Lecture 3+4 (Bio-2040)

Animal Characteristics

A set of characteristics that define what we call animals.

4 characteristics that make an animal

1) Eukaryote

2) Have no cell wall

3) Heterotrophic

4) Multicellular

Exemption to being heterotrophs as animals

Some animals live in symbiosis with algae, therefore are not only heterotrophs.

Other animals live associated to chemosynthetic bacteria and therefore don’t need to eat

Exemptions to being multicellular animals

A zygote is a single cell, therefore all animals are single celled at some point in there life

Steps of animal architecture

• how complex

• Which symmetry

• Need for a secondary cavity

• What type of development

Why are unicellular organisms small

There metabolism is based on osmosis and therefore requires a high surface area to volume ratio

Complexity increases…

Cell specialization and intercellular dependency

Complexity decreases….

Average cell size

Tissue

A group of cells carrying on a similar function

Epithelial tissue

The coverage or lining of internal and external surfaces, including skin and organs

Connective Tissue

A tissue that binds, protects and supports and gives structure to other tissues and organs

Muscular

Tissue allowing movement by contraction of cells + fibres. At least 3 types

Types of muscle tissue

• smooth

• Cardiac

• Skeletal

Neural Tissue

Tissue controlling and coordinating other tissues. Reception and conduction of stimuli done by neurons and glias

Porifera

Aquatic filter feeders with a basic morphology. They are diploblastic. Instead of a mesoderm they have a mesoglea or mesophyl

Body shapes of porifera

• ascon

• Sycon

• Leucon

Diversity of Porifera

Includes about 8,500 species, most marine habitats. Play important roles for water quality and habitat

Choanocytes

Collar cells, the main and most unique cells in sponges. It can be distinguished by a flagellum and a collar

Collar in Choanocytes

Retains food particles

Flagellum in choanocytes

moves the water

Amoebocytes

multipurpose accociated cells for digestion

Spicule

form the skeleton

Sclerocyte

Cell that secretes spicules

Porocyte

Waterflow regulation

Archaeocyte

digestion

pinacocyte

T-shaped epithelial cell

Fragmentation Asexual Reproduction

A portion of the sponge detaches and builds a new one

Gemmula’s Asexual Reproduction

“seeds” filled with amoebocytes that are sealed during harsh conditions and released once conditions improve

Sponge Sperm

derived from choanocytes

Sponge Oocytes

derived from archaeocytes

External Sexual Reproduction (Sponges)

Sperm and Oocytes are released into the column

Internal Sexual Reproduction (Sponges)

Sperm released in water are caught by another sponge and moved into the mesoglea, where oocytes are waiting

Parenchyma

the product of the fertilization

Dispersal Stage

Important for genetic exchange in sessile species, after drifting the larva will settle and form a new sponge

Classification of Porifera

Based on shape and minerals forming the spicules

Calcarea

3-ray, calcarean (CaCO3) spicules. Mainly in shallow water

Hexactinellida

Glassy sponge with 6-ray siliceous spicules. All deep-sea

Demospongiae

Various shapes, siliceous and collagen. 80% of all sponges. all Leucon

Spherical Symmetry

in many protozoans (not in animals). Infinite plains to divide by

Radial Symmetry

Mainly Cnidarians and Ctenophores. Round or Tubular that can be divided across 2+ plains

Bilateral Symmetry

most animals, divided across one plain

Cnidarians

Diploblastic organisms have mesoglea instead of mesoderm

Gastrovascular Cavity

where extra-cellular digestion takes place

Endoderm

a layer of cell lining the gastrovascualr cavity

Mesoglea

A matrix with cells and fibres that is prominent in the medusa. Works as a hydrostatic skeleton that provides shape and helps float or drift. In a polyp, it is thin and not important.

Ectoderm

Epidermis with a net of sensory cells (ocelli, statocytes) around the top

Cnidocyte

Unique cells with harpoon-like structures (nematocytes) are used for hunting