Construct a dichotomous key to classify crustacens,archnids,centipeeds,millipeeds and insects
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Answer:
How to Make a Dichotomous Key
Step 1: List down the characteristics. ...
Step 2: Organize the characteristics in order. ...
Step 3: Divide the specimens. ...
Step 4: Divide the specimen even further. ...
Step 5: Draw a dichotomous key diagram. ...
Step 6: Test it out. ...
Dichotomous key for animals. ...
Dichotomous key for insects.
Answer:
classes. In this lesson we will examine how arthropods are divided into these subphyla, and then we will consider the details of one well-known subphylum: Crustacea. We will also take a look at one of the arthropod classes that contains many feared and reviled species: the arachnids.
The sheer number of arthropod species (over one million and growing!) presents a substantial challenge for scientists trying to subdivide them into distinct groups based on their evolutionary relatedness. Just to give you an idea of some of the conflicts that exist in the field of arthropod systematics, some scientists have suggested (based on molecular data) that some species within the group Crustacea are actually more closely related to insects (in the group Hexapoda) than they are to other crustacean species. This is currently a controversial topic, and in this lesson we will consider the established, traditional groupings of arthropods. In this classification, arthropods are divided into five subphyla:
Trilobitomorpha (Trilobites).
Chelicerata.
Crustacea.
Myriapoda.
Hexapoda.
The Subphyla and Classes Table lists the classes within each of these subphyla and shows an example of a typical member of each subphylum.
Subphyla and Classes of Arthropods
Subphylum Class Examples Common members
Trilobitomorpha Trilobites (extinct)
Extinct
Myriapoda
Chilopoda
Diplopoda
Pauropoda
Symphyla
Centipedes
Millipedes
Chelicerata
Arachnids
Xiphosura
Pycnogonida
Spiders
Scorpions
Mites
Ticks
Horseshoe crabs
Sea spiders
Crustacea
Remipedia
Cephalocarida
Branchiopoda
Maxillopoda
Malacostraca
Lobsters
Crabs
Shrimp
Barnacles
Krill
Hexapoda
Collembola
Diplura
Protura
Insecta
Ants
Flies
Grasshoppers
Beetles
Butterflies
Moths
Bees
Springtails
How are each of these groups related to each other?
A phylogenetic tree showing the relationships between different arthropod subphyla.
Pauropoda.
Symphyla.
Myriapods are all terrestrial animals and are nearly all herbivores (plant-eaters). The exceptions are the predatory centipedes. Members of this class are characterized by having a modified pair of appendages called forcipules on their heads that function as poison claws. These are shown in Figure below. Their prey ranges from other invertebrates to vertebrates, such as mice and frogs, and can vary widely depending on the size of the centipede species. As plant-eating organisms, the other three classes of myriapods play a critical role in many ecosystems by breaking down dead plant matter for use by other organisms.
A centipede head showing the modified appendages that function as poison claws called forcipules. This adaptation is critical to the predatory lifestyle that distinguishes centipedes from other classes of myriapods.
The body of myriapods, as shown in Figure below, is divided into two major regions: the head and the trunk. The head possesses a single pair of antennae for sensing the environment and simple eyes.
The general body plan of a myriapod. Notice the similarities to many annelids: the segments are nearly identical, and each has a pair of appendages. Unlike annelids, the myriapod appendages are jointed.
There are also several sets of modified appendages found on the head that function as mouthparts. These include the mandible and the maxillae. The mandible and maxillae are features shared by myriapods, crustaceans, and hexapods. The mandible is a jaw-like structure that is used to grasp, bite, and even chew food. The maxillae are usually used for manipulating food in the mouth and swallowing. Figure below shows the mandible of a crustacean. The myriapod mandible and maxillae are actually more similar to those of insects. You will learn more about the features of insect mouthparts in the next lesson on insects.
A close-up view of the mouth region of a crustacean. The various mouthparts that can be seen in this photograph include 1- the ventral groove, 2 – the labrum (upper lip), and 3 – the mandible. The mandible functions essentially like a jaw for chewing food.
The trunk is made up of nearly-identical, repeating segments with a pair of appendages located on each one, as shown in Figure above. Millipedes are an exception to this, as they have two pairs of appendages on each segment. This occurs because each segment of a millipede is actually two segments fused together. The two smaller classes of Myriapoda, Pauropoda and Symphyla, have only a few hundred species each. The Symphyla and Pauropoda essentially look like small centipedes. They are usually only a few millimeters long (about the size of the letter “l” on this page), while centipedes and millipedes range from a few millimeters to 30 centimeters (slightly longer than a sheet of paper) in length.