Question

can someone answer of all questions related to that topic please

Crustaceans 8. Describe the different appendages crayfish have (dissection video) 9. What are gills used for? Describe their appearance/physiology. Are they the same as fish gills? As mollusk gills? 10. Describe how crayfish swim 11. How do male fiddler crabs use their two different sized claws when feeding? When mating? 12. Describe the lifecycle of a blue crab (use the video to help!) 13. Why are blue crabs so important to the estuary? 14. Describe molting in blue crabs 15. How many different types of appendages do blue crabs have, and what are their uses? 16. What are the differences between an Ostracod's "shell” and a real bivalve shell (i.e., clams)?

Answer 1

8.Like all crustaceans, a crayfish has a fairly hard exoskeleton that covers its body. its body is divided into two main parts, the cephalothorax and the abdomen. The cephalothorax consists of the cephalic (or head) region and the thoracic region. The part of the exoskeleton that covers the cephalothorax is called the carapace. The abdomen is located behind the cephalothorax and consists of six clearly divided segments. The cephalothorax consists of 13 segments. Each segment of both the cephalothorax and the abdomen contains a pair of appendages. The head (or cephalic) region has five pairs of appendages. The antennules are organs of balance, touch, and taste. Long antennae are organs for touch, taste, and smell. The mandibles, or jaws, crush food by moving from side to side. Two pairs of maxillae hold solid food, tear it, and pass it to the mouth. The second pair of maxillae also helps to draw water over the gills. Of the eight pairs of appendages on the cephalothorax, the first three are maxillipeds, which hold food during eating. The chelipeds are the large claws that the crayfish uses for defense and to capture prey. Each of the four remaining segments contains a pair of walking legs. In the abdomen, the first five segments each have a pair of swimmerets, which create water currents and function in reproduction. The sixth segment contains a modified pair of uropods. In the middle of the uropods is a structure called the telson, which bears the anus. The uropod and telson together make up the tail fan. The crayfish moves backward by forcing water forward with its tail fan.

Figure 14.22 External structure of a male crayfish. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2nd antenna - 2nd antenna 1st antenna 1st antenna Cheliped (1st pereopod) Cheliped (1st pereopod) Rostrum 1st maxilliped Compound eye 2nd pereopod 2nd maxilliped - Mouth 3rd maxilliped 3rd pereopod Carapace - 3rd pereopod 4th pereopod 1st (copulatory) pleopod of male 5th pereopod Abdomen Telson Uropod Pleopods 3-5 Sternum Anus Telson - Uropod

9.The Gills of Crayfish are located in between he carapace and the lateral body wall

They need gills to breathe if they can't breath they can't live!!

There are two sets of gills on each side of the crayfish When water passes through the gills, the dissolved oxygen diffuses into the bloodstream. When it's inside the gills, the carbon dioxide found in the blood stream is released to the water

Gills

10. Crayfish swim by beating pairs of paddles called swimmerets on each body segment. The swimmerets move in sequence, starting at the back of the animal and moving forward. The movements of each segment keep a precise difference in timing, while varying in speed and force.

11.Fiddler crabs (Genus Uca), are sexually dimorphic -- the males have one large and one small front claw while the females have two small claws. The males use their small claw for feeding and the large one to attract females for mating, threaten other males and as a weapon when fighting. As a flag the claw needs to be as large and light as possible so that it is easy to manoeuvre. As a weapon it needs to be heavy, with a thick cuticle, short pincers (dactyl and polex), and large muscle to close them.Fiddlers feed by scraping the surface sediment up in their small claws, transferring it to the mouth where the complex mouthparts sift out the organic matter.

Mating : When a female is ready to mate (i.e. she has ripe ovaries), she will leave her own burrow and wanders through the population of waving males. ... The male then leaves the area and wanders around to find an empty burrow or to fight another male for its burrow.

12.

