Systematics

Systematics is the science of categorizing organisms into like groups and establishing their relationship relative to each other.

Seven major categories are used to classify organisms:

kingdom phylum class order family

genus species

Systematics

kingdom:

phylum:

class:

order:

family:

genus:

species:

In case of humans:

Animalia

Chordata

Mammalia

Primates

Hominidae

Homo

sapiens

Note that Homo sapiens is italicized. Another acceptable notation would be tounderline the Genus and species… Also note that the first letter of the Genus iscapitalized, whereas the species is not.

Systematics – Domains and Kingdoms

Note that Taxonomies are constantly changing. Part of the reason is new information(mostly based on molecular biology) being discovered about different groups.

Here for example, it is suggested that there should be three Domains, each of whichwould then contain the various Kingdoms. Other suggested changes are occurring at the other taxonomic levels of classification…

Systematics –Kingdoms

Relationships are not quite as simple as suggested by this figure.

Ideally, each branch point is where a new form(i.e. adaptation) has created two distinct formsfrom a single common ancestor.

Kingdom Animalia

Animal features:

1. Multicellular

2. Heterotrophic

3. Lack cell walls

4. Motile (at least at some stage of life)

5. Typically can reproduce sexually (although there is a lot of variation)

6. Most can rapidly respond to external stimuli

Kingdom Animalia – Phylum Porifera

Phylum Porifera – Sponges (9000-10,000 species)

General features:

Cellular level of organization with no tissues or organs

Adults are typically asymmetrical

Cells tend to be totipotent

Adults are sessile suspension-feeders; larval stages are motile

Skeletal elements, when present, composed of calcium carbonate,silicon dioxide, and/or collagen fibers

An ancient group, probably originated from flagellated protistancestors

Can reproduce sexually or asexually

Kingdom Animalia – Phylum Porifera

Sponges are essentially made up of a loose aggregate of cells… You could even passa sponge through a mesh, and the individual cells would come back together to reform the animal.

Kingdom Animalia – Poriferan Body Plan

Kingdom Animalia – Poriferan Body Plan

Choanocytes (collar cells) produce water flow through the sponge body.Why is water flow such an important part of biology of sponges?

Feeding

Gas exchange

Waste removal

Reproduction

Kingdom Animalia – Poriferan Body Plan

Sponges depend on the water flowfor every aspect of their lives.

The only way they can get larger isby creating complex series of watercanals throughout the body.

The different body forms are: A. asconid B. simple syconoid C. complex syconoid D. leuconoid

Kingdom Animalia – Poriferan Body Plan - Spicules

Sponges use spicules made up ofsilicon dioxide and calcium carbonatefor both structural support as well asfor defense against potential predators.

Cells called sclerocytes are responsible for producing the spicules.

The spicules can have many forms.They vary from one species to the next, and have different shapes, sizes,forms, and make-ups.

In addition to the spicules, spongesuse layers of the protein collagenfor additional structural support.this intercellular matrix is referred to as the spongin.

Kingdom Animalia – PoriferaSponge Classification:

1. Class Calcarea - Sponges with calcium carbonate spicules.

2. Class Demospongiae – Sponges with siliceous spicules, spongin fibers, orboth. Approximately 90% of all poriferans, they include boring sponges, bath sponges, and many other forms…

3. Class Hexactinellida – Deep water sponges with siliceous six-pointedspicules and long siliceous fibers… includes the Genus Euplectella, or the Venus’s flower basket.

Kingdom Animalia – Porifera

Sponges are often very colorful. Why do you thinkthis is?

Kingdom Animalia – Cnidariacorals, sea anemones, jelly fish, box jellies, hydra, sea fans

Phylum Cnidaria (~3000 species); general characteristics:

Have tissue level of organization, with two tissue layers (diploblastic)

Have radial symmetry

Have specialized stinging structures called cnidae

Have only one opening to the body cavity / digestive cavity

Have no head, no centralized nervous system (only a nerve net), no discrete gas exchange, excretory, or circulatory systems

Exhibit alternation of asexual polypoid and sexual medusoid generations.

Kingdom Animalia – CnidariaGeneral body forms

2 body forms: Polyp and Medusa

2 tissue layers (diploblastic), ectodermto the outside (blue), and endoderm to the inside (yellow). The layer in between is just a jelly-like materialcalled the mesoglea (it is not a truetissue)

Only one opening to the gastrovascular cavity acts as mouthand anus

Kingdom Animalia – CnidariaGeneral body forms

Cnidarians have radial symmetry:

Kingdom Animalia – Cnidaria

All cnidarians have specialized stinging or adhesive structures called cnidae

When triggered, the the cnidocyte cellsdischarge the cnidae. A specialized formof cnidae called the nematocyst, has a harpoon like structure that enters theflesh of the potential predator or prey,releasing neurotoxins.

Discharge acceleration isat 40,000g!!!

Need both physical and chemical stimulation to induce release. Why do you think this is?

Kingdom Animalia – Cnidaria

No matter what the size or shape of the cnidarian, they all have cnidae, and theyare all made up of one or more of polyp or medusoid body forms

Kingdom Animalia – Cnidaria

In general, cnidariansalternate betweensexual medusoid and asexual polypoid forms

There are a lot ofexceptions though…

Kingdom Animalia – Cnidarian Classification

1. Class Hydrozoa – Both polyp and medusa present, with both marine and freshwater forms represented. Includes hydra, siphonophora, and the Portuguese man-of-war.

Kingdom Animalia – Cnidarian Classification

2. Class Anthozoa – Medusa absent, these are entirely marine cnidaria including corals, sea anemones, sea fans, sea pens, and zoanthids.

Kingdom Animalia – Cnidarian Classification

3. Class Scyphozoa - Medusa dominant (although both body forms are present), these are entirely marine cnidaria including the jelly fish.

Kingdom Animalia – Cnidarian Classification

4. Class Cubozoa – Meduasa cuboidal in shape, these marine cnidaria include the box jellies.

Kingdom Animalia – Cnidarian Diversity

Hydra Box jelly Jelly fish Sea fan

Sea pen

Corals Zoanthids Sea anemone

Kingdom Animalia – Symbiosis in Cnidaria

Many cnidarians live in symbiosis with unicellular algae… This symbiosis maybe the reason for their great success in otherwise nutrient poor waters of the tropics...

Kingdom Animalia – Platyhelminthes

Have tissue level of organization, with three tissue layers (triploblastic – with endoderm, ectoderm, and mesoderm)

Have bilateral symmetry

Have only one opening to the body cavity / digestive cavity

Have cephalization (and at least at some stage of their lives, so will all the animals that we’ll discuss from now on).

Are hermaphroditic, with complex reproductive systems

Phylum Platyhelminthes – flat worms (~20,000 species); general characteristics:

Can be free-living or parasitic Have great regenerative abilities!!!