Chapter 33 - An Introduction to Invertebrates Flashcards
Invertebrates -
are animals that lack a backbone
Phylum Porifera -
Animals in the phylum Porifera are known informally as sponges
Filter feeders -
filter out food particles suspended in the surrounding water as they draw it through their body
The spongocoel -
water is drawn through the pores into a central cavity
The Osculum
where water flows out of the sponge through a larger opening
tissues
groups of similar cells that act as a functional unit as in muscle tissue and nervous tissue.
Choanocytes
lining the interior of the spongocoel are flagellated choanocytes, or collar cells (named for the finger-like projections that form a “collar” around the flagellum). These cells engulf bacteria and other food particles by phagocytosis
Mesohyl
gelatinous region separating the body of a sponge consisting in two layers of cells
amoebocytes
named for their use of pseudopodia. These cells move through the mesohyl and have many functions. For example, they take up food from the surrounding water and from choanocytes, digest it, and carry nutrients to other cells. Amoebocytes also manufacture tough skeletal fibers within the mesohyl.
totipotent
capable of becoming other types of sponge cells
Hermaphrodites -
meaning that each individual functions as both male and female in sexual reproduction by producing sperm and eggs
Sequential hermaphroditism -
They function first as one sex and then as the other
eumetazoans (“true animals”)
members of a clade of animals with tissues
Cnidarians -
diversified into a wide range of sessile and motile forms, including hydras, corals, and jellies (commonly called “jellyfish”). Yet most cnidarians still exhibit the relatively simple, diploblastic, radial body plan that existed in early members of the group some 560 million years ago
the gastrovascular cavity -
a central digestive compartment with a single opening to this cavity functions as both mouth and anus
Polyps
cylindrical forms that adhere to the substrate by the aboral end of their body (the end opposite the mouth) and extend their tentacles, waiting for prey
A medusa (plural, medusae) -
resembles a flattened, mouth-down version of the polyp. It moves freely in the water by a combination of passive drifting and contractions of its bell-shaped body. Medusae include free-swimming jellies
cnidocytes
cells unique to cnidarians that function in defense and prey capture. Cnidocytes contain cnidae (from the Greek cnide, nettle), capsule-like organelles that are capable of exploding outward and that give phylum Cnidaria its name
nematocysts
contain a stinging thread that can penetrate the body surface of the cnidarian’s prey
noncentralized nerve net
Cnidarians have no brain. Instead, movements are coordinated by a noncentralized nerve net that is associated with sensory structures distributed around the body. Thus, even though it lacks a brain, the animal can detect and respond to stimuli from all directions.
Medusozoa -
All cnidarians that produce a medusa are members of clade Medusozoa, a group that includes the scyphozoans (jellies) and cubozoans (box jellies) shown in Figure 33.6a, along with the hydrozoans. Most hydrozoans alternate between the polyp and medusa forms,
Anthozoa
Sea anemones and corals belong to the clade Anthozoa. These cnidarians occur only as polyps
exoskeleton
external skeleton of calcium carbonate
Bilateria
whose members exhibit bilateral symmetry and are triploblastic. Most bilaterians also have a digestive tract with two openings (a mouth and an anus) and a body cavity
lophotrochozoans
unique morphological features are widely shared within the group—in fact, the lophotrochozoans are the most diverse bilaterian clade in terms of body plan. This diversity in form is reflected in the number of phyla classified in the group: Lophotrochozoa includes 18 phyla, more than twice the number in any other clade of bilaterians.
Flatworms
(phylum Platyhelminthes) live in marine, freshwater, and damp terrestrial habitats. In addition to free-living species, flatworms include many parasitic species, such as flukes and tapeworms.
triploblastic
lack a body cavity. Their flat shape increases their surface area, placing all their cells close to water in the surrounding environment or in their gut. Because of this proximity to water, gas exchange and the elimination of nitrogenous waste (ammonia) can occur by diffusion across the body surface.
protonephridia -
networks of tubules with ciliated structures called flame bulbs that pull fluid through branched ducts opening to the outside
planarians
abundant in unpolluted ponds and streams, planarians prey on smaller animals or feed on dead animals. They move by using cilia on their ventral surface, gliding along a film of mucus they secrete. Some other rhabditophorans also use their muscles to swim through water with an undulating motion. features a pair of light-sensitive eyespots as well as lateral flaps that function mainly to detect specific chemicals
Syndermata
the rotifers (former phylum Rotifera) and the acanthocephalans (former phylum Acanthocephala), should be combined into a single phylum
rotifers
have an alimentary canal, a digestive tube with two openings, a mouth and an anus. Internal organs lie within the hemocoel (see Figure 32.9b). Fluid in the hemocoel serves as a hydrostatic skeleton. Movement of a rotifer’s body distributes the fluid throughout the body, circulating nutrients.
parthenogenesis
Some species consist only of females that produce more females from unfertilized eggs, a type of asexual reproduction
acanthocephalans
a group of highly modified “rotifers.” All acanthocephalans are parasites that have complex life cycles with two or more hosts
Ectoprocta and Brachiopoda
Bilaterians in the phyla Ectoprocta and Brachiopoda have a lophophore, a crown of ciliated tentacles around their mouth (see Figure 32.12a). As the cilia draw water toward the mouth, the tentacles trap suspended food particles. Other similarities, such as a U-shaped alimentary canal and the absence of a distinct head, reflect these organisms’ sessile existence
Ectoprocts
are colonial animals that superficially resemble clumps of moss. (In fact, their common name, bryozoans, means “moss animals.”) In most species, the colony is encased in a hard exoskeleton studded with pores through which the lophophores extend
Brachiopods -
superficially resemble clams and other hinge-shelled molluscs, but the two halves of the brachiopod shell are dorsal and ventral rather than lateral, as in clams. All brachiopods are marine. Most live attached to the seafloor by a stalk, opening their shell slightly to allow water to flow through the lophophore
molluscs
molluscs are marine, roughly 8,000 species inhabit fresh water, and 28,000 species of snails and slugs live on land. All molluscs are soft-bodied, and most secrete a hard protective shell made of calcium carbonate.
