28: Invertebrates Flashcards
Phylum Porifera, Phylum Cnidaria, Superphylum Lophotrochozoa, Superphylum Ecdysozoa, Superphylum Deuterostomia
What percentage of animal species are invertebrates?
Nearly 97%.
What is an amoebocyte?
A sponge cell with multiple functions, including nutrient delivery, egg formation, sperm delivery, and cell differentiation. AKA archaeocyte.
What is a choanocyte?
A sponge cell that functions to generate a water current and to trap and ingest food particles via phagocytosis. AKA collar cell.
What is a gemmule?
An environmentally-resistant structure produced by asexual reproduction in adult freshwater sponges wherein the typical sponge morphology is inverted.
What are invertebrata?
A category of animals that do not possess a cranium or vertebral column. AKA invertebrates.
What is mesohyl?
A collagen-like gel containing suspended cells that perform various functions in the sponge.
What is an osculum?
A large opening in the sponge’s body through which water leaves.
What is an ostium?
A pore present on the sponge’s body through which water enters.
What is a pinacocyte?
An epithelial-like cell that forms the outermost layer of sponges and encloses the mesohyl.
What is Porifera?
A phylum of animals with no true tissues, but a porous body with rudimentary endoskeleton.
What is a sclerocyte?
A cell that secretes silica spicules into the mesohyl.
What is a spicule?
A structure made of silica or calcium carbonate that provides structural support for sponges.
What is a spongocoel?
A central cavity within the body of some sponges.
How does sponge motility change depending on life cycle stage?
Sponge larvae are able to swim; however, adults are non-motile and spend their life attached to a substratum.
Which structures in sponge bodies enable water movement throughout the sponge?
Structures such as canals, chambers, and cavities enable water to move through the sponge to nearly all body cells.
Why is water vital to sponges?
Water is vital to sponges for excretion, feeding, and gas exchange.
How can the morphology of sponges be described?
The morphology of the simplest sponges takes the shape of a cylinder with a large central cavity, the spongocoel, occupying the inside of the cylinder. Water can enter into the spongocoel from numerous pores in the body wall. Water entering the spongocoel is extruded via a large common opening called the osculum. However, sponges exhibit a range of diversity in body forms, including variations in the size of the spongocoel, the number of osculi, and where the cells that filter food from the water are located.
Which class is the exception to tissue specialization in sponges?
Hexactinellids have specialized tissues.
What are the general components found in sponges?
Pinacocytes form the outermost layer of sponges and enclose the mesohyl. The gel-like consistency of mesohyl acts like an endoskeleton and maintains the tubular morphology of sponges. In addition to the osculum, sponges have multiple pores called ostia on their bodies that allow water to enter the sponge.
How are ostia formed?
In some sponges, ostia are formed by porocytes, single tube-shaped cells that act as valves to regulate the flow of water into the spongocoel. In other sponges, ostia are formed by folds in the body wall of the sponge.
Where are choanocytes located in sponges?
Choanocytes are present at various locations, depending on the type of sponge, but they always line the inner portions of some space through which water flows (the spongocoel in simple sponges, canals within the body wall in more complex sponges, and chambers scattered throughout the body in the most complex sponges). Whereas pinacocytes line the outside of the sponge, choanocytes tend to line certain inner portions of the sponge body that surrounds the mesohyl.
Which group of protists are choanocytes similar to and what is the significance?
Choanocytes and choanoflagellates are similar in appearance, which suggests that sponges and choanoflagellates are closely related and likely share a recent common ancestry.
Where are choanocytes embedded within sponges?
The cell body is embedded in mesohyl and contains all organelles required for normal cell function, but protruding into the “open space” inside of the sponge is a mesh-like collar composed of microvilli with a single flagellum in the center of the column.
How do choanocytes facilitate water movement throughout a sponge?
The cumulative effect of the flagella from all choanocytes aids the movement of water through the sponge: drawing water into the sponge through the numerous ostia, into the spaces lined by choanocytes, and eventually out through the osculum (or osculi).
How do choanocytes facilitate feeding in sponges?
