Date: ____________________________

Animals: Lower Invertebrates

J.1: Introduction to Animals

1. What makes an animal an animal? The key attribute share by all animals is obtaining nutrients by ingestion Requires a complex array of behaviours that include responding to stimuli in the

environment, thought, and unique physical structures Animals cover every conceivable method of obtaining nutrients The diversity is a factor that contributes to the level of development and degree

of specializations

2. How are the phyla organized? This phylogenetic tree organizes the 9 major phyla of Kingdom Animalia according to

their symmetry, level of development of their tissues, and body cavities. The organisms are increasingly more complex in tissue organization as you move

towards the right of the diagram

3. How do the organisms get organized into phyla?1. Body plans: this is based upon the type of symmetry displayed by the animal

i. Bilateral symmetry: one plane of symmetry dividing the animal into two relatively equal halves – a left and a righteg. Snakes, worms, fish, humans, etc.

ii. Radial symmetry: more than one plane of symmetry; can be divided in multiple ways to have two relatively equal halveseg. Jellyfish and hydra

iii. Asymmetrical: no symmetry to the body plan.eg. Sponges

2. Lateral surfaces: are found only in animals with bilateral symmetryi. Dorsal: the “back” or the surface not dedicated to the position of delicate

organ systems or openings into the body; generally the more exposed surface

ii. Ventral: the “front” or the surface that generally faces the groundiii. Anterior: revers to the head end where the nerve tissue aggregates to

from the brainiv. Posterior: revers to the hind end where the anus and tail (if present) are

located.

3. Radial symmetrical animals lack cephalization (no designated head or brain)i. Oral: the surface where the mouth is located and is protected and less

exposedii. Aboral: the opposite side from the mouth

4. What about the nature of the digestive system? Gastrovascular Cavity:

A sac-like system A single opening acts as both mouth and anus

Alimentary System A one-way system The mouth and anus are separate Contains specialized organs Very efficient

5. What about Movement?Sessile

Aquatic non-mobile animals Passive feeders that capture food from the water Have radial symmetry or are asymmetric

Mobile Show bilateral symmetry Search actively for food or better feeding areas, relocate due to environmental

conditions, hide from predators or prey, etc.

6. What about reproduction? All animals reproduce via sexual reproduction Generally gametes the haploid (n) sperm and ova combine to produce a

diploid (2n) zygote Asexual reproduction can occur in organisms with low levels of specialization Many animals – especially those that are parasitic – demonstrate

polymorphism The offspring will undergo many body shape changes before obtaining the

adult body shape The juvenile and adult forms often bear little resemblance to each other Metamorphosis occurs to achieve the adult form

Advantage: less stress on a single food source and allows for greater distribution

7. How does specialization affect Reproduction? The more highly specialized organisms engage in reproduction that ensures a

higher success of fertilization – namely internal fertilization Broadcasters: a process done by simpler aquatic animals

the gametes are shed into the water in hopes that fertilizations will occur

factors such as location and timing pay key roles Hermaphroditic: specialized with both male and female reproductive organs

produce both sperm and ova but do not engage in self-fertilization Done by less motile animals Cross-fertilization is promoted through the timing of release of the

different gametes

J.2: Phylum Porifera: Sponges

8. What are sponges? The simplest animals Characteristics include:

Sac-like body plan Generally considered to asymmetric or radially symmetrical Sessile Hermaphroditic Lack tissue, but have specialized cells Lacking in cephalization Pass water through their body cavity called a spongocoel

9. The anatomy of a sponge

A. Choanocyte: (collar cells) specialized cells that line the internal cavity and create a water current via movement with their flagella

B. Ectoderm: the outer protective skinC. Ostia: incurrent openings through which water enters the internal cavity –

have porocytes that regulate the size of the opening to control water flowD. Osculum: (excurrent opening) a common opening where the water leaves

from the internal cavityE. Amoebocyte: socialized cells that secrete salts and absorb and digest food

filtered from the water

F. Spicule: hard support structures H. Gemmule: asexually produce spore-like structures that are produced when

the water conditions become inclement; they are sent out the osculum with the “spent water”

10. How do sponges reproduce? Sponges are hermaphroditic Sperm are produced by amoebocytes and are released en masse through the

osculum When the sperm encounters sponge of the same species with mature ova,

fertilization follows and a zygote will develop It is a ciliated larva that swims away to find a place to become established and

grow Sponges can also reproduce asexually by budding Can also undergo regeneration to regrow damaged or missing portions