Diversity of Life: Domain Eukarya, Kingdom Animalia

1. This information is not an exhaustive zoology course. Instead, the primary objective is to understand the basic body organization of different groups of animals and which characteristics are used to organize animals into a set of evolutionary relationships--one of the primary functions of any classification system.
   
   
2. All of the basic body plans seen in extant animals seem to be derived from a time period in history referred to as the Cambrian Explosion--a time when numerous new animal designs appear in the fossil record.
   
   
3. All animals are multicellular, heterotrophic, and do aerobic respiration as their primary method of producing ATP.  Animals are also motile during some part of their life cycle (not necessarily as adults) and go through stages in embryonic development; during these stages , three basic tissues are formed--endoderm, mesoderm, and ectoderm. Animals also reproduce sexually, although there are some exceptions to this general characteristic.
   
   
4. There are several characteristics used to divide animals into major groups (phylum, phyla (pl)); some of them are in your text.
   
   
   1. Does the animal have true tissues or are the cells so loosely organized that there is no real division of labor among them? The only group without true tissues is Porifora--the sponges.
      
      
   2. Does the animal have radial or bilateral symmetry? If radial, it belongs in the groups Cnidaria (jellyfish, sea anenomes, etc) or Ctenophora (comb jellies). If bilateral, go to next decision point.
      
      
   3. Does the animal have a coelom? If it does not, it belongs to the Platyhelminthes (flatworms). If it does, we go to the next decision point. As we get into animals with bilateral symmetry, they actively move in the environment and we see concentration of sensory organs and the nerve tissue to process the inputs at the front end of the animal. This is called cephalization or development of an identifiable head.
      
      
   4. Is the coelom a true or false coelom? If false (meaning there is mesoderm derived tissue lining only one side of cavity), then the organism belongs to the phyla Rotifera or Nematoda. If a true coelom, we go to the next decision point.
      
      
   5. All of the animals above letter "d" (except sponges) have a sac-like digestive system--only opening in and out. The rest of the animals have a tube-within-a-tube digestive system--an opening at either end with a tube running between them. During the embryonic formation of that tubular gut, if the first opening to the outside becomes the mouth and second the anus, then the organisms are protostomes. Mollusca, Annelida, and Arthropoda all share this same embryonic pattern. If the first opening becomes the anus and a later opening the mouth, the animals are deuterostomes. This latter group includes Echinodermata and Chordata (where us mammals hang out with our vertebrate cousins).

Starting up the evolutionary tree the first characteristic is to determine if the organism has true tissues. Tissues would be similar appearing cells that work as a group to perform some activity. The only animal phylum without true tissues are the sponges. An excellent description of this phylum and how they function is found at the University of California Paleontological Museum (UCMP) at Berkeley. Be sure to look at the additional links given in the site. Sponges are filter feeders that pull water in and then out an excurrent opening. Small bits of food are captured by the collar cells (choanocytes).

All organisms beyond sponges have symmetry. Cnidarians are the only phylum with radial symmetry. Imagine a pie-lets say cherry. If you cut it in half you get two identical half circles. It doesn't matter what direction you cut, you get mirror images.The Cnidarians are all marine or aquatic and not active swimmers. the circular symmetry allows the them to sense the environment in all directions. They have only one opening into a gastrovascular cavity--serves to digest and distribute nutrients. This is referred to as a "sac-like" digestive system.Since these organisms have no organ systems, they have only two tissue layers--an outer ectoderm and an inner endure lining the gastrovascular cavity. Surrounding the mouth are tentacles usually equipped with stinging cells called nematocysts. These little "harpoons" contain toxins which stun or kill the prey. Since they are activated by a simple trigger mechanism, they can still sting when the animal has died. Be careful handing beached jellyfish, especially the beautiful Portuguese Man of War.

Cnidarians take one of two morphological forms - a floating bell-like form with tentacles hanging down as shown above or a sessile (attached" form with tentacles facing upwards as shown below. These two forms are known as the medusa and polyp forms respectively. Some species actually alternate between the two forms.

