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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 3 000 million years

ago

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

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3000

2000

1000

presentOCEANS LAND

First bacteriaSingle-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

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Distance of relationship

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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

groupsSome 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 proteinsGenetic 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

rubensOther, 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:

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the sequence before use in class

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