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Introducing biological classification

Introducing life in the oceans Evolution and relationships Summary How we classify living things

Introducing life in the oceans Evolution and relationships Summary How we classify living things

Life is thought to have started in the oceans, more than million years ago

For most of this time, nearly all life was in the oceans

Time (in millions of years before the present) present OCEANSLAND First bacteria Single-celled plants Seaweed-like plants First complex animals Jellyfish-like fossils Shelled fossils First fish Single-celled plants Land plants & invertebrates Tree ferns & vertebrates Dinosaurs Flowering plants 3000

Introducing life in the oceans Evolution and relationships Summary How we classify living things

Scientists use various techniques to decide how plants and animals are related to each other They can then build a family tree for all living things

Time Distance of relationship Bacteria Protozoa Single-celled algae Multicellular plants Multicellular animals Fungi

There are about 25 major groups of animals All of these are found in the oceans, and most are found only in the oceans

Here, we will look at six animal groups, which include some of the most important and abundant types in the oceans

First we will look at the main features of each group, and then show how they are related

Porifera (Sponges) Most simple multicellular animals, comprising colonies of amoeboid and flagellated cells. Body structure a hollow chamber, with the walls supported by silica or calcium carbonate spicules. Feed by drawing water into the chamber and filtering out small food particles

Coelenterates Body radially-symmetrical, consisting of two distinct layers of cells. Gut with a single opening, surrounded by tentacles. Tentacles bear stinging cells, used to capture or paralyse prey. Two basic body plans – sac-like attached ‘polyps’ and umbrella-shaped swimming ‘medusae’

Annelid worms Body segmented, long and thin and typically round or oval in section. Most body segments identical, separated from each other by septa. Closed blood system. Nervous system comprising a ventral nerve cord, with an anterior ring. Each segment may carry a single pair of bristly limbs

Arthropods External skeleton based on chitin, often mineralised. The limbs are multi-jointed, one pair per body segment. Bilaterally-symmetrical body typically divided into distinct regions. Blood circulates within the body cavity. Nervous system comprising a ventral nerve cord

Molluscs Unsegmented body divided into visceral mass and ‘head-foot’. Head bears mouth, foot used for locomotion. Visceral mass contains main body organs and is enclosed within ‘mantle’, which often secretes a shell. Blood system usually open, circulating within the body cavity

Echinoderms Unsegmented body, with obvious five-rayed symmetry. Skin with calcareous plates and spines. Tube-feet in skin used in locomotion. No blood system, and simple nervous system

Vertebrates Internal bony skeleton (cartilage in some groups) and segmented muscles. The backbone protects a dorsal main nerve cord, which is expanded in the head for form the brain. Well-developed blood system, with a heart with 3 or 4 chambers. Two pairs of limbs. Teeth composed of dentine and enamel

You will have seen obvious differences between the six groups Some groups contained very simple animals, other were more complex

We can build a family tree for these groups of animals

Sponges are the most primitive group of multicellular animals

PORIFERA (Sponges) Coelenterates are more complex than sponges, but still have relatively simple body structures

At this point, the tree branches into the two main groupings of complex animals PORIFERA (Sponges) COELENTERATES Molluscs, arthropods and annelids are grouped together on this side of the tree Vertebrates and echinoderms are grouped together on this side

PORIFERA (Sponges) COELENTERATES VERTEBRATES ECHINODERMS ANNELIDS ARTHROPODS MOLLUSCS

Introducing life in the oceans Evolution and relationships Summary How we classify living things

The relationships on these family trees are based on the degree of similarity between organisms

Similarity is determined in a number of different ways: Body form (anatomy) Development (embryology) Composition of chemicals such as proteins Genetic sequencing

The greatest degree of similarity exists between individuals within the same species We group species into larger units based on similarity

The common starfish has the species name Asterias rubens Other, very similar starfish also belong in the genus Asterias

All starfish are grouped together into the class Asteroidea Genus: Asterias Species: Asterias rubens Class: Asteroidea (about 1600 species) Starfish are grouped with other echinoderms into the phylum Echinodermata

All animals are in the kingdom Animalia Genus: Asterias Species: Asterias rubens Class: Asteroidea (about 1600 species) Phylum: Echinodermata (about 8000 species) Kingdom: Animalia (> 1 million species) Eukarya - organisms with a cell nucleus

Introducing life in the oceans Evolution and relationships Summary How we classify living things

Life evolved and diversified in the oceans Living things are related by a common ancestry You have seen that -

Animals have developed complex body plans from simple ancestors Classification is based on relationship You have seen that -

NOTES for USERS The material in this slide show is designed to support the teaching of science at Key Stage 1 A full description of the slide show, and linked activities for students, can be found on the National Marine Aquarium (NMA) web-site: Teachers are free to amend the slide show in whatever way they feel fit, or to use slides in other contexts. However, please note that neither the NMA nor the designers will accept responsibility for modifications, and original material remains copyright of the NMA Individual images used in the slides are copyright of NMA or STEP, except where acknowledged separately The slides have been set up to display as A4 landscape format. If they are incorporated into other slide sequences with different display settings, change in aspect ratio and text location will occur The slide sequence contains the minimum of effects and transitions. However, there are some automated animations, and teachers will wish to make sure that they are familiar with the sequence before use in class Use the PowerPoint notes viewer to obtain additional information for some slides