Invertebrate Zoology: Bauplan/Classification

1. Plato (427-347 BC) -Eidos
2. Aristotle (384-322 BC) -The Great Chain of Being
3. Nicolaus Steno (1638-1686) -What is a fossil? -tongue-stones or Glossopetrae
3. Carolus Linnaeus (1758) -development of Binomial Nomenclature
4. Jean-Baptiste Lamarck (1815 & 22) -Les Invertebrates
“…we perceive that, relative to the animal kingdom, we should chiefly devote our attention to the invertebrate
animals, because their enormous multiplicity in nature, the singular diversity of their systems of organization, and of their means of multiplication…, show us, much better than the higher animals, the true course of nature, and the means which she has used and which she still unceasingly employs to give existence to all the living bodies of which we have knowledge. (1803)
5. Charles Darwin (1859) -Living Cirripedia, The Balanidæ, (or sessile cirripedes); the Verrucidæ. Vol. 2
* On the Origin of Species

What are the Central issues in determining evolutionary relationships…
Assumption – “all living [organisms] evolved from a single ancestral form…and are related to one another.”
1. Homology – Morphological characteristics that share a common evolutionary (genetic) origin
2. Polarity – Direction of evolutionary change – ancestral state –vs– derived state


1. Phenetics –
(Numerical Taxonomy)
2. Evolutionary Systematics –
(Classical Taxonomy)
3. Phylogenetic Systematics –
(Cladistics)
* Linnean Classification –
* PhyloCode –

A Classification system developed by Robert R. Sokal and Peter H.A. Sneath. Phenetics is based on grouping taxonomic units based on their character states (morphological = form, meristic = number). Numerical algorithms are used to create a taxonomy using cluster analysis of the patterns of similarity. These clusters are
thought to represent the underlying genetic relationships.

System using anatomy and ultrastructure of the phenotype to infer the underlying genotype
Classical taxonomy is the basis for the Neo-Darwinian
Synthesis (1936 – 1947)
* G.G.Simpson – Paleontology
* RA Fisher/S Wright/JBS Haldane – Genetics
* E Mayr – Systematics, Population Ecology

System developed by Willi Hennig (1966)
Clades (Gr. = branch) are based on synapomorphies (= shared-derived characteristics) in monophyletic groups
of organisms.
Decisions are based on the most recent common ancestor.

* Linnean Classification – A phenotypically
based system dating from Linnaeus. Rankedbased
nomenclature
* PhyloCode – A genotype-based system
stemming from Hennig’s Cladistics. Cladebased
nomenclature

1. Number of Cells
2. Number of Tissue Layers
3. Body Cavity Development (Coelom)
Morphological Features…
4. Body Symmetry
5. Locomotion & Support
6. Feeding Mechanisms
Physiological Features…
7. Excretion & Osmoregulation
8. Gas Exchange & Circulation
9. Nervous System
10. Reproduction