A

abscess:

a localized accumulation of products of inflammation. Photo

acanthella:

an acanthocephalan larval stage between an acanthor and a cystacanth. Photo

acanthor:

the acanthocephalan larval stage that hatches from the egg. Photo

acetabulum:

a sucker not surrounding a mouth. Photo

acraspedote:

a cestode proglottid that does not overlap the one posterior to it. Photo

allergic reaction:

secondary immune response to an environmental allergen.

adeagus:

chitinized spear-like structure in male Anoplura.

adult:

general term for a developmental stage capable of producing gametes.

ala:

lateral expansions of the cuticle of nematodes.

amastigote:

a form of Trypanosomatidae with a short flagellum. Photo

amoeboid:

irregular and changeable in shape; movement by extension of pseudopodia. Photo

apical complex:

a structure in merozoites and sporozites of Apicomplexa, comprising a polar ring, conoid, and rhoptries, that aids penetration of host cells.

amphistome:

a fluke with the ventral sucker located at the posterior end of the body. Photo

anapolytic:

a cestode proglottid that does not detach from the strobila.

anchor:

any unusually large, hard, recurved structure used to aid attachment. Photo

apolysis:

detachment of a tapeworm proglottid.

aporal:

located on the side of the body opposite to the genital pore. Photo

appendix:

a blind-ending offshoot of the digestive tract.

armed:

possessing spines, hooks, or other hardened structures. Photo

asexual:

a form of reproduction not involving the fusion of gametes

autoinfection:

for parasites that normally transmit from host to host by a free-living stage, the rapid development and establishement of a parasite in the same host individual from which it originated.

axostyle:

a tube-like organelle in some flagellate protozoans. Photo

B

a centriole from which an axoneme arises. Photo

binary fission:

a mode of reproduction of unicellular organisms in which internal organelles are duplicated and then cytokinesis takes place.

bladder larva:

in Cestoda, a larval form in which one or more scoleces develop in a fluid-filled cyst. Photo

blood loss:

significant loss of blood as a result of a disease process, either through hemorrhage or ingestion.

bothridium:

a muscular projection of the side of the scolex of some tapeworms. Photo

bothrium:

a muscular longitudinal groove on the scolex of some tapeworms. Photo

brood capsule:

a capsule developing within a hydatid cyst, lined with germinal epithelium and capable of asexual production of protoscoleces. Photo

buccal capsule:

the lining of the oral cavity. Photo

bulla:

a non-living structure used for attachment. Photo

bursa:

an external male copulatory appendage, used to grip the female during mating. Photo

C

capitulum:

the region of the mouthparts in a tick. Photo

carapace:

a dorsal shield. Photo

caudal:

pertaining to the tail or posterior region.

cecum:

a blind-ending pouch leading off of an intestine. Photo

cement gland:

glands in male Acanthocephala whose secretions form a copulatory plug on the female. Photo

cement reservoir:

receptacle for secretions of the acanthocephalan cement gland. Photo

cephalic:

pertaining to the head or anterior end.

cephalothorax:

a body region formed by fusion of the head and thorax. Photo

cercaria:

a free-living larval stage of Digenea, usually possessing a tail. Photo

cercomer:

a vestigial structure formed on larval Cestoda, containing the embryonic hooks. Photo

cervical:

pertaining to the head or anterior end.

chalimus:

a late copepodid stage of some parasitic Copepoda, that possesses a filament used for anchoring.

chelicera:

the piercing mouthparts of Arachnida.

chemotaxis:

directed movement with respect to a chemical gradient.

chitin:

a tough, high molecular weight polymer used in construction of body parts of some invertebrates.

cilium:

motile, short, cylindrical organelle containing a longitudinal bundle of microtubules and surrounded by a plasma membrane; usually present in large numbers. Photo

cirrus:

the copulatory organ of Platyhelminthes. Photo

cirrus pouch:

an internal sac surrounding the terminal male genitalia of Platyhelminthes. Photo

clamp:

a complex set of sclerotized bars forming a pinching organ. Photo

cloaca:

an internal chamber containing the outlets of the digestive and urogenital systems.

coccidia:

general term applied to apicomplexan parasites which transmit by oocysts passed in the feces.

coenurus:

a bladder larva of Cestoda from which several scoleces bud from the internal germinative epithelium.