Food particles, including waterborne bacteria and algae, are trapped by the sieve-like collar of the choanocytes, slide down into the body of the cell, are ingested by phagocytosis, and become encased in a food vacuole.
How do choanocytes facilitate sexual reproduction in sponges?
Choanocytes will differentiate into sperm for sexual reproduction, where they will become dislodged from the mesohyl and leave the sponge with expelled water through the osculum.
What are the two crucial cells in sponges?
Choanocytes and amoebocytes.
How did amoebocytes get their name?
They are named for the fact that they move throughout the mesohyl in an amoeba-like fashion.
What are some of the functions of amoebocytes?
Delivering nutrients from choanocytes to other cells within the sponge, giving rise to eggs for sexual reproduction (which remain in the mesohyl), delivering phagocytized sperm from choanocytes to eggs, and differentiating into more-specific cell types.
What are some of the specific cell types that amoebocytes differentiate into?
Collencytes and lophocytes, which produce the collagen-like protein to maintain the mesohyl, sclerocytes, which produce spicules in some sponges, and spongocytes, which produce the protein spongin in the majority of sponges. These cells produce collagen to maintain the consistency of the mesohyl.
Why are spicules found in the mesohyl of sponges?
In some sponges, sclerocytes secrete small spicules into the mesohyl, which are composed of either calcium carbonate or silica, depending on the type of sponge. These spicules serve to provide additional stiffness to the body of the sponge. Additionally, spicules, when present externally, may ward off predators.
How is the presence and composition of spicules and spongin used to classify sponges?
Class Calcarea contains calcium carbonate spicules and no spongin, class Hexactinellida contains six-rayed siliceous spicules and no spongin, and class Demospongia contains spongin and may or may not have spicules; if present, those spicules are siliceous. Spicules are most conspicuously present in class Hexactinellida, the order consisting of glass sponges.
What is an example of large spicules?
Some of the spicules may attain giant proportions (in relation to the typical size range of glass sponges of 3 to 10 mm) as seen in Monorhaphis chuni, which grows up to 3 m long.
What are some example species of the three classes of sponges?
Clathrina clathrus belongs to class Calcarea, Staurocalyptus spp. belongs to class Hexactinellida, and Acarnus erithacus belongs to class Demospongia.
How do sponges perform digestion?
Their food is trapped when water passes through the ostia and out through the osculum. Bacteria smaller than 0.5 microns in size are trapped by choanocytes, which are the principal cells engaged in nutrition, and are ingested by phagocytosis. Particles that are larger than the ostia may be phagocytized by pinacocytes. In some sponges, amoebocytes transport food from cells that have ingested food particles to those that do not. For this type of digestion, in which food particles are digested within individual cells, the sponge draws water through diffusion. The limit of this type of digestion is that food particles must be smaller than individual cells.
How is diffusion used in sponges?
Several major body functions in sponges (gas exchange, circulation, excretion) are performed by diffusion between the cells that line the openings within the sponge and the water that is passing through those openings. All cell types within the sponge obtain oxygen from water through diffusion. Likewise, carbon dioxide is released into seawater by diffusion. In addition, nitrogenous waste produced as a byproduct of protein metabolism is excreted via diffusion by individual cells into the water as it passes through the sponge.
What is sponge fragmentation?
Where a piece of sponge breaks off, settles on a new substrate, and develops into a new individual.
What is sponge budding?
Where a genetically identical outgrowth grows from the parent and eventually detaches or remains attached to form a colony.
What are the modes of asexual reproduction in sponges?
Fragmentation, budding, and the formation of gemmules.
What are gemmules made of?
In gemmules, an inner layer of amoebocytes is surrounded by a layer of collagen (spongin) that may be reinforced by spicules. The collagen that is normally found in the mesohyl becomes the outer protective layer.
Why are gemmules useful?
In freshwater sponges, gemmules may survive hostile environmental conditions like changes in temperature and serve to recolonize the habitat once environmental conditions stabilize. Gemmules are capable of attaching to a substratum and generating a new sponge. Since gemmules can withstand harsh environments, are resistant to desiccation and remain dormant for long periods, they are an excellent means of colonization for a sessile organism.
Are sponges monoecious or dioecious?
