INVERTEBRATES
door Marc Kochzius & Thomas Merckx (2024-2025)
1. Introduc on
BIODIVERSITY
What is biodiversity?
“The sum total of all bio c varia on from the levels of genes to ecosystems.”
1,75 million species known, 7-20 million s ll to be discovered
3 hierarchical levels:
1. Ecological diversity: variety of different ecosystems
2. Organismal diversity: number of species
3. Gene c diversity: gene c difference within and between species
How many extant species are there?
2/3 of all species are invertebrates
Why is biodiversity important?
Provides essen al goods and services to human socie es
Value of coastal ecosystems = US$ 12,5 trillion
How is biodiversity threatened?
5-20% of the known species
Ex nc on caused by humans: started in prehistoric mes (coloniza on of islands of the Indo-
Pacific) 1/4 of the world’s bird species gone
Since 1600: 650 plant and > 480 animal species = ex nct
Definitions
Biological species A group of interbreeding natural popula ons that do not successfully mate or
reproduce with other such groups.
Cohesion species The smallest group of cohesive individuals that share intrinsic cohesive
mechanisms.
Ecological species A lineage which occupies an adap ve zone different in some way from that or
any other lineage in its range and which evolves separately from all lineages
outside its range.
Evolu onary A single lineage of ancestor-descendant popula ons which is dis nct from
species other such lineages and which has its own evolu onary tendencies and
historical fate.
Morphological The smallest natural popula ons permanently separated
species from each other by a dis nct discon nuity in heritable characteris cs.
Phylogene c The smallest group of organisms that is diagnos cally dis nct from other such
species clusters and within which there is parental pa ern of ancestry and descent.
Recogni on species A group of organisms that recognize each other for the purpose of ma ng
and fer liza on.
Elena Crommen - 1
,NEW SPECIES OF GIANT CLAM
= Largest bivalves
Morphological species concept based on 5 shell
measurements
Biological species concept based on spawning frequency
Phylogene c species concept based on phylogene c tree
based on mitochondrial DNA sequences
Conclusion: 4 different species
TREE OF LIFE: 3 DOMAINS OF CELLULAR LIFE
Phylogenomic consensus (= overeenstemming) on evolu onary rela onships within tree
Bacteria, Archaea & Eukaryota (Plantae, Fungi and Animalia)
METAZOA
Every phylogeny is a hypothesis!
Body symmetry
Radial symmetry Bilateral symmetry
Diploblas c animals Triploblas c animals
2 germ layers (ecto- and endoderm) 3 germ layers (ecto-, endo- and mesoderm)
Elena Crommen - 2
,Coelom
Coelomata Acoelomata
(Eu)coelomata Pseudocoelomata
True coelom Coelom
No coelom
Completely lined by mesoderm Lined by meso- and endoderm
e.g. Mollusca, Annelida,
e.g. Nematoda e.g. Platyhelminthes
Arthropoda and Echinodermata
Development: Protostomia vs. Deuterostomia
Protostomia Deuterostomia
Cleavage: spiral and determinate Cleavage: radial and indeterminate
Cell division diagonal to ver cal axis of embryo; Cell division parallel/perpendicular to ver cal
early determina on of cells axis; early embryonic cells can s ll develop
complete embryo ( twins)
Coelom forma on: schizocoelie Coelom forma on: enterocoelie
Solid masses of mesoderm split and form Folds of archenteron form coelom
coelom
Blastopore: mouth develops from blastopore Blastopore: anus develops from blastopore
Elena Crommen - 3
, 2. Porifera
DIVERSITY
8000 described species (mostly marine, ± 150 in freshwater)
3 groups: Demospongiae, Calcarea and Hexac nellidae
o Demospongiae: siliceous spicules and/or spongin (80-90% of all species)
o Calcarea: calcite spicules (500 extant species)
o Hexac nellidae (glass sponges): siliceous spicules (400 extant species)
Growth forms
Massive sponges Encrus ng sponges Boring (= borende) sponges
Sponge body types
Asconoid design:
Hollow cylinder
Limited to small body size (1 mm in diameter)
Pinacoderm (= surface covered by monolayer of flat
cells)
Choanoderm (= atrium/spongocoel lined with a
monolayer of flagellated collar cells (choanocytes)
Os a (= small pores)
Osculum (= large opening in upper, free end of body
Synocoid design:
Improvement of area-to-volume ra o by alterna ng
surface inpockets (= incurrent canals) with interior out
pockets (= choanocyte chambers)
Size in cen meters
Prosopyles (= opening between incurrent and
choanocyte chambers)
Elena Crommen - 4
door Marc Kochzius & Thomas Merckx (2024-2025)
1. Introduc on
BIODIVERSITY
What is biodiversity?