To understand the blue crab life cycle, we will follow a female blue crab from birth to reproduction. The blue crab starts her life as a larva, an early-life stage that looks completely different than her adult form. She will spend 31-49 days going through seven larval stages called zoea. In each stage she is similar in appearance, but is slightly larger than in the last stage. Even this early in life, crabs have a hard outer shell (exoskeleton). In order to grow and change stages, the larva must molt, which means shed or cast off its shell. During molting, the exoskeleton splits, and the soft-bodied larva backs out of the hard shell. The animal remains soft for a short while, and swells up by absorbing water. Then, minerals from the seawater (especially calcium) harden the outer covering, forming a new exoskeleton. When the larva loses the extra water, it shrinks and leaves space within the exoskeleton for growth.

Megalopal stage

During this part of her life, the crab floats in the open water offshore where salinity is relatively high. She probably feeds on microscopic algae and other small larvae (plural form of larva). After the last zoeal stage, the crab enters a megalops stage, which lasts 6-20 days. This is the first step toward obtaining the typical crab form-the body becomes wider with legs protruding from the sides, but with the abdomen still stretched out behind.

Juvenile blue crab approximately 4mm (1 1/2 inches) wide

The megalopa takes advantage of tidal currents to move into estuaries where salinity is lower, food is abundant, and shelter is easy to find. There, she molts to a true crab form, but is only 2 mm wide (about twice the width of a paper clip wire). As a juvenile, she is omnivorous, meaning she will eat both animal and vegetable substances, such as fish, shellfish, and aquatic plants. She also must avoid predators such as spotted sea trout, red drum, black drum, sheepshead, and other crabs. She continues to molt, growing larger each time until she reaches adult size (about 130-139 mm or 5¼ - 5½ in.) after 18-20 molts. The amount of growth with each molt varies depending on water salinity, temperature, and other environmental factors. She should reach harvestable size (127 mm or 5 in.) within one year.

Molting blue crab

During her adult life, the female blue crab remains in the estuary, although usually in higher salinity water than males. She eats fish, crustaceans, worms, and mollusks, and may be preyed upon by large fish, birds, and mammals (including humans). Her molting rate increases during warmer months, although water temperatures greater than 30oC (86oF) appear to inhibit molting. During the cooler winter months her activity slows, although in the warmer Florida waters she will not need to slow down as much as blue crabs in more northern areas, who bury in the mud to wait for spring.

Mating blue crabs--the male is on top craddling the female

Sometime between March and December, when temperatures exceed 22oC (72oF), the female crab moves into the upper waters of the estuary where male crabs are concentrated. Most female blue crabs reach a terminal molt, after which they no longer grow. This molt coincides with the onset of sexual maturity when mating occurs. Evidence suggests that some females molt a second time after becoming mature, allowing them to produce more batches of offspring. Because of the hard exoskeleton, mating must occur directly after a molt, while the female is still soft. To ensure he will be there when she is ready, a male will usually cradle a pre-molt female in his legs. He also protects her during the vulnerable period after she molts, until her shell becomes hard again. After mating, the female moves offshore into higher salinity water while the male remains in the estuary for the rest of his life. Along the west coast of Florida, female crabs also migrate northward toward the Apalachee Bay region.

Overgeous (egg-bearing) female blue crab

The female can retain sperm for a year or more before extruding eggs. This allows crabs mating in fall or winter to wait until warmer weather to hatch their eggs. Eggs are fertilized as they pass out of the crab's body and are deposited under the apron. The apron is actually the curled-under abdomen, and has small appendages to which the eggs attach. Egg masses have an average of two million eggs, and can have up to eight million eggs. At first the egg mass appears orange due to the high amount of yolk in each egg, then turns brown as yolk is consumed and eyes develop. After one to two weeks the eggs hatch into zoea larvae.

Thus the cycle of life is complete. Only one out of every one million (0.0001%) eggs survives to become an adult. Predators, adverse environmental conditions, and disease all take their toll on the millions of larvae that hatch from one female. Yet some do survive, enough to renew the population and start a new generation of blue crabs.

13.

As both predator and prey, blue crabs are a keystone species in the ecosystem.

• Blue crab larvae are part of the Bay’s planktonic community, serving as food for menhaden, oysters and other filter feeders.
• Juvenile and adult blue crabs serve as food for fish, birds and even other blue crabs. Striped bass, red drum, catfish and some sharks depend on blue crabs as part of their diet. Soft shell crabs that have just molted are particularly vulnerable to predators.
• Blue crabs are among the top consumers of bottom-dwelling organisms, or benthos. Opportunistic feeders, they eat thin-shelled bivalves, smaller crustaceans, freshly dead fish, plant and animal detritus, and almost anything else they can find.
• Because blue crabs feed on marsh periwinkles, they help regulate periwinkle populations. Scientists are concerned that a drop in blue crab populations could harm salt marsh habitat, as periwinkle populations rise and the snails over-feed on marshgrass.