Colorado tick fever:

a viral disease causing fever and muscle pains.

compact vitellarium:

vitelline glands coalesced into a single mass. Photo

copepodid:

a larval stage of Copepoda, between nauplius and adult.

copulatory bursa:

an external male copulatory appendage, used to grip the female during mating. Photo

coracidium:

a cestode oncosphere enclosed within a ciliated membrane and capable of swimming. Photo

cosmopolitan:

a more-or-less worldwide geographic distribution.

craspedote:

a cestode proglottid that partially overlaps the one posterior to it. Photo

cryptozoite:

a schizont of Plasmodium spp. that develops outside of the circulatory system. Photo

cuticle:

the non-living body covering of Nematoda and Arthropoda.

cyst:

general term for a membranous envelope of parasite origin, usually enclosing a larval parasite. Also, the parasite-envelope combination. Photo

cystacanth:

the larval stage of Acanthocephala that precedes the adult; it is usually encysted. Photo

cysticercoid:

a solid-bodied larva of Cestoda. Photo

cysticercus:

a bladder larva of cestoda from which a single scolex buds internally. Photo

cystogenous gland:

gland producing secretions which form a cyst around a parasite.

cytokinesis:

the separation of a single cell into two or more.

cytoplasm:

the internal contents of a cell excluding the nucleus.

D

daughter sporocyst:

a larval stage of Digenea produced by a mother sporocyst; it lacks a gut and is capable of asexual production of either rediae or cercariae.

daughter redia:

a larval stage of Digenea produced by a mother redia; it possesses a gut and produces cercariae asexually.

definitive host:

a host in which the adult stage of a parasite lives.

deirid:

specialized cervical papilla.

dendritic:

highly branched. Photo

dermatitis:

inflammation of the skin.

diagonal:

one located anterior and to the side of another. Photo

dioecious:

possessing separate sexes. Photo

diplostomulum:

a type of metacercaria in some Strigeiformes characterized by an oval shape with anterolateral pseudosuckers, living unencysted in host tissue. Photo

direct life cycle:

a life cycle involving only one host.

diverticulate:

taking the form of a branching pattern. Photo

diverticulum:

a lateral, often branched, offshoot of part of the digestive system; often present in large numbers. Photo

E

ecdysis:

molting of a cuticle.

ectoparasite:

a parasite that lives on the outer surface of a host. Photo

edema:

accumulation of excess fluids in the tissues.

egg:

a series of protective membranes enclosing a zygote and any subsequent developmental stages until their emergence from the membranes. Photo

ejaculatory duct:

in Nematoda and Acanthocephala, the terminal portion of the male reproductive system which connects to the cloaca and expels spermatozoa during copulation. Photo

embryonated:

an egg containing a fully-developed embryo. Photo

embryonation:

the processes of development of an embryo from a fertilized egg.

encapsulation:

the formation of a capsule of host tissue around a parasite as a host defense response.

encystment:

secretion of a cyst wall by a parasite around itself.

endosome:

RNA rich structure within the nucleus of some Protozoa. Photo

engorged:

possessing a swollen body after taking a blood meal. Photo

ensheathed:

a nematode larva which retains the cuticle from a previous molt. Photo

epimastigote:

a form of Trypanosomatidae with the flagellum arising anterior to the nucleus, and possessing an undulating membrane.

erythrocytic cycle:

the later part of the life cycle of malarial organisms in which erythrocytes of the vertebrate host are involved. Photo

esophagus:

the muscular or glandular portion of the digestive tract between the mouth and stomach or intestine.

excretory vesicle:

a bladder into which the excretory ducts empty.

exflagellation:

the release of microgamete from a microgametocyte of malarial organisms. Photo

exoerythrocytic cycle:

the first part of the life cycle of malarial organisms in which tissues of the vertebrate host other than the blood are involved. Photo

extracellular:

located outside of host cells, in tissues or in body cavities.