A few species of jellyfish have toxins fatal to humans. As an example, look at the box jelly found in waters off the coast of Australia and Indonesia.

Jellyfish also become food as well. Many sea turtles feed on jellyfish. This habit is why they eat plastic bags which clog their digestive tract leading to death. Humans eat jellyfish as well, particularly in Asia.

As you can see  in the image, these animals can get quite large.

Does the animal have a coelom? If it does not, it belongs to the Platyhelminthes (flatworms). A coelom is a cavity between the gut and the outer body wall.

Without a coelom there is no room to coil up organs n a cavity; if you want a longer intestinal tract to extract more nutrients from food, then the whole animal has to lengthen.  Flatworms have a sac-like digestive system like the Cnidaria. There are three groups of flatworms:

1. Turbellaria - mostly free-living worms like those in the image at beginning of this section. Those are Planaria and are very common and have been used in research for many years. Easy to raise, they have remarkable regeneration capabilities.
   
   
   
2. Cestoda or tapeworms - You have probably already heard of them. They are ribbon-like and are parasites of a large number of animals, including humans. The head attaches inside the host and segments with eggs are shed in feces. The worms are most often found in the intestinal tract. While tapeworms may also be found in other parts of the body, those are reproductive dead ends unless you are eaten by another animal. Many vertebrates are hosts to tapeworms.
   
   
3. Trematodes or flukes - These leaf-like worms are all parasitic. They may be found in a variety of tissues/organs depending on the species--liver, lungs, brain, blood.  They cause permanent damage and eventually death if untreated. In the blood fluke image, the much smaller male permanently lives in the groove of the female and spends entire life fertilizing her eggs.

Liver Fluke

Blood Fluke

Is the coelom a true or false coelom? If false (meaning there is mesoderm derived tissue lining only one side of cavity), then the organism belongs to the phyla Rotifera or Nematoda. Nematodes are very common worms and are referred to as roundworms. Roundworms can be any size from microscopic to to close to a half meter in length. They have bilateral symmetry with no segmentation. They have a complete (tube within a tube) digestive tract. The rest of the animals have a tube-within-a-tube digestive system--an opening at either end with a tube running between them. During the embryonic formation of that tubular gut, if the first opening to the outside becomes the mouth and second the anus, then the organisms are protostomes. Nemotoda, Rotifera, Mollusca, Annelida, and Arthropoda all share this same embryonic pattern. If the first opening becomes the anus and a later opening the mouth, the animals are deuterostomes. This latter group includes Echinodermata and Chordata (where us mammals hang out with our vertebrate cousins).

Soil nematodes can be beneficial or pests. Others may infect plants and animals. A few are human parasites which cause serious diseases in the intestinal tract, eyes (blindness), and lymphatic system. Filarial worms block lymphatic ducts prevents fluid from moving out of appendages and cases severe edema. They are transported by mosquito vector.

Rotifers are aquatic organisms that also have a tube-within-a-tube digestive tract and a pseudocoelom. Their characteristic feature are circles of cilia around the mouth area that give the appearance of rotation.

Annelid worms have a true coelom that is filled with fluid as well as a complete digestive system (= tube-within-a-tube  system). The fluid acts as a hydrostatic skeleton that the circular and longitudinal muscle groups press against. They are protostome animals with bilateral symmetry. Most show obvious segmentation externally. There are three major groups of annelid worms:

1. Polychaete worms have paddle like extensions on each segment (parapodia) with bristles at the end of each parapodium (see image above). Many are filter feeders tentacle-like appendages that circulate water with food particles that are absorbed. A few are active predators, such as the clam worms.
2. Oligochaete worms have less obvious heads and lack parapodia. Like earthworms which are the poster child for this group, they do have short, stiff bristles on each segment that press against the substrate and allow them to move.
   
3. The Hirudinea are the leeches. They have a sucker like mouth and most feed on body fluids; a few are free living. They cut into the skin and their saliva has an anticoagulant to prevent the blood from clotting. They  were historically used by "doctors" to cure almost anything and are still used today.
   
