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Lab 12: Animals Part 1: Sponges, Radiata, and Protostomes Last week we made it to the end of the branch of the phylogeny that contains plants and discussed the most diverse group: angiosperms. Now we will return to the main branches of the eukaryotes and work our way up another branch (see the big phylogeny in the taxonomy lab). I say this because I want to highlight that we are now starting over in our evolutionary path. The groups we are discussing from now on are not derived from plants. They make up a separate branch in their own right. KINGDOM ANIMALIA Animals are probably the most interesting organisms to us humans; they provide us food and clothing, they are our pets, our friends, and our family. They are incredibly diverse in body shape, ecology (filling just about every niche imaginable), and personality. They are what most people think of when they think of life. You don’t see too many Discovery Channel shows about plants, but they devote whole weeks to animals. Therefore, we will spend two labs studying this kingdom. We will begin the study of animals by first defining what makes an organism fit into the Kingdom Animalia. All organisms in the Kingdom Animalia (also called the Metazoa) are multicellular heterotrophs and do not have a cell wall around their cells. They are also motile (meaning they move) during at least one stage of their life cycle. Their development is also unique and involves gametes (sperm and egg) that fuse to form a zygote, which divides into a ball of cells called a morula, which then becomes a hollow ball of more cells called a blastula. ANIMAL DEVELOPMENT Sexual animals can be said to have the accompanying, very generic, lifecycle: GAMETES: Gametes include sperm and ova (eggs). Only the gametes are haploid (as opposed to plants, which have alternating haploid and diploid generations, although in higher plants, the haploid generation is reduced). An unfertilized egg is an ovum, even though we use the term elsewhere (e.g., birds laying fertilized “eggs” are actually laying zygotes). ZYGOTE: When a sperm meets an ovum, the DNA from the two cells is combined forming a single diploid cell in a process called fertilization. This diploid cell is now called a zygote. The zygote is the same size as the egg since (1) no nutrients have been added and (2) the sperm only donates its DNA, not its cytoplasm. The gametes do not fuse, only the DNA fuses. MORULA: Almost immediately, the zygote begins to divide into two cells (a process called mitosis). These two cells divide into four, the four into eight…and so on. When the zygote has reached a solid ball of smaller cells, it is called a morula. Again, all the stuff inside the morula was in the ovum to begin with. That’s why the egg is comparatively so large. BLASTULA: The morula divides and divides and divides until it consists of thousands of cells. Eventually it becomes a more distinctive structure. Cells migrate to the outside, until they form a hollow ball. This is the blastula stage. The blastula is an embryonic stage consisting of a sphere of cells with a fluid-filled central cavity. All animals undergo a blastula stage. It is the only developmental trait shared by all members of the kingdom.

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At this point, in all metazoans, the sphere consists of only 1 germ layer. The germ layers in an embryo are the layers of cells from which the organs are derived (not to be confused with germ line cells- the cells from which the gametes are derived). The fluid-filled cavity is called the blastocoel (coel means cavity). GASTRULA: In most animals, the blastula continues developing more germ layers through a process called gastrulation, eventually forming a gastrula. Gastrulation converts the single-layered blastula into a 2- or 3-layered gastrula.

Here is how it happens: Step 1: Formation of the gut cavity One side of the blastula bends inward toward the blastocoel in a process called invagination. This forms a new internal cavity (the gut cavity or archenteron, literally “old gut”, or gastrocoel). The opening to this new cavity is the blastopore. The cells surrounding the closed blastocoel form the ectoderm or outer germ layer. The cells surrounding the gut cavity form the endoderm or internal germ layer. In this way, the gastrula now has 2 germ layers.

Invagination forms the gut, or digestive tract. In some animals, like jellyfish, invagination stops before it goes all the way through the blastula. These animals have an incomplete digestive tract. There is only one opening to the gut, so food and waste goes through the same opening (mmm mmm good).

In most animals, invagination continues through the blastocoel until the archenteron breaks through the other side. These animals have a complete digestive tract. Their bodies are basically a tube-within-a-tube. One opening forms the mouth, the other the anus. Step 2: Formation of mesoderm and coelom In some animals, development stops at two germ layers. These animals are called diploblastic. (no name for animals with 1 layer). Other animals go on to form a third germ layer, the mesoderm. These animals are called triploblastic.

The mesoderm eventually grows to fill the entire blastocoel, but it forms another hollow cavity, the body cavity or coelom. The coelom lies inside the space previously occupied by the blastocoel.

- There are slides of the egg, blastula, and gastrula stages of

fish and frogs. Look for the hollow ball of the blastula and the tiny line of invagination of gastrulation. Although we won’t get to these groups until next week, they make a good representation of these crucial animal-specific features.

