Shrimp Dissection

Arthropoda Quiz

Arthropoda Test

Crustacean Anatomy Quiz

Clean Up Song

Background information of Common Crustaceans

Crustaceans are a group of hard-bodied animals that are members of the phylum Arthropoda that they share with such other organisms as spiders, scorpions, centipedes,millipedes, insects, and horseshoe crabs. Arthropods are characterized by having an exoskeleton (composed of a carbohydrate polymer called chitin, minerals, mostlyCaCO3, and proteins) and segmented appendages. Crustaceans are a sub-group of arthropods that are segmented, primarily aquatic, and use gills to breath. There are manytypes of crustaceans that are surprisingly dissimilar to the eye – brine shrimp, crabs, copepods (zooplankton), lobsters, and barnacles. The species of crustaceans that areimportant for aquaculture are all in the class Malacostraca. All adult members of the Malacostraca have 19 segments (1-5 are the head, 6-13 are the thorax, and 14-19 are the abdomen), although some of the segments may be partially fused, such as the cephalothorax, or carapace, of lobsters (head and thorax fused).

In addition to being malacostracans, the major groups of cultured crustaceans ― lobsters, crabs, crawfish, shrimp and prawns ― are members of the order Decapoda, having five (5) pairs of walking legs (pereiopods) on segments 9 –13. In some species (Maine lobster, crabs, and some prawns) the first pair are clawed, or chelate, and may be used for capturing food or defense; penaeid shrimp order Decapoda, having five (5) pairs of walking legs (pereiopods) on segments 9 –and the palinurid lobsters (Caribbean spiny lobster) have no chelated appendages. There are also appendages on the abdomen, called pleopods, which may be modified for swimming (swimmerets) and/or hold fertilized eggs (females). Most decapod crustaceans (with the exception of crabs) have a fan-shaped tail (called the

telson) comprised of several uropods. The abdomen, equipped with the paddle-like telson serves for locomotion, and it is often used to rapidly escape from potential predators.

Decapod crustaceans, and all arthropods for that matter, are housed in a hard exoskeleton, called the carapace, which is comprised of a carbohydrate polymer, called chitin, minerals (mostly CaCO3), and proteins. This structural arrangementposes a unique challenge for growth, similar to a knight who has

outgrown his metal armor. In order to grow, the animal must shed the old carapace, secrete a new, larger one that it will eventually fill and shed again (figure). This process ofshedding the exoskeleton is called ecdysis or molting. The molt cycle is normally triggered by external stimuli (light and temperature), as well as internal signals, which initiatethe secretion of the hormone ecdysone, which facilitates the molting events that follow. It requires a series of physiological steps ― breaking down the old shell, storing theCaCO3, regenerating missing limbs, building carbohydrate reserves for chitin production, and finally the physical act of extraction from the old, hard carapace and inflating (withwater) the new soft carapace to a larger size. For the next day or so, the shell is soft (hence the term soft-shelled crabs), and the animal is immobile and highly vulnerable topredation. Once the shell has hardened the animal will resume its regular activities. Usually a few days before ecdysis, the crustacean will find a secure hiding place and suspendfeeding activities.

There are two components to growth by molting that scientists use: 1) the

intermolt period ― the duration, or time between, successive molts, and 2) the molt increment the increase in size from a single molt (expressed as the % weight gain afterthe molt). Both are size and age dependent. Juvenile crustacean molt frequently (short intermolt period) and experience significant weight increases (molt increment). Asthey grow older (and larger), the intermolt period gets longer and longer, and the weight gain (as a percentage) declines.

The process of molting poses the most physiological stressful and dangerous period during the animal’s life. Under culture conditions, particularly during the

crustacean’s larval period and metamorphosis, but also throughout life, mortality is most likely to occur during ecdysis. Nutrient deficiency is often the culprit, such as “molt death syndrome”, first discovered in hatcheries for Maine lobsters (but probably not limited to that species) that were determined to be caused by vitamin C deficiency. Thereare likely other dietary requirements for successful molting yet to be discovered.

