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What's New! Ask a Marine Scientist: answers to Arthropod questions! Index To Questions LOBSTERS AND SHRIMPS CRABS BARNACLES
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LOBSTERS AND SHRIMP
A: We'll try to answer a couple of these questions, but as it seems that you're doing a report on lobsters, we'll let you do some of the research yourself!! Your local or school library would be a good place to start. Lobsters are a type of crustacean, within the phylum Arthropoda - this should be a help to you when searching for information. There are many, many different kinds of lobsters all over the world. You haven't given your general location, so we'll give you some information about the american lobster, Homarus americanus. This animal is sometimes called the northern lobster. It ranges from the coast of Labrador in Canada, to as far south as Virginia. These lobsters are found on the East coast of North America, and can reach a length of 60 cm and a weight of almost 20 kg. (see the records page on the oceanlink site: http://oceanlink.island.net/records.html The american lobster is a scavenger. It eats a wide variety of items, including living or dead fish. This explains why lobster traps are baited with dead fish. Males and females mate, and females carry the eggs attached to the outside of her body for 10-11 months before they hatch. The hatchlings are very tiny, and are planktonic - this means that they float around with the oceans currents. By the time they reach about 25 mm (1 inch) in length, they settle down and become bottom dwelling animals. Growth is quite slow: a 900 gram (2 pound) animal is about 4 years old.
Q: What are the differences between Homarus americanus and Homarus gammarus? Distribution and physiology? A: Homarus americanus is commonly known as the American lobster, and Homarus gammarus is the European lobster. The American lobster ranges along the east coast of North American from Labrador to North Carolina, and is found from very shallow water to the edge of the continental shelf (200 m depth). The European lobster ranges along the European and Mediterranean coasts, although it is not found as deep as H. americanus. American and European lobsters are fairly similar in external morphology, with large claws, a cylindrical cephalothorax and an abdomen that is well-developed and slightly flattened dorsoventrally. The average American lobster is approximately 25 cm in length and weighs a little less than 1 kg, while the European lobster is generally of smaller size.
Q: I was wondering if you could tell me what the life cycle of the lobster is. A: -potential mates find eachother by sight, sound, and/or smell -mating couple manoevers into position and semen is pumped along the first two pairs of male pleopods (swimmerets) -fertilized eggs are retained by the female by being cemented onto her pleopods -development of nauplius larva (unsegmented phase with three appendages that will form future antennules, antennae, and mandibles) occurs within the egg -several molts lead to the protozoea (thorax and abdomen appear, and carapace takes shape) -larva hatches in the zoea stage (remainingtrunk segments and limbs are in place, and carapace has fused with thorax), locomotion is controlled by the thoracic appendages -several more molts lead to the postlarva or megalops which has complete set of segments and functional appendages. -from there, succesive molts lead to the typical adult stage -adults continue molting and growing throughout their lives
A: Yes, lobsters do indeed have heads. They are in the phylum Arthropoda (along with insects, spiders, mites, crabs etc.) One of the characteristics of this group of animals is (to quote a textbook), "a high degree of cephalization". What this means is that they have heads. The sense organs are concentrated in the head area, and they have a distinct brain. You can divide a lobster up into three seperate regions: head, thorax (where the legs are, and which contains most internal organs) and the abdomen. Of course, if you are dividing a lobster up, I'll take the abdomen, thanks.
Q: I work in a Hands on
science Center and we deal marine mammals of the Estuary. the
Estuary that we located near is the Hudson bay. My question
is Can you tell me about A. I am guessing that you are referring to the albino lobster, which is a rare form of the American lobster, Homarus americanus. There are several different colour phenotypes among the American lobster, including the usual green, blue, and albino. The differences in color are related to pigments in the exoskeleton of the animal. The albino and blue colors are the result of rare combinations of recessive alleles in lobster populations. It is similiar to albino individuals in human populations. The genes for such charcteristics are present in a population, but they are rarely expressed in the phenotype of individuals.