Sponges are monoecious (hermaphroditic), which means that one individual can produce both gametes (eggs and sperm) simultaneously.
When does gamete production occur in sponges?
In some sponges, production of gametes may occur throughout the year, whereas other sponges may show sexual cycles depending on water temperature. Sponges may also become sequentially hermaphroditic, producing oocytes first and spermatozoa later.
How do oocytes and spermatozoa arise in sponges?
Oocytes arise by the differentiation of amoebocytes and are retained within the spongocoel, whereas spermatozoa result from the differentiation of choanocytes and are ejected via the osculum.
How do spermatozoa reach the oocytes of other sponges?
Ejection of spermatozoa may be a timed and coordinated event, as seen in certain species. Spermatozoa carried along by water currents can fertilize the oocytes borne in the mesohyl of other sponges.
Where are sponge larvae found?
Early larval development occurs within the sponge, and free swimming larvae are then released via the osculum.
Are adult sponges motile?
Sponges are generally sessile as adults and spend their lives attached to a fixed substratum. They do not show movement over large distances like other free-swimming marine invertebrates. However, sponge cells are capable of creeping along substrata via organizational plasticity. Under experimental conditions, researchers have shown that sponge cells spread on a physical support demonstrate a leading edge for directed movement. It has been speculated that this localized creeping movement may help sponges adjust to microenvironments near the point of attachment. It must be noted, however, that this pattern of movement has been documented in laboratories, but it remains to be observed in natural sponge habitats.
What is Cnidaria?
A phylum of animals that are diploblastic and have radial symmetry.
What is a cnidocyte?
A specialized stinging cell found in cnidarians.
What is the epidermis?
The outer layer (from ectoderm) that lines the outside of the animal.
What is extracellular digestion?
When food is taken into the gastrovascular cavity, enzymes are secreted into the cavity, and the cells lining the cavity absorb nutrients.
What is the gastrodermis?
The inner layer (from endoderm) that lines the digestive cavity.
What is a gastrovascular cavity?
An opening that serves as both a mouth and an anus, which is termed an incomplete digestive system.
What is a medusa?
A free-floating cnidarian body plan with mouth on underside and tentacles hanging down from a bell.
What is the mesoglea?
The non-living, gel-like matrix present between ectoderm and endoderm in cnidarians.
What is a nematocyst?
A harpoon-like organelle within a cnidocyte with pointed projectile and poison to stun and entangle prey.
What is a polyp?
A stalk-like sessile life form of cnidarians with mouth and tentacles facing upward, usually sessile but may be able to glide along surfaces.
What does it mean to be polymorphic?
Possessing multiple body plans within the lifecycle of a group of organisms.
What percentage of cnidarians are marine species?
Nearly all, about 99%.
How do cnidarians use toxins?
Cnidarians contain specialized cells known as cnidocytes containing organelles called nematocysts. These cells are present around the mouth and tentacles, and serve to immobilize prey with toxins contained within the cells. Nematocysts contain coiled threads that may bear barbs. The outer wall of the cell has hairlike projections called cnidocils, which are sensitive to touch. When touched, the cells are known to fire coiled threads that can either penetrate the flesh of the prey or predators of cnidarians or ensnare it. These coiled threads release toxins into the target and can often immobilize prey or scare away predators.
What are the two body plans of Cnidaria?
Polyp (or “stalk”) and medusa (or “bell”).
What is an example of each cnidarian body plan type?
An example of the polyp form is Hydra spp.; perhaps the most well-known medusoid animals are the jellies (jellyfish).
How motile are the cnidarian body plans and where are their oral sides oriented?
Polyp forms are sessile as adults, with a single opening to the digestive system (the mouth) facing up with tentacles surrounding it. Medusa forms are motile, with the mouth and tentacles hanging down from an umbrella-shaped bell.
What is an example of a polymorphic cnidarian?
The colonial hybrid called an Obelia.
What are the two types of sessile polyps in Obelia?
The first is the gastrozooid, which is adapted for capturing prey and feeding; the other type of polyp is the gonozooid, adapted for the asexual budding of medusa.
How do gonozooids produce new polyps?
