Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
22 Cards in this Set
- Front
- Back
Phylum Molusca |
Molluscs, snails, slugs, clams, chitons, octopi, squid, etc... - 50,000 spp. (+35,000 fossil spp.) - diverse in body form, ecology, feeding habits. - most marine, but some in freshwater and terrestrial systems. - many are of considerable economical importance as food and pests. |
|
Phylum Mollusca : The true body cavity. |
- Eucoelmate animals -- have secondary body cavity that develops after the blastocoel has filled with mesoderm - Eucoelmate cavities arise in two different ways -- Schizocoely- Mesoderm splits apart on each side; the splits enlarge to form the cavity - occurs in molluscs, annelids, and anthropods -- Enterocoely- body cavity arises from outpocketing (coelomic vesicles) of the embryonic gut. - Occurs in echinoderms and chordates. |
|
Characteristics of Mollusca |
- Defined on the basis of the ancestral body plan; modern groups have diverged in various ways. - Primitive body plan: -- body divided into head, foot, and visceral mass -- presence of a shell to enclose a soft body -- the shell is secreted by a modified epidermis, the mantle. -- along the overhang of the shell, the mantle partially surrounds a space called the mantle cavity -Mantle cavity: -contains gills, the anus, and the excretory pores - a feeding structure called the radula. |
|
The molluscan shell |
Shell has three distinct layers - outer periosracum, made of conchiolin protein. - a middle layer, the prismatic layer, consisting of a blend of conchiolin and CaCO3 (chalky in consistency) - an inner layer, the nacreous layer, made of CaCO3 crystals (and sometimes some conchiolin) -- pearly in texture. |
|
Phylum Mollusca : Integument |
- Epidermis is a single cell layer. -- under the shell, the epidermis is a thickened mantle -- the mantle secretes the shell - Epidermis on the underside of the foot id frequently ciliated and supplied with mucous glands. - enables molluscs to glide over surfaces (ciliary swimming in a slime trail). |
|
Phylum Mollusca : Skeletal system |
- the shell of molluscs serves as an exoskeleton -- it provides from muscle attachment -- it provides for body support -- it also provides protection for the soft tissue underneath. |
|
Phylum Molusca : Muscular system |
- musculature is complex and regionally specialized. - body wall generally bears an outer circular layer, a middle diagonal layer, (sometimes 2) and an inner longitudinal layer. - also, specific muscles to.... -- move the radula and odontophore -- extend and retract the foot -- close the shell (bivalves) |
|
Phylum Molusca : Feeding and digestion |
Snails: herbivores (grazers), scavengers, and predators - use their radula in various ways in feeding. Chitons: grazers- use radula to scrape algae from rock surfaces Cephalopods: predatory- use arms & tentacles to capture prey, beak and radula to dismember it. |
|
The Molluacan Radula |
- conaists of a "belt" of chitinous teeth that slides over a cartilaginous tongue like odontophore. - specialized muscles pull the radula back and forth over the odontophore. - other muscles enable the odontophore to be protruded and retracted. Bivalves: - filter feeders- use mucus on their gills to trap food and particles. - deposite feeders- use tentacles flanking the mouth to extract food particles from sediments. |
|
Phylum Mollusca : Digestive system |
- mouth (with or without radula) - esophagus - stomach -- sorting & extracellular digestion -- associated digestive glads- more extracellular and/or intracellular digestion. - intestine - anus |
|
Phylum Mollusca : Excretion |
- the metanephridium- true kidney - has two open ends -- the first receives the wastes from the coelomic (pericardial) cavity, which leads into a coiled nephridial tubule. -- the second is a nephridial pore emptying out in the mantle cavity. |
|
Phylum Mollusca : Gas exchange |
- Gills or Lungs Gills: - gills occur in all molluscan classes -- primitively associated with the mantle cavity -- consists of a series of filaments projecting from each side of a supporting axis. -- filaments are ciliated, which generates a water current over the gill surfaces. -- the gills are vascularized to allow gas exchange with the blood. Lungs: pulmonate snails - mantle cavity has been sealed off from the outside , leaving only a small opening, the pneumostome. -inside lining of mantle cavity is moist and highly vascularized to facilitate gas exchange with air. - some pulmonates are secondarily aquatic, but still breath air. - others have developed secondary gills in the lining of the mantle cavity and exchange gases with water. |
|
Phylum Molusca : Circulatory function |
Open system: -blood is not channeled into capillary beds, but is emptied into tissue spaces within or surrounding the organs themselves. -blood spaces are interconnected and collectively = the hemocoel. Dorsal Heart: -one or two posterior auricles and an anterior ventricle - an aorta extends anteriorly from the ventricle. --ventricle pumps blood into the aorta, which empties into the anterior part of the hemocoel; -- after circulating through the hemocoel, the blood is collected by veins that carry it to the auricles. -- the auricles pass the blood bsck to the ventricle. |
|
Nervous and Sensory System |
