Lab 8
tagmata
-Tagmais a specialized grouping of multiple segments into a coherently functional morphological unit. Plural= Tagmata -
segmentation in arthropods
-have segmented bodies -series of repeating units
crustacea
-head, thorax, abdomen -some have cephalothorax and abdomen
mandibles in arthropods
-(function as jaws, sideways compared to ours) -The mandible are a mouthpart used for chewing (biting, cutting). It is similar to our mandible (lower jaw), but the arthropods use their pair of mandibles in sideways motion instead of up and down.-Crustacea, Hexapoda, and Myriapoda have mandibles. -Chelicerates do not have mandibles
features of exoskeleton in arthropods
-Hard enough for protection -Light enough for mobility -Versatile thickness and flexibility: see at right -structural support -attachment for muscles for locomotion -protecting against predators of the same scale -prevention of water loss (desiccation) -an integral part of sensory receptors
arthropods circulatory system
-Also like molluscs, arthropods have an open circulatory system. For some arthropods, the blood distributes nutrients to the cells of the body and in some arthropods it also distributes gases. -Although the specific details vary among arthropods, the basic idea is very similar to what you learned about in molluscs: -A dorsal heart to pump the blood into arteries. Valves prevent blood from flowing back into the heart. -The arteries deliver blood to the hemocoel. -The blood drains back to the space surrounding the heart. The hemocoel in arthropods is much more extensive than in molluscs. -The blood returns and enters the heart through openings on the heart called ostia.
arthropod diversity and success
-Arthropods are the last protostome that you will study. -A few weeks ago, you learned that most animals belong to the clade Protostomia. -The vast majority of animals within this clade are arthropods. -They have radiated to occupy every conceivable type of ecological niche. -After the first arthropods made a success of aquatic habitats, members of the phylum eventually became, not only the first animals to make the land their home, but also the only invertebrates to fly and to successfully adapt on a large scale to life on land.
arthropod nervous system
-Arthropods have a variety of sophisticated sensory receptors sensitive to: mechanical stimuli, touch, vibration, water current, sound waves, taste, smell, light, gravity, humidity. -variety and sophistication
Tree Thinking
-Arthropods, like all animals, belong to Metazoa. -Like all animals with tissues, they also belong to Eumetazoa within Metazoa. -They have bilateral symmetry and are triploblastic, so within Eumetazoa they also belong to Bilateria. -Within Bilateria, they also belong to Protostomia. -And within Protostomia, they also belong to Ecdyozoa
joint appendages arthropods
-Being encased in a hard external skeleton also constrains movement unless there is something in the body plan to relieve it. -And arthropods do have an answer. Freedom of movement is provided by jointed appendages, which as you see above is where the name of this phylum come from. There is movement possible at each joint, just as in our bodies. The limbs are paired, as you might expect for a bilaterally symmetrical organism
versatile cuticle as exoskeleton in arthropods
-Being encased in a non-living hard skeleton could place a constraint on growth. -This constraint is relieved by the process of ecdysis. By periodically molting the hard exoskeleton and replacing it with a new, larger one, growth is possible. -Individuals are vulnerable after molting and before the new exoskeleton hardens. It has been reported that approximately 85% of arthropod deaths occur during molting. This includes potentially difficult molts late in life, when the individual has become relatively large
book gills (horseshoe crab)
-Book gills are located on the ventral side of the horseshoe crab. They are covered with flaps of exoskeleton. Lift the flap and see layers of gills like pages in a book. -They are similar to the gills of crabs, which are aquatic crustaceans. But horseshoe crabs are not really crabs. They belong to the group of arthropods called Chelicerata. This group includes spiders, and as you will see in the next slide, spiders use book lungs for gas exchange. The difference between book gills and book lungs is that the book lungs have to be protected from desiccation since spiders are terrestrial and so are placed inside the body. Horseshoe crabs are aquatic and do not need to protect the book gills from desiccation since they live in water.