Q: Interesting factoids about crayfish.... at least 5 please...What is the ecological importance of crayfish to the environment, humans and humans. Can you tell us about the larval lifecycle of the crayfish? A. 2. Crayfish are in the class Malacostraca along with isopods (sowbugs), amphipods, euphausiids (krill), beachhoppers, mantis shrimp, and a very large order, the Decapoda, that contains many kinds of shrimp, and crabs. 3. Malacostracans are characterized by a trunk with eight thoracic and six abdominal somites, each bearing a pair of biramous appendages. There is lots of other info on crayfish on the internet, so I'll let you do some digging yourself. A really good site that I found was: So check this out. It has some good info on the anamtomy, reproductive biology and ecology of crayfish.
Q: Can you please tell me the common and scientific name of the prawns that are harvested commercially on the West Coast of BC? Also a little bit of info on their habitat, size, and sex life etc. A: Of the 85 species of shrimp that live of the coast of BC, six species are commercially harvested in British Columbia. They are the pink shrimp (Pandalus borealis), the prawn (Pandalus platyceros), the humpback shrimp (Pandalus hypsinotus), the coonstripe shrimp (Pandalus danae), the sidestripe shrimp (Pandalus dispari), and the smooth pink shrimp (Pandalus jordani). Many of the otherspecies make good eating as well, but are not found in the numbers or concentrations needed to make a viable commercial industry. The habit and habitat of local shrimp is highly varied. Some species are found only on specific kinds of seaweeds, algae, or host animals while others are free-swimming or scrounge along the rocky or muddy bottom. Some are scavengers, and other are active hunters. Their size varies widely as well, from a few millimeters to 5cm in length. Local shrimp have several different reproductive strategies as follows: a) keeping the eggs on the underside of the tail (ovigery) until they hatch b) being ovigerous until the eggs are fertilized, then releasing them In the pink shrimp, a brood will hatch in March and April with an equal sex ratio for males and females. The females breed in mid-November and are ovigerous throughout the winter. In the spring o the male's 2nd year, they begin to change sex through a series of transitional molts and by 30 months, all of the original brood are female and are ovigerous for the following winter (the ex-males being fertilized by the new batch of males for that year). Few pink shrimp live to see their fourth year. That is only one example of a reproductive strategy employed by shrimp. There are nearly as many strategies as there are species in BC waters, let alone in the tropics.
Q: How long do brine shrimp live, and is that what zooplankton mostly is ? I know there is crustaceans and jellies , but what is the most common in Monterey Bay , Cal.? Do any zooplankton eat bacteria ? Can you help me find out more also ? A: Brine shrimp (Artemia species) live for a short period of time. The average life cycle for brine shrimp is 50 days, throughout which the female will produce 75 nauplii larva per day. The larvae mature in around 8 days, during which they go through 15 molts. Zooplankton is made up of all sorts of animals, from microscopic single-celled animals to giant jelly fish. Crustaceans do make up a large majority of zooplankton all over the world. I'm sure the Monterey Bay area is no different. In the zooplankton food web, bacteria form the base level. They are fed upon by tiny single celled and multi celled animals, which in turn are fed upon by large animals, and so forth and so on. Brine shrimp eat microalgae and other tiny bit of food that they filter out of the water. If you want to see some good pictures of zooplankton, try the links in our Marine Links section and scroll down to the zooplankton links section.
Q: Do you know of any symbiotic relationships existing between jellyfish and shrimp, particularly off the coast of China? If no, what about sea anemones and shrimp in that area? I'm trying to interpret an 1814 Chinese text on marine life. Thank you for your help. A. Offhand, I do not recall any shrimp symbionts with jellyfish. However, there are some known cases of symbiosis of shrimp with anemones. On example from the Pacific is the association of the shrimps Heptacarpus kincaidi and Lebbeus grandimanus with anemones of the Urticina genus. Typically, the shrimp are more closely associated with the anemones during the day than at night. It is believed that the shrimp associate witht the anemones primarily for protection against predators.