Ancestrally - a circumesophageal nerve ring - two pairs of nerve cords extend posteriorly (one pair into the foot and the other into the visceral mass (often forming a loop).) - each pair of nerve cords is connected by transverse nerves, producing a "ladder type" arrangement. Gastropods - three pairs of anterior ganglia -- a pair of dorsal cerebral ganglia -- a pair of lateral pleural ganglia -- a pair of ventral pedal ganglia - posteriorly, paired parietal ganglia and visceral ganglia. Sensory Systems -snail tentacles: mechano- and chemoreceptors - arms and suckers of cephalopods - highly sensitive to both chemical and mechanical stimulation. -Osphradia: a patch of sensory epithelium -- surface is often rigid or folded to increase surface area. -- in gastropods --- highly developed in predators and scavengers --- serves as a chemoreceptor to locate prey or dead animals in the water. --- located on the mesenteries attached to the gills. -- in bivalves --- serves not only as a chemoreceptor, but also measures the amount of sediment entering the siphons. --- located inside the exhalent siphon. |
|
Molluscan eyes |
-eyes developed in snails, cephalopods - lenses form images - the cephalopod eye (octopus and squid only) is built much like that of a vertebrate -- photoreceptors directed toward the source of light, rather than toward the bscj of the eye as in vertebrates. -- focusing is done by muscles moving the lens back and forth in the cavity of the eyeball, rather than by changing the shape of the lens. |
|
Reproduction and development |
- Gasteopods are mostly hermaphroditic; all other groups mostly dioecious. - different methods of sperm transfer. -- primitively, eggs and sperm are shed into the water --- in some, fertilization may occur in the females mantle cavity and the developing of eggs can be brooded there. -- in many gastropods, there is copulation. --- the male system has a penis. --- female system has glands to add nutrients and form a capsule around the eggs. -- in cephalopods, sperm is placed in a packet (spermatophore) and transferred to the female with the tip of a modified tentacle. |
|
Reproductive systems |
- consists of an anterodorsal gonad (ovary or testis) and a system of gonoducts (oviduct or vas deferens). -- gonoducts may empty to the outside via a separate gonopore. -- or they may empty into the nephridial tube ( in this case the gametes leave through nephridiopore). - a more complex hermaphroditic system is seen in the pulmonate snails. |
|
Larval stages |
- Two characteristic larval stages, not present in all groups. --Trochophore : top shaped, with a band of cilia in the middle, and ciliary tufts at both ends. --Veliger: shell is beginning to develope, has a ciliated velum (consisting of two flaps) allows for swimming. |
|
Class Polyplacophora |
- chitons - characterized as follows: -- shell consists of eight dorsal plates surrounded by a fleshy girdle (Mantle). -- foot is flattened, used for locomotion. -- mantle cavity is a groove around the foot underneath the shell; gills lie in the mantle cavity -- Found in rocky intertidal habitats. |
|
Class Gastropoda |
- marine snails, land and aquatic snails, sea slugs, land slugs. - 40,000 species (plus 15,000 fossil spp.) - shell, when present is univalved and usually coiled - exhibit a developmental phenomenon called torsion. -- 180° counterclockwise rotation of the visceral mass. -- moves the mantle cavity anteriorly, as well as the anus. - foot is flattened and used for locomotion - use radula to feed as herbivores, scavengers, or predators.
SUBCLASS Prosobranchia -marine snail -distinguished by the following characters: -- shell present, although it may be reduced -- shell typically has an operculum --- a horny plate attached to the foot, which seal the shell when the animal is withdrawn inside. -- gills present in mantle cavity l, moved into a forward position. -- mostly dioecious.
SUBCLASS Opisthobranchia -sea slugs (nudibranchs), sea hares. - Opisthibranchs are distinguished by the following characters: -- reduction or loss of shell -- partial or complete detorsion ; anus and gills on right side of body. -- gills exposed along dorsum (the name "nudibranch" means naked gill). -- hermaphroditic SUBCLASS Pulmonata -land snails, aquatic snails, land slugs -Pulmonates have lungs (see respiratory system) - may be secondarily modified for breathing aquatically - shells lack an operculum - hermaphroditic |
|
Class Bivalvia |
- clams, oysters, mussels, scallops, etc. - have a bivalved shell, with the two valves held together by hinge teeth And powerful adductor muscles. - inner surfaces of shell covered by a thin mantle - siphons Bring water in and out of the mantle cavity. - use their gills for filter feeding on particulate matter suspended in the water. Radula has been lost. - foot is spade shaped and used for digging. |
|
Class Cephalopoda |
- Nautiluses, octopuses, squid, cuttlefishes, and extinct ammonoids. - foot produced into arms and tentacles that surround the mouth, as well as a ventral siphon. -- water in the mantle cavity forces out through the siphon to generate jet propulsion (excellent swimmers) - shell present (ammonoids. Nautiloids) reduced and covered by the mantle (squid, cuttlefish) , or absent (octopuses). - excellent vision (eyes similar to those of vertebrates), highest intelligence among invertebrates. - dioecious; sperm transfer via a spermatophore placed inside the females mantle cavity using a modified tentacle. |