tagmatization in arthropods
-During development segments fuse to form functional groups called tagmata (tagma= singular) -Specialization of appendages associated with different tagmata
terrestrial chelicerates: book lungs
-Gas exchange surface is located internally -Book lungs are layers of thin, page-like structures filled with blood. They are located in an air-filled space in the body. -Air enters through slits in body wall and passes over moist surface of vascularized book lungs. -Gas exchange occurs between air and and blood in book lungs: oxygen into blood and carbon dioxide into the air -Blood then transports gases from book lungs to rest of body where gas exchange occurs between blood and cells: oxygen to cells and carbon dioxide into blood, blood returns to book lung
movement in arthropods
-In arthropods a hydrostatic skeleton is not possible with an exoskeleton. One of the requirements of a hydrostatic skeleton is a flexible body wall which is not true of the hard exoskeleton. -Muscles and the Jointed Appendages provide movement -In arthropods, muscles are arranged as localized bands of muscles and are organized into antagonists at joints such as flexors and extensors. One group contracts and bends the joint one way, then it relaxes and the other contracts and bends it the other wayThis is similar to the arrangement of our own muscles except in Arthropods the muscles are attached to the inside of the skeleton
features of exoskeleton result in constraint to size in arthropods
-Molting: Arthropods shed their rigid exoskeleton and go through a "squishy" stage until new exoskeleton hardens. The laws of physics make it clear that a large terrestrial animal with no means of protection or body support will deform and have a difficult time moving. Natural selection would probably act against a large animal that faced so many extra challenges when molting. Exoskeleton weight and strength: If you scaled up an ant 4X proportionally (keeping its exoskeleton thickness the same in relation to its body), the ant's legs would crumple under the strain of holding up its body.
two types of eyes in arthropods
-Ocelli (Latin, "little eye"):single lens, simple cup that is light sensitive, generally non-image forming -Image forming compound eyes: many separate units each with lens -Some arthropods have only ocelli, some only compound, and some have both
functions of cuticle as an exoskeleton
-Protective barrier, keeps some things in and others out: •prevents loss of water (desiccation) from body •prevents pathogens and parasites from entering -Protection from predation and physical injury -Responsible for structure, support and form -Movement •Rigid skeleton for muscle attachment •Soft and flexible at hinge-like at joints -Sensing •The cuticle is non-living, so the cuticle itself cannot provide sensory information. However, the cuticle is modified so that sensory nerve endings are lodged in parts of the cuticle modified into bristles, peglike projections, cones, pits, or slits in the cuticle. These sensory receptors are specialized to sense chemical, temperature, touch, gravity, and humidity sensations
Book Lungs - Chelicerata Subphylum
-Spiders are terrestrial arthropods. They can't have their gas exchange structure suspended in air or they would dry out and not be able to do diffusion. Their gas exchange structure has to be internal -Imagine a modified book gill of the horseshoe crab with all its layers, placed inside a chamber in the body that remains humid. -Then imagine a small opening on the ventral side of a spider that allows air to come in and out, but not enough to dry the surface out. -The layers of blood-filled "pages" in the chamber could then exchange gases with the air. -You have just imagined a book lung!
arthropod digestive tract
-The digestive tract is generally typical and really not that different from our own or many of the animals you are learning about: •Foregut (mouth, esophagus, stomach) where ingestion, transport, storage, and mechanical digestion occur •Midgut (digestive gland, intestine) where chemical digestion and absorption occur •Hindgut (rectum, anus) where water absorption occurs and feces are prepared and then eliminated
Tracheal system-Hexapoda and Myriapoda Subphyla (arthropods)
-The tracheal system is a gas exchange adaptation for terrestrial life in insects and centipedes and millipedes. The gas exchange surface is the individual cells of the body which are internal, so there is no risk of desiccation. It is a series of branching tubes extending from opening in body wall that carry air to and and from each individual cell. When the air reaches the cells, gas exchange occurs between the air in the tube and the moist surface of the cell. -Through small openings on the body called spiracles (, air enters the body and travels through a series of branching tubes called tracheae (plural, trachea singular) (. The spiracles can be closed to prevent desiccation.The tracheae branch into smaller tubes called tracheoles. Air travels through these tubes to the surface of the cells (. Gas exchange occurs between the air in the tubes and the individual cells.Blood plays no part in the gas exchange of the tracheal system.SpiracleTracheaeSmallest tubes terminating on cellsLarger and more active insects, such as moths, butterflies, bees and wasps, show breathing movements -that is they actively pump air through the tracheal system. This is why the abdomen pulses in these insects.
