Class Malacostraca

Kate Atkinson, Ruby Berin, Niki Geller, Maddie Tanda

Characteristics

● Two chambered stomach ● Centralized nervous system ● Usually eight legs (first two sometimes pinchers) ● Three part body (Head, thorax, and abdomen) o Usually the head consists of 5 segments o Thorax consists of 5-8 o ● They usually have paired eyes and they are usually stalked o Abdomen consists of 6 A stalked eye means that the eye is held away from the body, giving them a o wider range of vision ● Appendages hanging from the abdomen called pleopods, or swimmerets Used for swimming, brooding eggs, catching food, and (in isopods) gills ● Some have a carapace

What makes them unique?

● The most numerous and most successful of the four major classes of Crustacea ● Their members constitute more than two-thirds of all living crustacean species ● They exhibit the greatest range of size (less than one millimetre, or 0.04 inch, to a limb spread of more than three metres, or 10 feet) and the greatest diversity of body form ● They are abundant in all permanent waters of the world ● They have developed specialized organelles sensitive to odors, sounds, vibrations, and physical contact and added more appendages to the mouthpart ● This lead to the terrestrial malacostraca to make better use of the environment around them

Body Plan: External

● Hard exoskeletons, composed of chitin and calcareous material o Carapace o Soft at the joints for movement ● Jointed appendages, which are specialized in certain species for different functions o Claws, pincers, etc.

Body Plan: Internal

● Hemocoel (blood-filled coelom) ● Striated muscles (with flexors/extensors) ● Gas exchange through thinner cuticle or gills ● “Open” circulatory system (no separation of blood by vessels) ● Excretory organs in antennae regulate composition of body fluid ● Supraesophageal ganglia (control eyes/antennae) and subesophageal ganglia (control mouth, appendages, etc) connect ● Molting (process of making a larger cuticle); more common in juveniles ● Ecdysis (shedding of the cuticle)

Isopoda

● Can live in a wide variety of habitats, some being marine (and can live on the ocean floor), others can be terrestrial (in moist environments) ● Vary in size, ranging from 0.3 mm to 50 cm in length ● Have two pairs of antennae with one pair feeling along the ground ● Female Isopods carry eggs in a pouch called a “marsupium” ● Isopods eat fungi, decaying plant matter, plant growth, and dead animal matter ● Certain species roll into a ball to protect themselves from predators like ants, spiders, toads, and frogs ● Over 10,000 species of isopods worldwide

Armadillidium vulgare: Pill bug

● They aren’t bugs, they are terrestrial crustaceans related to shrimp ● They molt 4 or 5 times in their lifetime ● On rare occasions you may find a bright blue or purple roly poly then it is known to be sick, but it isn’t harmful to humans ● Females can reproduce without a male by a process called parthenogenesis

Deto echinata: Horned Isopod

● Known as a horned isopod because of the long curved 'horns’ that extend from the rear of each thoracic segment, longer in males ● Usually found with kelp and other drift algae on rocky shores ● Feeds on washed-up algae, carrion or live prey ● Eggs emerge from brood pouches as adults ● Can reach up to 30 mm in length

Bathynomus giganteus: Giant Isopod

● Gigantism in the species is the result of the pressure from it’s deep sea habitat, on the sea floor ● 7 ½ to 14 inches in length as an adult ● Can survive for up to four years without food

Amphipoda

● 9,500 species ● No carapace, laterally compressed bodies ● Have different types of legs, unlike isopods ● Are found in a wide variety of aquatic environments (from freshwater to that with twice the salinity of the ocean) ● No metamorphosis

Talitrus Saltator: Sandhopper

● Stay buried underneath the sand during the daytime, and emerge at night in order to feed on vegetation ● Were given their name because of their ability to hop when disturbed ● One antenna is always much longer and thicker than the other

Pariambus typicus

● Require water of higher salinity ● Can grow to a size of 7 mm ● Males exhibit a pair of vestigial lobes (not shown) ● Found mainly in the North Seas

Hyperia galba: Big-eye Amphipod

● They live in jellyfish, just under the bell ● Live off of the jellyfish eggs ● Found in the ocean’s pelagic zone

Euphausiacea

● Scientists suspect that the total weight of all the Antarctic Krill in the world is more than the total weight of all humans on earth​ ● The number of krill is declining, and this is due to global warming and a large krill fishing industry​ ● Can be found in water as deep as 2,000m​ ● Filter feeders that eat diatoms

Euphausiacea (continued)

● Divided into two families: ​ 1. Bentheuphausiidae: consists only of Bentheuphausia amblyops, a deep-water krill 2. Euphausiidae: Other 89 known krill species. Bioluminescent ​ ● Range in length from 8-70mm, the largest at 14cm​ ● Have a hard, calcified exoskeleton with three segments: the cephalon, thorax, and abdomen​ ● Head has 5 segments, thorax has 8, tail has 6 (each segment with a pair of appendages)

Bentheuphausia Amblyops

● Found in the southern part of the North Atlantic Ocean ● Only species in its family ● Are a deep red color with white gills ● Live in the deep sea

Euphausia Superba: Antarctic Krill

● Probably the most abundant animal species on earth in terms of mass ● Can live up to 6 years ● Can gather in groups with densities reaching 10,000 krill per cubic meter ● Bioluminescent

Euphausia Crystallorophias: Ice Krill

● Lives more south than any other krill species ● Have been found in water as deep as 4,000 meters ● Food source for fish, whales, and penguins

Decapoda

● Typically have ten legs (five pairs of legs) ● Most species have the first pair modified as claws ● In front of the main pair of legs there are three appendages that are used in handling food ● On top of the head there are compound eyes that are located on eyestalks ● Most are predators or scavengers but some feed on algae and the land crabs will eat fruits and leaves ● Most have gills that project upward from near the base of the thoracic appendages and are enclosed within a protective gill chamber ● Reproductive organs are found at the dorsal part of the thorax o In males there is a single pair of testes and the sperm ducts open at the fifth pair of legs (at the base) o Females oviducts open to the exterior at the base of the third pair of legs ● All decapods have the ability to regenerate

Stenorhynchus seticornis: Arrow Crab

● Prey on feather duster worms and bristle worms and pick through detritus but will also catch slow-moving fish ● Three to six centimeters ● They shed their exoskeleton and the new skin hardens with calcium carbonate (obtained by the water and by eating the old shell)

Procambarus alleni: Blue Crayfish

● They are pretty aggressive towards each other ● They range from seven to eight inches ● They like to have lots of hiding places around them because they are boring

Panulirus interruptus: California Spiny Lobster

● They do not have any claws ● To protect themselves they use the spines along their bodies ● They make loud sounds with their antennae to scare off predators ● They may shed 40 times before they reach the harvest size

Hymenocera picta: Harlequin Shrimp

● They go out to hunt mainly at night because they are shy ● Usually will stay in a pair with a male and a female ● Adults eat sea urchins