Biodiversity

Definitions

Radial – a structure in which similar parts are arranged around a central axis like the spokes of a wheel. Any section through the mouth and down the body length divides the body into identical halves.

Bilateral – or two-sided symmetry, a structure in which a central longitudinal plane divides the body into two equal but opposite halves (i.e. left and right hand sides).

Definitions

Zero – some animals lack true tissues.

Diploblastic – animals that have only two germ layers (ectoderm and endoderm).

Triploblastic – animals that have three germ layers (ectoderm, mesoderm and endoderm).

Equivocal – this information is unknown for this particular taxa.

Definitions

Acoelomate – a solid-bodied animal lacking a cavity between the gut and the outer body wall.

Pseudocoelomate – an animal whose body cavity is not completely lined by mesoderm. Unlike true coelomates, the body cavity is derived from the blastocoel rather than from the mesoderm.

Coelomate – an animal that possesses a true coelom (fluid-filled body cavity lined by tissue completely derived from the mesoderm).

Definitions

Present – division of the body of an organism into a series of similar or identical units recurring along the length of the body. In each unit there is a pattern of muscle blocks, blood vessels, excretory organs, epidermal structures and elements of the nervous system. In many taxa groups of segments have become specialised for a variety of functions e.g. walking, feeding and sensory reception.

Absent – the body is not divided into segments.

Definitions

Absent – some animals lack a skeleton.

Hydrostatic skeleton – a skeletal system composed of fluid held under pressure in a closed body compartment.

Exoskeleton – a hard encasement on the surface of an animal, such as the shell of a mollusc, that provides protection and points of attachment for muscles.

Endoskeleton – a hard skeleton buried within the soft tissues of an animal, such as the bony skeletons of vertebrates or the cartilaginous skeleton in sharks.

Polymorphic – there are examples of a number of different types of skeletons.

Definitions

Absent – some animals lack a gut.

One way gut – these animals have a digestive tube (alimentary canal) that extends between two openings, a mouth and an anus. Food moves along the canal in a single direction.

two way gut – this is found in animals with a relatively simply body plan. These animals have a gastrovascular cavity that is a digestive sac with a single opening. The gastrovascular cavity functions in both digestion and the distribution of nutrients throughout the body and therefore has a dual role as both mouth and anus.

Polymorphic – there are examples of different types of gut.

Definitions

Absent – an organism lacking a coelom (acoelomate) or a pseudocoelomate (where the body cavity is not completely lined with or derived from the mesoderm).

Protostomes – a developmental mode in which the coelom develops from the splitting of solid masses of mesoderm cells.

Deuterostomes – a developmental mode in which the coelom is forms as outpockets of mesodermal tissue.

Note: Protostomes and deuterostomes development also differ in the fate of the blastopore. In protostome development, the mouth develops from the blastopore. In deuterostome development, the blastopore forms the anus. Protostome development is also characterised by cells which undergo spiral cleavage, whereas in deuterostome the cleavage is radial (see Campbell p.660 8th Ed).

Definitions

Absent – some animals lack a circulatory system.

Open – a circulatory system in which fluid called hemolymph bathes the tissues and organs directly and there is no distinction between the circulating fluid and the interstitial fluid.

Closed – a circulatory system in which blood is confined to vessels and is kept separate from the interstitial fluid.

Water vascular system – unique to echinoderms, a network of hydraulic canals branching into tube feet that function in locomotion, feeding and gas exchange.

Polymorphic – there are examples of different types of circulatory systems.