“The sum total of all bio c varia on from the levels of genes to ecosystems.”
1,75 million species known, 7-20 million s ll to be discovered
3 hierarchical levels:
1. Ecological diversity: variety of different ecosystems
2. Organismal diversity: number of species
3. Gene c diversity: gene c difference within and between species
How many extant species are there?
2/3 of all species are invertebrates
Why is biodiversity important?
Provides essen al goods and services to human socie es
Value of coastal ecosystems = US$ 12,5 trillion
How is biodiversity threatened?
5-20% of the known species
Ex nc on caused by humans: started in prehistoric mes (coloniza on of islands of the Indo-
Pacific) 1/4 of the world’s bird species gone
Since 1600: 650 plant and > 480 animal species = ex nct
Definitions
Biological species A group of interbreeding natural popula ons that do not successfully mate or
reproduce with other such groups.
Cohesion species The smallest group of cohesive individuals that share intrinsic cohesive
mechanisms.
Ecological species A lineage which occupies an adap ve zone different in some way from that or
any other lineage in its range and which evolves separately from all lineages
outside its range.
Evolu onary A single lineage of ancestor-descendant popula ons which is dis nct from
species other such lineages and which has its own evolu onary tendencies and
historical fate.
Morphological The smallest natural popula ons permanently separated
species from each other by a dis nct discon nuity in heritable characteris cs.
Phylogene c The smallest group of organisms that is diagnos cally dis nct from other such
species clusters and within which there is parental pa ern of ancestry and descent.
Recogni on species A group of organisms that recognize each other for the purpose of ma ng
and fer liza on.
Elena Crommen - 1
,NEW SPECIES OF GIANT CLAM
= Largest bivalves
Morphological species concept based on 5 shell
measurements
Biological species concept based on spawning frequency
Phylogene c species concept based on phylogene c tree
based on mitochondrial DNA sequences
Conclusion: 4 different species
TREE OF LIFE: 3 DOMAINS OF CELLULAR LIFE
Phylogenomic consensus (= overeenstemming) on evolu onary rela onships within tree
Bacteria, Archaea & Eukaryota (Plantae, Fungi and Animalia)
METAZOA
Every phylogeny is a hypothesis!
Body symmetry
Radial symmetry Bilateral symmetry
Diploblas c animals Triploblas c animals
2 germ layers (ecto- and endoderm) 3 germ layers (ecto-, endo- and mesoderm)
Elena Crommen - 2
,Coelom
Coelomata Acoelomata
(Eu)coelomata Pseudocoelomata
True coelom Coelom
No coelom
Completely lined by mesoderm Lined by meso- and endoderm
e.g. Mollusca, Annelida,
e.g. Nematoda e.g. Platyhelminthes
Arthropoda and Echinodermata
Development: Protostomia vs. Deuterostomia
Protostomia Deuterostomia
Cleavage: spiral and determinate Cleavage: radial and indeterminate
Cell division diagonal to ver cal axis of embryo; Cell division parallel/perpendicular to ver cal
early determina on of cells axis; early embryonic cells can s ll develop
complete embryo ( twins)
Coelom forma on: schizocoelie Coelom forma on: enterocoelie
Solid masses of mesoderm split and form Folds of archenteron form coelom
coelom
Blastopore: mouth develops from blastopore Blastopore: anus develops from blastopore
Elena Crommen - 3
, 2. Porifera
DIVERSITY
8000 described species (mostly marine, ± 150 in freshwater)
3 groups: Demospongiae, Calcarea and Hexac nellidae
o Demospongiae: siliceous spicules and/or spongin (80-90% of all species)
o Calcarea: calcite spicules (500 extant species)
o Hexac nellidae (glass sponges): siliceous spicules (400 extant species)
Growth forms
Massive sponges Encrus ng sponges Boring (= borende) sponges
Sponge body types
Asconoid design:
Hollow cylinder
Limited to small body size (1 mm in diameter)
Pinacoderm (= surface covered by monolayer of flat
cells)
Choanoderm (= atrium/spongocoel lined with a
monolayer of flagellated collar cells (choanocytes)
Os a (= small pores)
Osculum (= large opening in upper, free end of body
Synocoid design:
Improvement of area-to-volume ra o by alterna ng
surface inpockets (= incurrent canals) with interior out
pockets (= choanocyte chambers)
Size in cen meters
Prosopyles (= opening between incurrent and
choanocyte chambers)
Elena Crommen - 4