Q: Would it be accurate to call a shrimp a "sea cockroach"? Why or why not? A: One thing that makes biology extremely confusing is the use of common names. I am sure you could probably come up with at least a dozen different common names for shrimps, but it does not necessarily mean that the name is accurate. Both shrimps and cockroaches are classified in the phylum Arthropoda (animals with jointed appendages). But both shrimps and cockroaches are classified differently within the phylum Arthropoda. Cockroaches are classified in the class Insecta, which is the largest group of animals on earth with more than 750,000 described species and is mainly a terrestrial group. Shrimps are classified in the subphylum Crustacea, containing 38,000 known species and are found mainly in the salt and freshwater. Shrimps and cockroaches are not related closely and are both highly specialized animals that are adapted for living in completely different habitats. Perhaps the common name, "sea cockroach" came from how common shrimps, I am not certain. To answer your question I would have to say no, it is not accurate to call a shrimp a "sea cockroach", using latin genus and species names is the most accurate and universal naming system for living organisms.
Q: I once read that Lobsters have the same vertebrae system of a human and that they CAN/DO feel pain, and do experience itching for example the same way a human does. Could you please confirm/deny this for me? Thank you very much for your time and expertise. A: I think I have to deny
this information. Lobsters are invertebrate organisms, and don't
have bones at all, but instead have their structural skeleton
on the outside of their bodies as a hard calcified shell.
Q: 2 1/2 years ago my son found a crayfish in a pond, we brought it home and it lives in an old fish tank. How long do they usually live and 2 days ago we noticed about 4 row of sacks filled with little balls in each sack. The sacks are under the tail section of the crayfish, we notice it trying to grab them with it's back pincher claws---are they eggs--if so how did it become pregnant---it has been alone for the entire time. A: I did not find information
directly on crayfish reproduction, but quite a bit of work
has been done on lobsters, and they are closely related, so
I suspect the information I found on lobsters would also be
relevant to your crayfish.
Q: Q: I saw a huge lobster, (no claws)while on a night dive. It was about four feet long. What is the record? Regards CB Texas. A: rom what I can tell it is possible that you saw a species of Spiny Lobster which have no claws. The record for a lobster is actually under four feet long. The water column you were diving in may have magnified the lobster that you were viewing while on your dive. The world record for a lobster is for a North American Lobster (Homarus americanus) at 42 pounds 7 ounces in 1934 which is absolutely massive for a lobster!.
CRABS
Q: My first graders have a Hermit Crab for a pet. They would like to know how to determine if the crab is a boy or girl. A: "Sexing land hermit
crabs out of the shell is straightforward. Females have well-developed
pleopods (the small legs) on on the left side of the abdomen,
and a gonopore (an opening through which eggs or sperm are
released) at the base of the second pair of walking legs. Pleopods
are absent or at best vestigial (small) in males, and the coxae
of the last pair of legs are, in most species, produced into
stout, somewhat tubular structures (the legs have a wide, tubular
look to them)." Some male hermit crabs have one very large
front claw to fight with other males with.
A:Carcinus maenas is sometimes called the green crab, and is a very common resident on the seashore from Labrador, Canada to New Jersey. This crab also lives in Europe, and has been seen in other parts of the world as well, probably after "hitching a ride" on ships. The crab is a very typical shore crab. It lives in the intertidal zone, which is the area of the beach that is covered and uncovered by the tides each day. This means that sometimes the crab is underwater, and sometimes it is in the air. The crab has to have ways of dealing with this - during high tide, when it is covered by water, the crab moves about, looking for things to eat like seaweed, snails, dead fish, and anything else that it can catch. It is also very careful during high tide not to get eaten by large fish. During low tide, the crab usually hides in crevices, and under stones, and is very still. In this way, the crab can avoid drying out, and can hide from birds like gulls that may try to eat it. If you remove an intertidal crab like Carcinus maenas from the beach, and put it in a place far away from high and low tides, it will still be active for part of the day, and hide under rocks for during a different part of the day. This is because the crab has a "clock" that is built in. The crab's "clock" tells it when it is high tide, and when it is low tide, even when there are no tides around for it to see!
Q: My husband caught a very huge bluecrab here in Florida. Our question is: What is the biggest bluecrab caught and if there is a record of one, how big was it? Thankyou! A: The blue crab (Callinectes sapidus) is the most commercially important crab species occuring along the eastern and Gulf coasts of the United States. The carapace width of C. sapidus can reach 209 mm (8.2 in), although unfortunately I could not find a record of the largest specimen caught. For more information on this species, check out the Blue Crab Info Homepage which contains information on biology, ecology, fisheries and links to other sources.
