Question 1: Echinoderms
Phylum Echinodemata gets the name from the Greek which means spiny skin. Therefore, members of this phylum have spiny skin although others do not have the spiny skin. Echinoderms have radial symmetry meaning they have appendages mostly occurring in a group of five with few in exception. One rare characteristic that occurs in the echinoderms is the water vascular system. This refers to a hydraulic system, usually with sea urchins and the sea stars and used for locomotion, waste transportation, food and respiration. This system comprises of canals that connect tube feet. The movement can be caused by the contraction of the muscles thus forcing the water into the tube feet. This causes them to extend and pushing them to the ground. The process is followed by relaxation thus allowing the feet to retract.
The aboral (top) surface of the sea star is usually spiny under close examination. There are some bumps on the surface referred as Dermal Branchiase which absorbs oxygen from water. Again, there are Pedicellarria organs which are pincher like on the skin used for plucking things from the surface of the sea star. Gain on the aboral surface of the sea star there is a single colored spot called madreporite which is calcareous filled with tiny holes and it acts as a filter.
Starfish or sea stars are opportunistic feeders which are mostly predators feeding on benthic invertebrates. Some species have specialized feeding systems that include aversion of their stomachs as well as suspension feeding.
Question 2: Fish Movement
Fish have fins for movement or locomotion. The biggest fin is the caudal fin used for rapid forward movement. On the top, there are dorsal fins while the underneath has anal fins which help in lateral stability. There is also pectoral fins located behind the gill operculum which are the covers and help in hovering as well as slow turning. Again, Pelvic fins are small for open swimming however, bigger on bottom dwellers that use them for resting. Vertebrae can be hinged to make movement of the backbone free, mostly in the horizontal side. They also have a certain coating of mucous that has minimized friction, with the waters and protective amour scales allowing efficient flexibility of the fish for swimming.
Water is usually denser medium as compared to air, and therefore, movement in fish poses certain problems that have been catered by natural selection. The importance of having streamlined body shape is to lower the energy needed to move via water. This could be achieved through the streamlined shape of the fish to reduce the friction from the water currents. There is need for reduced drag or surface resistance and this is achieved through possession of scales as well as oily secretions. Again, to enhance movement in fish, powerful muscle are used as blocks to propel the tail from side to side to achieve rapid forward motion as much large tail is needed to put the force generated by the muscles. There is also presence of fins to ensure stability. The density also needs to be regulated by use of swim bladder, aimed at assisting in floating freely.
The function of gills of a fish migrates from a simple adaptation called countercurrent exchange. In the process, blood in the capillaries flows through the opposite direction with the water within the adjacent channels. This leads to diffusion of gases faster within the fluids thus having a huge difference within the gas concentration in the gas and the fluid, which means a high concentration gradient as compared to the fluids with a small difference.
Within the fish gill, low-oxygen blood flows into the capillaries, where it encounters water at the end of the travel via the gills that is relatively low in oxygen gas. After that, as the blood flows in the opposite direction to the water, it comes across "fresher" water which has higher oxygen concentrations. Therefore, there occurs a steep diffusion gradient that favors oxygen transfer into the blood along the capillary.
Question 3: Sensory Systems of Fishes
The shark’s ears, eyes, and nose are situated near the sharks’ mouth. However, sharks detect their prey through sensory receptors that run along the sides. The receptors comprise of the lateral line which is an organ that has similar function like the ear that could feel pulses, vibrations within the water covered area. A shark can sense the wailing of a prey in stress and swim towards it to investigate.
Immediately after it gets close to potential prey, the shark can use yet another sense which is the electroreception. This organ which is also called ampullae of Lorenzini; it lies inside a small pore on the snout of the shark. Living things found in seawater (salty) produce an electrical field faintly that the shark is able to feel within a short distance, therefore, allowing it to sense creatures that buried the sea floor. Another trigger is the muscle contractions, which produce small surge of electrical shock or alert that the shark can sense using electroreception.