F

fecal smear:

a diagnostic technique in which a sample of feces is spread thinly on a glass slide, stained and examined microsopically for parasites.

festoon:

rectangular areas separated by grooves along the posterior dorsal margin of ticks. Photo

filariform:

possessing a simple, tubular esophagus.

fixation artifact:

any change in the structure of an organism induced during its preservation or other processing; used all too often as the basis for describing new species.

flagellum:

motile, long, cylindrical organelle containing a longitudinal bundle of microtubules and surrounded by a plasma membrane; usually present singly or in small numbers. Photo

fluke:

common name for Digenea and Monogenea. Photo

follicular vitellaria:

vitelline glands present as small follicles dispersed throughout the body, connected by a system of ducts. Photo

furca:

an external, sclerotized, forked structure used for attachment.

furcocercous:

a cercaria possessing a forked tail. Photo

G

gamete:

a mature reproductive cell, usually haploid, which fuses with another gamete of the opposite sex to form a diploid zygote.

fork-tailed.

gametocyte:

the sexual stage of Sporozoa. Photo

gametogony:

cell division resulting in the formation of gametes.

ganglion:

an assemblage of nerve cell bodies.

genital pore:

the common external opening of the male and female reproductive systems.

genital atrium:

an external depression (usually) containing the genital pore. Photo

genital primordium:

a small collection of cells in a larval organism from which the reproductive tract will develop.

germinal epithelium:

a cell layer capable of giving rise asexually to new individuals.

giant nucleus:

macroscopic nuclei in the body wall of some Acanthocephala. Photo

gnathosoma:

the body region containing the mouthparts.

gonopod:

appendages surrounding the genital opening of female Anoplura. Photo

granuloma:

a site of inflammatory cell reaction at a site of infection. Photo

gravid:

containing fully developed eggs.

gravid proglottid:

a proglottid containing a uterus with fully developed eggs and in which other components of the male and female reproductive systems have fully or partially degenerated. Photo

gross pathology:

macroscopic abnormalities in structure caused by external agents or disease, and their study. Photo

gubernaculum:

a sclerotized structure on the dorsal wall of the cloaca of Nematoda, used to support the spicules.

gynecophoric canal:

a ventral longitudinal groove in the surface of male Schistosomatidae. Photo

H

Haller's organ:

an oval organ on the tarsus of ticks. Photo

haemorrhage:

discharge of blood from blood vessels. Photo

hair loss:

significant loss of hair resulting directly or indirectly from a disease process. Photo

hamulus:

large hooks on the opisthaptor of Monogenea. Photo

hemimetabolous:

developmental pattern in Insecta, in which a series of nymphal stages are produced.

hermaphrodite:

an individual possessing male and female reproductive systems (not necessarily simultaneously). Photo

heteroxenous:

a life cycle in which more than one host individual is parasitized.

hexacanth:

a six-hooked embryo of cestoda. Photo

histopathology:

microscopic abnormalities in cell and tissue structure caused by external agents or disease, and their study. Photo

holometabolous:

developmental pattern in Insecta, involving larva and pupa.

homoxenous:

a life cycle in which only one host is parasitized.

hook:

a hard, curved structure, usually of complex shape, used for attachment of parasite to host. Photo

host specificity:

the degree to which a parasite is capable of infecting and developing within only a limited number of host species.

hyaline:

clear and acellular. Photo

hydatid:

a bladder larva of Cestoda characterized by internal (and often external) chambers lined by germinal epithelium. Photo

hydrostatic skeleton:

a skeletal system in which support is derived by internal fluid pressure.

hypostome:

sclerotized, median, ventral mouthparts of ticks, often with recurved teeth used for attachment. Photo

I

immature proglottid:

body segment of Cestoda containing only rudiments of the genital organs. Photo

indirect life cycle:

A life cycle in which at least one of the larval stages is parasitic, in a different host than the adult.

inflammation:

a local response to cellular injury that can include capillary dilation, leucocytic infiltration, redness, heat and pain. Photo

intercellular:

present in tissues, in the spaces between cells. Photo

intermediate host:

a required host infected by a larval parasite. Where more than one intermediate host is required, they are numbered in sequence as first, second, etc.

internal seminal vesicle:

an expansion of the vas deferens within the cirrus pouch to store sperm prior to copulation.

intracellular:

present within cells. Photo

invaginate:

to retract an organ, turning it inside-out in the process. Photo

irritant:

any agent that induces an inflammation.

J

J1-J4

first through fourth juvenile, or larval, stages of nematodes

juvenile:

an immature individual, often resembling the adult but lacking fully-developed reproductive organs.

K

karyosome:

large nuceolar bodies in the centre of nuclei of some Protozoa.

kinetoplast:

a conspicuous part of the mitochondrion of Trypanosomatidae.

kinetosome:

a centriole from which an axoneme arises.