   

Mollusks are protostome animals with a unique set of characteristics found in all groups of mollusks. There is visceral mass in which you would find the internal organs. This mass is covered to varying degrees with a structure called the mantle. The mantle secretes the shell when present; there are a large number that do not have shells. Then there is a muscular "foot" that contains feeding organs, sensory organs, and provides motion. These animals have an open circulatory system. There are four groups of organisms:

1. Polyplacophora or chitons: these animals have a large, ventral muscular foot for movement. There are dorsal, hardened plates that overlap for protection. They feed on algae.
   
   
   Ventral Foot
2. Gastropods: This group contains a number of visually different but evolutionary related animals: the classic snail with a spiral shell that are mostly marine or aquatic, the colorful marine nudibranchs with no shell, and land or air breathing snails and the ever popular slugs.
   
   
   Nudibranchs have no shells. These brightly colored sea slugs contain toxins which is what the color advertises. The dorsal appendages you see are their uncovered gills==nudi=uncovered, branch=gills.
   
   
   Land snails are air breathing and either have shells or may lack shells. Those without shells are called slugs. Both types are common in tidewater Virginia but less so in drier climates. They are often garden pests as they find growing vegetables irresistible.
   
   
   
   
   
3. Bivalves: As you probably can guess from the name, this group has two shells with a hinge that allows the shells to close and protect the soft body inside. Clams, scallops, and oysters are all familiar examples of bivalves. They are all marine or aquatic and are filter feeders.
   
   The shell is secreted by the mantle that covers the visceral mass. The muscular foot can extend out side the shell digging as in the clams or can produce incredibly strong fibers that mussels use to attach to rocks.
   
4. The last group are the cephalopods. This group includes fascinating and intelligent octopuses, and squids along with ancient chambered nails. All have tentacles and are highly mobile. Squids and octopuses have excellent vision and the ability to change their skin color and even texture for camouflage. Both also eject ink into the water to confuse predators and hide their escape. Squids and octopuses also have the ability to move rapidly by ejecting a jet of water out a siphon that is like a jet engine.
   
   
   

The amazing brains of cephalopods--a TED talk.

Arthropods are the largest group of animals on Earth--the beetles alone outnumber all other species together. Ants and terminates outnumber all other animals combined. They have adapted to every environment that will support life. They are the first animals to master flight. They have exoskeletons that usually contain chitin. In order to grow they have to periodically shed the old exoskeleton for a slightly larger one. They are quite vulnerable until the new exoskeleton hardens. There are excellent web sites that summarize their characteristics very succinctly.

Biological Diversity:  Segmented Bodies with Segmented Appendages

Introduction to the Arthropods at UCMP

The Arthropod Story: Understanding their evolution (at UCMP)

Organisms included in this large Phylum include:

 The Arachnids--spiders, ticks, and scorpions. Arachnids have body parts (cephalothorax and abdomen) and eight legs. Most secrete a venom when they bite to paralyze or kill their prey. They then inject digestive enzymes and can suck out the liquified internal organs of the prey. Fortunately very few have venom that is dangerous to humans and they only attempt to bite when they feel threatened. They feed on many insects and other small organisms and provide a valuable service by doing so  At the same time, they are preyed on by birds, small mammals and larger insects. 

Closely related are the horseshoe crabs that you may have seen on the beach. They lay eggs by the millions on eastern beaches in the springiest as sea birds are migrating northward and need to refuel on their way. For humans, a component of their blue blood is used to ensure vaccines are bacteria free. A needle is used to drain a third of their blood for a clotting agent used to make a liquid called Limulus amebocyte lysate (LAL). The product doesn’t kill bacteria, but envelopes it with a jelly coating, signaling to scientists that harmful endotoxins, which live on the walls of bacteria, are present, Business Insider reported in 2018. If these toxins enter the bloodstream, they can cause fever, hypotension, nausea, toxic shock syndrome and even death.