Q: At the beach, my six year old aked "A crab lives in the sea, on the sand and buries itself in a hole under the sand, so how does it breathe". We have not been able to find an naswer, so can you help? A: Crabs use their gills to take oxygen out of the water, much like a fish. However, crabs can survive for long periods out of water, and some live almost exclusively on land. As long as a crab can keep it's gills moist, oxygen from the air will diffuse into the moisture, and then into the gills. One way to keep their gills from drying out is to seek out cool, dak and moist hiding places when on land. This way they can keep breathing, and stay hidden from predators. Also, they have articulating plates around their gills that help seal them in and prevent drying out. Land crabs have even more adaptations to prevent drying out. They drink water from dew and the ground, they get it from food, and even from water vapour. They also store water in their bladder, blood, and specialized pockets throughout their bodies.
Q: I want to know what the sand crabs that I find at the beach in Del Mar eat? What is there scientific name and how lond long do they live? A. If the crab you found is in fact a Pacific sand crab, then its scientific name is Emerita analoga. This crab has a smooth, egg-shaped body and flattened legs with no claws. This animal is found on wave swept sandy beaches, and typically moves up and down the beach in accordance with the tides. The sand crab is a filter feeder, and uses long feathery antennae to intercept plankton (tiny, floating organisms) and detritus from the water. The lifespans of most invertebrates are not very well established. Mortality rates are usually high, and few individuals ever make it to adulthood. Also, crabs moult frequently, which means it is difficult to follow the lifespan of most crabs in the field. I would estimate the average lifespan of these animals to be around 2-3 years, if they are lucky. Most of those sand crabs probably don't even make it to reproductive age.
Q: I have recently acquired a pair of hermit crabs and I was wondering if you could tell me anything about their feeding habits. Thanks!! A. Hermit crabs are scavengers that feed on whatever is available. They will feed on pieces of mussel, dead fish, plankton and other forms of suspended material. Once again, I would recommend that you return these creatures to the wild.
Q: I've just read that most crabs are isotonic with seawater- does this mean that they have the same concentration of salt in their body as sea water? If not, how much different is it- specifically for velvet swimming crabs? A. Most marine invertebrates have physiological adapations for osmoregulation, and the control of tissue solute concentrations or osmotic pressure. Some animals are stenohaline, tolerating only a narrow range of external osmotic concentrations, while others are euryhaline, and able to function within a wide range of external salinities. I don't know if you are familiar with the terms osmoconformers and osmoregulators. These terms describe two different strategies for dealing with osmotic changes. Osmoconformers reduce the concentration and osmotic gradients between the blood and external medium. This pattern is commonly exhibited in most marine and brackish water crustaceans. By maintaining a hyperosmotic internal concentration when in a dilute medium, osmoregulators place less of a burden on their internal tissues. The problem of osmotic influx can be overcome by reducing permeability to water, increasing efflux of water via the urine, and increasing the uptake of salts from the dilute medium. There are usually specialized boundary epithelia, notably the gills, gut and excretory organs that are responsible for active transport of salts to and from the medium. There has been lots of research done in this area of crustacean biology. In terms of the velvet crab, I am not sure what mechanisms are employed. That is something that you are going to have to do some digging for. I would suggest searching academic libraries and databases using keywords like CRUSTACEAN OSMOREGULATION and PHYSIOLOGY.
