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Invertebrate Zoology


Kingdoms: Protista, Chromalyeolata & Animalia






Kingdom: PROTISTA (Protozoa)


Phylum: Sarcomastigophora

Class: Rhizopoda (Sarcodina)

Order: Amoebina

Order: Testaceea

Order: Heliozoa

Order: Radiolaria

Order: Foraminifers


Class: Mastigophora (Flagellata)

Subclass: Phytomastigina

Order: Eglenoidea

Order: Volvocina

Order: Dinoflagellata


Subclass: Zoomastigina


Phylum: Apicomplexa (Sporozoa)

Class: Aconoidasida

Class: Conoidasida




Phylum: Heterokontophyta

Phylum: Haptophyta

Phylum: Cryptophyta

Superphylum: Alveolata

Phylum: Ciliophora

Class: Ciliata (Infusoria)

Subclass: Protociliata

Subclass: Euciliata

Class: Phyllopharyngea
class: Suctoria




SubKingdom: Parazoa

Phylum: Porifera -- Sponges


SubKingdom: Metazoa (Eumetazoa)

Phylum: Ctenophora

Phylum: Cnidaria

Phylum: Platyhelminthes

Phylum: Nemertinea
Phylum: Acanthocephala

Phylum: Rotifera

Phylum: Gastrotricha

Phylum: Bryozoa (Ectoprocta)




Phylum: Brachiopoda

Phylum: Phoronidea

Phylum: Nematoda (Nemathelminthes)

Phylum: Nematomorpha (Gordiacea)

Phylum: Echinodermata

Phylum: Mollusca

Phylum: Onychophora -- velvet worms

Phylum: Annelida

Phylum: Arthropoda

Subphylum: Crustacea

Class: Branchiopoda  brine shrimp etc.

Class: Remipedia -- blind crustaceans

Class: Cephalocarida  horseshoe shrimp

Class: Maxillopoda  barnacles, fish lice,


Class: Ostracoda  seed shrimp

Class: Malacostraca  lobsters, crabs,



Subphylum: Trilobitomorpha

Class: Trilobita  trilobites (extinct)


Subphylum: Myriapoda

Class: Chilopoda  centipedes

Class: Diplopoda  millipedes

Class: Pauropoda -- related to centipedes

Class: Symphyla -- garden centipedes


Subphylum: Chelicerata

Class: Arachnida  spiders, scorpions, etc.

Class: Xiphosura  horseshoe crabs, etc.

Class: Pycnogonida  sea spiders

Class: Eurypterida  sea scorpions-extinct


Subphylum: Hexapoda

Class: Insecta  insects (Entomology)

Class: Entognatha: Collembola, Protura,


Phylum: Hemichordata

Phylum: Chordata


List of Plates

Glossary (Scientific Terms)

Sample Examinations

Grants & Donations

Bibliography, Citations


CLICK on underlined file names & illustrations for details:




Invertebrate zoology is a biological discipline that involves the study of invertebrates. Although vertebrates possess many characters in common with invertebrates they are distinguished by possessing a backbone. Invertebrates lack a backbone. Invertebrates comprise over 95 percent of all animal species and certainly more than that percentage in animal biomass. They have been extensively used in biological researches of heredity, embryology and regeneration. They also have had great practical importance related to insect damage, the causes of human and animal disease and directly as food, pearls, buttons, etc.


As we proceed to examine the various characteristics of the different animals it becomes obvious that a common bond unites all animals in that we must all respire, consume food, excrete wastes and reproduce.