tracheal system: hexapoda and myriapoda
-This is another gas exchange strategy adapted to terrestrial life so the gas exchange surface is located internally -Air enters through openings in body wall called spiracles. It then travels through a series of branching tubes. Eventually, tubes branch near enough to each individual cell for efficient diffusion of gases to occur -Gas exchange occurs between air in the tubes and individual cells: oxygen into cells and carbon dioxide into tubes, air travels back to outside of body through same tubes
4 gas exchange strategies in arthropods
-Two strategies are used by aquatic arthropods and are very similar in how they do gas exchange. They are Gills and Book Gills. -Two strategies are adaptations to terrestrial life and they do gas exchange in different ways. They are Book Lungs and Tracheal System.
subphylum crustacea - gas exchange
-Use gills for gas exchange -The gills are underneath the carapace and are attached to walking legs
gas exchange in subphylum chelicerata
-book lungs -recall that horseshoe crabs are chelicerates and have book lungs
adaptations for terrestrial life
-challenge: Desiccation, loss of water across body -solution: Well-developed waxy layer in cuticle (Hexapoda, Chelicerata) surface -challenge: Gas exchange surfaces exposed to air will dry out -solution: Gas exchange strategies that place gas exchange surface internally: Book Lungs (Chelicerata), Tracheal System (Hexapoda and Myriapoda), Spiracles that close (Hexapoda) -challenge: support of land without the aid of buoyancy of water -solution: hard exoskeleton supports weight of body on land -challenge: loss of water with excretions of nitrogeneous waste -solution: nitrogeneous waste in forms of solid, uric acid -challenge: Many aquatic animal release gametes into their watery environment and fertilization occurs in the water. However, if terrestrial animals did this, the gametes were dry out and perish. -solution: Fertilization occurs internally with male placing sperm inside female
subphylum crustacea
-crayfish -The diversity of body forms and lifestyles of crustaceans is enormous. There are crustaceans in every type of marine and freshwater environment, and terrestrial forms. Members of Crustacea display a very high degree of variation in the tagmata and the appendages. -They are so diverse that it is difficult to use one crustacean as a representative. For learning purposes, we are going to use the crayfish as the representative. -Crustacea have 3 tagmata-head, thorax and abdomen. In some species, like the crayfish the head and thorax are fused together to form a cephalothorax which is covered by a single large shield called the carapace. -The cephalothorax has legs which may be specialized for use in walking or feeding. -The crayfish has five pairs of walking legs. The first pair is modified into a large claw called a cheliped. -The abdomen has appendages usually used for swimming, water circulation over gills, and in females they carry fertilized eggs -not well developed waxy layer in exoskeleton -terrestrial crustaceans are confined to moist habitats -compound eyes, often, as in crayfish, they are on stalks -2 pairs of antennae -crayfish have appendages of abdomen, some, like the crayfish, use them to hold fertilized eggs -high degree of specialization of the appendages for a variety of functions -a characteristic you can always look for to identify a crustacean is two pairs of antennae
four arthropoda subphyla
-crustacea: crayfish -myriapoda: centipede -hexapoda: grasshopper -chelicerata: garden spider and friends
subphylum chelicerata
-garden spider and friends -2 Tagmata: Prosoma (fused head and thorax) and Opisthoma (abdomen) -waxy cuticule -no mandibles -no antennae: In fact, chelicerates don't appear to have a defined head, when you look at the diagram to the right it appears that the head is missing compared to a hexapod -eyes are ocelli -First Two Appendages: 1st pair of appendages: chelicerae= in spiders there is a fang at the tip that injects venom into prey; 2nd pair of appendages: pedipalps= sensory, feeling, food manipulation, copulation
cuticle in arthropods
-just like the other group of ecdysozoans, nematodes), arthropods also have a cuticle. The cuticle is to a large extent responsibile for the success of this phylum. -The cuticle is on the outside of the body and is secreted by the epidermis. It is non-living. -The outer layer of the cuticle is a thin waxy layer. In arthropods well-adapted to terrestrial habitats, this layer is well-developed. The waxy layer is a barrier against evaporation of water from the body and hence prevents desiccation, an important consideration for terrestrial animals. The inner hardened layer is composed of chitin and reinforced by the addition of minerals and/or proteins . The thickness and flexibility of this layer varies in different parts of the body and in different arthropods. -The cuticle forms an exoskeleton in arthropods. An exoskeleton supports the body from the outside. The segments and limbs of arthropods are encased in this hard external skeleton.
