Dissections

Digestive System: Food is transported into a muscular stomach, found roughly in the midpoint of the visceral mass. The bolus is then transported into the caecum for digestion. The caecum, a long, white organ, is found next to the ovary or testis. In mature squid, more priority is given to reproduction and so the stomach and caecum often shrivel up during the later stages of life. Finally, food goes to the liver (or digestive gland), found at the siphon end of the squid, for absorption. Solid waste is passed out of the rectum

Circulatory System : Squid have three hearts. Two branchial hearts, feeding the gills, each surrounding the larger systemic heart that pumps blood around the body. The hearts have a faint greenish appearance and are surrounded by the renal sacs - the main excretory system of the squid. The kidneys are faint and difficult to identify and stretch from the hearts (located at the posterior side of the ink sac) to the liver. The systemic heart is made of three chambers, a lower ventricle and two upper auricles.

Nervous System: The giant axon of the squid, which may be up to 1 mm in diameter, innervates the mantle and controls part of the jet propulsion system.

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: In female squid, the ink sac is hidden from view by a pair of white nidamental glands, which lie anterior to the gills. There are also red-spotted accessory nidamental glands. Both of these organs are associated with manufacture of food supplies and shells for the eggs. Females also have a large translucent ovary, situated towards the posterior of the visceral mass.

Male squid do not possess these organs, but instead have a large testis in place of the ovary, and a spermatophoric gland and sac. In mature males, this sac may contain spermatophores, which are placed inside the mantle of the female during mating.

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 head end of the squid bears 8 arms and two tentacles, each a form of muscular hydrostat containing many suckers along the edge. These tentacles do not grow back if severed. In the mature male squid, one basal half of the left ventral tentacle is hectocotylised — and ends in a copulatory pad rather than suckers. It is used for intercourse between mature males and females.

The mouth of the squid is equipped with a sharp horny beak mainly made of chitin [1] and cross-linked proteins, and is used to kill and tear prey into manageable pieces. the beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species.[2] Captured whales often have squid beaks in their stomachs, the beak being the only indigestible part of the squid. The mouth contains the radula (the rough tongue common to all molluscs except bivalvia and aplacophora).

The eyes, found on either side of the head, each contain a hard lens. The lens is focused by moving, much like the lens of a camera or telescope, rather than changing shape like a human eye.

The majority of squid are no more than 60 cm long, although the giant squid may reach 13 m in length. In 2003, a large specimen of an abundant[3] but poorly understood species, Mesonychoteuthis hamiltoni (the Colossal Squid) was discovered. This species may grow to 14 m in length, making it the largest invertebrate. It also possesses the largest eyes in the animal kingdom. Giant squids are often featured in literature and folklore with a frightening connotation. The Kraken is a legendary tentacled monster possibly based on sightings of real giant squids.

In February 2007, a Colossal Squid weighing 495 kg (1,091 lb). and about 10 metres (33 feet) long, was caught by a New Zealand fishing vessel off the coast of Antarctica.

Digestive system: Starfish have a complete digestive system with their mouth on the underside and the anus on top. Food enters into the starfish through the mouth, gets digested and then the waste comes out the top. The starfish can also extend its stomach so the food is liquidated and digested outside of the body.

Circulatory system: There are three systems. Perivisceral coelom (outside of various organs), Water vascular system (tube feet extended throughout each arm), and Hemal system (closest resemblance to a circulatory system). The hemal system extends though each arm as well and is most effective way to transport the nutrients from the digestive tract.

Nervous system: Made up of a radial nerve through each arm and a nerve ring in the center of the starfish. The nerve ring doesn't really do much and it is up to the radial nerves to somehow coordinate 5 different arms.

Excretory system: No formal one

Reproductive system: Separate sexes with gonads. The sperm fertilizes the eggs out in the ocean.

Integumentary system: Tough skin protecting the vital organisms. Some species have spikes for additional protection.

Body plan: Radial symmetry, no head.

Starfish live in temperate and tropical waters. They are bottom dwellers but can live in a range of depths, mostly shallow marine environments.

Digestive system: A mollusk (clam) feeds itself through a siphon system which leads to its mouth. It then goes to a digestive gland and onto the intestines.

Circulatory system: A heart, blood vessels, and obviously blood.

Nervous system: No formal nervous system but it does have ganglia which monitors the nerve impulses.

Excretory system: Clams have anuses and an organ called the nephridium that gets rid of the waste.

Reproductive system: A gonad. The clam is either male or female and reproduces sexually.

Integumentary system: A hard outer shell and a soft body. It uses a muscular foot for movement.

Body plan: A thick, soft, and fleshy body is protected by the outer shell. It ranges in size (anything from a few centimeters to multiple feet in width. Clams also have bilateral symmetry.

Clams live in the water, such as bays, estuaries, mud flats, sand, and can tolerate a range of salinities (from brackish to saltwater conditions). Clams have hatchet-footed, which makes them a mollusk.

The digestive system of a crayfish is simple in comparison to those of vertebrates, but more complex than other invertebrates. The tract is composed of the foregut (enlarged stomach/specialized grinding), the midgut, and the hindgut (leads to anus/regulates salt and water). The digestive gland excretes an enzyme that helps in digestion and absorbs nutrients.

The circulatory system is made up of the heart and three arteries extending to the dorsal, anterior, and posterior areas of the body. The heart pumps the blood across the gills which absorbs the oxygen from the water and sends it back to the heart and adjoining arteries.

The crayfish's nervous system is composed of a ventral nerve cord which has fused with segmental ganglia and the supresophageal and subesophageal ganglia.

The excretory organs, which are part of the excretory system, are located at the base of the crayfish's second antenna.

Crayfish have separate male and female sexes. Mating happens in the spring after the female as molted.

The crayfish has a jointed exoskeleton which they shed to allow growth.

The body is divided into two parts: the cephalothorax and the abdomen. The cephalothorax has sensory, feeding, and locomotr functions and the abdomen has locomotor and visceral functions.

Crayfish typically live in freshwater ecosystems (lakes and streams), water logged fields, stagnant ditches, subterranean cave waters. Basically any where there is muddy water which many places to hide. The crayfish is definitely an arthropod.