foot
a muscular foot, usually used for movement
a visceral mass
containing most of the internal organs
a mantle
a fold of tissue that drapes over the visceral mass and secretes a shell (if one is present)
the mantle cavity
a water-filled chamber, which houses the gills, anus, and excretory pores
a radula
a straplike organ used to feed as it scrapes up food
Polyplacophora
chitons, Chitons have an oval-shaped body and a shell composed of eight dorsal plates. The chiton’s body itself, however, is unsegmented. A chiton can also use its foot to creep slowly over the rock surface. Chitons use their radula to scrape algae off the rock surface.
Gastropoda
snails and slugs, Gastropods move literally at a snail’s pace by a rippling motion of their foot or by means of cilia—a slow process that can leave them vulnerable to attack. Most gastropods have a single, spiraled shell into which the animal can retreat when threatened. The shell, which is secreted by glands at the edge of the mantle, has several functions, including protecting the animal’s soft body from injury and dehydration. One of its most important roles is as a defense against predators
Bivalvia
clams, oysters, and other bivalves. Bivalvia are all aquatic and include many species of clams, oysters, mussels, and scallops. Bivalves have a shell divided into two halves. The halves are hinged, and powerful adductor muscles draw them tightly together to protect the animal’s soft body. Bivalves have no distinct head, and the radula has been lost. Some bivalves have eyes and sensory tentacles along the outer edge of their mantle
Cephalopoda
squids, octopuses, cuttlefishes, and chambered nautiluses. Cephalopods are active marine predators. They use their tentacles to grasp prey, which they then bite with beak-like jaws and immobilize with a poison present in their saliva. The foot of a cephalopod has become modified into a muscular excurrent siphon and part of the tentacles
a closed circulatory system
in which the blood remains separate from fluid in the body cavity
ammonites
Shelled cephalopods called, some of them as large as truck tires, were the dominant invertebrate predators of the seas for hundreds of millions of years until their disappearance during the mass extinction at the end of the Cretaceous period, 66 million years ago
Threats to molluscs are especially severe in two groups:
freshwater bivalves and terrestrial gastropods
Annelids
segmented worms that live in the sea, in most freshwater habitats, and in damp soil. Annelids, which have a coelom (and no hemocoel), range in length from less than 1 mm to more than 3 m
Polychaeta
the polychaetes, a paraphyletic group
Oligochaeta
the oligochaetes, a subgroup of the polychaetes
Hirudinea
the leeches, a subgroup of the oligochaetes
errantians
many errantians are mobile; some swim among the plankton (small, drifting organisms), while many others crawl on or burrow in the seafloor. Many are predators, while others are grazers that feed on large, multicellular algae. The group also includes some relatively immobile species
Sedentaria
Sedentaria, tend to be less mobile than those in Errantia. Some species burrow slowly through marine sediments or soil, while others live within tubes that protect and support their soft bodies. Tube-dwelling sedentarians often have elaborate gills or tentacles used for filter feeding
a cuticle
a tough external coat
molting
aka ecdysis, or when a cuticle is shed
nematodes
nematodes , or roundworms, are found in most aquatic habitats, in the soil, in the moist tissues of plants, and in the body fluids and tissues of animals. The cylindrical bodies of nematodes range from less than 1 mm to more than 1 m long, often tapering to a fine tip at the posterior end and to a blunter tip at the anterior end. A nematode’s body is covered by a tough cuticle (a type of exoskeleton); as the worm grows, it periodically sheds its old cuticle and secretes a new, larger one. Nematodes have an alimentary canal, though they lack a circulatory system. Nutrients are transported throughout the body via fluid in the hemocoel. The body wall muscles are all longitudinal, and their contraction produces a thrashing motion.
arthropods
with segmented body, hard exoskeleton, and jointed appendages
an open circulatory system
in which fluid called hemolymph is propelled by a heart through short arteries and then into the hemocoel—the body cavity surrounding the tissues and organs
Chelicerates
(clade Chelicerata) are named for clawlike feeding appendages called chelicerae, which serve as pincers or fangs. Chelicerates lack antennae, and most have simple eyes (eyes with a single lens).
book lungs
gas exchange is carried out by book lungs, stacked platelike structures contained in an internal chamber (Figure 33.33). The extensive surface area of these respiratory organs enhances the exchange of and between the hemolymph and air
complete metamorphosis
Insects with have larval stages specialized for eating and growing that are known by such names as caterpillar, maggot, or grub. The larval stage looks entirely different from the adult stage, which is specialized for dispersal and reproduction.
echinoderms
slow-moving or sessile marine animals. Echinoderms have a coelom. A thin epidermis covers an endoskeleton of hard calcareous plates, and most species are prickly from skeletal bumps and spines
water vascular system,
a network of hydraulic canals branching into extensions called tube feet that function in locomotion and feeding