When the reproductive buds of gonozooids mature, they break off and become free-swimming medusae, which are dioecious (either male or female). The male medusa makes sperm, and the female medusa makes eggs. After fertilization, the zygote develops into a blastula, which develops into a planula larva. The larva is free swimming for a while, but eventually attaches and a new colonial reproductive polyp is formed.
What are the membrane layers of cnidarians?
All cnidarians show the presence of two membrane layers in the body that are derived from the endoderm and ectoderm of the embryo. The outer layer (from ectoderm) is called the epidermis and lines the outside of the animal, whereas the inner layer (from endoderm) is called the gastrodermis and lines the digestive cavity. Between the two membrane layers is a non-living, jelly-like mesoglea connective layer.
How complex is the anatomy of cnidarians, in terms of tissues and organs?
In terms of cellular complexity, cnidarians show the presence of differentiated cell types in each tissue layer, such as nerve cells, contractile epithelial cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as the presence of intercellular connections. However, the development of organs or organ systems is not advanced in this phylum.
How is the cnidarian nervous system organized?
The nervous system is primitive, with nerve cells scattered across the body. This nerve net may show the presence of groups of cells in the form of nerve plexuses or nerve cords. The nerve cells show mixed characteristics of motor as well as sensory neurons. The predominant signaling molecules in these primitive nervous systems are chemical peptides, which perform both excitatory and inhibitory functions. Despite the simplicity of the nervous system, it coordinates the movement of tentacles, the drawing of captured prey to the mouth, the digestion of food, and the expulsion of waste.
How do cnidarians perform digestion?
The cnidarians perform extracellular digestion in a gastrovascular cavity.
How is gas exchange and circulation in cnidarians performed?
Cnidarian cells exchange oxygen and carbon dioxide by diffusion between cells in the epidermis with water in the environment, and between cells in the gastrodermis with water in the gastrovascular cavity. The lack of a circulatory system to move dissolved gases limits the thickness of the body wall and necessitates a non-living mesoglea between the layers. There is no excretory system or organs, and nitrogenous wastes simply diffuse from the cells into the water outside the animal or in the gastrovascular cavity. Because there is no circulatory system, nutrients must move from the cells that absorb them in the lining of the gastrovascular cavity through the mesoglea to other cells.
How many species of Cnidaria are there?
The phylum Cnidaria contains about 10,000 described species.
What are the classes of Cnidaria?
Anthozoa, Scyphozoa, Cubozoa, and Hydrozoa.
Which cnidarians are included in the class Anthozoa?
The class Anthozoa includes all cnidarians that exhibit a polyp body plan only; in other words, there is no medusa stage within their life cycle.
What are some motile and non-motile examples of the cnidarian classes?
The anthozoans (sea anemones and corals) are all sessile species, whereas the scyphozoans (jellyfish) and cubozoans (box jellies) are swimming forms. The hydrozoans contain sessile forms and swimming colonial forms like the Portuguese man o’ war.
What are some examples of anthozoans?
Sea anemones, sea pens, and corals.
How many species of anthozoans are there?
There is an estimated number of 6100 described species.
What are some morphological characteristics of sea anemones?
Sea anemones are usually brightly colored and can attain a size of 1.8 to 10 cm in diameter. These animals are usually cylindrical in shape and are attached to a substrate. A mouth opening is surrounded by tentacles bearing cnidocytes.
How is the mouth of a sea anemone linked to the gastrovascular cavity?
The mouth of a sea anemone is surrounded by tentacles that bear cnidocytes. The slit-like mouth opening and pharynx are lined by a groove called a siphonophore. The pharynx is the muscular part of the digestive system that serves to ingest as well as egest food, and may extend for up to ⅔ the length of the body before opening into the gastrovascular cavity.
How is the gastrovascular cavity of sea anemones divided?
The gastrovascular cavity of sea anemones is divided into several chambers by longitudinal septa called mesenteries. Each mesentery consists of one ectodermal and one endodermal cell layer with the mesoglea sandwiched in between. Mesenteries do not divide the gastrovascular cavity completely, and the smaller cavities coalesce at the pharyngeal opening. The adaptive benefit of the mesenteries appears to be an increase in surface area for absorption of nutrients and gas exchange.
