Mollusca Flashcards
3 unique characterisitcs of Mollusca
Mantle
Radula
Foot
Mantle
In molluscs, forms a surface or dorsal epithelium which produces calcareous spicules or shells
Radula
In molluscs, feeding organ made up of cuticular band of teeth (lost in bivalves)
- feedi my structure contaiing rows of sharp, chitinous teeth
- radula has a firm ribbon, made of chotin and protein with rows of teeth
Foot in molluscs
Formed from the ventral body wall for locomotion
Second largest animal phyum is
Moluscs
100,000+ species
Molluscs include fmailiar names like
Clams, snails, slugs, squids, chitons, and tusk shells
Body plan of molluscs
Soft, triploblastic, bilaterlaly symmestrical
Molluscs have _____ organs
Visceral
Under
Visceral mass of molluscs is covered by a fold of skin called a ____
Mantle, a thin, fleshy fold of dorsal body wall covering the body. It encloses a space between itself and the body which is callrd the mantle cavity
Coelom of molluscs
Is greatly reduced. It is restricted to the pericardial cavity and to small spaces within kidneyes and gonads. Spaces amongst the viscera contain blood and form haemocoel
Molluscs have shells conisiting primarily of ____
Clacium carbonate set in a protein matrix
-organic material may comprime about 35% of the shells dry weight in soke gastropod speices and up to 70% of the dry weight in bivalves
Shells have 3 layers:
- Periostracum: outer organic layer which is thin
- Prismatic layer: calcarous, thick middle layer
- Nacreous layer: calcareous inner layer which is thin
Ctenidia
Mollusc gills
- present in the mantle cavity
- used for respiration; could serve as food collection and sorting
- serve as outlet for digestive, reproductive and excretory systems
Apart from cephalopods, respiration in molluscs is via…
A countercurrent mechanism (blood and water flowing in opposite directions)
Afferent vessels carry deoxygenated blood to the ctenidia to be oxygenated.
Efferent vessels carry blood to oxygenated blood from the ctenidia to the heart and other organs
Osphradium
Chemoreceptor/tactile (touch) organ
-lies adjacent to the ctenidium
In molluscs
Odontophore
In molluscs, cartilaginous structure that support the radula
Hemocoel
First phylum to have it
In molluscs, known as the blood csvity
- serve as a hydrostatic skeleton; provide support and movement for some molluscs
- molluscs vary in size from microscopic form to 12m long squids
Blood is blue
2 subphylums of molluscs
Aculifera: members have calcareous spicules in ondividual cells in mantle cavity.
Conchifera: lack spicules and mantle tissues secrete one to many clacerous shells.
Aculifera classes
Polyplacophora: consists of chitons, snial like molluscs with 8 part overlappijg scale shells.
Aplacophora: some have slender foot; radula may be present or absent
Conchifera classes
Monoplacophora: one family: Neopilina galantheae, Micropilina arntzi
Gastropoda: True snails and slugs (most diverse class in molluscs)
Bivalvia: molluscs with hinged two-part shells (clams, oysters, mussels, scallops)
Cephalopoda: Molluscs with large heads, large eyes and grasping tentacles (octopus, squid, cuttlefish)
Scaphopoda: Tooth shells and tusk shells
Polyplacophora
Bear an armorlike, eight plated dorsal sell. Have broad ventral foot that is adapted for suction to rocks and other substrates and a mantle that extended byond the shell in the form of a girdle
-commonly known as chitons
Polyplacophorans lack which parts?
Real head, eyes and tentacles around mouth
Body plan of Polyplacophora
Elongated, bilaterally symmetrical flattened body and a broad ventral foot
- mantle bearing cuticular spicules covers at least a great part of the body
- mouth lies centrally in a reduced head, the anal and excretory apertures are posterior
Nervous system of Polyplacophora
Ladder-like with slightly developed ganglia
Aesthetes
In polyplacophora, sensory light receptor secreted by the mantle tissue that can peotrude through shell holes
Habitat of Polyplacophora
- shoreline; some inhabit the intertidal zone (area between the high and low tide)
- abundant and important aspect of the sea floor.
- can be at shore or deep water
Movement of Polyplacophora
Accomplished by subtle waves of muscular activity called pedal waves
When disturbed, the chiton can press the ___
Girdle tightly against the substrate, then lift the central portion of the foot to create suction.
Chitons can also generate suction aided by ____
Mucus secretions that holds the animal tightly against the substratum.
Adaptive to heavy wave function habitat
Mouth organization of Polyplacophora
- the mouth of chitons has no tentacles, but has a veil of muscular tissue derived from the mantle. Feed with radula like all molluscs.