Zoology may also be divided further into other principal categories such as:


Arthropodology = The study of arthropods, including Arachnology (spiders & mites), Entomology (insects) and Carcinology (crustaceans). Malacology = The study of mollusks. Invertebrate Paleontology = The study of extinct invertebrates. For a classification of Invertebrates as treated herein please see Table 1. However, the principal groups may also be noted as follows:


Arthropoda -- insects, arachnids, crustaceans

Nematoda -- round worms

Mollusca -- squid, snails, bivalves

Annelida -- segmented worms (earthworms, leeches, polychaetes)

Nemertinea -- ribbon worms

Platyhelminthes -- flat worms

Acoelomorpha (controversial phylum: probably Platyhelminthes)

Rotifera -- wheel animals

Ctenophora -- Comb jellies

Cnidaria -- jellyfishes, corals, sea anemones, hydras

Porifera -- sponges

Echinodermata - starfishes, sea urchin


The arrangement of the various subgroups is based on ever increasing complexity and presumed evolution of the most primitive [(e.g., Protista (Protozoa)] to the more advanced organisms. Previous names of groups are included in parentheses. There continues to be wide disagreement on classification, and although further rearrangements are expected as more biological and biochemical data are forthcoming, the presented design should enable identification of major orders, families and genera. The Protista (Protozoa) are included herein as a primitive precursor group. Emphasis has been placed on morphological and behavioral characteristics that are easily discernable, and a simple diagrammatic style suitable for lecturing is used for most of the illustrations. A binocular microscope with a 20X magnification is advisable for those wishing to view living and preserved specimens. Greater detail on a particular group or species may be found by referring to publications listed in the Bibliography or through Internet searches.


This is a self-contained database with a minimum of links outside its limits. Independent Internet searches are encouraged for greater detail on a particular animal group.



Kingdom: PROTISTA (Protozoa) -- unicellular microbes, plankton


Phylum: Sarcomastigophora , Class: Rhizopoda (Sarcodina)


[Mycetozoa have been included in the Myxomycetes or Amoebozoa of Mycology]


The above differ also in their nuclear content. Foraminifer and Radiolara use asexual reproduction. Flagella also occur in the Sarcodina. There are many that form symbiosis with algae. For example, Zoochlorellae are Heliozoa with green algae; Zooxanthellae are Radiolaria with yellow algae.


Their importance ranks high. Endomoeba histolytica is a notorious intestinal parasite and they serve as an important link in the food chain.


The Protista that have been called Protozoa, or "First Animals" are more like the early primitive animals than any other living forms. They have changed less than other groups. They are usually single-celled animals that may exit in a colony. But each individual cell retains its independence. Their simplicity is often deceiving. Amoebe, for instance, do all the basic functions as humans. However, the cells of Protozoa are so complex that they have frequently been regarded as "acellular." There are all grades of cellular differentiation from very primitive as in amoeba and advanced as in the higher ciliates and flagellates. There are definite openings for the taking of food developed. Locomotor structures appear and contractile structures show up, which function as muscle fibers. The bases of the cilia and flagellae are connected. Different grades of reproduction occur from binary fission, complete sexual differentiation and an alternation of sexual generations. Protista have reached the point of multicellular organization. Flagellates are shown to be the most developed and it is believed that they resemble the original stock group that gave rise to both plants and animals. At one time all Protista were believed to have evolved from the flagellates.


The Class Rhizopoda (Sarcodina) is characterized by pseudopodia, which are organelles that are not true organs. They serve in locomotion and food getting. The cytoplasm of the cell is not provided with many visible structures that possess specific functions. Amoeba proteus is a common fresh water rhizopod that occurs in calm, semi-stagnant water. It is microscopic in size and its form is indefinite.


Ingestion & Digestion of Food.-- The cytoplasm of A. proteus consists of two parts: (1) a plasmagel that includes a clear layer and an outer portion of endoplasm, and (2) a plasmasol, which is a fluid or the inner endoplasm. The organism is holozoic, taking in solid food consisting of algae (diatoms) and other protozoa into its body. The food is captured by the pseudopodia, and a food cup is formed that engulfs the food bringing it inside in a food vacuole. Another means of feeding occurs where the food slips past the cell membrane and thereby enters the cell. There is no vacuole formed in this type. Digestive enzymes diffuse into the vacuole and dissolve the food. Indigestible portions are left in the vacuole. Protein and carbohydrate enzymes are present in abundance, but there are few fat enzymes. Egestion is accomplished by the vacuole migrating to the edge of the amoeba and eventually becoming located on the outside of the organism.