L

L1 - L4:

first through fourth larval stages of nematodes.

lacuna:

a canal within the tegument of Acanthocephala. Photo

lacunar system:

a ladder-like network of lacunae.

larva:

general term for any life cycle stage between egg and adult. In insects it is he stage which hatches from the egg.

larviparous:

producing eggs which hatch within the female and emerge as larvae.

Laurer's canal:

a blind canal terminating at the base of the seminal receptacle in Digenea; possibly a vestigial vagina.

lemniscus:

paired structure attached to the inner, posterior part of the neck of Acanthocephala. Photo

lesion:

physically damaged area of host tissue caused by a foreign agent.

ligament sac:

one or two thin sacs arising at the base of the proboscis receptacle of Acanthocephala and extending to near the genital pore; the reproductive organs are enclosed. Photo

lip:

a fleshy projection around the oral opening of nematodes. Photo

lobate:

having a lobed structure, or with an irregular margin suggestive of the presence of separate lobes. Photo

loculus:

a sucker-like depression. Photo

lycophore:

ciliated, 10-hooked larva of Cestodaria.

M

macrogamete:

a female gamete.

macrogametocyte:

the cell producing a female gamete.

macronucleus:

the larger of two types of nucleus found in Ciliata, mainly concerned with daily activities such as feeding and maintenance. Photo

mammilae:

ornamental surface projections.

mandible:

one of the paired mouthparts of Arthropoda. Photo

mange:

disease characterized by hair loss and crusted exudates resulting from mite infestation.

marginal hooklet:

a small hook, usually occurring in large numbers around the periphery of a complex attachment organ. Photo

mature proglottid:

body segment of Cestoda containing functional male and female reproductive organs. Photo

maxilla:

one of the paired mouthparts of Arthropoda.

maxilliped:

one of the paired head appendages of Crustacea.

Mehli's gland:

unicellular glands surrounding the ootype of Platyhelminthes. Photo

merozoite:

a daughter cell resulting from schizogony. Photo

mesocercaria:

unencysted larval form between cercaria and metacercaria; only in Alaria.

metacercaria:

last larval form of Digenea; usually encysted. Photo

metacestode:

a larval cestode that is infective to the definitive host.

metacryptozoite:

a merozoite developed from a cryptozoite.

metacyclic trypanosome:

stumpy trypomastigote lacking a free flagellum that is found in vector and is infective to the vertebrate host.

metamerism:

division of the body into a succession of similar or identical segments. Photo

metamorphosis:

a morphological transformation into a fundamentally different form.

microfilaria:

a poorly differentiated first stage larva released by some nematodes into the bloodstream of their host. Photo

microgamete:

a male gamete.

microgametocyte:

the cell producing the male gametes.

micronucleus:

the smaller of two types of nuclei found in Ciliata, mainly concerned with reproduction.

miracidium:

the ciliated larva of Digenea that hatches from the egg. Photo

mitochondrion:

compartmentalized, membranous organelle containing enzyme systems for energy metabolism.

monostome:

a fluke lacking a ventral sucker.

monoxenous:

a life cycle in which only a single host is used.

monozoic:

possessing one set of reproductive organs. Photo

mother sporocyst:

a larval stage of Digenea formed after penetration of the miracidium into a mollusc; it lacks a gut and gives rise asexually to daughter sporocysts or rediae.

mother redia:

a larval stage of Digenea formed after penetration of a miracidium into a mollusc, or produced by a mother sporocyst; it has a gut and produces daughter redia asexually.

multilocular hydatid:

a hydatid cyst with a thin, external cyst wall and asexually budding in internal brood capsules as well as externally-budding brood capsules.

myzorhynchus:

central, muscular projection on the scolex of Tetraphyllidea. Photo

N

nauplius:

a larval stage of Copepoda that hatches from the egg.

neascus:

a type of metacercaria of Strigeiformes in which there is a thin, loose-fitting cyst wall.

neck:

in Cestoda, a region of active cell division immediately posterior to the scolex, from which new proglottids are formed; in Acanthocephala, the region between the most posterior hook of the proboscis and the proboscis sheath. Photo

neotenic:

attainment of sexual maturity in a life cycle stage otherwise possessing larval characteristics.

nit:

common term for the egg of a sucking louse. Photo

nucleus:

membrane bound organelle containing the cell's DNA. Photo

nymph:

a larval stage of Arthropoda that resembles the adult.

