Role of genes in Development
The tremendous increase in diversity during the Cambrian
explosion is a puzzle.
Developmental genes may play an especially important role.
Changes in developmental genes can result in new
Cnidaria is divided into three classes- Anthozoa c , Scyphozoa c , Hydrozoac
Marine, Sea Anemones, Sea Pansies, Corals, Sea Fans.
Solitary or colonial, brightly colored.
Only exist as polyp, medusoid stage is absent. Polyp undergoes, ase
PORIFERAP (Latin porus pore; ferre to bear)
Aquatic, majority marine, few fresh water.
Sedentary, limited movement.
Size, few mm to more than a meter in diameter & height.
Brightly colored. Color from endosymbionts or cell pigments
Diversity of Protozoa
Some of the important groups of protozoa are as follows:
Includes Paranema & Euglena.
Includes fresh water, marine or brackish water forms.
The body is elongate with an invagination called the res
Eumetazoa: The Radiata
The subkingdom Eumetazoa contains animals that evolved distinct tissues.
Two distinct cell layers form in the embryos of these animals: an outer ectoderm and
an inner endoderm.
Cnidaria or Coelenterata
(gr. Knide, nettle +L. aria; l
(Platy-Flat, Helminth- Worm)
Includes 20,000 extant sp.
Habitat- Free living forms- terrestrial, fresh water, marine; parasites, symbionts.
Size 1mm- 30cm long. Most 1-3cm. Some tape worms may attain a length of
Include round worms, around 20,000 described species.
Very abundant, found free living in soil, aquatic habitat, as parasites of plants &
Size, usually small, 1mm- 5 cm in size, few parasites may attain a length of
INTRODUCTION TO BILATERIA
Five Key Transitions in Body Plan of Animals
1. Evolution of Tissues
The evolution of tissues is the first key transition in the animal body plan.
The simplest animals, the Parazoa, lack defined tissues and organs. Ex. sponges
Large subgroup of mostly motile protists is protozoa.
Protozoa are considered as first animals (proto-first; zoan-animals).
It is a polyphyletic taxon which includes nearly 65,000 described sp.
of plant-like, animal-like a
Composed of fewer than 100sp.
Also called sea walnuts or comb jellies.
Marine, found abundant in warm waters, though some occur in artic and temperate regions.
They are planktonic, floating in surface waters, but fe
Classification- grouping things together on the basis of features they have in common.
The science of classification is called taxonomy.
Purpose-to organize the vast number (10-100 million kind) of known living organisms into
Neurulation: Initiating the Nervous
Gastrulation produces an embryo with three
Organogenesis occurs next and involves the
formation of organs and organ systems.
Neurulation occurs early in organogenesis and
begins the formation of t
Modes of insect development
Ametabolous - insect development with no metamorphosis. Immature stages appear very similar to
the adults, except that they lack genitalia.
Hemimetabolous - insect development in which ther
ORIGIN OF METAZOA
Metazoa are multicellular animals.
Theories for the origin of Metazoa
It was originally proposed by Ernst Haeckel
in 1874 and later modified by Metschnikoff
1883 and later by Libby Hyman in 1940.
Metazoa derived from colo