Complete  digestive  tract  à    

ß  Incomplete  digestive  tract  

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ANIMAL DIVERSITY We will now explore the diversity of animals, starting with the oldest group and moving to more “complex” creatures. Like it says in the definition above, all animals are multicellular, meaning that this trait evolved early in their history. Even so, the oldest animals, and the first group that we will discuss, is barely multicellular even today. SPONGES (PHYLUM PORIFERA) The parazoa are animals that have neither tissues nor organs and do not have a discernible symmetry (the name means “next to animals”). The only phylum that falls into this category that we will see is the phylum Porifera, the sponges. Yes, these are the “natural”

bath sponges that you can buy at a fancy toiletry shop. They are also weird little creatures. Adults are very sessile (sedentary). They are basically bags of cells that serve different functions living together as a whole organism. Flagellated cells move water and food particles from the water around them, through the body into the main cavity, and engulf the food. Mobile cells take the food, digest it, and distribute it to the other cells. The flagellated cells then move the water out through a main body cavity. The flagellated cells can become germ cells for reproduction or any part that breaks off can form a new sponge.

- Look at the whole mounts and the slides to see the loose associated of these cells, lack of tissue, and direction of water flow. These slides are labeled Grantia or Leucosolenia. You can also see the spicules (basically shards of calcium or silica that support and protect the sponge) in the slides labeled gemmules or spicules.

*True tissues and nerves After the split from Porifera, we come to our first key adaptations in animals: true tissues and nerves. Yay!! A tissue is an integrated group of cells that work together with a common function. This is an indication of higher coordination and more advanced development than what sponges have. A nerve is a bundle of motor and/or sensory cells that carry impulses, and allow coordinated movement of parts and greater responses to the environment. Every animal except sponges has these things (unless it lost them, evolutionarily speaking) and they are called Eumetazoa.

EUMETAZOA Eumetazoa have symmetric body plans too. This means that you can divide the body into mirror images. There are two types of symmetry and this divides the Eumetazoa into the Radiata and Bilateria.

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RADIATA The less diverse branch of animals after true tissues and nerves evolved leads us to the world of radial symmetry, the group is appropriately named Radiata. Radial symmetry, meaning that you can divide the body into more than two equal parts, works for organisms that are sessile, like anemones, or that spend their lives floating, like jellyfish, because their world comes at them from all sides. There is no left/right or front/center, only a bottom/top. The only phylum that we will be studying in this clade is the Phylum Cnidaria, which includes jellyfish, sea anemones, and coral.

PHYLUM CNIDARIA The cnidarian body cavity has two layers during development, these are generally called germ layers, so cnidarians have two germ layers: an endoderm and an ectoderm making them diploblastic. The endoderm typically becomes the lining of the gut and the ectoderm becomes the outside of the body and the nerves. The rest is filled with a “jelly” called mesoglea.

Since there is no space between the digestive tract and the outer body wall, there is no body cavity. Organisms with this structure are called acoelomates (a means “no”, coelom means “body cavity”).

“Jellyfish has been floatin’ so long and so slack, he ain’t got a jelly bone is his jelly back.” -Jimi Hendrix

Cnidarians also have specialized cells in tentacles called a cnidocytes that contains a spear-like nematocyst. They use these for capturing prey, but this is what hurts when you brush up against a jellyfish. Coral look very much like sea anemones, but lay down homes for themselves out of hard calcium carbonate. These shells build up as many individuals lay down tiny layers over thousands of years. They are ecologically critical since they provide food and shelter to numerous sea creatures as coral reefs.

- We have various cnidarians as whole mounts and slides, so you should be able to recognize them and what makes them unique. Cnidarian slides are labeled Metridium (an anemone) Obelia, Aurelia, and Hydra. In these, you can see the multiple polyps budding off of each other with their many tentacles. The free-swimming form is called a medusa. We may also have slides of the cnidocytes and living Hydra.

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BILATERIA *Bilateral symmetry, 3 germ layers

The other branch after the evolution of true tissues and nerves belongs to the Bilateria. This group is composed of organisms with bodies that can only be divided into 2 equal parts. They are much more active than the Radiata and usually have sophisticated methods of locomotion. Since they move in one direction, their world comes at them mostly from the front. Therefore their mouths, sensory organs (like eyes), and prey-capturing devices are in the front (= cephalization). It’s better to know where you’re going than where’ve you been. And their locomotory structures on are the sides.

Bilateria also have more complex bodies with more complex development. They are triploblastic, meaning they all have three germ layers: endoderm, mesoderm, and ectoderm. These layers develop into many important parts later on: PROTOSTOMES vs DEUTEROSTOMES There is a large split in the Bilateria, based in part on how the organisms develop. No need to memorize these features. Many of the taxa within these groups have shifted their developmental features further and so these traits are not always consistent. Protostomes

1. spiral and determinate cleavage pattern (the way cells in a zygote divide shortly after fertilization) 2. schizocoelous formation of the coelom, meaning the mesoderm is solid then splits to form the body

cavity (this may have evolved separately in the vertebrates) 3. the blastopore (a temporary opening in the early stages of development) becomes the mouth

Deuterostomes

1. radial and indeterminate cleavage pattern 2. enterocoelous formation of the coelom, meaning the mesoderm forms hollow pouches that are pinched

off to form the body cavity 3. the blastopore becomes the anus

We will first look at the Protostomia, which is divided into two clades: the Lophotrochozoa and the Ecdysozoa.