Crustacea:  Crustaceans are probably familiar to you. The group includes lobsters, crabs, crayfish, shrimp, copepods, barnacles, and krill. All crustaceans have two pairs of antennae, a pair of mandibles, a pair of compound eyes, and two pair of maxillae on their heads, followed by a pair of appendages on each body segment. Like insects, the body is usually divided into a head, thorax (where legs are attached), and an abdomen. Krill are a basic food item for large ocean predators such as whales as well as seals, penguins, fish, and squid. Their numbers have been rapidly falling due to overharvesting and warming of water in the oceans surrounding Antartica. 

Many crustaceans are food for humans as well as animals in their food web and overharvesting as human population grows is an issue. This has been an issue in many other areas. As a result there are strict regulations on catching lobster, blue crab and other species with heavy fines for violations if caught.

Barnacles are common filer feeders worldwide. They attach to surfaces and use feathery appendages to sweep through the water and capture small particles food in the water. Some of the first serious work on the anatomy and taxonomy was does done by Charles Darwin between his return from the voyage of the Beagle and publishing the Origin of Species. 

Millipedes and Centipedes:  These are common animals in many environments. They are all worm like with appendages on each segment. Millipedes have two pairs of appendages on each segment. They feed on dead and decaying vegetation and are not at all harmful. When treated they role up into a ball.Centipedes, however, are predators. They have one pair of appendages per segment. The segments are flattened and the appendages on the first segment are modified as large poisonous fangs. Very few are dangerous to humans but they can make a painful bite. Some can get as large as 25 centimeters. 

Insects:                                 

Insects are the largest group of arthropods or any other taxon. There are over a million identified species and probably thousands not yet identified. We find them in all terrestrial and aquatic ecosystems. There are very few marine species. There are a number of common characteristics. The body is composed of three segments (head, thorax, abdomen). They have a pair of compound eyes and three simple eyes. They have a pair of antennae and two pairs of wings. There will also be three pairs of walking legs. They have a complete digestive systems and open circulation. Terrestrial insects have a unique respiratory system - a tracheal systems of tubes that go through the animal.  Aquatic insects usually have gills. 

Echinoderms are the first group we come to that are deuterostomes. Echinoderms have a number of unique characteristics. While the larvae are bilateral but adults have radial symmetry. They are mostly bottom dwellers and radial symmetry allows them to feed in any direction. the calcium containing plates act as an endoskeleton. for movement and manipulation of food echinoderms have a unique water vascular system. Sea stars are predators while sea urchins feed on algae. 

Chordates are deuterostomes as well as the echinoderms. Chordates have four characteristics in common:

1. Phayngeal gill slits. These are actually used for breathing in some species. In other species the gill slits and arches between become integrated into skull structures.
2. A dorsal nerve cord (arthropods had a ventral nerve cord) that runs the length of the body. Embryonically, the cord starts off as a hollow structure.
3. A cartilaginous rod that runs under and supports the nerve cord. In vertebrates with a skeletal structure the notochord disappears in the adult.
4. A post-anal tail. In invertebrates the anus is at the end of the body. In chordates the tail extends beyond that.

Chordates include a wide variety of animals. This will not be a comprehensive survey but go over the evolutionary advances and unique characteristics for the two subphyla and the classes of vertebrates. 

There are two subphyla that include invertebrate chordates. Not all chordates exhibit vertebrae but these two groups have all four chordate characteristics at some point in their life cycles.

Subphylum Urochordata:  The Urochordata are far removed from the typical vertebrates. They are referred to as tunicates and the adult form is a sessile filter feeder with only pharyngeal gill slits as a chordate characteristic. However, the larvae exhibit all four characteristics. They draw water in through one siphon. It passes through the gill slits where food particles are trapped in mucous. The water then exits through another siphon. some members are colonial and drift in the water column--they are called salps. With warming of antarctic waters these animals are more common and krill populations declining. This change is impacting the food web greatly as sales contain far less nutrition than krill.

