Question

Compare and contrast different anatomical/ physiological adaptation in TWO animal species. Compare an organ system and an anatomical feature. Include relevant diagrams/figures within your write-up.

Answer 1

In this particular question, we would be contrasting between a vertebrate and an invertebrate. Before going deep into the example of each of the two mentioned categories and describing them, we should know exactely what they are.

1 Vertebrates: All the species of animals with a characteristic feature of having a backbone or a spinal column. Eg. all the mammals, reptiles, birds, amphibians.

We would be describing a reptile - crocodile in it.

2. Invertebrates: They are the ones which lack a backbone or spinal column. Eg. arthropods, mollusc, annelid etc.

We would be describing a annelid - earthworm in it.

Crocodile ( Anatomy)

Body:

In general, the body form of crocodilians is "lizard-like". They have a long tail and the limbs are short and straddled sideways from the body rather than being erect beneath it, as in mammals. The elongated snout of crocodilians is probably one of their most distinctive features. The head is typically one seventh of the total body length, regardless of whether the species has a narrow or broad snout. The shape of the head is intimately associated with the way crocodilians position themselves in water.

Crocodilians have a "minimum exposure" posture in water, in which only the eyes, the cranial platform (overlying the brain), ears and nostrils lie above the waters' surface. All the sensory apparatus is thus exposed while the most of the snout length, and the bulk of the body, is hidden. To potential prey, the exposed areas of the head give little indication of the real size of the predator's body.

This "minimum exposure" posture has been important to crocodilians throughout their evolution. Alligators, for example, have a broader snout than crocodiles, but, when in their "minimum exposure" posture in water, the two appear identical - the increased snout width is under the water. The changes in snout shape have not compromised this basic crocodilian posture, even though the two groups have been separated from each other for some 60 million years

Nasal Disk/Palatal valve:

The nasal disc on the tip of the snout contains two nostrils, each with a protective valve or flap at their opening. These lead into canals that pass through the bone of the snout, and open into the back of the throat. Along these canals are chambers in which "smell" is sensed - crocodilians have a very good sense of smell. A second route of breathing is through the mouth. At the back of the throat is a palatal valve that can be opened or closed. When basking on land with the mouth open, crocodilians breathe mostly through their mouth (the throat/palatal valve is open). When in water, the mouth is usually closed and they breathe mostly through their nostrils. When prey are being held in the water, the mouth may be open, but the palatal valve is closed, preventing water going down the throat - and breathing takes place through the nostrils.

Eyes:

The eyes of crocodilians are specialised in a number of ways. Firstly, they are protected by a transparent eyelid that moves sideways across the eye when the animal submerges or attacks prey. Above and below the eye are the conventional eyelids, which cover the eye completely. The eyeballs themselves can be drawn into the eye sockets, presumably to avoid injury during attacks on prey or when fighting with other crocodiles. The eyes of crocodilians are focused for aerial distance viewing, and it is unlikely that their vision underwater is good.

As in many other nocturnal animals, the pupils close to a vertical slit in bright light and open to a full circle in the dark. At the back of the eyeball, behind the retina, is a thin layer of guanine crystals (retinal tapetum). Light passing through the retina is reflected back through it by these crystals. This image intensifying device, in combination with at least two different types of receptors in the retina, allow crocodilians to see better in low light situations. Alligators and caimans have colour vision, and it is likely that all crocodilians have it.

When a spotlight or torch is shone on a crocodilian at night, a red reflection from the eyes results. This "eyeshine" is a reflection of light from the retinal tapetum, and it can be seen from quite a distance away. Most crocodilian hunting takes place at night, using the "eyeshine" to detect the animal.

The eyes of crocodilians are very close together, and only 7 cm separates them in a 5 m long animal. They are oriented forward, resulting in binocular vision. This allows objects, especially potential prey, to be oriented precisely. Since the degree of overlap is small, crocodilians usually orient their head towards potential prey before attempting to approach it.

Ears:

The ear flaps are two rectangular flaps of tissue just below the edge of the cranial platform. There is an eardrum on either side, but the auditory canal that it covers, is continuous from one side of the head to the other. This appears to be yet another adaptation to assist in pinpoint orientation of potential prey. The high degree of development of the middle and inner ears indicates the effectiveness of crocodilian hearing over a wide range of frequencies (100-6000 Hz). Indeed the crocodilian ear is considered the most specialised within the Class Reptilia.