subphylum myriapoda
-many feet -Low Level of Tagmatization, 2 tagmata, Head and Trunk -Terrestrial but do not have well-developed waxy layer in exoskeleton -1st trunk appendages modified into Poison claws that stab prey and inject poison strong enough to subdue small vertebrates -Goes with Feeding Strategy as PredatorRest of trunk appendages have same morphology (form) -Centipede has one pair of walking legs on each segment; project to side of body = designed for speed -Type of eyes are ocelli. Can be just a few like the photo on the left, or a cluster of ocelli like the photo on the right, which makes it look like a compound eye. As ocelli, they are not image forming. Only light and dark. -Since eyes do not form images, antenna play important sensory role.They are highly sensitive and contain many touch and chemical sensory receptors -one pair of antenna
chelicerata
-protosoma (cephalothorax) and opisthosoma (abdomen) -head is reduced
reasons for arthropod success
-segmentation + tagmatization; makes possible many variations on mouthparts, walking legs, etc. which allows arthropods to explore wide range of ecological niches (explained on next slide) -versatile exoskeleton; adaptation to terrestrial life -variety of gas exchange strategies; adaptation to terrestrial life -excretion of uric acid, adaptation for terrestrial life -internal fertilization, adaptation for terrestrial life -small size: exploit many more niches compared to larger animals -produce many offspring in a lifetime, offspring mature rapidly, large amount of genetic diversity -complex behavior and evolution of social systems -complete metamorphosis (86% of insects); different stages of life use different parts of habitat reducing competition -flight
subhylum hexapoda
-six footed -grasshopper -3 tagmata: Head, Thorax, Abdomen -Waxy exoskeleton: Is it restricted to moist habitat? -3 pairs of walking legs on thorax, Wings on thorax -No appendages on abdomen
gas exchange in centipedes
-tracheal system -For most species the spiracles remain open at all times which is another reason they must live in moist habitat—air can enter the spiracles and cause desiccation. -Terrestrial, confined to moist habitats:due to lack of waxy layer in cuticle and open spiracles
gas exchange in grasshopper
-tracheal system -able to close spiracle which decreases desiccation. -They are found in all habitats on land and in fresh water. There are very few marine hexapods
aquatic arthropods: gills and book gills
-use the same overall strategy (which is the same strategy as the gills of a mollusc) -Both have lots of surface area and are exposed to surrounding water. -Water passes over gills/book gills. Gas exchange occurs between surrounding water and blood: oxygen into blood and carbon dioxide into water -Blood then transports gases from gills to rest of body where gas exchange occurs between blood and cells: oxygen to cells and carbon dioxide into blood, blood returns to gills
are arthropods coelomates
-yes but the coelom is reduced -Arthropods have a coelom. But similar to the molluscs, the coelom of arthropods is reduced to space surrounding the heart. -The main body cavity is the hemocoel. Recall that a hemocoel is composed of connected spaces around tissues and organs
arthropod gas exchange
A specialized gas exchange surface must have these characteristics: -Moist surface and must be protected from dessication -Thin and permeable to gases -Lots of surface area -Vascularized
excretion of nitrogenous waste in arthropods
Aquatic arthropods excrete nitrogenous waste in form of ammonia. Ammonia is toxic and must be eliminated quickly. It is soluble in water so aquatic arthropods can excrete it in the water around themand it will be carried away. Notice in the diagram on right that the chemical structure for ammonia is similar to the amino group from the protein. This means it does not require a lot of energy to convert amino acids into ammonia Terrestrial arthropods excrete nitrogenous waste in form of uric acid. These arthropods need to conserve water. Uric acid is non-toxic, insoluble in water, precipitates as a solid with little loss of water to eliminate it from body. This is an important adaptation to terrestrial life. Also notice in the diagram to the right how much more complex the chemical structure for uric acid is compared to the amino group. It requires more energy to make, but the conservation of water is worth it
success of arthropods defined in three ways
Diversity:a million species identified and many, many yet to be recognized (Compare this to 60,000 vertebrate species) Abundance:it is estimated that there are 1018, or a billion billion, arthropods on Earth; it is estimated that there are some 200 million insects for every human being on earth; Arthropods constitute 84% of all known animal species. Distribution: they live in every type of environmental habitat--sea, freshwater, on land, and in the air.
what does vision look like with a compound eye
In reality, the compound eye produces an image of one pixelated flower, so it is slightly blurry
gills in aquatic crustaceans
gas exchange occurs between the water and the blood in the gills just as in the mulluscs
Myripoda (Arthropoda)
head and trunk
hexapoda
head, thorax, abdomen
