Add your Article
- Chemistry and Materials
- The hottest soup in New York
- The Incredible Shrunken Kids
- Sweeeet! The Skinny on Sugar Substitutes
- E Learning Jamaica
- Results of GSAT are in schools this week
- 2014 GSAT Results for Jamaican Kids
- E Learning in Jamaica WIN PRIZES and try our Fun Animated Games
- GSAT Exam Preparation Jamaica
- E Learning in Jamaica WIN PRIZES and try our Fun Animated Games
- GSAT Scholarship
- Scotiabank Jamaica Foundation Grade Six Achievement Test (GSAT) Scholarships
- GSAT Exams Jamaica Scholarships
- Access denied - Disabled boy aces GSAT
- GSAT Exam Preparation
- Results of GSAT are in schools this week
- GSAT Mathematics
- 10 Common Mistakes When Preparing for the GSAT Math Test
- Secrets of an Ancient Computer
- GSAT Mathematics Quiz, Teaching Math, teaching anxiety
- Human Body
- Workouts: Does Stretching Help?
- Sea Kids See Clearly Underwater
- Teen Brains, Under Construction
- Parents
- What Not to Say to Emerging Readers
- How children learn
- Raise a Lifelong Reader by Reading Aloud
- Plants
- Bright Blooms That Glow
- White fuzzy mold not as friendly as it looks
- Plants Travel Wind Highways
Crustaceans
Published: 07/01/2010
Picture your last seafood meal, and you're probably seeing a crustacean. Crustaceans are mostly water-dwelling invertebrates (no spine), characterized by a jointed body and limbs, and a hard outer shell called an exoskeleton. Although some species live on land, the most common and identifiable crustaceans are ocean-dwellers, such as lobsters, crabs, and even shrimp and barnacles. The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. They include various familiar animals, such as lobsters, crabs, shrimp and barnacles. The majority are aquatic, living in either fresh water or marine environments, but a few groups have adapted to terrestrial life, such as terrestrial crabs, terrestrial hermit crabs and woodlice. The majority are motile, although a few taxa are parasitic and live attached to their hosts (including sea lice, fish lice, whale lice, tongue worms, and Cymothoa exigua), and adult barnacles live a sessile life, attached head-first to the substrate. The scientific study of crustaceans is known as carcinology. Other names for carcinology are malacostracology, crustaceology and crustalogy, and a scientist who works in carcinology is a carcinologist, crustaceologist or crustalogist. Crustaceans have three distinct body parts: head, thorax, and abdomen (or pleon), although the head and thorax may fuse to form a cephalothorax. The head bears two pairs of antennae, one pair of compound eyes and three pairs of mouthparts. The thorax and pleon bear a number of lateral appendages, including the gills, and the tail ends with a telson. Smaller crustaceans respire through their body surface by diffusion, and larger crustaceans respire with gills or, with abdominal lungs In common with other arthropods, crustaceans have a stiff exoskeleton which must be shed to allow the animal to grow (ecdysis). Various parts of the exoskeleton may be fused together; this is particularly noticeable in the carapace, the thick dorsal shield seen on many crustaceans. Crustacean appendages are typically biramous; this includes the second pair of antennae, but not the first, which is uniramous. There is some doubt whether this is an advanced state, as had been traditionally assumed, or whether it may be a primitive state, with the branching of the limbs being lost in all extant arthoropod groups except the crustaceans. One piece of evidence supporting the latter view is the biramous nature of trilobite limbs. Although a few are hermaphroditic, most crustaceans have separate sexes, which are distinguished by appendages on the abdomen called swimmerets or, more technically, pleopods. The first (and sometimes the second) pair of pleopods are specialised in the male for sperm transfer. Many terrestrial crustaceans (such as the Christmas Island red crab) mate seasonally and return to the sea to release the eggs. Others, such as woodlice lay their eggs on land, albeit in damp conditions. In many decapods, the eggs are retained by the females until they hatch into free-swimming larvae. Those crustaceans that have hard exoskeletons reinforced with calcium carbonate, such as crabs and lobsters tend to preserve well as fossils, but many crustaceans have only thin exoskeletons. Most of the fossils known are from coral reef or shallow sea-floor environments, but many crustaceans live in open seas, on deep sea-floors or in burrows. Crustaceans tend, therefore, to be rarer in the fossil record than trilobites. Some crustaceans are reasonably common in Cretaceous and Caenozoic rocks, but barnacles have a particularly poor fossil record, with very few specimens from before the Mesozoic era.
Crustaceans