Q: Medical uses for the blood of the Horseshoe Crab ? A. Their blood does indeed have uses in medicine. Horseshoe crab blood reacts very strongly in the presence of endotoxin - a lipopolysaccride that resides on membranes of gram-negative bacteria. Endotoxin essentially serves as a name tag for those bacteria because it is not found on any other cells. In humans, the immune system gets very agitated when it finds endotoxin and therefore can make people feel very sick. The horseshoe crab immune system is not as complicated as the one we have, so their blood subsumes that role. In the presence of bacterial endotoxin, horseshoe crab blood coagulates into a gooey glop and thereby contains the bacterial infection. The part of horseshoe crab blood that reacts with bacterial endotoxin has proven to be the most sensitive assay for bacterial contamination of medical supplies, and so is purifed for medical uses. Answered with the help of Jim Hitt MD/PhD student at SUNY Health Science Center, Syracuse University, New York
Q: How do crabs find food in the dark A: Good question! Crabs do not rely on vision like you and I do, when looking for food. Crabs cannot see very well and usually only use their vision when their prey is very close. Crabs find their food in the dark (or in the light) by something called "chemoreception". This is kind of like our sense of smell. They have very sensitive chemoreceptors (or smell organs) on their antennae and in their mouthparts and distributed throughout their body. So, crabs can "smell" the chemicals that their prey put out in the water and follow these "smells" to find food. Crabs are primarily scavengers (feed on dead things) or predators.
Q: Are decorator crabs born in a egg or alive? A: Decorator crabs, and other large crabs called Decapods, first lay eggs. These eggs are carried by the mother outside her body, under a flap called her abdomen, or telson. These eggs are actually outside the mother, the flap does not completely enclose them. When the eggs hatch, they are released as a type of larvae called a zoea. Zoea have very big eyes and do not look at all like the adult crab. They float near the surface of the water and feed on small particles. These zoea are very tiny. After several zoea stages (separated by molting periods), they metamorphose into megalops larvae. When an animal undergoes metamorphosis they change appearance from one thing to another. This is how a caterpillar becomes a butterfly! Megalops look more like an adult crab and are bigger than the zoea. Finally, the megalops metamorphoses into an adult crab!
Q: I saw a spooky looking crab on the beach with a tail like a dagger. I would like to know what it is as I am worried about going back to the ocean now. A: What you saw was most likely
a horseshoe crab (Limulus polyphemus). These crabs have the physical
description that you mentioned in your email and they are harmless
to humans. The horseshoe crabs are more related to spiders and
scorpions than to normal crabs. But they are harmless so you
should be able to walk by the ocean again.
Q: Someone told my mother that hermit crabs carry head lice. Is that true? A: The only possibility that I can think of is hermit crabs getting sea lice which sometimes can happen to sea creatures but sea lice are not head lice. So hermit crabs do not carry head lice.
Q: I work in education and have been asked a number of times about the "foaming phenomenom" that our exhibit shore crabs display when they are sitting out of the water. I have told our volunteers that this foaming is a way to keep their gills moist. I just wanted to make sure that there isn't some other reason they would be doing this. A: You have already got the answer though. Basically the crab is aerating its gills to keep them moist and this causes the foam that you see.
BARNACLES Q: Are barnacles crustaceans? A. Yes, barnacles are crustaceans. They belong to the Class Cirripedia, the only sessile group of the crustaceans.
A: When you are walking along the beach at low tide, and see some barnacles on the rocks, they look like nothing more than white bumps at first. A closer look will show you that they look like tiny white "volcanoes" that have their tops sealed (dead barnacles are hollow inside). If you are lucky enough to see some barnacles in a tide pool, and observe them closely, you'll see a tiny fan-like projection coming out of the barnacle, and waving back and forth.The actual barnacle animal lives inside the volcano-like shell that it made for itself. Barnacles are very closely related to crabs and shrimp, believe it or not! The barnacle has a segmented, jointed body, just like a crab. It is cemented to the rocks on its head, and uses its legs (the "fan" that we talked about earlier) to sweep back and forth through the water to catch food. It builds a volcano-like shell around itself for protection, and once it settles down, it never moves again.The food that the barnacle catches with its feet consists of tiny animals and plants (plankton) that are floating around in the ocean at the mercy of the currents. The barnacle sweeps up some of these tiny organisms, and transports them to its mouth.If you are very lucky, and are a good beachcomber, you might find a barnacle "moult" floating on the waves. This moult is the exoskeleton (like skin) of the barnacle, and it had to shed it in order to grow. Crabs and shrimp do this too. The barnacle moult will show you exactly what the living barnacle looks like inside its shell.