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LOPHOTROCHOZOA "crest-bearing animals" For the rest of this lab, we will focus on the Lophotrochozoan Protostomes. This group is named after a feeding structure (the lophophore) and a type of larva (trochophore.) PHYLUM PLATYHELMINTHES (“flatworms”) The phylogenetic relationship of Platyhelminthes to other animals is still uncertain, however, they are most likely lochotrochozoans. At any rate, they are really flat. Flatworms are often thin, ribbon-like creatures and are often thought of as parasites, although there are many free-living species. There is no true body cavity in flatworms, so they are considered to be acoelomates. Free-living flatworms (Class Turbellaria) live in many aquatic ecosystems and some are terrestrial. Famously represented by the freshwater genus Planaria, which has its mouth/anus in the middle of its body on a long pharynx, but despite that, they are kinda cute, with two eyespots on the head area.

- Look for slides marked Planaria wm, to see the entire worm - The slides marked Planaria cs or 3 sections, shows a cross section through the

body, which will show the digestive system and mesoderm filling the body. - We may also have living specimens; it is fun to watch them eat.

The rest of the flatworms are represented by endoparasitic forms; meaning they live inside a much larger host and feed off of it from within. They have many adaptations to facilitate this lifecycle including the following:

• Specialized structures to attach to the host, such as suckers and hooks

• A multinucleated skin that can withstand the host’s immune system  

• Reduced digestive systems and mouths; they often just absorb pre-digested food through their very flat bodies. They also excrete wastes such as CO2 and nitrogen through diffusion. The flat body increases surface area without gaining volume.

• Very complex lifecycles and a devotion to reproduction. The life cycle below is an example (no need to memorize it). This is the life cycle of the tapeworm Diphyllobothridum latum. Thought puberty was hard? Try this:

Since the life cycle is so complex, most of the offspring won’t make it all the way through. Therefore, most of their bodies are devoted to reproduction. They put out as many offspring as they can and hope at least one of them makes it all the way through. Up to 80% of the body can be devoted to uterus and testis. These lifecycles are important to discover since many flatworms infect humans and livestock. Sometimes in order to reduce infection of a fluke, you have to kill some snails.

Note:  the  term  “worm”  means  a  long  skinny  animal.    Although  taxonomists  once  put  all  of  them  into  one  group,  the  Vermes,  this  is  no  longer  accepted.    Animals  with  this  body  type  are  much,  much  more  diverse  than  this  simple  character  leads  one  to  think.    

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Flukes (Class Trematoda) Fasciola is the largest intestinal fluke of humans. Heavy infection can cause abdominal obstruction and pain. These flukes go through multiple stages:

1. Adults lay eggs in the intestine, which leave in the stool 2. The eggs develop into free-swimming miracidia, which embed

themselves into a snail. 3. Inside, the snail, the miracidia undergo asexual reproduction forming

rediae. 4. The rediae can form swimming, tadpole-like cercariae, which encyst on plants 5. The worm then waits inside the cyst until the plant is eaten by a mammalian host

Clonorchis lives in the human liver and can cause cirrhosis of the liver. Schistosoma is called the blood fluke because they live in blood vessels. Their eggs can cause an allergic reaction with painful symptoms. They are unique in having separate males and females with different morphologies.

- We have slides of all the flatworms mentioned above. Look for the reproductive structures and

the structures used to attach to the host.

Tapeworms (class Cestoda) Tapeworms are parasites in the digestive tracts of other organisms. Since they live in a bath of mostly digested fluid (thanks to the host) they can absorb all the nutrients they need through the skin with no need for a mouth or digestive system of their own. Basically their bodies consist of a hooked head region and a repeating body of reproductive segments.

- Look for slides of Taenia (livestock parasite) or Dipylidium (parasite of pets and children). Notice the “head area” (scolex) and the repeated pouches (proglottids) containing sperm and eggs.

- We also have whole specimens. *Complete digestive tract and circulatory system The following Lophotrochozoa are the first animals we will see with a complete digestive tract, meaning that food moves into the mouth, is processed in the body, and leaves through the anus in one continuous direction. This gives them that tube-in-a-tube design. They also have a circulatory system, meaning there is an organ that pumps blood and distributes nutrients and oxygen throughout the body.

