Marine animals, general

X. Marine animals.

A. General.

1. More variety than plants, with some phyla exclusively found in the oceans.

2. Invertebrates versus vertebrates, the usual way to break up this multitude of species in the study of zoology.

a. 5% of the animals are vertebrates, the remainder are invertebrates.

b. Artificial categorization of sorts, comparing one subphylum versus the rest of the phylum Chordata and all the other phyla of invertebrates.

c. May make more sense to compare Arthropods versus all else, or even Insects versus non-insects.

d. Reflects the bias of the investigators, but also there is some biological basis for this categorization. The vertebrates represent the most complex (highest evolved?) group of animals so that a study of the simpler versus the complex might be in order.

3. The phyla of animals may be categorized as subphyla by some workers (or even classes by others). There are some phyla that are not listed that may be considered valid by some workers. There are splitters and lumpers in zoologists.

4. The vast diversity is often overwhelming, but all animals must meet the same basic needs for existence.

a. Procurement of food.

b. Procurement of oxygen.

c. Perpetuation of the species, or reproduction.

d. Maintenance of water balance.

e. Removal of metabolic wastes

5. The body structures and physiology of animals reflect their adaptations to meet these

problems of existence, but they are also correlated with:

a. Type of environment.

b. Size of animal.

c. Mode of existence.

6. Marine environment versus the terrestrial:

a. More stable and uniform, with the concentrations of salts and dissolved gases fluctuating

b. Buoyancy provides support, so that the largest IS in the oceans.

invertebrates and vertebrates are all marine forms.

c. Composition of sea water is isotonic to the tissue fluids of most marine animals.

d. Buoyancy and uniformity make sea water an ideal medium for animal reproduction:

1). Eggs can be shed and fertilized in sea water and develop as floating

embryos and larvae with minimal water balance difficulties.

2). Little danger of desiccation, salt imbalance, or of being swept away by

rapid currents, as may be present in rivers.

3). Larvae can be transported by ocean currents to allow for fairly wide

dispersal.

4). Larvae can obtain food for development without a large amount of yolk

in egg.

7. Increase in size leads to surface area to volume ratios decreasing. In small animals, the exchange of gases and wastes are carried out by diffusion and internal transport instead of by organs for excretion.