However, the challenge for most crustacean culture (with the exception of penaeid shrimp) is the tendency for aggressive and cannibalistic behavior ― non- molting animalsattacking the vulnerable, unprotected soft-shelled one (a particular problem in tank systems). Providing habitat to create a complex environment offers some shelter for post-molt animals, but such a strategy compromises water flow, can create stagnant pockets of uneaten feed and feces, and complicates tank cleaning and harvesting. In somecases, Maine lobster culture and blue crab shedding operations, animals are individually housed to prevent cannibalistic predation. Even the Caribbean spiny lobster, agregarious crustacean under normal conditions, will become cannibalistic when its dietary requirements are not met. Decapod crustaceans are fairly anatomically similar withregard to reproduction, although spawning behavior and larval development are quite variable. Crustacean gonads are paired, elongate organs located in the thorax and/or abdomen. The oviducts are tubules, usually terminating on the last pair of walking legs for males and the third from the last pair in the females. A gonad-stimulating hormone, produced in the thorax stimulates egg production, and once the ovaries are fully developed (and the males are ready to copulate) some crustaceans release chemical signalscalled pheromones into the water to attract potential mates. Copulation often occurs when the females are in the process of molting, at which time the male releases itsgametes, often in the form of a sperm mass or packet called the spermatophore using specially modified appendages, and the female usually has a receptacle that is used tohold the male gametes until fertilization. Most female crustaceans carry the fertilized eggs beneath the abdomen attached to the periopods.

The larval development of decapod crustaceans that may have potential for aquaculture is highly variable and is one of several critical components to realizingcommercial-scale farming. The Maine lobster, Homarus Americana for example,

has a very short-lived larval period (4 stages, 10 days), although the femal may carry the eggs for almost year before that hatch. In contrast, the Caribbean spiny lobster,Panulirus argus, will remain berried for just a few weeks before releasing the larvae, but it has a protracted larval cycle (12 stages lasting as much as 400

days). Clearly, hatchery production of spiny lobsters is not economically viable, and collection of post-larvae from the wild is currently being evaluated for commercial spinylobster aquaculture. Maine lobsters have been successfully reared in hatcheries for decades, but other obstacles are confronted later on in the production cycle (guess what?).

The male blue crab (Callinectes spp.) will mate at any time during its last three intermolts (they live for 2 to 3 years), while the female will mate only once during her molt from juvenile to adult. She will spawn (release her eggs) 1- 10 months after copulation, and will carry up to two million eggs under her abdomen apron (berried) for a week to 10 days. The hatched larvae undergo eight (8) stages that may last from 40 to 70 days, dependent upon temperature and food availability.

Freshwater crawfish (Procambarus spp.) may spawn year-round in warm climates, mating occurring in the spring and the eggs fertilized in the fall (six months) while the female remains in a burrow. The eggs are attached to the pleopods and fanned(or oxygen) for two to three weeks. Upon hatching, the juveniles (no planktonic larval period) remain attached to the females for about two molts before assuming their ownbenthic existence. They will mature in three to five months and live for up to four years.

The adult decapod may be an active predator, a scavenger, or an omnivore, and in almost all crustaceans the mouthparts break up the food that passes food throughthe esophagus into the cardiac stomach, pyloric stomach, and finally the intestines. Between the two stomachs is the “gastric mill” which helps to grind the food, while thehepatopancreas releases digestive enzymes.

Lophophorates

-A lophophore is a unique feeding structure

-A set of ciliated tentacles in the shape of a horseshoe used for filter feeding

-There are three groups of lophophores

-Ectoprocta (Bryozoans)

-Phoronida

-Brachiopoda (Lamp Shells)

The Bryozoans

(Moss Animals)

-The bryozoans are the only lophophore I want you to know.

-The reason is it can be easily confused for coral

-Bryozoans form a large colony made up of individuals called zooids

-There group skeleton usually looks like fine lace