L35 (Animal Diversity II: Invertebrates) Key Terms

planarians

a free-living flatworm found in ponds and streams

trematodes

trematodes parasitize a wide range of hosts, and most species have complex life cycles with alternating sexual and asexual stages. Many trematodes require an intermediate host in which larvae develop before infecting the final host where the adult worms live

tapeworms

adults live mostly inside vertebrates. In many tapeworms, the anterior end, or scolex, is armed with suckers and often hooks. Tapeworms lack a mouth and gastrovascular cavity; they simply absorb nutrients across the tapeworm’s body surface

alimentary canal

complete digestive tract, consisting of a tube running between a mouth and an anus

parthenogenesis

a form of asexual reproduction in which females produce offspring from unfertilized eggs

ectoprocts

a sessile, colonial lophotrochozoan; also called a bryozoan

brachiopods

a marine lophotrochozoan with a shell divided into dorsal and ventral halves; also called lamp shells

visceral mass

one of the three main parts of a mollusc; the part containing most of the internal organs

mantle

one of the three main parts of a mollusc; a fold of tissue that drapes over the mollusc’s visceral mass and may secrete a shell

radula

a straplike scraping organ used by many molluscs during feeding

gastropods

snails and slugs: move by rippling motion of foot or by cilia, have a single, spiraled shell, use radula to graze on algae or plants

bivalves

the molluscs are all aquatic and include many species of clams, oysters, mussels, and scallops, have a hinged shell divided into two halves, no head and no radula, gills are for feeding and gas exchange

cephalopods

active marine predators that use their tentacles, have a muscular excurrent siphon

annelids

segmented worms in moist environments, have a coelom (no hemocoel),

errantians

mobile marine members, some swim, others crawl, some are predators, other are grazers, many have body segments with prominent paddle-like parapodia

sedentarians

annelids that tend to be less mobile than Errantia, some burrow slowly while others live within tubes, those that live in tubes have gills and tentacles for filter feeding

molting

a process in ecdysozoans in which the exoskeleton is shed at intervals, allowing growth by the production of a larger exoskeleton

nematodes

aka roundworms, are found in aquatic habitats, have a cylindrial body with a fine tip and blunt tip, covered in a cuticle, have an alimentary canal but no circulatory system, nutrients are transported via hemocoel

arthropods

a segmented ecdysozoan with a hard exoskeleton and jointed appendages. Familiar examples include insects, spiders, millipedes, and crabs

open circulatory system

a circulatory system in which fluid called hemolymph bathes the tissues and organs directly and there is no distinction between the circulating fluid and the interstitial fluid

chelicerates

an arthropod that has chelicerae and a body divided into a cephalothorax and an abdomen. Living chelicerates include sea spiders, horseshoe crabs, scorpions, ticks, and spiders

arachnids

a member of a subgroup of the major arthropod clade Chelicerata. Arachnids have six pairs of appendages, including four pairs of walking legs, and include spiders, scorpions, ticks, and mites

myriapods

a terrestrial arthropod with many body segments and one or two pairs of legs per segment. Millipedes and centipedes are the two major groups of living myriapods

crustaceans

carbs, lobsters, barnacles, etc thrive in a broad range of aquatic/marine environments, many have specialized appendages such as two pairs of antennae, three or more appendages are modified as mouthparts, the others are legs and genitals, small ones use gas exchange, large ones use gills, most have separate sexes

insects

radiated in response to the origin of new plant species, undergo either complete/incomplete metamorphosis, have complex organ systems such as a tracheal system and a heart

complete metamorphosis

the transformation of a larva into an adult that looks very different, and often functions very differently in its environment, than the larva

incomplete metamorphosis

a type of development in certain insects, such as grasshoppers, in which the young (called nymphs) resemble adults but are smaller and have different body proportions. The nymph goes through a series of molts, each time looking more like an adult, until it reaches full size