Brain:

The brain is relatively small, and lies directly below the midline of the cranial platform. Here, it is protected from the teeth of other crocodilians, and also lies in a position where it can heat rapidly when an animal is basking. This is important, because the brain must evaluate signals being received from the eyes, ears and nostrils, and like other reptiles, it probably functions more efficiently within a "preferred" temperature range. The "smell" or olfactory functions of the brain are particularly important, and prominent olfactory lobes extend forward to the nasal chambers.

Jaws and Teeth :

Crocodilian jaws are designed for grabbing and holding prey. The teeth are conical and designed to penetrate and hold, rather than cut and chew. In the Gharial, Tomistoma and other narrow-snouted species such as the Australian Freshwater Crocodile, the teeth can be very sharp indeed. The teeth of the upper and lower jaws intermesh perfectly when the jaws are closed, giving yet another means of holding firmly whatever they grasp.

Teeth are often lost, but beneath each one is a replacement ready to fill the vacancy. Replacement of teeth occurs roughly every 20 months, throughout life, but slows down as the animal gets older, and may stop altogether with the oldest and largest individuals. The number of teeth varies from 60 in the Dwarf Crocodile to 110 in the Gharial. Saltwater Crocodiles have 66 teeth, 18 on each side of the upper jaw and 15 on each side of the lower jaw.

The muscles that close the jaws are capable of generating enormous power. They are able to crush turtle shells with ease, and a large Saltwater Crocodile holding a pig's head can simply crush the skull by flexing the muscles from a "standing start". Yet the muscles that open the jaws have little strength. For example, a rubber band around the snout of a 2 m long crocodilian is sufficient to prevent it opening its mouth. In contrast, two strong people equipped with an assortment of levers are required to force open the mouth of a 1 m long crocodilian against the action of the muscles holding it shut.

Although crocodilian jaws are capable of enormous power, they are also capable of delicate and gentle action. Large adults can pick up and roll unhatched eggs between their jaws, gently squeezing them until they hatch. Most species of crocodilian carry newly hatched young down to the water in their mouths.

Heart:

The crocodilian heart is quite unique. Other reptiles have a three-chambered heart (two atria and one partially divided ventricle). Crocodilians, like mammals and birds, have a four-chambered heart (two atria and two separate ventricles). In the three-chambered reptile heart, blood destined for the lungs (deoxygenated blood) can mix in the partly divided ventricle with blood destined to go out to the body (oxygenated blood from the lungs). In mammals and birds such mixing is impossible. But in crocodilians the blood vessels draining the left and right ventricles have an interconnecting aperture (the Foramen of Panizza) between them, which allows some mixing of blood, but outside of the ventricles. The mixing of blood can be advantageous to a diving reptile.

Adaptations for a life in water

Crocodilians can move about on land - with surprising speed, particularly when alarmed or angry - but their bodies are mainly adapted for a life in water. The nostrils, eyes and ears lie along the top of the head so that the animal can hear, see, smell and breathe when the rest of the body is submerged.

When completely under the water, the ears are covered by small flaps of skin which can be closed to make the ears watertight. The nostrils can also be closed by special muscles, and the eyes have a 'third eyelid' which gives protection when diving.

There are special bony flaps in the throat which allow a crocodile to eat when submerged or breathe when its jaws are open underwater.

Crocodilians, being cold-blooded reptiles, have to avoid extremes of temperature. When it is fairly cool, they rest on a waterside bank, allowing the sun to warm their body. During the hottest part of the day, the animals will move into the shade or water to prevent their body from overheating.

Earthworm:

Earthworms Help The Environment     Earthworms are more than just fish bait. They are the main contributors to enriching and improving soil for plants, animals and even humans. Earthworms create tunnels in the soil by burrowing, which aerates the soil to allow air, water and nutrients to reach deep within the soil. Earthworms eat the soil which has organic matter such as decaying vegetation or leaves. Plants cannot use this organic matter directly. After organic matter is digested, the earthworm releases waste from their bodies called castings. Castings contain many nutrients that the plant can use. Some people even use earthworm castings as garden fertilizer.