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PHYLUM MOLLUSCA (“soft bodies”) Mollusks are incredibly diverse in their physical appearance and numbers (they are the second most numerous phylum of animals, with 85,000 species), but they all have a body plan in 3 parts:

1. Foot- for movement 2. Visceral mass- holds internal organs 3. Mantle- fold of tissue that drapes the visceral mass. Secretes shell when present.

They are mostly marine, but some of the snails are pretty good at living on land. Examples: Gastropods “stomach foot”

Includes snails, whelks, slugs, nudibranchs and weirder things. Most possess a contain single spiraled shell and feed by scrapping with a spiny, conveyor-belt like radula. Slugs and some aquatic groups have lost the external shell. - Look for the assorted shells and jarred specimens - We may also have live specimens; can you see the radula at work?

Cephalopods “head foot”

This group includes some of the smartest sea creatures like octopi, squid, nautilus, and cuttlefish. The nautiloids still have an external shell, but squid only have a small, thin internal strip, and octopi lost it completely. Members of this group are often fast moving predators that capture prey with long tentacle-arms and break it apart with a beak-like radula - Look for the plexiglass-embedded and jarred specimens

- You may also dissect a squid. Do this by cutting (with scissors) the mantle from the siphon (funnel) to

the tip. Open the flaps to reveal the organs. You can also cut into the mouth to see the hard beak. The anatomy of a male squid is shown below.

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Bivalves “two folds” These mollusks are surrounded by a two-parted symmetrical shell (hence the name), hinged together on one side. Bivalves include clams, mussels, oysters, and scallops. They feed by sucking in water through an incurrent siphon, washing it over mucus-coated gills which catch the food, and then pushing it out through the excurrent siphon. - Look for shells and jarred specimens - You may have the opportunity to dissect a clam: Here’s how

Rules: 1. Take a clam from the bucket 2. Make sure that it has been wedged open (DO NOT use one totally closed. They are hard to

open and are not preserved = stinky!!) 3. Find the hinged end 4. Insert a scalpel close to the shell and the hinged end to cut the muscles that hold the shell

closed (DO NOT wave the scalpel around crazily, this will damage all the stuff inside). 5. Once the muscles are cut, you can open the valves and look inside

Know: 1. Foot (hard muscular structure used to hold the clam to a substrate) 2. Mantle (lining next to the shell, it secretes the shell, remember?) 3. Gills (soft ribbed structures) 4. Stomach 5. Heart (toward the hinge) 6. Large adductor muscles that hold the shell closed 7. Incurrent siphon (part of the mantle, might be hard to see) 8. Excurrent siphon (part of the mantle, might be hard to see)

The  Snail    The  snail  he  lives  in  his  hard  round  house,  In  the  orchard,  under  the  tree:  Says  he,  "I  have  but  a  single  room;  But  it's  large  enough  for  me."    -­‐Anonymous  

 

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PHYLUM ANNELIDA (“segmented worms”) This group includes the very familiar earthworms and leeches, but most annelids (e.g., polychaetes) actually live in the ocean. There they swim or build long tubes to live in. *Segmentation Annelids have a segmented body plan. Segmentation is when the body is subdivided along its length into a series of repeated units called segments. It allows greater flexibility and mobility and more specialization of body regions. Arthropods also have distinct segmentation, leading zoologists to place the two groups together, but more recent genetic studies suggest that annelids are sister to the soft-bodied mollusks. Annelids move by contracting longitudinal and circulatory muscles to pinch and pull the hydrostatic skeleton. They are hermaphroditic, but reproduce sexually. Types: Polycheates

The majority of annelids are polycheates. The group is named after the many hairs called setae (poly + cheate) on the sides of the body. Most are aquatic. Many form long tubes on hard surfaces in the ocean. From this little home, they filter the water. - Look for the polychaete tubes on some of the mollusk shells (think about it; a worm made that) and

jarred specimens.

Oligocheates These annelids have only a “few setae.” Although most of these are aquatic, this group also includes the more familiar earthworms. - Look at the slides of the earthworm Lumbricus in cross

section. Notice the tube-in-tube body design. The center tube is the gut (or intestine). The body is surrounded by muscles that squeeze the tube either circularly or longitudinally.

- You can also cut one open if you want. o Place a worm on the dissecting tray, with the

clitellm up. o Use scissors (not a scalpel) to cut just inside the

upper skin from the mouth to past the clitellum o Observe the segmentation. This segmentation

continues to their organs, several of which are repeated throughout the body. Notice the multiple hearts. The large tube in the middle consists of the pharynx, a muscular structure that sucks food into the mouth, where it then moves through the esophagus to the crop where it is stored, and later to the gizzard, where it is ground up. Which do you think is tougher, the crop or the gizzard? Why?

Hirudinea This group consists of leeches. Leeches are mostly aquatic and endoparasites of vertebrates. They use a three-sided cutting tool to draw blood from their victims. Their spit includes both an anticoagulant to prevent clotting and keep the meal coming and an anesthetic so their host doesn’t get wary. They can engorge themselves on blood, growing several times their normal size.