Q: What is the species name for the giant marine isopod that lives in a deep ocean trench off of Mexico? (It may be the largest isopod on earth) I believe they have live specimens on display of this species at the Florida State Aquarium in Tampa. What does this species eat and does it have to be "kept" under high pressure? A: The giant marine isopod you're referring to is Bathynomus giganteus, which can grow to a length of 38-46 cm. This organism is carnivorous and is known to eat other animals such as sponges, fish, shrimp and worms. It doesn't appear that B. giganteus needs to be kept under pressure in the aquarium, although it does require a water temperature of about 8 degrees Celsius. For more information and pictures of the giant isopods housed at the Florida Aquarium, check out the deep sea isopods from the WhoZoo page.
Q: Why are there not many marine insects? A: The question of why there so few marine insects, is a complicated one, that many marine entomologist have tried to answered. There are many specualtions, though a conclusive answer has yet been determined. About 3% of all insect species (25,000 to 30,000 species) are aquatic or have aquatic larval stages. Only a few hundred of these species are marine or intertidal. In fact, no known marine insect remains submerged throughout their lives. Most marine insects are found estuaries, saltmarshes, mangrove swamps and intertidal zones, which are "bridging" habitats between land and ocean. Insects are highly evolved for terrestrial environments, and to return to the ocean they must overcome physiological problems of respiration and osmoregulation as well as the physical constraints of buoyancy and surface tension. Many insects have evolved flight adaptations, such as a reducing body weight and increasing their surface-volume ratio, which make it difficult to penetrate air-water interfaces. Wings and water also do not mix too well, perhaps this is why many marine insects have become wingless. Suggestions have been made that the physiology of the muscular and/or nervous system of an insect is so specialized that it cannot tolerate the physical and chemical conditions of ocean water. Another speculation is that insects must evolve both osmotic regulation and underwater respiration to live in the marine environment. But these adaptations differ so much physiologically that few insects have successfully evolved both. Yet, another suggestion has been that crustaceans (crabs, shrimps, amphipods, etc.) occupy most of the niche space and therefore left no room for insects to expand into the ocean habitat. Terrestrial insects have been studied much more extensively than marine insects and there is definitely a lot of research that needs to be done. If you are interested in researching more about marine insects I suggest you go to your local library and take out Lanna Cheng's book "Marine Insects".
Q: We discovered little white almost clear bugs(about the size of a grain of sand)in our bathing suits while recently swimming in Ocean City, Maryland. They caused a stinging itchy feeling which is why we went home and washed off and then discovered what appeared to be mites. We were told by another individual vacationing that they were called Sea Mites and they had found many in their swim suits as well that morning. I tried looking them up on the internet and could not locate anything on such a creature. Do they exist? They did look very much like a head lice but in all the years we have been going to the ocean, I have never heard of them. Additionally, they were everywhere in the morning but by afternoon they had disappeared. Thanks. A. There are several species of Trombidiform mite that live in the marine environment. These mites are in the Order Halacaroidea, Family Halacaridae. These mites are similar to terrestrial species that are known as "chiggers". Halacarid mites usually live in association with other vertebrates or on algae, and feed on livng and dead tissue. These little guys have biting mouthparts, and are known to sometimes bite people. The bites often tend to itch, and the itchiness is caused by the human body's reaction to the oral secretions of the mites (much like mosquitoes).
Q: What can you tell me about Copepods? They are causing real problems where I work as they keep clogging our water intake filters. A: Copepods form a large and
successful assemblage or organisms and are represented in marine,
estuarine and freshwater habitats. There are about 7500 different
copepod species in the world today. Some of these organisms are
planktonic in nature while others can crawl around between sand
grains. Where these animals thrive they are likely to be the
most numerous non-microscopic animals. Copepods are a major species
because they eat a lot of smaller organisms than themselves and
are consumed by other larger animals such as fishes. Eating animals
and in turn being comsumed my others makes them an important
animal in the food chain.
Q: Is it true that a lobster is related to a cockroach. A: Yes the cockroach and the lobster are related. They are both from the same phylum namely Arthropoda.
see also: OceanLink's Arthropod page |
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