Blue crabs also support a large recreational fishery in the Bay, and are the estuary's highest-valued commercial fishery. Over the past 60 years, blue crabs have dominated Chesapeake Bay fisheries, with an estimated one-third of the nation’s blue crab catch coming from the Bay.

14. Blue crabs are invertebrates meaning they lack a spinal column. Instead, the blue crab has a rigid exoskeleton (hard shell.) The shell grows in discrete stages interspersed by molting, but the growth of internal tissue is more continuous. In order for the crab to grow larger, it must periodically shed its smaller shell through a process known as molting (or, more accurately, ecdysis.) Early in its molting cycle the crab slowly begins to form a new soft shell underneath its existing hard shell.

When a blue crab has grown sufficiently to require a larger shell, the following events occur:

Precdysis (pre-molt or “peeler” stage)

• Molting hormones are released.
• The hypodermis detaches from the existing hard shell. The hypodermis is a layer of cells directly beneath the shell.
• The hypodermis produces enzymes which begin to dissolve the shell components. Much of the existing shell is recycled causing it to become thin. Inorganic salts are resorbed from the shell and stored internally.
• A new inner soft shell slowly forms underneath the existing shell. When this new shell has fully formed, the crab will be ready to molt.

Ecdysis (molting or “busting” stage)

• The crab stops eating and seeks shelter in order to avoid predation. During this process the crab is highly vulnerable to predators, including the two-legged variety!
• The crab rapidly absorbs water which causes its tissues to swell and split the old shell open across the back between the lateral spines. Fracture planes in the claws split open to allow the claws to be pulled through.
• The crab begins the slow, arduous process of backing out of its old shell, which is then discarded.
• The newly molted crab pumps water into its tissues in order to inflate the shell to its new size. The new shell will be roughly one-third larger (33%) than the old shell. The new shell reaches its full size within six hours after molting.

Postecdysis (postmolt or “soft shell” stage)

• The salvaged inorganic salts are rapidly redeposited to help thicken and harden the new shell. The new shell will only harden in water (the hardening process stops if the crab is removed from the water) and will take approximately two to four days to fully harden.

15.

The blue crab is a decapod, which means it possesses ten appendages, of which four pairs are segmented walking legs. Its last pair of legs is paddle-shaped, permitting the crab to swim more actively than most other crab species. These legs, called the paddle fins, are flexible so that they can be rotated in a sculling action that allows the crab to propel itself through the water. The crab is capable of swimming at burst speeds of up to one meter per second.

The largest appendages are a pair of segmented arms ending in pincer-like claws, which the crab uses for defense and to grasp and crush prey. The carapace is the shell that covers and protects the crab. Eyes, mouth, and antennae are located at the front edge of the carapace.

Crabs have an outer hard shell called an exoskeleton. Unlike skin, the hard shell can't stretch to accommodate growth, so the crab must molt, or shed its shell, in order to grow. As the crab grows, the shedding process occurs again and again, as often as 25 times.

16. Bivalves vary greatly in overall shape. Some, such as the cockles, have shells that are nearly globular; cockles can jump by bending and straightening their foot. Others, such as the razor clams, are burrowing specialists with elongated shells and a powerful foot adapted for rapid digging. The shipworms, in the family Teredinidae have greatly elongated bodies, but their shell valves are much reduced and restricted to the anterior end of the body, where they function as scraping organs that permit the animal to dig tunnels through wood.

Ostracod Their bodies are flattened from side to side and protected by a bivalve-like, chitinous or calcareous valve or "shell". The hinge of the two valves is in the upper (dorsal) region of the body. Ostracods are grouped together based on gross morphology. While early work indicated the group may not be monophyletic;and early molecular phylogeny was ambiguous on this front, recent combined analyses of molecular and morphological data found support for monophyly in analyses with broadest taxon sampling