Biological classification

Classificacion of living things is essential to any study of animals and plants, it is usually based on anatomical similarities and differences and is called taxonomy (Taxis means arrangement and nomos means method). The modern taxonomic system was developed by the Swedish botanist Carolus (Carl) Linneaeus (1707-1788). To distinguish different levels of similarity, each classifying group, called taxon (pl. taxa) is subdivided into other groups. The broadest category is the domain, followed by kingdom, phylum, class, order, family, genus and species, the most specific one. The members of a particular species are similar enough to allow interbreeding to result in fertile offspring. To complicate a little bit more we also have intermediate grades such as subclass, suborder, superfamily, subfamily and subgenera.

In 1990 Carl Woese introduced the taxon domain, he divided all the living things in three domains that are organised based on the difference between eukaryotes and prokaryotes. The three domains are as follows:

Archea (Archeabacteria) consists of archeabacteria, bacteria which live in extreme environments. The kingdom Archaea belongs to this domain.

Eubacteria consists of more typical bacteria found in everyday life. The kingdom Eubacteria belongs to this domain.

Eukaryote encompasses most of the world's visible living things. The kingdoms Protista, Fungi, Plantae, and Animalia fall under this category.

Under the three domains we have six kingdoms Plants, Animals, Protista, Fungi, Eubacteria and Archae (or Archabacteria). The first two are commonly understood and will not be expounded here.

Protista, the third kingdom, was introduced by the German biologist Ernst Haeckel in 1866 to classify micro-organisms which are neither animals nor plants. Since protists are quite irregular, this kingdom is the least understood and the genetic similarities between organisms in this kingdom are largely unknown. For example, some protists can exhibit properties of both animals and plants.

Fungi are organisms which obtain food by absorbing materials in their bodies. Mushrooms and moulds belong in this kingdom. Originally, they were part of the plant kingdom but were recategorised when they were discovered not to photosynthesise.

Eubacteria are bacteria, made up of small cells, which differ in appearance from the organisms in the above kingdoms. They lack a nucleus and cell organelles. They have cell walls made of peptidoglycan.

Archae (or Archaebacteria) are bacteria which live in extreme environments, such as salt lakes or hot, acidic springs. These bacteria are in their own category as detailed studies have shown that they have unique properties and features (ex. unusual lipids that are not found in any other organism)which differ them from other bacteria and which allow them to live where they live. Their cell walls lack peptidoglycan. Here is a diagrama of the the taxa in hierarchical order:

Now we can return to our seashells. Seashells belongs to the phylum Mollusca of the animal kingdom that is the larger phylum of invertebrates and has around 85 000 species. This philum is the second phylum with larger number of specimens comprising 23% of all the named marine organisms, but exists mollusks living in fresh water and terrestrial habitats. This animals are highly diverse, not only in size and in anatomical structure, but also in behaviour and in habitat. The phylum is typically divided into 9 or 10 classes, of which two are entirely extinct. Six of this classes are related to seashells: Gastropoda, Bivalvia, Cephalopoda, Scaphopoda, Polyplacophora and Monoplacophora that will be describe in others messages. Cephalopods mollusks, such as squid and octopus, are among the most neurologically advanced of all invertebrates—and the giant squid is one of the largest known invertebrate species. The gastropods (snails and slugs) are by far the most numerous mollusKs in terms of classified species, and account for 80% of the total.

Mollusks have developed such a varied range of body structures, it is difficult to find defining characteristics to apply to all. The most general characteristic of mollusks is that they are unsegmented and bilaterally symmetrical; the presence of a mantle with a significant cavity used for breathing and excrecion, and an organized nervous system.

Here are 2 examples of seashells biological classification :

Domain: Eukaryota

Animal: Kingdom

Phylum: Mullusca

Class: Gastropoda

Subclass: Caenogastropoda

                                               Order: Neogastropoda

Superfamily: Conoidea

Family: Conidae

Genus: Conus

Species: pertusus

Domain: Eukaryota

Animal: Kingdom

Phylum: Mollusca

Class: Bivalvia 

Subclass: Heterodonta

Infraclass: Euheterodonta 

Order: Veneroida 

Superfamily: Cardioidea

Family: Cardiidae 

Subfamily: Fraginae

Genus: Corculum

Species: roseum