Earthworm Anatomy 1. Segmented Body Earthworms are classified in the phylum Annelida or Annelids. Annelida in Latin means, “little rings.” The body of the earthworm is segmented which looks like many little rings joined or fused together. The earthworm is made of about 100-150 segments. The segmented body parts provide important structural functions. Segmentation can help the earthworm move. Each segment or section has muscles and bristles called setae. The bristles or setae help anchor and control the worm when moving through soil. The bristles hold a section of the worm firmly into the ground while the other part of the body protrudes forward. The earthworm uses segments to either contract or relax independently to cause the body to lengthen in one area or contract in other areas. Segmentation helps the worm to be flexible and strong in its movement. If each segment moved together without being independent, the earthworm would be stationary.
2. Digestive System The digestive system is partitioned into many regions, each with a certain function. The digestive system consists of the pharynx, the esophagus, the crop, the intestine and the gizzard. Food such as soil enters the earthworm’s mouth where it is swallowed by the pharynx. Then the soil passes through the esophagus, which has calciferous glands that release calcium carbonate to rid the earthworm’s body of excess calcium. After it passes through the esophagus, the food moves into the crop where it is stored and then eventually moves into the gizzard. The gizzard uses stones that the earthworm eats to grind the food completely. The food moves into the intestines as gland cells in the intestine release fluids to aid in the digestive process. The intestinal wall contains blood vessels where the digested food is absorbed and transported to the rest of the body.
3. Circulatory System Another important organ system is the circulatory system. The earthworm has a closed circulatory system. An earthworm circulates blood exclusively through vessels. There are three main vessels that supply the blood to organs within the earthworm. These vessels are the aortic arches, dorsal blood vessels, and ventral blood vessels. The aortic arches function like a human heart. There are five pairs of aortic arches, which have the responsibility of pumping blood into the dorsal and ventral blood vessels. The dorsal blood vessels are responsible for carrying blood to the front of the earthworm’s body. The ventral blood vessels are responsible for carrying blood to the back of the earthworm’s body.
4. Respiratory System Earthworms do not have lungs. They breathe through their skin. Oxygen and carbon dioxide pass through the earthworm’s skin by diffusion. For diffusion to occur, the earthworm’s skin must be kept moist. Body fluid and mucous is released to keep its skin moist. Earthworms therefore, need to be in damp or moist soil. This is one reason why they usually surface at night when it is possibly cooler and the “evaporating potential of the air is low.” (www.amonline.net.au/factsheets/earthworms.htm) Earthworms have developed the ability to detect light even though they cannot see. They have tissue located at the earthworm’s head that is sensitive to light. These tissues enable an earthworm to detect light and not surface during the daytime where they could be affected by the sun.
Earthworm Reproduction Earthworms are hermaphrodites where each earthworm contains both male and female sex organs. The male and female sex organs can produce sperm and egg respectively in each earthworm. Although earthworms are hermaphrodites, most need a mate to reproduce. During mating, two worms line up inverted from each other so sperm can be exchanged. The earthworms each have two male openings and two sperm receptacles, which take in the sperm from another mate. The earthworms have a pair of ovaries that produce eggs. The clitellum will form a slime tube around it, which will fill with an albuminous fluid. The earthworm will move forward out of the slime tube. As the earthworm passes through the slime tube, the tube will pass over the female pore picking up eggs. The tube will continue to move down the earthworm and pass over the male pore called the spermatheca which has the stored sperm called the spermatozoa. The eggs will fertilize and the slime tube will close off as the worm moves completely out of the tube. The slime tube will form an “egg cocoon” and be put into the soil. The fertilized eggs will develop and become young worms.

Adaptations

Movement
Earthworms are adapted for life underground. Their streamlined shape allows them to burrow through soil. They have no skeletons or other rigid structures to interfere with their movement. The earthworm’s body is divided into segments. Each segment has a number of setae or very small bristles that earthworms use to help them grip the soil as they move.

An earthworm moves by using two different sets of muscles. Circular muscles loop around each segment, and longitudinal muscles run along the length of the body. When the circular muscles contract, the earthworm stretches, becoming longer and thinner. The earthworm uses its setae to anchor the front of its body in the soil. Now the longitudinal muscles contract and the earthworm becomes shorter and wider or it bends from one side to the other, pulling the body forward. The earthworm withdraws the front setae and uses its rear setae to anchor itself at the back. The earthworm uses its circular muscles to lengthen and push itself forward again.

Senses
Earthworms have a head, though they have no eyes, nose or ears. The earthworms’ skin provides some of the services we normally associate with our own sense organs. Light-sensitive cells are scattered in their outer skin, mainly at the ends of their bodies. They allow earthworms to detect light and changes in light intensity. Earthworms don’t use a nose, mouth or lungs to breathe like we do. Instead they use oxygen that is dissolved in the moisture on their skin and from the surrounding environment. Earthworms cannot hear but they can sense vibrations.

Reproduction
Mature earthworms have a clitellum or a saddle. The size, shape, colour and position of the clitellum varies between species. The clitellum means the earthworm is an adult and is ready to mate and lay eggs. Earthworms reproduce by forming a small egg sac – called a cocoon – at the clitellum. The cocoon slides off of the earthworm’s body and is deposited in the soil.