O

oncomiracidium:

the ciliated larva of Monogenea that hatches from the egg.

oncosphere:

the six-hooked embryo that develops within the egg of Cestoda.

one-host tick:

a tick that attaches to one host as a larva, and stays on that host until development is complete and mating has occurred.

oocyst:

a cyst containing sporozoites in the Apicomplexa. Photo

ookinete:

the motile zygote of malarial organisms.

ootype:

the region of the female reproductive system in Platyhelminthes that is surrounded by Mehli's gland and receives ducts from the vitellaria and seminal receptacle. Photo

operculum:

a lid-like region on an egg that allows the larva to escape. Photo

opisthaptor:

posterior attachment organ on Monogenea. Photo

opposite:

located lateral to one another. Photo

ovarian ball:

fragments of ovary of Acanthocephala that float free in the body cavity until fertilization. Photo

ovary:

organ of female reproductive system that produces ova. Photo

oviduct:

a short duct that carries ova from the ovary to the ootype.

ovijector:

a muscular modification at the termination of the female reproductive tract of Nematoda that controls the release of eggs.

ovisac:

external appendage on female Crustacea in which eggs are brooded until they hatch. Photo

P

papilla:

an external projection of the cuticle or tegument. Photo

parabasal body:

a Golgi body connected by a filament to a kinetosome.

parasite:

an organism studied by parasitologists.

parasitemia:

a measure of the number of parasites present in the peripheral blood.

paratenic host:

a host in which a parasite survives, and can be transmitted to another host, but does not develop.

parenchyma:

cellular matrix within which the internal organs of Platyhelminthes are contained. Photo

parthenogenetic:

development of an unfertilized egg into a new individual.

pedipalp:

lateral jointed oral appendages on Arachnida. Photo

pedunculate:

occurring on a stalk. Photo

pellicle:

the thick, often sculptured external coat of many Protozoa.

penis:

organ of the male reproductive system used to introduce spermatozoa into the female reproductive tract.

pharynx:

muscular pumping organ at posterior of esophagus. Photo

phasmid:

a lateral sensory pit on the tail of some Nematoda.

phyllidea:

leaf-like lateral projections on the scolex of some Cestoda. Photo

plasma membrane:

the unit membrane enclosing the cytoplasm of a cell.

plerocercoid:

last larval form found in the second intermediate host of many Cestoda with aquatic life cycles. Photo

pleural plate:

chitinized regions on the sides of the abdomen of Insecta. Photo

polar:

located at one or both ends.

polyzoic:

possessing multiple sets of reproductive organs. Photo

poral:

located on the same side as the genital pore. Photo

presoma:

the proboscis, neck and supporting structures and organs in Acanthocephala.

proboscis:

a protrusible, armed attachment organ in Acanthocephala. Photo

proboscis sheath/receptacle:

a muscular sac ant the anterior end of Acanthocephala into which the proboscis may be withdrawn. Photo

procercoid:

larval form found in the first intermediate host of many Cestoda with aquatic life cycles. Photo

proglottid:

a single segment of strobila of Cestoda. Photo

prohaptor:

anterior attachment organ of Monogenea. Photo

progenesis:

precocious sexual development of an organism that is still morphologically at a juvenile stage.

promastigote:

a form of Trypanosomatidae with the flagellum arising anterior to the nucleus, and lacking an undulating membrane. Photo

prostate gland:

secretory structure located within the cirrus pouch of Digenea.

protandry:

in hermaphrodites, the development of the male reproductive system before the female system.

protoscolex:

the juvenile scolex formed by asexual budding within coenurus or hydatid larvae of Cestoda. Photo

pseudocoelomate:

possessing internal organs that float free within the coelom, not covered by a peritoneum.

pseudocyst:

an intracellular accumulation of protozoans causing enlargement of the host cell and giving the appearance of a cyst, but not surrounded by a cyst wall of parasite origin.

pseudopodium:

an extension of the body of Protozoa used for locomotion. Photo

pseudosucker:

a modification of the body surface that functions as a sucker but bears no morphological resemblance to one. Photo

pupa:

a life cycle stage in insects in which major morphological transformations from a worm-like larva to a winged adult occur.

pyriform:

tear-drop shaped. Photo

Q

Q fever:

a rickettsial disease transmitted by ticks and lice.

