The Shape of Life: Episode 2 - Life on the Move

From the stationary sponge to all the moving creatures in the world, cnidarians, a group that includes corals, sea anemones, sea pens and jellyfish, were the organisms that started it all. It is first thought that these organisms evolved with an evolutionary edge of motion in order to food, and indeed this is true.

Along with their non-hydrodynamic body shape, each species of jellyfish has a specific propulsion movement in order to obtain their food. When propelling through the water, they push the water towards their tentacles, allowing them to capture prey - a completely new innovation in comparison to the stationary sponge.

Fish Resources

Fishes may not be the most diverse species in comparison to insects, but they are surly one of the most important. In recent news, many of the fish populations around the world have been declining due to anthropogenic interactions, as well as the fact that 1 out of every 4 people have fish as their main part of their diet. Therefore, it’s quite obvious that fish are being over fished.

Most of the businesses may have been affected by it already, seeing a decline in the amount and size of the fish. This has already been noticed here in the CNMI, and yet, people continue to dump out their trash into the ocean telling their egocentric-selves that the ocean will clean it up for them. Ever seen a diaper fish? And no, it’s not literally a diaper… People need to open their minds and actually think what they need to do in order to protect not only the fishes, but as well as both fresh and salt water.

Sea Floor in a Shoebox

Chapter 8 Critical Thinking

1. Hagfishes and lampreys are the only living representatives of a very ancient group. Why do you suppose there are still some of these jawless fishes around?

For one thing, nature revolves around the fat that those organisms that are more successful than others will live longer. As for both hagfishes and lampreys, they are the most well adapted species of the class Agnatha, since they are still living today. It’s simply when you place natural selection into play – only the best survive. Hagfishes and lampreys may have not been the “top” predator when before, but in the overall outcome, they are the most successful ones since they are “living fossils.”

2. A deep-water shark, new to science, is collected for the first time. The specimen is studied in detail, but its stomach is empty. How could you get a rough idea of its feeding habits? The specimen is a female, and its reproductive tract is found to contain 20 eggs. Can you tell the type of development characteristics of this species?

· A factor which makes this question very broad is the fact that there is little to no information for this scenario. And although hypothesis may be assumed, giving that it has been studied in detail and has an empty stomach, one can derive the answer to be that the shark is a filter feeder, or in such cases that it has a slow metabolic rate because of its lifestyle, which therefore means that the food that has been consumed prior to its capture has moved from the shark’s stomach and into it’s intestine.

· Out of the three types of shark egg development – viviparous, oviparous, and ovoviviparous, as well as the factor that it has not been observed in a contained or wild environment, there would be no way of proving the type of developmental characteristics of the newly found species yet.

3. Individuals of some species of bony fishes change sex, some to maintain more males than females, others more females than males. What are the advantages and disadvantages of each situation? Are there any advantages and disadvantages in having an equal number of males and females?
• The advantage for maintaining more males than females is that it would ensure that the most dominant male(s) would be able to mate to pass on their traits making their offspring genetically advantageous in comparison to other offsprings whose parents may have not been the dominant of the group; however, due to the amount of females, there would be less offspring.
• An advantage that more females than males offers is that that certain species would produce more offspring; but, because of that, the survival rate of the offspring would be low.
• As for the equal amount of males and females, for one, there would be a higher amount of offspring > to the scenario where there would be more males then females; yet, there would be an average survival rate, as for the factors dealing with genetics, well; it would quite hard to determine this factor since juvenile fishes are exposed to a vast amount of danger when they are maturing.

DISSECTION: SEA STAR (STARFISH)

Pictures found in: Sea star

Digestive System: The digestive system of a sea star is quite complex, with its mouth on its underside and anus on the top. They feed by everting, part of their stomach inside out through the mouth to envelop the food. The stomach then secretes digestive enzymes produced by large digestive glands that extend into the arms. The digested food is carried into the glands for absorption and the stomach pulled back inside the body.

Circulatory System: Sea stars do not have a circulatory system.

Nervous System: Sea stars have a network of nerves that coordinates movements of tube feet and spines in the absence of a brain.

Excretory System: There is no formal excretory system present in sea stars.

Reproductive System: Sea stars reproduce by means of broadcast spawning where the males and females discharge there eggs and sperm into the water where they are fertilized.

Integumentary System: The integumentary system of a sea star consists of five arms and spines or bumps all over its body. The spines are protective and also help with respiration.