- We have whole specimens and perhaps living specimens in lab today.

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*Nonliving cuticle The Ecdysozoa share two important traits that are intertwined. This group has a body covered in a layer of nonliving material secreted by the epidermis called a cuticle. Cuticles are usually composed of structural protein like collagen (in nematodes) and the sugar chitin (in arthropods). The cuticle is a tough outer layer and is the functional equivalent of a skeleton. It provides structure and rigidity and gives the muscles leverage in order to move the body. Cuticles are also usually waxy. Wax is water resistant, meaning that less water is lost from the body. This is an adaptation that allows the Ecdysozoa to live in much drier environments than Lophotrochozoa. Think about all the other animal groups that we have discussed: jellyfish, planarians, leeches, snails, clams and squid; all of them live in water or in really wet environments like soil, right? Just like seeds for plants, the cuticle allows an escape from wet habitats. But because the entire body is wrapped in a nonliving protective coating (like shellacking a table), it leaves one little problem: there is no room to grow. That’s where the other trait comes in. All Ecdysozoa grow by periodically shedding this outer layer in a process called ecdysis (hence the name of the group). Ecdysis involves secreting a new soft layer under the old hard layer, breaking open the hard cuticle, squeezing out of it, wiggling or blowing up the new cuticle to allow growth, and then letting the new, slightly larger cuticle dry and harden.

Ecdysozoa are by far the most numerous, diverse, and ecologically successful animals on Earth.

PHYLUM NEMATODA (“roundworms”) Nematodes are basically hollow, fluid filled tubes. The fluid surrounded by the cuticle is a hydroskeleton. This fluid allows them to move by pinching part of the body, which expands another part of the body, sort of like squeezing a balloon. Since they only have longitudinal muscles, this gives them a wiggling type of movement. They have a complete digestive system, but possibly lost some mesoderm covering the digestive tract, therefore they have a pseudocoelom (or “fake body cavity”).

Although most famous as internal parasites, such as dog heartworms and pinworms, nematodes are perhaps the most numerous group of organisms on Earth. They are everywhere. Usually they are too small to see, but believe me, they are everywhere. A single rotting apple on the ground in an orchard can have 90,000 roundworms on it. They are probably in you and on you right now. Despite their usual small size, roundworms in whales can grow to 9m long!!!

New wet body  

Old dry cuticle  

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Enterobius vermicularis, the pinworm, is the most common worm parasite in the US. It seems that we are its natural host, it evolved to live in us. It can be found in 30% of children and 16% of adults. It normally lives in the intestine, but at night, females will crawl out the nearest opening, the anus, and lay eggs there. Her movements and the presence of the eggs causes itching. This usually results in scratching and it’s only a matter of time before they end up in the mouth of their host again. Doctors often diagnose this condition by having the parent strategically place tape on the infected area and looking for eggs stuck to the tape. Trichinella spiralis infects the muscle tissue of mammals. Once there they can hunker down in an encapsulated ball called a cyst. In this form, they are immune to toxins and their host’s immune system. Only extreme heat can break the cyst. This is why you can get trichinosis from undercooked pork. Ascaris lumbricoides is a large intestinal worm found in humans; the ones that we have were probably extracted from pigs. If too numerous they can block the intestines and are especially common in humans living in the southeastern United States.

- We have slides of all of the nematodes listed above. - We also have whole specimens of Ascaris, which you can dissect. Take one of

these and cut it longways to see the tube-in-tube design. Make sure you wash your hands after lab today. I’m not kidding. Their eggs can survive formaldehyde.

- And you can see living nematodes in Caenorhabditis elegans and by taking a piece of moss, add a bit of water, and look for the wiggling worms.

PHYLUM ARTHROPODA (“jointed legs”) No words can describe the diversity in form and lifestyle that the arthropods possess. There are over 1 million species. 80% of animals arthropods. You know them as crabs, shrimp, lobsters, spiders, scorpions, centipedes, and insects. They are everywhere and fill almost every conceivable niche; from internal parasites, to scavengers, to decomposers, to herbivores, to alien-like predators (seriously the monster in the Alien movies is based on an insect). They are bloodsuckers, sapsuckers, nectar suckers. They build structures that rival the best human architects; spider’s silk is stronger than steel and incredibly flexible, some termites build towers that go 125 feet underground to 20 feet above ground; vespid wasps make paper. They and their kin have been swimming in the seas for 500 million years. They’ve walked the earth for 400 million. They are even the first group to evolve true flight (although our group, vertebrates, has done it the other 3 times, so take that insects!).

