1
Noncoelomate Invertebrates
Chapter 32
2
Invertebrate Phylogeny
• Two Approaches– Traditional reconstructions are based on
key aspects of body architecture. lumping phyla that share fundamental
aspects of body plan– New reconstructions employ molecular
comparisons. focus on differences in ribosomal RNA
sequences
3
Traditional Protostome Phylogeny
4
Novel rRNA Protostome Phylogenies
• Two major clades– Lophotrochozoans
flatworms mollusks annelids
– Ecdysozoans roundworms arthropods
5
rRNA Protostome Phylogeny
6
Parazoa
• Sponges (Porifera)– most lack symmetry– adults are sessile– little coordination among cells– three functional layers
choanocytes mesohyl outer epithelial layer
spicules
7
Parazoa
• Beating of flagella lining interior draws water in through numerous pores.
– Small organisms are filtered out of the water, which flows through passageways and eventually out an osculum.
• Reproduction done by fragmentation as well as sexually.
8
Sponges
9
Radiata
• Distinct tissues– epidermis and nervous system develop
from ectoderm– gastrodermis develops from endodermis
• True body symmetry– Radiata
Cnidaria Ctenophora
– Bilateria all others
10
Radiata
• Cnidarians– nearly all marine– carnivorous
cnidocytesnematocysts
– two basic body plans polyps and medusae
– fertilized eggs give rise to planulae– internal extracellular digestion
11
Two Body Forms
12
Cnidarians
13
Radiata
– Classes of Cnidarians Hydrozoa - hydroids Scyphozoa - jellyfish Cubozoa - box jellyfish Anthozoa - sea anemones and corals
• Ctenophorans (comb jellies)– propel through the water by means of
eight comb-like plates of fused cilia
14
Bilateral Acoelomates
• Bilateral symmetry– digestive tract is only internal cavity
• Phylum Platyhelminthes: the flatworms– Flatworms are among the simplest
bilaterally symmetrical animals, but they have a definite head at the anterior end, and do possess organs.
15
The Bilateral Acoelomates
• Flatworms– cannot feed, digest, and eliminate food
simultaneously– absorb food directly through body walls– have excretory system
flame cells– most are hermaphroditic
16
Flatworm Architecture
17
The Bilateral Acoelomates
– Class Turbellaria: turbellarians only one of three classes are freeliving
– Class Trematoda: flukes life cycle liver fluke Clonorchis sinensis
miracidium - eggs (passed in feces) rediae - elongated, nonciliated larvaecercariae - tadpole-like larval stagemetacercariae - adult stage
18
The Bilateral Acoelomates
– Class Cestoda: tapeworms hang on to inner walls of their hosts by
specialized terminal attachment organs, and absorb food through their skins.
scolex - attachment organneck - unsegmentedproglottids - repetitive segments
19
The Bilateral Acoelomates
• Phylum Nemertea: ribbon worms– simplest animals that possess a complete
digestive system mouth and anus
20
The Pseudocoelomates
• Internal body cavity– pseudocoel serves as hydrostatic skeleton
gains rigidity from being filled with fluid under pressure
– lack a defined circulatory system
21
The Pseudocoelomates
• Phylum Nematoda: roundworms– bilaterally symmetrical unsegmented worms
covered by flexible, thick cuticle– mouth equipped with stylets– food passes through mouth as result of
sucking action of pharynx– lack flagella or cilia– reproduction is sexual– Trichinella regularly parasitize humans
22
Roundworms
23
Nematode-Caused Diseases
• Trichinosis - Trichinella• Pinworms - Enterobius• Intestinal roundworms - Ascaris• Filariasis - Filaria
24
The Pseudocoelomates
• Phylum Rotifera: rotifers– small, bilaterally symmetrical, basically
aquatic animals with a crown of thick cilia at their heads
– well developed food processing apparatus– “wheel animals”
• Phylum Cycliophora– relatively new
circular mouth surrounded by fine, hairlike cilia
Top Related