Subphylum Cephalochordata:  The cephalochordates are small bottom filter feeders that are referred to as lancelets or Amphioxus.  Found in shallow tropical waters , they exhibit all four chordate characteristics.

Jawless fish:  There are two groups referred to as jawless fish - the hagfish and the lampreys. The classification of these changes often. 

Class Myxini - The hagfish has a cartilaginous skeleton and a partial cranium - bony covering around brain. They are scavengers in deep water oceans. Their "claim to fame", however is the mass quantities of a mucous-like slime they can produce. With no jaws, they grab chunks of decaying flesh and pull it off by literally tying their body in a knot.

Hagfish Feeding on Whale Carcass

Class Petromyzontiformes - Lampreys are also jawless but do have cartilaginous vertebrae and a cranium. They feed by attaching their sucker-like mouth to a fish and using their horny teething rasp-like tongue to scrape away flesh. They became a major pest in the great lakes after the Welland Canal provided them an entry around Niagra Falls. 

Now we move on to the development of jaws and all the rest of the vertebrate classes will have jaws.

The Placoderms are the first fish known to have jaws They are extinct and are known only through fossil remains.

Class Chondrichtyes - The Chondrichthyes are fish with jaws and skeletons completely composed of cartilage. This group includes the familiar sharks and rays along with a lesser known group called ratfish. They exhibit all the chordate characteristics and have a two chambered heart with a single blood circuit. Some lay eggs and some sharks retain the eggs internally until young are fully developed. Some are predators like the sharks you are familiar with already (please don't count "sharknado") while some are filter feeders, including the largest members of the shark family.

 Be sure to look in different directions using your cursor

Manta rays feed on crustaceans and a few are filter feeders. Cow nosed rays are in the Chesapeake bay and also eat clam and oysters. This puts them in competition with watermen at times.

Class Osteichthyes:  Osteichyes are fish with bony skeletons. The oldest group are the lobe finned fish that include a small group called lungfish. These fish are able to come out of the water for periods of time - a helpful adaptation to the shallow ponds they inhabit in Africa, South America, and Australia.

The other group of lobe finned fish are the Coelocanths. Thought tho be long extinct, they were rediscovered in deep waters (300 to 2300 ft) off the coast of South Africa in 1938. The lobed fins resemble the limbs of early amphibians.

The largest number are in the ray fin group - meaning that you can see ray-like structures within the paired fins. These are the fish you would normally catch and make up much of the worlds protein source - at least where they haven't been overfished. 

There are over 24,000 identified species so far; they are the most successful marine and fresh water group of animals.  You can browse the preceding link or the internet for examples. Closer to home, there are many species in the Chesapeake Bay area, many of commercial significance. 

Class Amphibia:  This link on Amphibia gives the general characteristics found in the class.Information on life history and morphology is given at this UCMP page. The important differences are related to the fact that these animals are found on land. This terrestrial existence requires changes in skeletal anatomy, circulatory system, and means of obtaining oxygen. Amphibians are stilled tied to open water for reproduction. Eggs are laid in water or in very moist conditions with sperm spread externally to swim to eggs. While a few amphibians have adapted to drier conditions, most require moisture to keep their skin moist (most oxygen absorbed through skin) and to successfully reproduce. You have probably heard frogs or toads calling.; here is a site with recordings of calls of different species. If you are interested in more of the tidewater or coastal plain species use these two sources:

Virginia Herpetology Society

Amphibians and Reptiles of North Carolina
Both sides includes calls of the frog/toad species found in each state along with maps to show where they are found.

Eastern Toad

Leopard Frog

Virginia has the largest diversity of salamanders in North America. Many of these are threatened or endangered due to habitat loss (just look around at all the wooded areas being cleared for housing or new business--each of those provides habitat (home) for a large number of species.

Virginia's hellbender salamanders are large and endangered.