Amoeboid Movement.-- The plasmagel and plasmasol are interchangeable, the former holding the latter under some pressure. When the plasmagel weakens or converts to plasmasol anywhere on the animal, the pressure forces the plasmasol out into a pseudopodium. The plasmasol sets into a gel all along the edges of the pseudopodium in the form of a tube. The posterior end of the cell then crumples up while converting plasmagel to plasmasol so as to form the new extension.


Circulation is accomplished by movements of the animal itself, and respiration and excretion are simple diffusions through the cell membrane. The Contractile Vacuole is usually located at the posterior end of the amoeba. This is a water regulating mechanism that pumps out water that moves into the cell by osmosis. There is an incidental expulsion of water products. With an increase in the salt concentration of the medium the contractile vacuole slows down and finally stops. A reduction of salt concentration results in a reactivation of the vacuole.


Support & Protection.-- There is little support needed in a suspended animal like Amoeba, and there are no protective mechanisms. However, when unfavorable environmental conditions occur Amoeba forms a cyst that can resist drying, temperature extremes, etc.


Sensitivity & Conduction.-- Amoeba behaves as if it had a nervous system, which it does not. A stimulus applied at one point on the animal body may cause any other portion to react. The animal perceives and responds to environmental changes. There is a positive response to food and weak light, and a negative response to all other stimuli. It generally responds in some way to light, temperature, touch and chemical reactions. There are no visible sensory or motor apparatus in the cytoplasm, but Amoeba is regarded as being generally sensitive.


Reproduction is entirely asexual being effected by binary fission (cell division). Size determines when A. proteus will reproduce, which is usually 150 microns. Sexual processes doe occur within the class but not in this genus.




In the Phylum Sarcomastigophora Class Mastigophora (Flagellata) movement is primarily by means of a flagellum. Amoeboid stages may occur in some phase of the life cycle, however. But adults always move by the flagellum. When parasitic they do not form spores. Nutrition is holozoic, saprophytic or parasitic. The Subclass Phytomastigina include green flagellates while Zoomastigina are the colorless flagellates.


The Phytomastigina includes the genus Euglena.



These animals occur primarily in fresh water and an abundance of them may produce a green scum. Their size varies from 25-500 microns and the body wall is more rigid than that of the amoebae. There is a rigid, grooved wall or pellicle present, however the ecto- and endoplasm are not well defined. Nutrition is holophytic where the animal manufactures it own food by photosynthesis. But in darkness it will live on dissolved nutrient material and thus is saprophytic. Food is stored in paramylum bodies, and pyrenoid bodies occur in the center of the chloroplasts, which serve to regulate them. In darkness chlorophyll disappears from the cell. Circulation, excretion and respiration are the same as in Amoeba proteus.


Contractile vacuoles are located around the reservoir whose function is to serves as exit to the vacuoles. Locomotion is by movements of the flagellum. The flagellum has a central core and is spirally wound with cytoplasm. The flagellum separates into two extension in the reservoir and terminates in basal bodies.



As for sensitivity, there is an eyespot, which is positive to weak or moderate light but negative to strong light or arkness. Conduction is like Amoeba. The basal bodies serve as a coordinating mechanism because their removal discoordinates the flagellum. Reproduction is asexual with longitudinal binary fission. All parts are regenerative and there is no sexual reproduction in Euglena although others of the class do show it. Cyst formation occurs to withstand adverse environmental conditions.


Some species in the Phytomastigina order Dinoflagellata have an armor plate (cellulose armor) that is occasionally shed and replaced. The order is a large group of importance in marine habitats as plankton. Dinoflagellates produce the "Red Tide" in oceans that results in widespread fish kills.


The flagella have been termed "Frog Flagella" that are diagrammed as follows:



In the Subclass Zoomastigina nutrition is holozoic, saprophytic and parasitic. The animals are colorless. The flagella are very numerous and their arrangement is anterior with one flagellum extended anteriorly and the other trailing. They may be fastened to the side of the organism by an undulating membrane.