The nonliving cuticle of arthropods is hardened by chitin forming a tough exoskeleton. In order to move, arthropods are also endowed with segmentation with thinner, flexible cuticle between the segments. Their exoskeleton is much like a suit of armor (as modeled by Dr. Doom on the left. The comic Doom, not the movie Doom. The movie Doom was stupid). The muscles are attached to the inside of these rigid tubes. The different segments and parts of the exoskeleton can be fused together or modified to form tools that serve innumerable functions. See the insect figure below for examples of this utility. The combination of these two adaptations, segmentation and exoskeleton, combine to create the diversity we see today and the most successful phylum ever to have existed.

- We have whole specimens and some slides of various arthropods.

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Chelicerates Chelicerates were probably the first arthropods to crawl out onto land. They are different from the other arthropods because they do not have mandibles. Their pocketknife of tools consists of six pairs of appendages including: chelicerae for feeding, pedipalps for sensing and grabbing, and 4 pairs of walking legs. They usually have two main body segments: • cephalothorax (head + thorax fused together)- houses the mouth

and mouthparts and the center of the nervous system, and where the appendages are attached

• abdomen- where most of the organs, including those for reproduction are housed.

Examples: Xiphosura- this group includes the horseshoe crabs, which are neither horses, nor shoes, nor crabs. It is a very ancient lineage (500+ million years). The chelicerae and pedipalps are pincerlike and used for gathering food.

Arachnida- this is a diverse group; note that all of these groups are arachnids, but only Aranae are spiders. Here are some common orders:

• Aranae “Spiders” o Chelicerae are fangs o Pedipalps are sensory structures o Eight simple eyes o Silk production

• Scorpionida “scorpions” o Chelicerae are small o Pedipalps are pincers o Poisonous tail

• Opiliones “harvestmen, daddy longlegs” o Chelicerae are pincer-like o Pedipalps are sensory structures o Typically scavengers o They do not have fangs or venom and are not spiders.

Therefore, they are not the most venous spiders!

• Acari “ticks and mites” o Chelicerae are fused into tube for sucking blood o Ectoparasites or vertebrates o Usually a minor nuisance, but chiggers in large numbers can be painful

and ticks often serve as vectors for bacterial-based diseases o Look at slides of mites and ticks

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Myriopoda “many feet” The myriapods consists of the centipedes, millipedes, and a couple of other more obscure groups. They have two major segments (head and trunk), one pair of antennae, 1-2 maxillae, and eyes that consist of groups of ocelli. They seem to have lost the compound eyes found in other arthropods. Class Chilopoda “lip foot” There are about 3000 species of centipedes. Centipedes are agile carnivores, feeding on insects and earthworms. Centipedes are dorsoventrally flattened and they kill their prey with a venom claw near the head and chew it up in their mandibles. Therefore, you shouldn’t handle centipedes for too long because they can give a bit of a poke. For the most part, there is a pair of legs per segment (hence the common name that means “one hundred feet”). Especially the foot-long Scolopendra. House centipedes, Scutigera, which can be found scurrying with their colorful legs across the walls of dorm rooms are harmless and actually help reduce the number of unwanted pests.

Class Diplopoda “two feet” To this class belong the millipedes. There are about 10,000 species of millipedes. They tend to be less active than centipedes and are mostly herbivorous or eat decaying plant matter. They have a rounded body and can roll into a ball when disturbed. They can also expel noxious chemicals from repugnatorial glands. Therefore, if you can, refrain from licking millipedes. They will mess you up. With the exception of the first couple of segments, each segment typically has 2 pairs of legs (hence the name millipede which is referring to their “thousand feet”. “Thousand feet?” you may say, but doesn’t that mean “million feet?” No it does not. Look it up).

Crustacea The crustacean include the shellfish: crabs, shrimp, and lobsters, but also barnacles, isopods, brine shrimp (sea monkeys), copepods and other strange creatures. Crustaceans are typically aquatic (although pillbugs, or rolliepollies, which are isopods, are common terrestrial crustaceans). Most are small and make up the zooplankton of oceans (like krill), but we are more familiar with the larger crabs, shrimp, and lobsters.

Their body plan is also made of a cephalothorax and abdomen. A unique feature is that each appendage is ancestrally divided into two branches, a condition call biramy. As such, they typically have two pairs of antennae used for sensing, and a pair of appendages on almost every segment of the body. The typical crustacean has 5 pairs of walking legs, in some the first pair is modified to be chelipeds (or pincers). Many, like crayfish, also have swimmerets on the other segments. These small feather appendages help them swim. They usually breathe through gills. Their cuticle also contains calcareous deposits making it very strong, but rather heavy, thus limiting their movement on land (water helps hold up the heavy cuticle).