Marbeled Salamander

Spotted Salamander

Five Lined Skink

Class Reptilia: Reptiles made a complete break from the open water requirement for life and especially reproduction. With their scaly skin to prevent water loss and legs strong enough to walk on land without the buoyancy of water, they spread across the relatively unpopulated land masses. But their major advance was the development of the amniote egg. The embryo develops in a water filled membrane inside the shelled egg with yolk for nutrients. These eggs could be laid on land and the embryo still has the protection of the water environment. Since the shell was built while still inside the female reproductive tract, fertilization had occur internally. This led to a wide variety of physical and behavioral adaptations. 

While reptiles have successfully colonized almost all land areas, they have a limited ability to control their body temperature internally. Lower temperature means less metabolic activity. So, they are often sluggish in early morning and actively seek out sunshine to warm up. Conversely, when it is hot, they have to use the environment to help cool themselves and are often in the shade or in burrows to cool down. Please read the above link concerning the evolution of reptiles. The two herpetology sites presented in the amphibian section of this also cover reptiles.

Black Racer - commonly referred to as a Black Shake

The following video on fresh water turtle species is from Louisiana  but the species are much the same our local Tidewater area.

Class Aves:  When we think of birds we think of flight. While bats also fly, birds are clearly the masters of vertebrate flight along with all the adaptations that support that. They have lighter bones, feathers, and a skeleton modified to support flight muscles. Birds have colonized all continents. Some are aerial acrobats while others fly for days at a time. We now understand that the same taxonomic clade contains dinosaurs, crocodilians, and birds. They feed on all kinds of items from plants and their fruit and seeds to insects, fish, and even other birds. Some have even learned to use tools to obtain their food. Ornithology is popular and bird watchers are found all over the globe. The following videos will give a glimpse of that world. 

Class Mammalia:  Welcome to the mammals.  Well, you are one so hopefully you already have a good idea of the characteristics. Mammals have hair, they have three small bones in the middle ear to improve hearing on land, and they produce milk to nourish offspring. If you are thinking of retaining the fetus internally for development, not all mammals do that. Let's look at the groups of mammals. 

Monotremes:  Monotremes have three mammalian characteristics but actually lay eggs. The eggs placed in a pouch and stay there until the they hatch. After the young hatch, the mother provides milk. However they do not have distinct nipples; the milk oozes out on the chest area and the young lick it off. There are very few and they are found only in Australia and New Guinea. There is one species of platypus and originally four species of the spiny echidna. Adults to not have teeth but do have a bony area in the mouth. 

Marsupials:  Marsupials had a fairly wide spread range at one time but are now mostly confined to Australia and some nearby islands plus one species in the Americas. Most people are familiar with koalas, kangaroos, and maybe the Tasmanian devil (probably from bugs bunny cartoons). There are also wombats, tree kangaroos, and the extinct Thylacine. Marsupials were once widely found in South America (known from fossil data) but it is thought that development of the Panama isthmus allowed placental mammals to migrate into South America where they out competed the local marsupials. In this group the young are born very early and the embryo has to crawl from the bath canal into the pouch. If successful, it attaches to a nipple and completes development in the pouch. The Virginia opossum has been very successful east of the Rocky Mountains. It is also found in the Pacific Northwest after being introduced into California and is now found in Ontario and British Columbia, Canada. Other opossum species are found in Central and South America. 

Placental Mammals:  The placental mammals are a diverse group characterized by the formation of a placenta to nourish the young in the uterus until birth. Gestation periods vary with the animal but larger animals can have gestation periods of up to two years (elephants). Human gestation is, of course nine months. Small rodents may have gestation times measures in a few weeks.

After birth, the young nurse on mothers milk until weened. Rodents and bats are the most numerous orders of mammals. The Systematics link on the Berkeley UCMP  Eutheria (placental mammals) page will give you more information on some of the other orders. Mammals may be herbivores, carnivores, or omnivores. Dentition will match the life style. Primates are placental mammals as are each of us. 

If you are interested in human evolution, use these web pages:

Fossil Hominids

Deep Time:  the history of the earth