Several genera of the Zoomastigina are of great importance to humans and animals because of their parasitic habits. Trypanosoma causes "African Sleeping Sickness", Trichomonas is a parasite of humans and animals, Leishmania causes a skin disease known as "Oriental Sore," and Giardia is a severe human intestinal parasite. Also of importance is that species may also produce oils instead of paramylum, which results in foul-smelling and foul-tasting water. On the other hand, termites possess a Zoomastigina symbiont that is of mutual benefit.


Phytomastigina have a well-developed and pronounced colonial arrangement, which is true also of the Zoomastigina but not as pronounced. The Phytomastigina genus Pandorina has 16-32 cells while Volvox has hundreds of cells in a gelatinous matrix. Any division of labor limits the boundary between colonial organisms and multicellular organisms. Volvox may be sometimes regarded as multicellular, but reproductive cells in Volvox function only to reproduce the organism. Species in the order Protomonadina possess a funnel-shaped collar similar to cells that are found in the Porifera.



Sexual reproduction in the Phytomastigina is especially prevalent. Isogametes of identical appearance and behavior are formed or heterogametes may be the case as in Volvox.




All members of the Phylum: Apicomplexa (Sporozoa) are parasitic, and all produce spores at some stage. There are no locomotory organelles in the mature stage, although the immature forms may possess them. Life cycles vary from simple to complex.


The incitant of malaria, Plasmodium vivax, has one of the most complicated life cycles. There are alternates of sexual with asexual reproduction. Malaria is considered to be one of the most important diseases of humans and it also affects animals extensively. Its life cycle is as follows:



Other important diseases found in the Apicomplexa are Texas Cattle Fever, Nosema (affecting honeybees and silkworms) and Coccidiosis (in chickens).



Please see following plates for Example Structures of the Protista:


Plate 65 = Kingdom: Protista -- Development characteristics

Plate 1 = Different body shapes in Rotifera.

Plate 2 = Protista: Sarcomastigophora: Rhizopoda: Amoebina: Amoeba proteus

Plate 3 = Protista: Sarcomastigophora: Rhizopoda: Foraminifera & Radiolaria

Plate 4 = Protista: Mastigophora: Eglenoidea: Euglena viridis

Plate 5 = Protista: Mastigophora: Phytomastigina: Volvocina: Volvox globator

Plate 6 = Protista: Sarcomastigophora: Mastigophora & Apicomplexa (Pandorina sp.,

Trichonympha sp., Trypanosoma rhodesieusi & Plasmodium vivax



The Kingdom: CHROMALYEOLATA (Infusoria)


Included here are the ciliates and water molds. Members possess cilia as locomotory organelles. There are two kinds of nuclei present in some members (1) micronuclei and (2) macronuclei). Reproduction is by conjugation. This section will discuss the Superphylum: Alveolata Phylum: Ciliophora.


In the Class Ciliata there are two subclasses: Protociliata and Euciliata. The Protociliata (e.g., Opalina) is a very small group all members of which are parasites or commensals. There are neither macro- nor micronuclei but rather the nuclei are scattered and all of the same size. There is no conjugation and the group may be transferred to the Mastigophora. The Euciliata are the true ciliates where macro- and micronuclei and conjugation are present.


Cilia are common in many of the Ciliata and an undulating membrane occurs in Paramecium's gullet. Membranelle exist that generally surround the food-gathering portion of the body. These are paddle-like and my also function in locomotion. Vorticella is a representative genus. Cirri or leg-like tuft cilia are present in Euplotes which are fused cilia that look and act like legs. These have been called "crawling cilia."


Nutrition is mostly holozoic and many are saprozooic, living off the dissolved organic matter that is taken in through the body wall. Some species are also parasitic.


Contractile structures or myonemes are present, which serve as muscle cells. Such are found in the stalk of Vorticella.



Some species of ciliates occur in the digestive tract of animals and actually assist in cellulose digestion. Balantidium coli is present in humans.