R

redia:

an intramolluscan stage of digeneans, possessing a gut. Photo

relapsing fever:

a bacterial disease characterized by repeated periods of fever and moderate mortality.

reticulocyte:

young erythrocytes that have recently lost their nucleus.

retroinfection:

a type of autoinfection whereby larval parasites just passed in the host's feces re-enter the anus and establish a new infection.

rhabditiform:

possessing an esophagus with a narrow central region and a terminal bulb. Photo

ring stage:

the young trophozoite of Plasmodium spp., so named because a large central vacuole and peripheral nucleus give it the appearance of a signet ring. Photo

Rocky Mountain spotted fever:

a rickettsial disease transmitted by ticks and characterized by an extensive rash.

rosette:

a posterior series of flaps, resembling the petals of a carnation, used as an organ of attachment by Gyrocotyle. Photo

rostellum:

a central protrusion, eversible or not, on the scolex of some Cestoda. Photo

S

Saefftigen's pouch:

a fluid-filled, muscular sac used to manipulate the copulatory bursa of male Acanthocephala.

schistosomule:

a migratory stage between cercaria and adult of the schistosomes; equivalent to the metacercarial stage in other digeneans.

schizogony:

a form of asexual reproduction characterized by multiple mitoses and cytokineses that form numerous daughter cells.

schizont:

a cell undergoing schizogony in which the cytokineses are not complete. Photo

Schuffner's dots:

stippling present on the membrane of erythrocytes infected with some species of Plasmodium, visible only under proper staining.

sclerite:

a hardened, curved structure usually supporting a clamp. Photo

sclerotized:

partially composed of sclerotin, a highly resistant and insoluble protein of arthropods and some other invertebrates.

scolex:

the attachment organ of Cestoda. Photo

scutum:

a dorsal plate covering the entire dorsal surface of some adult male ticks, and the anterior dorsal surface of nymphs and females.

secondary infection:

damage of host tissues by one species of parasite that enables entry of other species of pathogen.

seed tick:

a tick larva.

selector apparatus:

a collection of cells in the reproductive tract of female Acanthocephala that forms a series of channels capable of directing immature eggs back into the pseudocoele and passing mature eggs into the uterus. Photo

seminal receptacle:

organ of female genital system used to receive and store spermatozoa.

seminal vesicle:

a distal expansion of vas deferens.

serial polyembryony:

the development of zygotes within other zygotes.

sessile:

not elevated above the substrate on any sort of stalk.

seta:

fine external spine or hair. Photo

sexual:

reproduction involving the fusion of male and female gametes.

soma:

general term referring to the main body region excluding appendages.

spermatheca:

organ of female genital system used to receive and store sperm. Photo

spicule:

sclerotized rods, often of complex shape, present in the cloaca of male Nematoda and used to guide spermatozoa during copulation. Photo

spine:

a short, rigid external projection on the body, often used to aid attachment. Photo

spiracular plate:

lateral opening of the respiratory system of some Arthropoda. Photo

spore:

small, non-motile transmission stage containing a single infective organism; resistant to environmental conditions. Photo

sporoblast:

a cell that produces a spore.

sporocyst:

an early developmental stage capable of asexual reproduction:

in sporozoans it is usually enclosed within an oocyst; in digeneans it is an intramolluscan stage lacking a gut. Photo

sporogony:

multiple fission of a zygote that forms large numbers of sporozoites.

sporoplasm:

amoeboid transmission stage of Myxospora and Microspora. Photo

sporozoite:

a daughter cell resulting from sporogony within an oocyst. Photo

sporulation:

the process of forming spores or sporozoites. Photo

sternum:

the mid-ventral region.

stichosome:

a column of stichocytes that surround and secrete into the esophagus of Trichurata. Photo

stoma:

the region of the oral opening.

strobila:

the region of the body of Cestoda that is posterior to the neck, and is usually segmented. Photo

strobilocercus:

a type of cysticercus in which some segmentation is already evident.

stylet:

a short, sharp spine often used to aid penetration of a host.

subterminal:

occurring close to, but not at, an extremity.

sucker:

a (usually) circular structure with some mechanism to grip another surface within its margins. Photo

sucking disk:

shallow depression in ventral surface of some Protozoa which aid attachment to host; the beating of flagella lowers pressure in the disk area. Photo

syncytium:

a fusion of cell bodies but with retention of separate nuclei.

syzygy:

reproductive process in some gregarines in which male and female gametocytes partially fuse and encyst, then bud off gametes which fuse to form zygotes.

