Invertebrate Zoology
Lecture 1: Introduction &
Bauplans (begin)
Lecture outline
 Introduction to course
 Animal Bauplans
Bauplan Overview
 Defined
 Key functions of animal bodies
 Limited options
 Bauplan as mix of ancestral and derived features
Key aspects of body plans (begin)
 Symmetry
 Cellularity, body size, germ layers, body cavity
Introduction to Course
 See handouts!
Animal Bauplans
Bauplan overview
 Definition: “A structural plan or design”
Organ systems and whole animals
How does structure relate to function?
Bauplan, overview
 Key functions of animal bodies
Make a list—audience participation!
Bauplan overview
 Limited options
Recurring themes in
body plans
 Types of symmetry
Some aspects vary
more freely
 Reproductive structures
Bauplan overview
 What limits options?
Structural constraints
 Head and bilateral symmetry
 Exoskeleton and size limits
Genetic constraints
 The mutation must arise for
the character to exist
Several other
constraints…
 Examples?
Bauplan overview

Bauplan is a mix of
ancestral and derived
characters
 Example: chambered
nautilus


Ancestral molluscan
features (such as…?)
Derived cephalopod
features (such as…?)
Bauplans: key features
 Symmetry
Asymmetry
Radial symmetry
 Many variations
Bilateral symmetry
Bauplans: key features
 Cellularity, size, germ layers, body cavity
Advantages to >1 cell?
 S/V ratios (understand this!)
 Specialized cell types (=multicellularity)
Size constraints even with >1 cell. Why?
 How overcome in the most “simple” animals?
Bauplans: key features

Cellularity, size, germ
layers, body cavity
 Development of internal
systems

Such as…?
 Same principles apply:
elongation, folding etc…
to maximize surface area


Example 1: Ctenidium
Example 2: Kidney
Littorina (a snail),
partial internal view
Bauplans: key features

Cellularity, size, germ
layers, body cavity
 Which derived characters
promote complexity?
 Embryonic germ layers
 Porifera: none!
 Cnidaria & Ctenophora:
diploblastic
 All others: triploblastic
 NAME THOSE LAYERS!
Bauplans: key features

Cellularity, size, germ layers, body cavity
 Which derived characters promote
complexity?

Body cavities
 Additional space with gases and nutrients
 Additional surface area (exchange)
 Allows for larger body/ larger organs
 Cushions organs
 Can serve as hydrostatic skeleton
Bauplans: key features

Cellularity, size, germ
layers, body cavity
 Which derived characters
promote complexity?
 Body cavity
 None if not
triploblastic!
 Acoelomate =
triploblastic but no
body cavity
 Blastocoelomate
(Pseudocoelomate)
=body cavity from
blastocoel
 Eucoelomate = body
cavity from mesoderm