenidium is known as
Osphradium (G: smell)
What are the feeding apparatuses?
R - radula
O - odontophore
M - mouth
E - esophagus
odontophore-radular assembly + complex musculature
Buccal mass
(bucca = L: cheek), or the Odontophore Complex
consists of a firm ribbon composed of chitin and protein, along which are found numerous rows of sharp, chitinous teeth
Radula
The ribbon is produced from a Radular sac and is underlain by a supportive cartilage-like structure called
Odontophore ( G: tooth bearer)
Feeding of molluscs is through
rasping
True or False
As old teeth are worn down or broken off at the anterior end of the radular ribbon, new teeth are continually being formed and added onto the ribbon’s posterior end in the radular sac.
True
extends its proboscis and harpoons the fish through a “lightning strike cabal”
of toxins causing almost instantaneous immoblilization of prey.
. Conus striatus
use net strategy to capture school of fish hiding in reefs at night.
Once it
has engulfed them, it uses a “nirvana cabal of toxins” to make the fish quiescent for stinging
them and causing an irreversible neuromuscular paralysis.
Conus geographus
What class has a defining characteristics of shell that forms 7-8 separate plates
Class Polyplacophora
G: many plate-bearing
How many species does Class Polyplacophora
800 species
organs derived from mantle extending from holes of plates (light receptors or secrete periostracum)
Aesthetes
True or False
Articulating plates are either partially or largely embedded from the mantle
True
What releases amylase-containing secretions into the stomach
Pharyngeal/sugar glands
What class has a shell that has a series of eight overlapping and articulating plates covering the dorsal surface
Class Polyplacophora
A chiton’s thick lateral mantle is called
Girdle
Class that is not shell bearing
Class Aplacophora
Class defining characteristics:
- cylindrical,
- vermiform body with the foot forming a narrow keel
Class Aplacophora
How many species in Class Aplacophora are in deep ocean
300 species
True or False
Class Aplacophora have segmented body with numerous calcareous spines embedded in the outer cuticle
False
Unsegmented body
Defining characteristics:
- 3-6 pairs of ctenidia
- Multiple pairs of pedal retractor muscles
- 6-7 pairs of nephridia
Class Monoplacophora
G: one shell bearing
Single, unhinged limpet-shaped shell
How many extant species of Class Monoplacophora
20 extant species
All marine collected at great depths of 2,000m
Defining characteristics:
- Visceral mass and nervous system become twisted 90-180 degrees (torsion) during embryonic development
-Proteinaceous shield on the foot (operculum) to which columellar muscle attaches
Class Gastropoda
A 180 degree counterclockwise twisting of the visceral mass, mantle, and mantle cavity during embryonic development
Positions the gills, anus, and openings from the excretory and reproductive systems just behind the head and nerve cords, and twists the digestive tract into a “u-shape“
Allows the mouth and the anus to exit the shell at the same point
TORSION IN GASTROPODS
- Reversal of torsion
- Takes place during the larval stage and the animal regains bilateral symmetry
- Nervous system becomes symmetrical and not twisted in the shape of 8
- Visceral loop and intestine becomes straightened
- Pulmonata, Opisthobranchia
Detorsion
- Marine and freshwater snails, predominantly marine
- Generally free-living and mobile
- Complete torsion
SC Prosobranchia
G: anterior gill; snails
Foot of SC Prosobranchia bears a rigid disc of protein called
operculum
- Soft, fleshy tube through which water is drawn into the mantle cavity and over the gill for respiration, locomotion, feeding, and reproduction
- Equipped with chemoreceptors which “smell” or “taste” the water, in order to hunt for food
Siphon
○ Includes sea hares, sea slugs, bubble shells
○ Almost all marine
○ < 1,100 species described
SC Opisthobranchia
G: posterior gill
- Sea slugs
- use nematocysts usurped from cnidarian prey for defense
- produce chemical defenses housed by cerata
- Possess rhinophores in the second pair of tentacles located dorsally of the head (chemosensors)
ORDER NUDIBRANCHIA
- Sea hares
- Found in shallow waters and rock pools
- Prominent tentacles on the head resemble rabbit ears
- Releases defensive secretion ink (purple) andopaline
E.g. Aplysia, Dolabella
ORDER ANASPIDEA
- Sea butterflies
- Foot modified to produce wing-like flaps called parapodia for swimming
ORDER PTEROPODA
Mantle cavity of SC Pulmonata is highly vascularized and functions as lungs through an opening called
pneumostome
Few are marine; if present, in intertidal zones and estuaries only
SC Pulmonata
- Mostly terrestrial or freshwater
- Few with operculum
- Possess long radula in keeping with herbivorous diet
- Head bears 2 tentacles
True or False
Torsion of SC Pulmonata can reach up to 180
False
Torsion limited to 90º so nervous system not greatly twisted and mantle cavity opens on the right side
chitinous or calcareous accessory organ that are thrust into the partner during mating among pulmonate gastropods
Love dart
DC:
- Two-valved shells
- Body is flattened laterally
Class Bivalvia (~ Pelecypoda) - G: two valved
Class bivalvia has _____ species which includes clams, scallops, mussels, and oysters
> 15,000 species
- Primarily marine, but about 10-15% are in freshwater
- Lack of cephalization
- Spacious mantle cavity
- Sedentary lifestyle
- Absence of radula/odontophore complex
- Diverse feeding habit
Class Bivalvia
- Includes Nucula sp.
- Morphologically primitive state of bivalve
- Bipectinate gills
- Deposit feeding
SC Protobranchia
G: first gill
- Include familiar bivalves such as clam, mussels, scallops
- Gills modified to collect suspended food particles
- Secretion of attachment by byssal or byssus gland in the foot
SC Lamellibranchia
G: plate gill; mussels
- Small group of carnivorous bivalves and on pieces of decomposing animal tissue
- All very deep marine water
- Ctenidium highly modified, lacking filaments and forming muscular septum perforated by ciliated openings
- Feed as vacuum cleaners sucking on small crustaceans and annelids
Stomach lined with chitin
SC Septibranchia
G: fence gill; shipworms
- DC:
○ tusk-shaped, conical shell open at both ends
○ development of anterior, thread-like adhesive feeding tentacle (captacula)
Class Scaphopoda
G: spade foot; tusk shell
DC:
○ Shell divided by septa with chambers connected by siphuncle (yellow arrows)
○ Closed circulatory system
○ Foot modified to form flexible arms and siphon
Ganglia fused to form a large brain encased in cartilaginous cranium
Class Cephalopoda
G: head foot;
Includes squids, octopi, Nautilus
- Fast-moving, active carnivores capable of complex behavior
- Exclusively marine
- Derivatives of the molluscan foot are the siphon, arms and tentacles (8-10)
- Possess two eyes with cornea, lens, iris, diaphragm and retina thus focusable and image-forming
- Closed circulatory system with systemic and branchial hearts
Class Cephalopoda
○ Soft-bodied, shell-less cephalopods
○ chromatophores overlay iridocytes
○ photophores
○ most have ink sac discharged through anus
Subclass Coleoidea
colored cells
chromatophores
reflective cells
iridocytes
light organs
photophores
True or False
female octopi have hectocotylized arms
False
Male octopi
Highly modified arm that transfers spermatophores
hectocotylus
Packets of sperms
Spermatophores
○ 5 or 6 species possessing true shell
○ shell divided by septa into series of compartments
○ septa penetrated by siphuncle
- cameral fluid in chambers
- Subclass Nautiloidea
calcified tube with enclosed strand of vascularized tissue
Siphuncle
Movement of Subclass Nautiloidea is through
Jet Propulsion