Tick  Tick  

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We have whole crayfish. You may need to be able to recognize some of the following anatomonical features:

Hexapoda: Insecta Insects are the most diverse of this most diverse group. At least 1 out of every 4 kinds of living thing on Earth is an insect. There may be up to 10 million different species of insects, with new ones being discovered constantly. Insects are some of the most important animals ecologically. They are decomposers, herbivores, predators, parasites, prey, soil turners, forest killers, and pollinators. They live on water, underwater, on ground, underground, on plants, inside plants, on other animals, and even inside other insects. Insects include some of the most economically important animals since they are food producers (like honey), food for other animals (like fish), pollinators of crops, and biocontrol agents. They can be pretty or pests or pretty pests. According to some sources, the manna that the exiled people of Egypt ate in the desert was actually the secreted wastes of an insect. The insect body plan consists of a head, thorax, and abdomen. Each of these segments can be broken up into more than one segment, and they can be modified beyond recognition, but they always serve the same basic functions. See the full page figure below for examples of different appendage functions. • Head- houses the mouthparts and nerve center: brain, eyes, and antennae. • Thorax- houses the muscles and appendages for locomotion: legs and wings (when present). • Abdomen- contains the digestive center, respiratory openings, and reproductive organs.

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Insects are very good at what they do. Below you will find a list of key adaptations that have helped them become so successful and dominate this world. Key Adaption One: Exoskeleton The exoskeleton is of course, not unique to insects, but insects have taken full advantage of it. The waxy coating that the exoskeleton provides maintains water balance, allowing insects to become truly terrestrial or remain in aquatic systems. Unlike most of the animals we’ve discussed thus far, insects no longer require constantly moist conditions. Instead, they can venture where no one has gone before.

Key Adaptation Two: Segmentation Again, insects have taken their segmentation to the max. Their jointed appendages have been modified over and over again to fill many different functions. The picture to the right is merely an example of what is possible. Key Adaptation Three: Small Size I am cheating a little on this one too, because it is not really a trait in itself, but rather a result of other traits. Insect breathe through a tracheal system, in which tubes bring oxygen to each cell in the body. That, in addition to the weight of the cuticle without the support of water, limits the size of insects, but this may actually benefit them. It allows more species in a smaller area. It also allows insects to take advantage of niches other animals are too large for (see pics below).

ß  Predaceous  diving  beetle  

ß  Desert  tenebrionid  beetle    

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Key Adaptation Four: Wings Many species glide; this method of traveling is much like parachuting and usually entails slowing a fall by trapping air in a membrane stretched between limbs (as in flying squirrels and colugo), toes (as in flying frogs), or ribs (as in flying snakes and flying dragons). Some of the organisms that glide are actually quite good at it and can go long distances and control their direction of descent. However, despite their common names, they are still required to start high and basically just fall gracefully. Alternatively, true flight allows the organism to take off from anywhere, move in any direction, and stay alight much longer. The benefits are many. With true flight, an animal can literally leave predators in their dust. They can spread their genes far and wide and enter new worlds. The difference is like the difference between a helicopter and a handglider. Despite its obvious potential, the evolution of powered flight is very rare. As far as we can tell, it has only happened four times. Compare this to something more complicated like internal fertilization that seems to come and go with whimsy. The insects were the first group to evolve powered flight, and they haven’t looked back since. Wing-related Key Adaptations: Wings were a great adaption, but further adaptations improved on the design. The first insects with wings looked much like dragonflies (see top right). Dragonflies and their kin are aerial acrobats and are some of the best flyers today. They can turn on a dime, fly backwards, and hover. They use their wings to snatch other insects from the air. However, their wings are rather large and are easily damaged.

A. Wing folding Later, insects solved this problem in part by folding the wings back over the body (see cockroach at left). This reduced the bulkiness of the wings and protected their delicate structure from harm. Today, those insects that can fold their wings are much more numerous than those that can’t.

B. Elytra A further improvement over wing folding was to convert the first pair of wings into protective structures that protest the folded hind wings, which remain functional for flight. This has happened independently in several lineages, including grasshoppers and hemipterans, which have leathery forewings. However, one group mastered the technique. Beetles (Coleoptera) have forewings that are hardened like shields. The hindwings then fold underneath these sheaths where they remain protected. The forewings are so modified that we’ve given them another name: elytra (singular: elytron).

With their wings protected, beetles were now free to go anywhere without damaging the thin membranous flight wings. They can dig underground, dive underwater, burrow into trees, and hide under rocks. And when necessary, the hindwings unfold from under their sheaths and the beetle flies away. Beetles are basically little tanks that fly.

With these modifications, the beetles have become the most diverse group of the most diverse group of the most diverse group of animals. 1/3 of insects are beetles. They are among the smallest and heaviest insects (both of which can still fly). They are equally diverse in habits and habitats.

C. Short Elytra But wait! There’s more. One family of beetles has even improved the elytron. Like I said, beetles are little tanks, but like tanks, they can be quite cumbersome. By shortening the elytra, staphylinid beetles regain some of their flexibility. They can now go even further into hiding. The family Staphylinidae is the most diverse group of beetles with over 46,000 species. This number is amazing considering they are not really economically important or overly pretty, so there is no alternative incentive to study them and name more

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species. The series of images below show a staphylinid beetle unfolding its hind wings in preparation for flight.