What do anemones feed on?
Sea anemones feed on small fish and shrimp, usually by immobilizing their prey using the cnidocytes.
How do sea anemones establish mutualistic relationships with hermit crabs?
Some sea anemones establish a mutualistic relationship with hermit crabs by attaching to the crab’s shell. In this relationship, the anemone gets food particles from prey caught by the crab, and the crab is protected from the predators by the stinging cells of the anemone.
How are clownfish able to establish mutualistic relationships with sea anemones?
Anemone fish, or clownfish, are able to live in the anemone since they are immune to the toxins contained within the nematocysts.
How do anthozoans reproduce?
Anthozoans remain polypoid throughout their lives and can reproduce asexually by budding or fragmentation, or sexually by producing gametes. Both gametes are produced by the polyp, which can fuse to give rise to a free-swimming planula larva. The larva settles on a suitable substratum and develops into a sessile polyp.
Which cnidarians are in the class Scyphozoa?
Class Scyphozoa includes all the jellies and is exclusively a marine class of animals.
How many species of Scyphozoa are there?
Class Scyphozoa includes about 200 known species
Which body plan type is found in scyphozoans?
The defining characteristic of this class is that the medusa is the prominent stage in the life cycle, although there is a polyp stage present. Scyphozoans display a characteristic bell-like morphology.
How large are scyphozoans?
Members can range from 2 to 40 cm in length but the largest scyphozoan species, Cyanea capillata, can reach a size of 2 m across.
How are the body plans of jellies organized?
In the jellyfish, a mouth opening is present on the underside of the animal, surrounded by tentacles bearing nematocysts. Scyphozoans live most of their life cycle as free-swimming, solitary carnivores. The mouth leads to the gastrovascular cavity, which may be sectioned into four interconnected sacs, called diverticuli. In some species, the digestive system may be further branched into radial canals. Like the septa in anthozoans, the branched gastrovascular cells serve two functions: to increase the surface area for nutrient absorption and diffusion; thus, more cells are in direct contact with the nutrients in the gastrovascular cavity.
Where is the nervous system found in scyphozoans?
Nerve cells are scattered all over the body. Neurons may even be present in clusters called rhopalia.
Which muscles do scyphozoans use to swim?
They possess a ring of muscles lining the dome of the body, which provides the contractile force required to swim through water.
How do scyphozoans reproduce?
Scyphozoans are dioecious animals with separate sexes. The gonads are formed from the gastrodermis and gametes are expelled through the mouth. Planula larvae are formed by external fertilization; they settle on a substratum in a polypoid form known as scyphistoma. These forms may produce additional polyps by budding or may transform into the medusoid form. The life cycle of these animals can be described as polymorphic, because they exhibit both a medusal and polypoid body plan at some point in their life cycle.
Which cnidarians are in the class Cubozoa?
This class includes jellies that have a box-shaped medusa, or a bell that is square in cross-section; hence, are colloquially known as “box jellyfish”.
How large are cubozoans?
They may achieve sizes of 15 to 25 cm.
Besides their bell, how do cubozoans differ from scyphozoans?
Cubozoans display overall morphological and anatomical characteristics that are similar to those of the scyphozoans. A prominent difference between the two classes is the arrangement of tentacles. This is the most venomous group of all the cnidarians.
What are some characteristics of cubozoan body plans?
The cubozoans contain muscular pads called pedalia at the corners of the square bell canopy, with one or more tentacles attached to each pedalium. These animals are further classified into orders based on the presence of single or multiple tentacles per pedalium. In some cases, the digestive system may extend into the pedalia. Nematocysts may be arranged in a spiral configuration along the tentacles; this arrangement helps to effectively subdue and capture prey.
What forms do cubozoans take?
Cubozoans exist in a polypoid form that develops from a planula larva. These polyps show limited mobility along the substratum and, like scyphozoans, may bud to form more polyps to colonize a habitat. Polyp forms then transform into the medusoid forms.
What is Malo kingi?
