NATIONAL OPEN UNIVERSITY OF NIGERIA
COURSE CODE : BIO 207
COURSE TITLE: LOWER INVERTEBRATES
, Course Code & Course Title: BIO 207: Lower Invertebrates
Course Writer: Dr. Patrick A. Audu
Course Editor
Programme Leader Dr. Ado Baba Ahmed
National Open University of
Nigeria, Lagos
Course Coordinator Mr. Adams, Abiodun E
National Open University of
Nigeria, Lagos
NATIONAL OPEN UNIVERSITY OF NIGERIA (NOUN)
, TABLE OF CONTENTS
CONTENTS PAGE
GENERAL INTRODUCTION …………………………………………… 1
MODULE 1: TAXONOMY OF INVERTEBRATES …………………… 2
Unit 1: Classification of Organisms …………………………………. 3
Unit 2: General Classification of Invertebrates…………………….. 7
Unit 3: A Systematic Approach to Lower Invertebrate Structure
and Levels of Organization …………………………………. 10
Unit 4: Phylum Sarcomastigophora ………………………………… 16
Unit 5: Phylum Ciliophora …………………………………………... 21
MODULE 2: THE STRUCTURE AND LEVEL OF ORGANIZATION
OF THE MESOZOA, PARAZOA AND METAZOA ……. 26
Unit 1: Mesozoa ………………………………………………………. 26
Unit 2: Parazoa ……………………………………………………….. 30
Unit 3: Classification and Characteristics of the Poriferans ………. 37
Unit 4: The Metazoa ………………………………………………….. 41
Unit 5: The phylum Cnidaria ………………………………………... 47
MODULE 3: STRUCTURE AND LEVELS OF ORGANIZATION
OF THE PLATYHELMINTHES …………………………… 52
Unit 1: The Phylum Platyhelminthes …………………………………. 52
Unit 2: The Turbellaria ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 55
Unit 3: The Trematoda …………………………………………………. 60
Unit 4: Class Cestoidea (Cestoda) ……………………………………… 64
Unit 5: The Phylum Nematoda ………………………………………… 71
, THE LOWER INVERTEBRATES
General Introduction
Earlier, you studied all animals together under the broad subject Animalia. From this level on,
we shall be examining their classification, characteristics and economic importance. All animals
along with the animal like organisms can be classified into two main groups, namely
invertebrates - animals (and animal-like organisms) without backbone and vertebrates - animals
with backbone.
The invertebrates are grouped into two; the lower invertebrates and the higher invertebrates. The
lower invertebrates are those invertebrates without specific organs. Take for example Porifera
which does not live on the tissue level of organization. Cnidarians and Ctenophorans have simple
tissues but are not advanced enough to form organs. Finally you arrive at the phylum
platyhelminthes which does form simple organs but lacks a tube within the digestive system
(acoelomate). A false coelem is first seen in the Nematodes. Higher developed invertebrates have
a true coelem like mollusks, annelids, echinoderms, and arthropods.
In this course, we shall introduce you to the lower invertebrates’ morphology and levels of organization,
by examining their classification and characteristics. We shall also be examining the adaptive features to
mode of life and the general aspects of the vital functions of some of these organisms.
4
COURSE CODE : BIO 207
COURSE TITLE: LOWER INVERTEBRATES
, Course Code & Course Title: BIO 207: Lower Invertebrates
Course Writer: Dr. Patrick A. Audu
Course Editor
Programme Leader Dr. Ado Baba Ahmed
National Open University of
Nigeria, Lagos
Course Coordinator Mr. Adams, Abiodun E
National Open University of
Nigeria, Lagos
NATIONAL OPEN UNIVERSITY OF NIGERIA (NOUN)
, TABLE OF CONTENTS
CONTENTS PAGE
GENERAL INTRODUCTION …………………………………………… 1
MODULE 1: TAXONOMY OF INVERTEBRATES …………………… 2
Unit 1: Classification of Organisms …………………………………. 3
Unit 2: General Classification of Invertebrates…………………….. 7
Unit 3: A Systematic Approach to Lower Invertebrate Structure
and Levels of Organization …………………………………. 10
Unit 4: Phylum Sarcomastigophora ………………………………… 16
Unit 5: Phylum Ciliophora …………………………………………... 21
MODULE 2: THE STRUCTURE AND LEVEL OF ORGANIZATION
OF THE MESOZOA, PARAZOA AND METAZOA ……. 26
Unit 1: Mesozoa ………………………………………………………. 26
Unit 2: Parazoa ……………………………………………………….. 30
Unit 3: Classification and Characteristics of the Poriferans ………. 37
Unit 4: The Metazoa ………………………………………………….. 41
Unit 5: The phylum Cnidaria ………………………………………... 47
MODULE 3: STRUCTURE AND LEVELS OF ORGANIZATION
OF THE PLATYHELMINTHES …………………………… 52
Unit 1: The Phylum Platyhelminthes …………………………………. 52
Unit 2: The Turbellaria ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 55
Unit 3: The Trematoda …………………………………………………. 60
Unit 4: Class Cestoidea (Cestoda) ……………………………………… 64
Unit 5: The Phylum Nematoda ………………………………………… 71
, THE LOWER INVERTEBRATES
General Introduction
Earlier, you studied all animals together under the broad subject Animalia. From this level on,
we shall be examining their classification, characteristics and economic importance. All animals
along with the animal like organisms can be classified into two main groups, namely
invertebrates - animals (and animal-like organisms) without backbone and vertebrates - animals
with backbone.
The invertebrates are grouped into two; the lower invertebrates and the higher invertebrates. The
lower invertebrates are those invertebrates without specific organs. Take for example Porifera
which does not live on the tissue level of organization. Cnidarians and Ctenophorans have simple
tissues but are not advanced enough to form organs. Finally you arrive at the phylum
platyhelminthes which does form simple organs but lacks a tube within the digestive system
(acoelomate). A false coelem is first seen in the Nematodes. Higher developed invertebrates have
a true coelem like mollusks, annelids, echinoderms, and arthropods.
In this course, we shall introduce you to the lower invertebrates’ morphology and levels of organization,
by examining their classification and characteristics. We shall also be examining the adaptive features to
mode of life and the general aspects of the vital functions of some of these organisms.
4