- 13-17 teeth per row ahd 24-150 rows
- some teeth capped with magnetite (iron compound that makes the teeth much harder).
- Radula used as a scrapper, or grater to remove small particles of food
Feeding of Polyplacophora
Food is drawn into the buccal cavity and moved along the oesophagus by mucus flow. The oesophagus is short, and leads to the rouded stomach, from which it is separated by a muscular sphincter. From the stomach the food moves in tbe intestines which leads to the posterior anus.
Feeding habits of Polyplacophora
Shows 7 feeding behaviours and food preferences
- omnivorous grazers: most common in chitons
- herbivarores: feed on plants, mostly algae (seaweed)
- detritivores: consume various mayter on the sea floor
- carnivorous grazers: feed on sessile aniamls like barnacles and corals
- spongivores: feed ok sponges
- xylophagous: feed on wood
- true predators: trap and pret on small invertebrates for food
Polyplacophora Reproduction
- Motly dioecious (non hermaphrodic)
- chrions have 1 single gonad which released ova or sperm through paried gonopores into mantle cavity. Gonopores are forward of the nephriopores.
- fertilization in open water or in mantle cavity of female. Some retain eggs and brood in mantle cavity.
- fertilized eggs develop into trochophore larvae. In non brooding species these have short, free swimming life before becoming young chiton.
- brooding species, trochophore larvae either remain in females mantle cavitt until they turn to young chitons or depart to join the oceans zooplankton
Class Aplacophora meaning
Without plate (no shell)
Class Aplacophora body type
typically possess worm like body
- body is unsegmented; outer cuticle possess many calcareous spines and scales
- typically lack visible foot
- small to medium sized (1mm-30cm)
- no head, nephridia (excretoy system) or shell
- all have dorsal gonad rather than posterior gonad
Class Aplacophora habitat
All marine
Sediment of icean floor
Is there a fossil record of Aplacophora
Nope
Nervouse system of Aplacophora
Basic and ladder like (with two cross connected chords) with well developed cerebral ganglion
Aplacophorans burrowing
- Inhabit depths from 16-17,390’
- one geoup live on hydroids (cnidarians), corals or oceans bottom
- other group burrows into ocean bottom and lives inside their tunnels upside down
Aplacophorans locomotion
- no well developed muscular foot
- move slowly with tiny bristles on their bodies called cilia or on a track of mucus produced by a groove underneath their body
- mucous ease the way for the worm-like molluscs as it glides over the track
Aplacophorans feeding
- head is poorly defined; visceral mass consists of a very simple and straight digestive system
- food is taken in, passes theough the circumpharyngeal muscle into the oral cavity where the radula rasps it
- fine food particles then pass into a single midgut organ that considts of a stomach and digestive gland. A short intestine absorbs the nutrients before the waste passes into the cloaca
Aplacophora sensory structures
- Consists of a simple cerebral ganglion and a lateral nerve cord
- lack specialized sense organs such as eyespots or electrucal or chemical sensors
Aplacophora reproduction
- some are hermaphrodites
- some may be monoecious or dioecious with single or paired gonad
- gametes then pass through gametoducts to the mantle cavity where they are then released outside the body.
- Chaetodermomorpha have externalized fertilization and Neomeniomorpha have internal fertilization and sometimes brood
Class Monolacophora unique characteristics
- members have ~8 pairs of foot retractor muscles
- possess 3-6 pairs of ctenidia (gills)
- possess 6-7 pairs of nephridia
- Have a single shell
- possess an anterior mouth with radula, single straight gut and posterior anus
Monoplacophora common name
Deep-sea limpets
Monoplacophora habitat
- All marine
- deep water dwellers, crawling on radiolarians, attactched to rocks and in devris collected from the bottom
Monoplacophoran shell
Have a single symmetrical shell, which vaires in shape and from flattened shieldlike plate to a short cone
- large and bilaterally symmetrical and has a single deprrssed, limpet-shaped valve
- apex of dhell lies vertically above the anterior margin in the median line
- margin of the shell is almost circular, being slightly elongated in the sagitall plane
- shell is thin, 3 layers and is thicker toward the margin than center
Monoplacophoran foot
Flat foot, similar to polyplacophorans
Round in outline and not very muscular
Monoplacophoran feeding
- feed by scraping up material from the surface they are resting on
- feed on protozoans, radiolarians, diatoms, foraminifera and sponges and detrius
Monoplacophora digestive system
Similar to gatropods, except back of the mouth is a curious cluster of frond-like appendages that serve to push the food into the pharynx. Mouth is located in fromt of the foot and the anus is located posteriorly in the pallial groove.