Paramecium is a representative genus in the Euciliata that occurs wherever bacteria are present. They are slipper-shaped with a lateral grove called the "Oral Groove." These organisms are uniformly clothed with cilia and the body surface has a pellicle. One large macronucleus and a small micronucleus are present. There are two contractile vacuoles at opposite ends each of which operates alternately with the other. A plasmagel and plasmasol are easily distinguishable and the average length is 200 microns.



Feeding.-- Bacteria are the principal food of Paramecium. Feeding involves cilia that beat a current of food into the oral groove and finally into the gullet. A modified group of cilia occur in the gullet to form the undulating membrane.



At the base of the gullet there is a food vacuole, which detaches like a bubble when it is full and then moves throughout the body in a well-defined path. The path of movement is first posterior, then anterior, and finally posterior with termination in the anus.



There is a constant circulation of plasmasol, which causes the food vacuoles to be carried around a cyclosis. The food vacuole is acid at first and later becomes alkaline.


Circulation.-- This is accomplished by cyclosis, and simple diffusion takes care of excretion and gas exchange.


Locomotion.-- The waving of cilia accomplishes locomotion. These resemble short, blunt flagella but they differ by their shorter length and numbers. Each cilium terminates proximally in a basal body that is interconnected with all basal bodies in the organism.


Support is given by the pellicle.


Protection is furnished by trichocysts, which simply serve as anchors while the cilia re waving food into the gullet. There is no cyst formation in Paramecium, the animal being hearty and can withstand extremes in oxygen and carbon-dioxide concentrations.


Sensitivity.-- Paramecium is indifferent to light except for one species that has a green alga symbiont. Actually all the cilia may be sensory and able to discriminate between edible and nonedible substances.


Coordination.-- There is coordination between the many cilia and may be brought about by the interconnections of their basal bodies. The presence of an "amotorium" or kind of central brain is obscure.


Reproduction.-- Paramecium reproduces by binary fission.



Conjugation is like that found in Ciliata and Suctoria. It occurs only in individuals with a macro- and micronucleus. Two conjugating individuals become sticky and pair. The micronucleus is involved in genetic transfer.


Conjugation in Paramecium


Step I = The micronucleus divides.

Step II = A second division occurs (--4 haploid micronuclei in each conjugant)

Step III = Three micronuclei degenerate; the one remaining divides again.

Step IV = There is a mutual exchange of micronuclei (one goes to mate and one remains


Step V = There is a fusion of two haploid micronuclei to form one diploid micronucleus.

Step VI = The cells separate from one another and are termed "exconjugants." The

macronucleus disintegrates.


Post Conjugation in Paramecium


Step I = 2N micronucleus divides to produce eight 2N micronuclei.

Step II = Four micronuclei enlarge to form macronuclei, while four micronuclei remain


Step III = The cell divides to produce four cells, each of which possesses one micronucleus

and one macronucleus.



Step IV = The macronuclei then grow enormously by forming the polyploid condition. They apparently regulate all the vegetative processes in the cytoplasm. In asexual reproduction the micronucleus always divides by mitosis while the macronucleus divides by splitting almost in half.




The Class: Phyllopharyngea, Subclass: Suctoria has cilia in immature stages and adults possess tentacles. They paralyze their prey and the suctorial tentacles suck the prey dry.



Macro- and micronuclei and conjugation are present. Adults are sessile and the group occurs in both fresh and salt water. Many are free living, some are commensals and a few are parasites. They have little economic significance.




Please see following plates for Example Structures of the Chromalveolata:


Plate 7 = Chromalveolata: Ciliophora: Ciliata: Paramecium multimicronucleatum

Plate 8 = Chromalveolata: Ciliophora: Ciliata: Nyclotherus sp., Opalina sp., Didinium nasutum &

Paramecium sp.

Plate 9 = Chromalveolata: Ciliophora: Ciliata & Phyllopharyngea (Euplotes patella & Ephelota sp.)

Plate 66 = Kingdom: Chromalyeolata, Phylum: Ciliata -- Paramecium structure






Bibliography Citations