LU2 Invertebrate Classification (Class by evolutionary relationship (All…
LU2 Invertebrate Classification
Class by Cell numbers
Made up of many cells with high degree of specialization / functions
eg. marine and freshwater invertebrates (metazoa)
Mollusks, crustaceans, annelids
Made up of a single cell with no membrane-bound organelles and without nucleus (DNA
floats freely in the cytoplasm)
Many marine and freshwater inverts are unicellular-Choanozoa
Protistst (phylum protista)
Class by body symmetry
Each right and left side of animal body are approx mirror image
Highly correlated with cephalization*. Results in distinct anterior and posterior end
Produces 2 mirror image when a slice is made parallel to the animal long (anterior and posterior axis).
Perpendicular cut to the mid line creates 2 dissimilar pieces
Crustacean and annelids
Animal body can be divided into 2 approx equal halves by any cut that passes tru the centre of the organism
Coral, jellyfish (Phylum Cnidaria)
Has no order pattern to their gross morphology
Some marine invert has this body formation
Many species with ext appearance are the epitome of uncontroversial radial symmetry have this symmetry
Sponges (Phylum Porifera)
Class by development patterns
Multi cellular invert have been divided into 2 group based on the number of distinguishable germ layers form during embryogenesis
No. of germ layers or embryonic tissue layers
2 distinct layer form during cell movement into anterior of embryo
Ectorderm - outer layer
Endoderm- inner most layer
Members of only 1/2 phyla considered to be diploblastic
Example: Corals, jellyfish, sponges
Most meatozoan are triploblastoic
During ootogeny of triploblastic animals, cells give rise to the third layer - mesoderm
Mesodermal layer lies btw outer ectodermal tissue and inner endodermal tissue
Example: Most invert taxa
Tripoblastic animal lacking internal body
Region lying btw the outer body wall and the gut of acoelomate is solid, occupied by mesoderm and there is no trace of an int body cavity during embryological dev.
Example: flatworms (phylum Platyhelminthes)
Region bte the outer body warm musculature endoderm of the gut is a fluid-filled cavity
Cavity is derived from blastocoel, int space developd in embryo prior to gastrulation.
Termed pseudocoel and organism housing said to be pseudocoelemate
Pseudo is not intended to disparage the coel the body cavity is genuine
Pseudo prefix is not a true coeleom.
Example: round worm (phylum Nematoda)
Triploblastic animal with a true coelom
Animal posessing such a body are coelomate or eucoelomate
Example: Mollusc and arthropod
Coelom formation may occur by 2 dissimilar mechanism
Mode of coelom formation is used to assign the coelomate into 2 major subgroups: Protostomes or deuterostomes
Embryonic mouth formation
Coelom formation occur by gradual enlargement of a split in the mesoderm
Coelom typically form tru evagination of the archenteron into blastocoel of embryo
Coelom of deuterostomes is formed from a part of what eventually becomes gut, coelom formation in this group of animals is termed enterocoely
Example: echinoderms, cephalochordates
Class by evolutionary relationship
Established by Carl Linnaeus in 1758
A hierarchical system
The members of any given taxon show a high degree of similarity and presumed to be more closely related to each other than to the members of any other taxon
All the members of any particular phylum are presumed to have evolved from a single ancestral form
Such groups, are said to be monophyletic
Theoretically, the members of one species are reproductively isolated from members of all other species
The species, therefore, forms a pool of genetic material that only members of that species have access to and that is isolated from the gene pool of all other species
The scientific name of a species consists of generic name and the specific name that are usually italicized in print or underlined in writing
Generic name begins with a capital letter, but the specific name does not (Eg:
Once the generic name is spelled out, it may be abbreviated when used subsequently, (Eg:
Class by habitat and lifestyle
This category reflect degrees of ecological similarity rather than the closeness of evolutionary relationships
For example, marine animal and terrestrial animal.
Marine animal are then divided into 3 parts which are subtidal, intertidal or open ocean
Some animals may be mobile (locomotion)of immobile(sessile) or sedentary(exhibiting only limited locomotive capabilities)
Besides that, some aquatic animals are benthic(lives on the ocean floor)Example,macrobenthic and meiobenthic and aquatic organisms that moves with respect to the movement of the medium(drifters)
Animals are differentiated based on how they feed. There are herbivore(plant eaters), carnivore( meat eaters) and omnivore( meat and plant eaters). Some species are filter feeder that removes small particles in the surrounding(suspension feeder)whereas others ingest sediment (deposit feeder).
Members from the same species often closely associate with those of another species.These symbiotic association relate to the feeding biology of one or both of the animals.
Ectosymbionts live near or on the body of the host, while endosymbionts live in the body of the host.
If the symbionts benefit each other their relationship is mutualistic or mutualism. When the benefit only goes to one participant and the other is not harm it is known as commensalism and the benefited other is called comensal.
And paratsites that generally subsisting on their host blood or tissue. This is known as parasitism. The boundaries between parasitism, mutualism, comensalism, and predation are not clear.
When a parasite kills its host it becomes a predator but if the parasite produces a metabolic end product that benefits the host then it is mutualistic.
These transitional forms make tidy categorization of animals into man made schemes difficult. Definition of some categories have been changed by various workers to improve the fit but every rule seem to have an exception.
*conc of nervous and sensory tissues and organs at one end of the animal