-radula ribbon of teeth is upside down
Monoplacophora nervous system
Composed of 2 pairs of simple ganglia (4 in total) that lead into four longitudinal chords. Have a statocyst for equillibrium
Monoplacophoran reproduction
Sexes are separate (diecious)
- females gave pair of ovaries and males a pair of testes.
- eggs and sperm are released intio water and fertilize externally
Class Gastropoda unique characteristics
- operculum (proteineous shield)
- exhibit torsion: twisiting of visceral mass and nervous tissue towards 90-180° during embryonic development
- asymetrical mollusca with a spirally coiled mantle and a shell of one piece enclosings corresponding visceral mass
Largest class of molluscs
Gastropoda
Snails and slugs
Gastropod lifestyle
Amphibious lifestyle: some are found on land, some aquatic (marine, brackish and fresh water), some alternate water and land.
Gastropod foot
Foot is behind head typically a flat, creeping organ
Gastropod head
Well developed head bearing eyes and tentacles
Buccal cavity
Gastropod organ containing odontophore with a radula bearing rows of chitinous teeth
Gastrod pod adults may lack a
Shell
Gastropod shell
- outermost covering of the body secreted by the mantle (calcereous shells)
- in terestrial slugs, the shell is reduced or absent
- typically coiled or spiral pattern
- shell in oke piece, usually one opening/aperature
Some have an operculum which is a proteinsceous covering of the shell opening
Columella and columella muscle
Columella holds the mantle cavitt more firmly in the shell; while columella muscle controls all movement of body inwards (retraction) and outwards from the shell.
Gastropod shell
Two forms of shell aperature dependinf on angle
Right side (dextral)
Left side (sinistral)
Gastropod torsion
- evolutionary adaptation in early development resulting in 180° twisting of the head and foot in reatiok to the visceral mass (mantle, shell and other body parts)
- as a result, the mantle cavity is moved from the rear and re-oriented over the head.
Purpose of torsion
- enable gastropods to withdraw the head and mouth into the shell
- ensures ctenidia and osphradia are siutated at the anterior during locomotion
- adjust the anus, so that it is situated above the head where the wastes are discharged/ unplesent substances released to ward off predators.
Gastropod movement
- most move by kuscle contraction through pedal waves along layers of sticky mucus released by the foot
- small species move by cilia on the ventral surface of the foot
Gastropod feeding
Vary from dentritus, herbivores, carnivores and omnivores
-may act as intermediate hosts for parasites (schistosome species)
Gastropod sensory system
- olfactory organs
- eyes
- ophradium (chemical and tactile)
-in terrestrial snails and slugs, olfactory organs on tips of 4 tentacles are most
Importsnt
-majority have simple visual oragns, eye spots on tip of tentacles. Range from simple ocelli to distinguish light and dark or more complex pit eyes and lens eyes (not super important ad most are nocturnal)
Gastropod respiration and circulatory system
-Almost all marine gastropods breathe woth a gill, but many freshwater species and majority of terredtrual have a pallial lung. Respiratory protein in hemocyannin, but may have hemoglobin
Gastropod reproduction
- varies greatly
- many marine species have separate sexes
- many terrestrial gastropods are hermaphrodites
- majoirty have internal fertilization but some prosobranch have external
True limpets classification
Subclass Eogastropoda Order: patellogastropoda
Largest species of gastropods are subclass
Orthogastropoda
What superorder of gastropods contains half of all species and must undergo external feritlization and egg give rise to free-swimming trochopore larvae
Caenogastropoda (Prosobranch)
Bivalve Body characteristics
- Hinged shell with left and right halves, capable of folding like a door, controlled by adductor muscles
- bilateraly symmestrical and laterally compressed body enclosed in bivalved shell
- mantle cavity is spacious, compared to other molluscs
- No radula or odontophore or head
Habitat of bivalves
- Most are sedentary or attached
- Aquatic (mostly marine)
Examples of Bivalves
Clams, oysters, scallops
Bivalve feeding
- suspension or filter feeding
- obtain food by filtering large amounts of water through the incurrent canal into their gills
- food trapped on thij mucus sheets on the gills are conducted anteriorly to the mouth hsing ciliaty mechanism
- uningested waste are ejected through the opening of the mantle cavity
- some are deposit feeders (protobranches)
Subclasses of bivalves
- protobranchia
- pteriomorphia
- paleoheterodonta
- heterodomta
- anomalodesmata
Subclass protobranchia characteristics
- habitst
- respiration
- feeding
- All marine and burrow is soft substrate
- possess small gulls for gas exchange
- gills are bipectinate (two combed)
- food materials collected in palp proboscides)
- mostly deposit feeders
- feed by extension of palp proboscidess through shell valves; collect myddy substrate and sort out nutrients beofre transferring to mouth otherwise ejected as pseudofaeces
Shipworm bivalve
-habitat and body
- shells mostly restricted to hesd reguon; used to burrow through wood; where they live
- posterior end has pallet for sealing up burrows when withdrawn
Shipworm bivalve feeding
Feed mainly on wood materials; digested by symbiotic bacteria in the portion of the stomach known as wood-storing caecum
-may filter feed on suspended particles/ microorganisms as a secondary dource of food
Class Scaphopoda are known as
Tooth shell or spade foot or tusk shell
Habitat of class scaphopoda
- Marine and live sendendary in burrows in sand/ mud substrates, usually in deep water
- members orient doen usually 30-40° where it is burried whith the larger end of shell deppest in the sediment
Class scaphopoda shell
NEVER SPIRAL
- possess linear, hollow, tusk-shaped, conical shells, which opens at both ends.