Key Adaption Five: Complete Metamorphosis The entognaths and first insects, like silverfish, undergo no metamorphosis. Instead, they add size and sometimes even segments with each successive molt. These groups are called ametabolous and undergo the following developmental cycle: Egg à Small à Larger à Largest More derived insects have something of a juvenile stage called a nymph. Nymphs are rather similar to the adult, but lack wings and functional reproductive parts. This type of life cycle is called incomplete metamorphosis; these insects are called hemimetabolous and go through the following stages: Egg à Nymph à Adult The majority of insect species (and that is why it is a key adaption) however, undergo complete metamorphosis. These insects spend time in a stage that is very unlike the adult, i.e., the larval stage. In this way they reduce competition between the stages and divide their labor:

A. Young- eat and grow B. Adult- disperse and reproduce

In order to transform the eating-machine larva into a reproduction-machine adult, there must be a period of breakdown and rebuilding of parts. Therefore, a third stage is required: the pupal stage. During this time, the insect is dormant and the parts are rearranged. This type of development is called holometabolism and goes something like this:

Egg à Larva à Pupa à Adult

Holometabolous Development

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Here is a possible phylogeny for the insect orders. I have added to it the places where each of these traits evolved. In each case, the number of species with the trait is more than the number without. This is why we think that they are key adaptations. The adaptation led to the diversity. Segmentation  

Exoskeleton  

Small  size  

INSECTS!  

Wings  

Wing  folding  

Elytra  

Short  Elytra  

In lab, you will find many of specimens of insects and their kin.

Some of these are small and are embedded in slides. Typically, these are insects that are very relevant pests of humans like fleas, lice, and bedbugs. You may want to look at these too.

Complete    metamorphosis  

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BIOL 1108 Lab 12 Animals Part 1 Name ______________________________________

1. If invagination is not complete during gastrulation, the result is

A. An incomplete digestive tract B. A blastula C. Spiral cleavage D. Deuterostomy E. An angry chicken

2. Animals are capable of getting energy and matter directly by

A. Performing photosynthesis B. Eating heterotrophs C. Eating autotrophs D. B and C E. All of the above

3. If you were to play hot potato with a

jellyfish, which of the following would you regret most?

A. Ectoderm B. Endoderm C. Cnidocytes D. Polyps

4. Bivalves capture food with their A. Gills B. Feet C. Radulas D. Tentacles E. Girlish charm

5. Which of the following is your favorite

arachnid? A. Horseshoe crab B. Lobster C. Spider D. Ant

6. Insects evolved from a crustacean. Which

of the following characters was lost in the insects?

A. Biramy B. Compound eyes C. Segmentation D. Exoskeleton E. Wings

7. What kind of symmetry does a nematode have?

A. None B. Radial C. Biradial D. Bilateral E. Hexagonal

Circle all of the following that are TRUE. 8. Sponges are not animals because they don’t move.

9. All nematodes are parasitic.

10. Most annelids are terrestrial.

11. Arthropoda is the most diverse group of organisms on Earth. 12. Centipedes always have a hundred legs.

13. Spiders shed their skin (i.e. cuticle).

14. Pinworm (Enterobius vermicularis) is the most common helminth (worm-like) parasite of people in

the U.S.

15. Daddy-long legs are the world’s most venomous spiders.

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16. Name three characteristics that make an

animal an animal. A.

B.

C.

17. Name three things that form during gastrulation. A.

B.

C.

18. Draw a blastula and a gastrula. Compare AND contrast them.

19. Match the germ layer with the organs/tissues it eventually gives rise to.

Endoderm _____ Mesoderm _____ Ectoderm _____

A B C

20. What is the function of a Platyhelminthes cyst?

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21. What are some costs AND benefits of the arthropod exoskeleton? 22. Squid and snails look very different, but are very closely related. What do

they have in common with each other, but not with other groups?

23. Draw a scolex and label its parts. What is its function? 24. Which part of the earthworm do you think is tougher, the crop or the gizzard? Why?

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25. Draw a phylogeny to depict the true relationships of the following groups. Their positions are correct, you just need to draw the tree that connects them properly.

Earthworm

Snail

Squid

Pinworm

Horseshoe Crab

Scorpion

Spider

Beetle

26. For each insect type, please put a check in the box for any and all traits that can be found in members of that group.

Insect Exoskeleton Segmentation Wings Wing

Folding Complete

metamorphosis Elytra

# of species in the insect’s

Order

Silverfish

Dragonfly

Grasshopper

Cicada

Monarch butterfly

Mosquito

Ladybug

27. Look up an estimate of how many species are in each type’s order and add to the table above. What

does this tell you about key adaptations?

28. What was your favorite insect in lab today and why?