Lateral lines of the fish comprise of neuromast, which are hair-like cells surrounded by a protruding cup like jelly. The neuromast lies at the bottom pit or groove that is visible. The function of these hair cells or sensory cells, which are found in all vertebrate ears, is to convert mechanical energy to electrical energy if triggered or moved. Auditory as well lateral line pathways are related since they share a lot of features. For example, in the case of toadfish, lateral line produce and configure messages to the brain incase prey approaches around half a body length distance. Again, the wave of water that would be produced if the prey fans the fins is like a whisper which can get the signal to the toadfish.
The weakly electric fish is a special type of fish that actively produces electric fields by the use of electric organs. The fish has specialized neural circuitry meant to detect distortions caused by objects field when triggered. Contrary to strongly electric fish like the electric eels, electric fields that are generated by weakly electric fish have a low in amplitude ranging (~1 mV/cm) which can be used for electro location.
Question 4: Amniote Egg
The amniotic eggs have a unique membranes comprising of chorion, amnion and allantois. The amnion is the membrane that surrounds the embryo which also makes a fluid-filled cavity within which the embryo develops. Chorions make up a protective membrane which runs around the amniotic egg. The allantois is applied closely against the chorion, as it functions as gas exchanger as well as storing metabolic wastes. These membranes form the urinary bladder in adults. In vertebrates, nutrients meant for development of embryo are stored in the yolk sac, which is much bigger in amniotes as compared to vertebrates. In addition to that there are suggestions that the major function of the embryonic membranes that are extra of the amniotic egg could have been to facilitate some interactions between the embryo and the mother though this refers to the vertebrates.
The calcareous shell is the basic block in the building of the amniotic egg. It controls some characteristics of a shell that make up organic material as well as calcium carbonate which shows shell physical properties like the structure, rigidity as well as breaking strength. Majority of those characteristics of calcium carbonate are preserved in eggshell that are fossilized, although organic matter cannot be preserved since it decays and usually lost on fossilization.
Echolocation in dolphins can give high pitched sounds. Immediately these sounds hit a block, echo would be back to the sender. Therefore, the dolphin can estimate the time the echo send and show the distance where the sound comes from. That is the mechanism of the echolocation. The echo would make the dolphin to estimate the distance and the size of the fish that is approaching. This information can be achieved through movement of the head.
Question 5: Whales
The evolution of whales shows most of the complex and amazing chain in the history of evolution. First, the pakicetids are a family of mammals resembling dogs though with hooves. Pakicetus common feature with modern whales is usually their ears and some resemblance with the teeth. Pakicetus are therefore believed to be ancestors of whales due to those shared features.
The next one is the ambulocetids that have cetacean ear structure similar to that of whales. They posses hind legs however, they are adapted for swimming as compared to walking.
Again it shows characteristics of that are with modern whales. This path of the water habitation shows some similarities.
The third fossil could be Kutchicetus from genus of order Remingtonocetidae, which existed in about 46 million years ago. The Kutchicetus was of sea otter in size. The remingtonocetids were the first to develop a mechanisms for sound transmission under the water, which might have got use for communication purposes, but importantly, starts the foundation for echolocation or sonar systems as in dolphins and whales. Another fossil are for Rodhocetids which have were discovered until 2001. The ankles showed some similarity with those of whale lineage which goes back via artiodactyls. The Rodhocetids portray double-spooled trochlea around its tibia, a unique feature for artiodactyls. Significant modifications are that the sacral vertebrae (our tailbone) are infused, unlike its predecessors, which increase power and flexibility. Its pelvis is still shares a joint with the sacrum, allowing it to bear weight on land, if it ever went on land. The hind limbs are shortened, and the nostrils have begun to creep up the skull. Within the evolution there existed Rodhocetus and the protocetids which represented a major evolution in whales.
Through the time Basilosaurus got modern whale resemblance. Which is quite big, up to 60 ft. long, with its pelvis no longer attached or in contact to the vertebral column? The Basilosaurus had lost the ability to support itself with the hind legs. It existed 40 to 34 million years back. Thus its fossils have been found in the Egypt Valley of the Whales with some smaller than the first fossil got in 1840.
Aetiocetus had baleen as well as complete set of teeth. Aetiocetus had a loose jaw, which resembled that of modern mysticetes. That was the latest fossil that led to discovery of whales.
Works Cited
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