T

tandem:

arrangement in which one object of a pair is behind the other. Photo

tarsus:

terminal segment on limb of Arthropoda. Photo

tegument:

the living, syncytial external layer on the body of Platyhelminthes and Acanthocephala.

tentacle:

long, thin, flexible structure capable of controlled movement. Photo

testis:

organ that produces spermatozoa. Photo

tetracotyle:

a type of metacercaria of Strigeiformes in which there is a thick, tight fitting cyst wall.

thorax:

mid-body region of Arthropoda from which limbs emerge.

three-host tick:

a tick in which the larva, nymph, and adult take their blood meals on three different host individuals, requiring that they drop off a host and seek a new host after each blood meal.

tibia:

the limb segment of Arthropoda from which the tarsus arises.

tick paralysis:

paralysis in the vertebrate host caused by toxins secreted during feeding by females of some ticks; occasionally fatal due to paralysis of respiratory system.

transmammary transmission:

transmission of a parasite from mother to offspring via milk.

transovarian transmission:

transmission of a parasite from a female to her eggs.

transplacental transmission:

transmission of a parasite from a mother's bloodstream to her fetus via the placenta.

trench fever:

a rickettsial disease transmitted by lice characterized by cycles of diminishing intensity of fever, headache and muscular pain.

tribocytic organ:

a glandular organ posterior to the acetabulum of Strigeoidea, that secretes proteolytic enzymes which digest host tissues. Photo

trophozoite:

a non-reproductive, feeding stage of Protozoa. Photo

trunk:

general term for main body region excluding appendages.

trypomastigote:

a form of Trypanosomatidae with the flagellum arising posterior to the nucleus, and possessing an undulating membrane. Photo

tularemia:

a bacterial disease of northern regions transmitted by various Arthropoda, characterized by an ulcer at the site of inoculation that may develop into a septicemia.

two-host tick:

a tick in which the larva and nymph, take their blood meal on one host, then the nymph drops off and molts; the adult seeks a new host from which to take a blood meal.

typhus:

a group of rickettsial diseases transmitted by fleas or lice, generally characterized by rash, fever, and involvement of kidneys and nervous system.

U

ulcer:

a localized breakdown of epithelial tissues.

unarmed:

lacking spines, hooks, or other hardened structures.

undulating membrane:

a region of some Mastigophora in which the surface pellicle is drawn up into a fin-like ridge by the flagellum. Photo

unilocular hydatid:

a hydatid cyst with a thick, external cyst wall and asexually budding in internal brood capsules only.

unembryonated:

an egg prior to the differentiation of the zygote into an embryo. Photo

unilateral:

an arrangement in which one type of structure (such as genital pores) occurs consistently on one side of the body. Photo

unsporulated:

not yet having undergone sporulation. Photo

uterine bell:

a funnel-shaped organ in female Acanthocephala that collects eggs floating within the body cavity and passes them posteriorly to a selector apparatus. Photo

uterus:

duct in female reproductive system used to conduct eggs towards the genital opening. Photo

V

vacuole:

intracellular cavity. Photo

vagina:

duct in female reproductive system used to receive copulatory organ of male. Photo

vas efferens:

duct in male reproductive system that carries spermatozoa away from each testis. Photo

vas deferens:

duct in male reproductive system into which all vasa efferentia drain. Photo

vector:

any agent that transmits a disease organism; also, general term given to blood feeding invertebrate host transmitting a parasite of vertebrates when the existence or location of sexual reproduction is unclear.

ventral gland:

glands on the ventral tegument of Notocotylidae, of uncertain function but suggested to be involved in respiration. Photo

vertebrate host:

general term given to vertebrate host of a parasite when the existence or location of sexual reproduction is unclear.

vitellaria:

glands in Platyhelminthes that produce yolk-filled vitelline cells which are carried to the ootype and placed around the fertilized ovum. Photo

vitelline duct:

a duct carrying vitelline cells from vitellaria to the ootype. Photo

viviparous:

producing live offspring within the body of the parent. Photo

vulva:

transverse slit in body wall of Nematoda and Acanthocephala through which female reproductive tract opens. Photo

W

X

Y

Z

---