Body Plan: Unlike many organisms, the sea star and the rest of its echinoderm family have a pentamerous radial symmetry and also lack a head. They have no anterior or posterior end or even a dorsal or ventral side. It is useful to refer to one of its surfaces as oral, because that is where the mouth is located, and an opposite side - referred to as aboral. They also have an endoskeleton similar to humans, that is secreted within the tissues, rather than externally.

Sea stars live in temperate and tropical waters. Some are bottom dwellers while many live mostly in shallow marine environments. They eat scraps of food, algal mats, or even deceased organisms. Others are active predators that will attack and eat clams, snails, sponges, corals, anemones.

DISSECTION: CLAMS

Pictures found in: Clams

Digestive System: Water is drawn into siphons formed by the fusion of the edge of the mantle which leads to its mouth then to its digestive glands and then to its intestines.

Circulatory System: Water is siphoned into its mantle which passes over its gills, where oxygen is then diffused into the blood and pumped through its body via impulses of the heart. CO2 is then diffused out as O2 takes its place within the gills.

Nervous System: A clam has no formal nervous system, but it senses its environment with the use of its ganglia that is located above the mouth and foot, cells along the edge of its mantle react to both light and touch.

Reproductive System: Each clam has a gonad - with each being either a male or female. They reproduces sexually through means of broadcast spawning where both egg cells and sperm cells are released into the water, where they get fertilized.

Integumentary System: Enclosed in a CaCO3 shell that is adapted to protect its soft body from predators. Its foot is used for locomotion.

Body Plan: Its soft interior is protected by a hard shell composed of CaCO3. It's body is covered by a mantle: a thin layer of tissue that secretes the shell. It is unsegmented and bilaterally symmetrical and has a ventral muscular foot that is used for locomotion.

Different species of clams live in different environments - ranging from fresh to saltwater. Clams are simple organisms. Clams are molluscs because they are soft bodied animals with an internal or external shell. The name of the phylum is derived from Latin word molluscus meaning soft.

DISSECTION: SQUIDS

Pictures found in: Squid

Digestive System: The squid has a flow through digestive system. Food enters their digestive tract through the squid's mouth and is digested into feces which is excreted through the anus.

Circulatory System: The squid has a closed circulatory system with three hearts. H2O and O2 enter the squid's body through its mantle where the respiratory exchange takes place in the gills. CO2 and H2O are then expelled from the body through a siphon.

Nervous System: A squid has a very complex nervous system compared to most invertebrates. Having They have a large brain that coordinates and stores information received around its environment. Also, by using their giant nerve fibers, they can rapidly conduct impulses, which allows them to capture their prey at great velocities.

Excretory System: The excretory system of a squid if also known as a metanephridium, which consists of a ciliated funnel opening into the body cavity and to a duct which opens to its exterior. These ciliated tubes assist in the pumping out waste products.

Reproductive System: The reproduction in squids is external - where the male uses a modified arm to transfer a spermatophore to the female.

Integumentary System: The integumentary system of a squid is enclosed in the mantle, which has two swimming fins along each side. These fins are not the main source of their motility. The skin of the squid is covered in chromatophores, which allows the squid to change color to suit its environment. The underside of the squid is also found to be lighter than the topside, in order to provide camouflage from both prey and predator (countershading).
Under the body are openings to the mantle cavity, which contains the gill and openings to the excretory and reproductive systems. At the front of the mantle cavity lies the siphon, which the squid uses for locomotion through means of jet propulsion. This is done by sucking water into the mantle cavity and quickly expelling it out of the siphon in a fast, strong jet. The direction of the siphon can be changed in order to suit the direction of travel.
Inside the mantle cavity, beyond the siphon, lies the visceral mass of the squid, which is covered in a thin skin. Under this are all the major internal organs of the squid.

Body Plan: The body plan of a squid includes its head and arms, mouth, and eyes.
The head end of the squid bears 8 arms and two tentacles. These tentacles do not grow back if severed.
The mouth of the squid is equipped with a sharp horny beak mainly made of chitin and proteins, and is used to kill and tear prey into manageable pieces.
The eyes of the squid, found on either side of the head, contains a hard lens, which is used much like the lens of a camera or a telescope for focusing; rather than changing shape, like a human eye, it moves mechanically.

Squids live in the ocean - a few, most notably the giant squid and the colossal squid live out in the colder open ocean. Many of the smaller species of squid rely on color changing patterns in order to communicate with each other and to attract prey as well. Squids are considered to be one of the most successful and highly complex of all invertebrates.