- larger aperatude is where the foot and head area are located.
- narrow end proteude above substrare
Class Scaphopoda feeding
Feed on microscopic animals like foraminiferans (shelled protozoan) using threadlike adhesive feeding tentacles called captaculac leading to the mouth
Class Scaphopoda lack which organs
Ctenidia, heart or cirulatory ststem; blood flow is through rhythymic movement thelugh large sinuses
No osphradium, but have specialized sensory receptors in the mantle cavity which function as respeiatory inlet and outlets, could seve similar role
Scaphopoda due possess these features
Foot, mantle cavity, radula, mantle tisue and shell
Class Cephalopod unique characterisitcs
- shells reduced or absent (most lack external shell, some have internal shells)
- foot is modified into arms and siphon
- closed circulatory system with arteries, veins and capillaries
- brain composed of fused ganglia protescted by a cartilaginous cranium
Cephalopod shell is divided by….
Septa into chambers which are linked by siphuncle (a strand of vascularized tissue, areanged in a tube composed of calcium carbonate
What is the most advanced class of molluscs and some exmaples of it
Cephalopods
Octopuses, squids, cuttlefish and nautilus
Cephalopod feeding
Carnivorous, feeding with tentacles, capable of fast moving
- crustaceans, fish, bivalves, jellyfish and other cephalopods
- are hunters and scavengers
- grasp and hold their pret with their arms and then break it into bite-sized pieces using their beaks; and they further process the food with a radula, a tongue-like form edges with teeth that scrapes the meat and pulls it into the cephalopods digestive tract
Habitat of class Cephalopods
- All marine
- found in all major bodies of water, primarily but not excluisvely salt water
- live at depths of 800’ but can survive at 3300’
- some trail their food source
- Nocturnal migration: some migrate vertically every day, spending most os the day in the dark depths hiding from predators and rising to the surface at night to hunt
Members of Cephalopods posses which mollusc features
Radula, ctenidia, mantle and foot
Siphuncle functions
Gas diffusion, liquid transport, maintaining osmotic pressure
What species of Cephalopod has a true shell
Nautilius sp.
Cephalopod locomotion
- mainly move by jet propulsion
- Nautilius sp. move by expelling wTer in and out of mantle cavirt via hollow thbe callaed a funnel or siphon
External anatomy adaptation of the squid
-Foot is modified into powerful muscular arms and extensible tentacles
Digestion and excretion of squid
Initiated in the stomach and completed un large associated caecum. Excretion is through one or more pairs of kident reffered to as a metanephridia
Heart of squids
Systemic heart: Single heart which circulates oxygenated blood from the gills to tissues
Pair of branchial heart which is associated with each gill
Chromatophores
In absence of an external shell, the skin is composed of several layers of colpured pigmanets which are overlaid by cells knon as irridocytes
-muscles of the skin and the brain control the expansion a d contraction of chromatophores, which change colpur for the purpose of camoflage, defense and courtship
All Cephalopods possess at least ____ arms and a ______
8
Pareot like bean
Cephalopod eyes
Simialr to humans with an iris, pupil, lens and in some a cornea
2 subclasses of Cephalopods
- Nautilodea: pocess external shell
- Coleoidea: pocess internal shells (squids and octopus)
- important orders: Decapoda: squids and Octopoda: Octopus
Mollusc reproduction
- all are diecuous
- some hermaprhodites
- fertilize external or internal
- larve stages vary from free living associated with fertilized eggs (Trochophore larve) or larvae with ciliated organs (velum) are termed Veliger
- Glochidium larva: modification of veliger larvae for ectopoarasitic life style on fish; found on some bivalve species; behavioural adaptation have enhanced the survival of the young stages and survival of species
5 characteristics of molluscs
- Poorly devleoped head
- Flat, musculr foot on ventral side
- Viseral mass
- Shell covering dorsal body
- Mantle to secrete shell
