Integrated Principles of Zoology Study Set 3

Biology

Quiz 20 :

Crustaceans

Quiz 20 :

Crustaceans

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What is a carapace
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The dorsal cuticular covering of the head which extends posteriorly and around the sides of animal and covers the thoracic and abdominal segments is called carapace.

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Briefly describe the function of antennal and maxillary glands in Crustacea.
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The antennal glands or maxillary glands are excretory and osmoregulatory organs of crustaceans.
The only difference between the two is that antennal glands open at the base of the antennae while maxillary glands open at the base of the second maxillae.
img The end sac of the antennal gland has a small vesicle and a spongy mass called a labyrinth. The Labyrinth is connected to the dorsal bladder by an excretory tubule. This dorsal bladder opens to the exterior by a pore on the ventral surface of the basal antennal segment. Hydrostatic pressure within the hemocoel provides force for filtration of fluid into the end sac. Filtrate is excreted as urine after the reabsorption of salts, amino acids, glucose and some water in the excretory tubule.
Nitrogenous wastes are excreted across thin areas of cuticle and especially through the gills. The antennal glands or maxillary glands mainly function to regulate ionic and osmotic composition of body fluids. Antennal glands act as an effective osmoregulatory device by forming dilute urine.

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Describe the molting process in Crustacea, including the action of hormones and the process of ecdysis.
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The process of molting involves the following steps-
• The Epidermal cells which are lying just below the endocuticle enlarge and separate
• They secrete a new epicuticle followed by secretion of a new exocuticle.
• In the space above the new exocuticle enzymes are released.
• These enzymes dissolve the old endocuticle.
• Animal absorbs water from its gut and increases the blood volume of the body.
• This increase in blood volume builds an internal pressure.
• This pressure causes the cuticle to split along preformed lines of weakness, which breaks the upper lying old exocuticle and old epicuticle.
• The new cuticle is stretched, deposition of the endocuticle, re-deposition of inorganic salts and other components and finally hardening of the cuticle.
img The action of shedding the hard cuticle to enable the body to increase in size is called ecdysis.
The action of hormones in molting and ecdysis cycle is in this way:
• The central nervous system receives stimuli for initiation from the environment.
• After receiving this signal, the production of a molt-inhibiting hormone by the X-organ decreases.
• A drop in the level of molt-inhibiting hormone promotes release of a molting hormone from the Y- organs.
• Molting hormone initiates processes leading to ecdysis.
• Once initiated, the cycle proceeds automatically without further action of hormones from X or Y organs.

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What is meant by homologous structures What is meant by serial homology, and how do crustaceans show serial homology
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What are the appendages on the head of crustaceans What other important characteristics of Crustacea distinguish them from other arthropods
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Compare and contrast Isopoda, Amphipoda, Euphausiacea, and Decapoda.
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What is a tongue worm, and where would it be found
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Briefly describe respiration and circulation in crayfishes.
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Define each of the following: tergum, sternum, telson, protopod, exopod, endopod, epipod, endite, and exite.
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Briefly explain the genetic determination of biramous and uniramous appendages.
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What is the photoreceptor unit of a compound eye How does this unit adjust to varying amounts of light
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What is a nauplius What is the difference between direct and indirect development in Crustacea
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How does a crayfish detect changes in position
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