CLASS GASTROPODA Flashcards
What are the characteristics of class Gastropoda?
Uni-valved, a-symmetrical, cephalisation
Describe the a-symmetrical shell
Coiled and torted
What are the tentacles?
They are chemoreceptive
What are statocysts?
A small organ for balance and orientation
What is an osphradium?
An organ that tests the incoming water
What is the planispiral?
An unstable, asymmetrical shell
Describe the consequences and solutions of an asymmetric shell
The lengthened shell and cone shape resulted in a stability problem, coiling and torsion solved this
What is torsion?
The visceral mass turning 180 degrees
Describe the gut shape
‘U’ shape
What is the problem with the gonoduct openings, kidney and anus being above the head?
A sanitary problem
What is the solution to the gonoduct openings, kidney and anus being above the head and restricted waterflow?
Tthere’s an opening for an exhalent current. Water goes into the mantle cavity & out the opening. e.g. keyhole limpets
Describe the shell
Whorls wrapped around central columella, oldest are smallest
What secretes the new shell?
The mantle margin around aperture
What is the function of the operculum?
Closes the aperture
What is the orientation of some shells?
Most are dextral (right coiled), few are sinistral (left coiled)
What organism is the excretion, respiration and circulation like?
The generalised mollusc
What are the exceptions to the similarities between the generalized mollusk and gastropoda?
The right metanephridium, gill and atrium are lost
Explain the changes of the pulmonates as a result of moving onto land
Both gills are lost, the mantle cavity is heavily vascularized and there’s a lung
Name the structure in a grazer
Radula
Name the structure in a hunting carnivore
Proboscis and a simplified gut
Name the structure in deposit, filter and suspension feeders
Modified gills, mucus nets and parasites
What is the flexible structure or water intake and how is it made?
The siphon, made by the anterior left mantle margin being rolled
In what kind of gastropods is the siphon well developed?
Predatory or scavenger snails
What other organism is the nervous system in gastropoda like and exceptions?
The generalized mollusk. Exceptions are torsion and cephalisation.
Explain the process of torsion
The visceral mass is twisted which brings the mantle cavity and anus to an anterior position above the head
Describe the reproduction process in early gastropods
Dioecious and external fertilization
What are some other reproduction traits of gastropoda?
Hermaphrodites, internal fertilization and behavior patterns are more complicated
What is simultaneous hermaphroditism?
Male and female at the same time
What is protandric hermaphroditism?
The individual changes sex at some point in its life, male to female
Name the groups of organisms that are simultaneous hermaphrodites
Pulmonata and Opisthobranchia
Name the groups of organisms that are protandric hermaphrodites
Prosobranchia (slipper snails
Name the groups of organisms that are protandric hermaphrodites
Prosobranchia (slipper snails
What kind of larva does archaeogastropoda have?
Planktonic trocophore larva
What kind of larva do most other gastropods have?
Derived veliger larva
How do veliger larva swim?
Using a ciliated velum
What does the veliger larva have before it settles?
A shell and torsion
What kind of development does the class Pulmonata have?
Direct