A tiny cubozoan jelly which is thimble-shaped and, like all cubozoan jellies, has four muscular pedalia to which the tentacles attach. M. kingi is one of two species of jellies known to cause Irukandji syndrome, a condition characterized by excruciating muscle pain, vomiting, increased heart rate, and psychological symptoms.
How many species of hydrozoans are there?
Hydrozoa includes nearly 3200 species; most are marine, although some freshwater species are known.
Which body plan types are found in hydrozoans?
Animals in this class are polymorphs, and most exhibit both polypoid and medusoid forms in their lifecycle, although this is variable.
How is the body plan of the hydrozoan polyp form organized?
The polyp form in these animals often shows a cylindrical morphology with a central gastrovascular cavity lined by the gastrodermis. The gastrodermis and epidermis have a simple layer of mesoglea sandwiched between them. A mouth opening, surrounded by tentacles, is present at the oral end of the animal.
What are some examples of colonial hydrozoans?
Many hydrozoans form colonies that are composed of a branched colony of specialized polyps that share a gastrovascular cavity, such as in the colonial hydroid Obelia. Colonies may also be free-floating and contain medusoid and polypoid individuals in the colony as in Physalia (the Portuguese man o’ war) or Velella (by-the-wind sailor).
What are some examples of solitary hydrozoans?
Members of Hydra are solitary polyps and members of Gonionemus are solitary medusae.
What is the distinguishing characteristic of hydrozoans?
The true characteristic shared by all the diverse species of hydrozoans is that their gonads for sexual reproduction are derived from epidermal tissue, whereas in all other cnidarians they are derived from gastrodermal tissue.
What is Annelida?
A phylum of vermiform animals with metamerism.
What is a captacula?
A tentacle-like projection that is present in tusk shells to catch prey.
What is a clitellum?
A specialized band of fused segments, which aids in reproduction.
What is a conispiral?
Shell shape coiled around a horizontal axis.
What is a corona?
A wheel-like structure on the anterior portion of the rotifer that contains cilia and moves food and water toward the mouth.
What is a ctenidium?
A specialized gill structure in mollusks.
What is a mantle?
A specialized epidermis that encloses all visceral organs and secretes shells. AKA pallium.
What is a mastax?
A jawed pharynx unique to the rotifers.
What is metamerism?
A series of body structures that are similar internally and externally, such as segments.
What is Mollusca?
A phylum of protostomes with soft bodies and no segmentation.
What is nacre?
A calcareous secretion produced by bivalves to line the inner side of shells as well as to coat intruding particulate matter.
What is Nemertea?
A phylum of dorsoventrally flattened protostomes known as ribbon worms.
What is a parapodium?
A fleshy, flat appendage that protrudes in pairs from each segment of polychaetes.
What is a pilidium?
A larval form found in some nemertine species.
What does it mean to be planospiral?
A shell shape coiled around a vertical axis.
What is a planuliform?
A larval form found in phylum Nemertea.
What is a radula?
A tongue-like organ with chitinous ornamentation.
What is a rhynchocoel?
A cavity present above the mouth that houses the proboscis.
What is a schizocoelom?
A coelom formed by groups of cells that split from the endodermal layer.
What is a seta/chaeta?
A chitinous projection from the cuticle.
What is a trochophore?
The first of the two larval stages in mollusks.
What is a veliger?
The second of the two larval stages in mollusks.
What are some characteristics of embryonic development in lophotrochozoans?
Animals belonging to the superphylum Lophotrochozoa are protostomes and have schizocoeloms.
How do schizocoeloms develop?
In protostomy, solid groups of cells split from the endoderm or inner germ layer to form a central mesodermal layer of cells. This layer multiplies into a band and then splits internally to form the coelom; this protostomic coelom is hence termed schizocoelom.
What characteristics distinguish lophotrochozoans?
As lophotrochozoans, the organisms in this superphylum possess either a lophophore or trochophore larvae. The lophophores include groups that are united by the presence of the lophophore, a set of ciliated tentacles surrounding the mouth. Trochophore larvae are characterized by two bands of cilia around the body.
What are some examples of lophophorates?
Lophophorata include the flatworms and several other phyla.
