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TERMGROUPDEFINITION
PALLIAL LINENPANIMALSPronunciation:

Etymology:

The pallial line is the line on the inside of the mollusk shell that delimits the portion of the shell to which the mantle is attached.
PALMATELY VEINEDADJ-PPLANTSPronunciation:

Etymology:

With veins radiating from the end of the leaf stalk to the tips of the lobes.
PALMELLOIDADJPLANTS, PROTISTSPronunciation:

Etymology:

Palmelloid (adj) describes a colonial form in which cells are dispersed in a mucilaginous matrix.
PAPPUS (PAPPUSES OR PAPPI)NPLANTSPronunciation:

Etymology:

Specialized calyx of hairs or scales.
PARABASAL BODYNPPROTISTSPronunciation:

Etymology:

Parabasal bodies are large modified golgi bodies that lie in association with the basal bodies and flagellar roots of the Parabasalotista.
PARACOELOMNANIMALSClick here
PARALLEL BASAL BODIESNPPLANTS, PROTISTSPronunciation:

Etymology:

Basal bodies are parallel when their orientation relative to each other is parallel.
PARALLEL EVOLUTIONNPEVOLUTIONPronunciation: pa-ra-LEL e-vo-LU-shun

Etymology: Parallel (evolution is defined elsewhere) comes from the Greek parallilos (παράλληλος), with the same meaning.

Parallel evolution occurs when closely related species evolve similar characteristics independently of one another in response to similar environmental pressures. Note that this is a kind of homoplasy that is different from convergent evolution.
PARAMYLONNPROTISTSPronunciation:

Etymology:

Paramylon is a storage carbohydrate that is a polymer of glucose. It is in a class of compounds called glucans. It is found in euglenoids and haptophytes.
PARAPHYLETICADJSYSTEMATICSPronunciation: pa-ra-fi-LEitik

Etymology: Paraphyletic is derived from two Greek roots that mean contrary to (para, παρά) and tribe (fyli, φυλή). The meaning is that it is something other than a tribe.

Paraphyletic (adj.) taxa may have a common ancestor, but they do not include all of the descendants of that ancestor. For example, the theropod dinosaur clade is paraphyletic if the birds are excluded.
PARAPHYSIS (PARAPHYSES)NPLANTS, PROTISTSPronunciation:

Etymology:

Sterile hair-like structures associated with fertile tissue, usually sporangia.
PARAPODIUM (PARAPODIA)NANIMALSPronunciation:

Etymology:

Parapodia are flap-like extentions of the body segments of certain polychaete worms. They possess setae or bristles and usually function in locomotion.
PARASITENECOLOGYPronunciation:

Etymology:

A parasite is a symbiotic organism that benefits from the relationship at the expense of the host.
PARAXIAL RODNPPROTISTSPronunciation:

Etymology:

A paraxial rod is a stiffened rod-like structure that lies alongside the axoneme of one of the flagella in the Euglenidae.
PARENCHYMANPLANTS, PROTISTSPronunciation:

Etymology:

Parenchyma is a type of tissue in which cells are somewhat irregular in shape and form a continuous region of cells.
PARENCHYMATOUS MESODERMNPANIMALSPronunciation:

Etymology:

Parenchymatous (adj.) refers to the formation of a multicellular organism or structure by cells that can divide in multiple planes and thus produce a mass of cells.

Parenchymatous mesoderm is connective tissue that fills the space between the musculature and the gut in acoelomates.
PARSIMONYNSYSTEMATICSPronunciation:

Etymology:

Parsimony literally means stinginess and refers to Occam’s Principle as it is applied to cladistic analysis. The preferred tree is the one with the smallest branch length, which represents the fewest number of changes.
PEDICELLARIA (PEDICELLARIAE)NANIMALSPronunciation:

Etymology:

Pedicellariae are small, claw-like structures among the tube feet of echinoids and asteroids. They function in protection and feeding.
PEDIPALPNANIMALSPronunciation:

Etymology:

Pedipalps are legs characteristic of chelicerates. They occur just anterior to the walking legs and can be modified as structures for transferring sperm in male spiders. Other chelicerates have modified them as pincers or claws.
PEDUNCLENANIMALSPronunciation:

Etymology:

A peduncle is a pillar-like attachment organ in sedentary animals like brachiopods, crinoids, and barnacles.
PELAGOSPHAERANANIMALSPronunciation:

Etymology:

The pelagosphaera is a distinctive larval form of the sipunculids. Clearly, it is a modified trochophore larva.
PELLICLENPLANTS, PROTISTSPronunciation:

Etymology:

A pellicle is a complex outer cellular covering that occurs within the bounds of the plasmalemma. Often synonymous with the term theca, a pellicle defines such groups as the euglenoid-kinetoplastid clade amd the Kingdom Alveolatae.
PELLICULAR STRIPNPPROTISTSPronunciation:

Etymology:

Pellicular strips are proteinaceous strips that run the length of the cell and for the pellicle in the Euglenotista. The pellicular strips can slide past each other in certain euglenoids and thus produce the characteristic metaboly of certain of their cells.
PELTATEADJPLANTSPronunciation:

Etymology:

Peltate (adj.) describes a leaf that is round with an unbroken margin and the petiole attached near the center.
PENDANTADJPLANTSPronunciation:

Etymology:

Hanging down.
PENNATEADJ OR NPROTISTSPronunciation:

Etymology:

Pennate (adj) describes a type of diatom that is bilaterally symmetrical. It is shaped like a penna of a fern leaf.
PEPONPLANTSPronunciation:

Etymology:

A unilocular, many-seeded, hard-walled berry that forms the fruit of some plants.
PERFECT FLOWERNPPLANTSPronunciation:

Etymology:

A flower with both male and female reproductive structures that are functional.
PERIANTHNPLANTSPronunciation:

Etymology:

A collective term for the outer, nonreproductive, parts of a flower, often differentiated into calyx and carolla.
PERICARDIAL CAVITYNPANIMALSPronunciation:

Etymology:

The pallial line is the line on the inside of the mollusk shell that delimits the portion of the shell to which the mantle is attached.
PERIDIOLENFUNGIPronunciation:

Etymology:

Capsules of spores enclosed within the cup-shaped peridium of bird’s nest fungi.
PERIDIUM (PERIDIA)NFUNGIPronunciation:

Etymology:

Outer wall of a fruiting body.
PERINUCLEAR BACTERIUM (PERINUCLEAR BACTERIA)NPPROTISTS, BACTERIAPronunciation:

Etymology:

Perinuclear bacteria are endosymbiotic methanogenic bacteria that occur around the nuclei of Pelomyxa.
PERIPATRIC SPECIATIONNPEVOLUTIONClick here
PERIPHYTON (COLLECTIVE NOUN, NO PLURAL)NECOLOGYPronunciation:

Etymology:

Periphyton is an attached community in an aquatic environment. Although literally, periphyton means attached to plants, the microscopic bacteria, algae, and “protozoa” which make up the periphyton community can be attached to any firm substrate.
PERISTOMAL TEETHNPPLANTSPronunciation:

Etymology:

Fringe of teeth around the mouth of the capsule.
PERISTOMENPLANTSPronunciation:

Etymology:

The mouth of the capsule.
PERITHECIUM (PERITHECIA)NFUNGIPronunciation:

Etymology:

General term for organ containing asci.
PERITRICHOUS FLAGELLUM (PERITRICHOUS FLAGELLA)NPBACTERIAPronunciation:

Etymology:

Peritrichous flagella are inserted on the sides but not on the end of a rod or spiral cell.
PERPENDICULAR BASAL BODIESNPPLANTS, PROTISTSPronunciation:

Etymology:

Basal bodies are perpendicular (or orthogonal) when their orientation relative to each other is at a right angle.
PETALOIDADJPLANTSPronunciation:

Etymology:

Petal-like or the petals and stamens in semi-double and double flowers.
PETALNPLANTSPronunciation:

Etymology:

Single segments of the carolla.
PETIOLENPLANTSPronunciation:

Etymology:

Petiole (n.) is that portion of the leaf that connects the blade to the stem.
PHAGOTROPHICADJANIMALS, PROTISTSPronunciation:

Etymology:

Phagotrophic (adj.) refers to a cell (or organism) that engulfs food particles.
PHARYNGIAL PUMPNPANIMALSPronunciation:

Etymology:

Pharyngial pump is a muscular pump connected to the buccal styles in tardigrades. It is used for sucking plant cell contents in feeding.
PHARYNX (PHARYNGES)NANIMALSPronunciation:

Etymology:

The pharynx is the anterior part of the digestive tract, just behind the mouth.
PHASMIDNANIMALSPronunciation:

Etymology:

A phasmid is a sensory organ of parasitic nematodes.
PHLOEM (NO PLURAL)ADJ OR NPLANTSPronunciation:

Etymology:

Phloem is food-conducting tissue and its elements function while they are alive. Phloem cell types include sieve tubes, companion cells, and phloem fibers.
PHOTORECEPTORNANIMALS, PLANTS, PROTISTSPronunciation:

Etymology:

A photoreceptor is any structure that detects light.
PHOTOTROPHICADJANIMALS, PLANTS, PROTISTS, FUNGI, BACTERIAPronunciation:

Etymology:

Phototrophs utilize light energy to provide metabolic energy. Sometimes this energy is stored asreduced organic compounds (food).
PHRAGMOBASIDIUM (PHRAGMOBASIDIA)NFUNGIPronunciation:

Etymology:

A basidium that is divided into more than one cell by transverse or longitudinal septa.
PHRAGMOPLASTNPLANTSPronunciation:

Etymology:

A phragmoplast is a microtubular array that is oriented parallel to the orientation of the spindle following mitosis. Thus it can be viewed as a persistent spindle. The phragmoplast involved in cytokinesis by the formation of a cell plate (a new cell wall by centrifugal formation).
PHRAGMOSPOROUSADJFUNGIPronunciation:

Etymology:

Having transversely, multiseptate spores.
PHYCOBILLIPROTEINNPLANTS, BACTERIAPronunciation:

Etymology:

Phycobiliproteins are proteinaceous pigments (e.g. phycoerythrin and phycocyanin) that occur in certain algae (Cyanobacteria and Rhodophyta).
PHYCOBIONTNFUNGIPronunciation:

Etymology:

The algal component of a lichen.
PHYLOGENETIC TAXONOMYNPSYSTEMATICSPronunciation: fi-lo-ge-NE-tik taks-O-mo-mi

Etymology: Phylogenetic is derived from two Greek roots that mean race (fyli, φυλή) and origin (genesi, γένεση). Taxonomy has been defined elsewhere.

Phylogenetic Taxonomy is a method of systematics in which classification systems are constructed by determining evolutionary relationships between groups. Usually, the phylogenies are inferred from cladograms. Thus, the method is called cladistics. Unlike numerical taxonomy, there is great effort made to determine whether the characters are primitive or derived (apomorphic) in order to determine evolutionary relationships between taxa.
PHYLOGENYNSYSTEMATICSPronunciation: fi-LA-ge-ni

Etymology: Phylogeny is derived from two Greek roots that mean race (fyli, φυλή) and origin (genesi, γένεση).

Phylogeny is the evolutionary history of a group of taxa. Phylogeny is applied to systematics in phylogenetic taxonomy to create a classification system.
PHYLOGRAMNSYSTEMATICSClick here
PHYLUM (PHYLA)NSYSTEMATICSPronunciation: FI-lum.

Etymology: Phylum is derived from the Greek word phyli (φυλή), which means tribe.

Phylum is a taxonomic level that defines a general body plan, particularly in animals, but also in all kingdoms of life. A phylum contains one or more classes. (See also Division)
PICOPLANKTON (NO PLURAL)NECOLOGYPronunciation:

Etymology:

Picoplankton are ultra small phytoplankton (<0.2-2µm).
PILEUS (PILEI)NFUNGIPronunciation:

Etymology:

Umbrella-shaped cap of mushrooms and toadstools.

Latin pleus, from Latin, cap
PILIDIUM (PILIDIA)NANIMALSPronunciation:

Etymology:

A pilidium is a ciliated, planktonic larval form of some Nemertinea. It has an apical tuft of cilia and is helmet-shaped.
PINNA (PINNAE)NPLANTSPronunciation:

Etymology:

A pinna is a webbed segment of a compound leaf. These may be subdivided into pinules, etc.
PINNATELY VEINEDNPPLANTSPronunciation:

Etymology:

With veins along each side of the leaf midrib.
PINNULE (PINNULES OR PINNULAE)NPLANTSPronunciation:

Etymology:

Pinnules are secondary lateral branches from structures like the arms of crinoids and leaflets of compound leaves.
PISTILNPLANTSPronunciation:

Etymology:

A single carpel in an apocarpous flower or the gynoecium in a syncarpous flower.
PIT CONNECTIONNPPLANTSPronunciation:

Etymology:

Pit connections (also called pit plugs) are perforations that occur at the junctions of cells in the red algae and fungi. The perforations are always plugged with proteinaceous material in the red algae, so they are not really cytoplasmic connections.
PLACENTATIONNPLANTSPronunciation:

Etymology:

The arrangement in which ovules are attached to the ovulary.
PLANKTER (SINGULAR ONLY; IF PLURAL, USE PLANKTON)NECOLOGYPronunciation:

Etymology:

Plankter is an ecological term for an individual member of the plankton.
PLANKTONIC LARVA (PLANKTONIC LARVAE)NPANIMALS, PROTISTSPronunciation:

Etymology:

A larval form that is free-floating in the plankton, usually in marine species.
PLANULA (PLANULAE)NANIMALSPronunciation:

Etymology:

The planula is a larval form of certain Cnidaria. They are bilaterally symmetrical, covered with ciliated epithelium, and free-swimming.
PLASMODIUM (PLASMODIA)NPROTISTSPronunciation:

Etymology:

A plasmodium is a multinucleate cell formed by nuclear divisions without cytokinesis.
PLASTIDNPLANTS, PROTISTSPronunciation:

Etymology:

Typically, a plastid is a photosynthetic organelle. A chloroplast is a plastid.
PLECTOSTELENPLANTSPronunciation:

Etymology:

A plectostele is a modified actinostele in which the segments are deeply cut and divided in the common cortex.
PLEOPODNANIMALSPronunciation:

Etymology:

Pleopods are the swimmerets of crustaceans.
PLESIOMORPHIC CHARACTERNPSYSTEMATICSClick here
PLEURILOCULAR GAMETANGIUM (PLEURILOCULAR GAMETANGIA)NPPROTISTSPronunciation:

Etymology:

A pleurilocular gametangium is a gametangial (gamete-producing) structure that has multiple cells or openings.
PLEUROCARPOUSADJPLANTSPronunciation:

Etymology:

Having the seta rising from a short lateral special branch.
PNEUMATOPHORENANIMALSronunciation:

Etymology:

A pneumatophore is a gas-filled modified polyp that is part of a free-floating colonial hydroid (Cnidaria).
POLAR FENESTRA (POLAR FENESTRAE)NPPROTISTSPronunciation:

Etymology:

Formed when the nuclear envelope doesn’t break down completely during mitosis, but is perforated at the ends.
POLAR FILAMENTNPANIMALSPronunciation:

Etymology:

Cellular organelle coiled inside spore. When a spore encounters a new host cell, the filament uncoils and injects the infective sporoplasm through the filament.
POLAR CENTRIOLENPPROTISTSPronunciation:

Etymology:

Polar centrioles occur at the poles of the nucleus, often one with polar fenestrae (polar openings).
POLAR FLAGELLUM (POLAR FLAGELLA)NPBACTERIAPronunciation:

Etymology:

Polar flagella are those that emerge from the poles of the cell (rods or spirals).
POLLEN (COLLECTIVE NOUN; BOTH SINGULAR AND PLURAL)NPLANTSPronunciation:

Etymology:

The collective mass of grains produced within the anthers of flowering plants or the male cones of a gymnosperm. In all seed plants, pollen is generated by the development of a microspore into a microgametophyte. The germination of the pollen grain leads to the development of a pollen tube, which delivers two sperm or sperm nuclei to the egg in the ovule. In flowering plants, mature microgametophyte has only two cells, a tube cell and a generative cell.
POLLEN WITH THREE APERTURESNPPLANTS
POLLEN CHAMBERNPPLANTSPronunciation:

Etymology:

In gymnosperms, a cavity just above the nucellus in the ovule, the site where pollen accumulates and germinates.
POLYHEDRAL PYRENOIDNPPLANTS, PROTISTSPronunciation:

Etymology:

A polyhedral pyrenoid is a pyrenoid (photosynthate assembly center that occurs in a chloroplast) that is angular in form.
POLYPNANIMALSPronunciation:

Etymology:

A polyp is a hydrozoid form of a Cnidarian.
POLYPETALOUSADJPLANTSPronunciation:

Etymology:

With a carolla of separate petals.
POLYPHYLETIC TAXON (TAXA; SEE TAXON)NPSYSTEMATICSPronunciation:

Etymology:

A group composed of unrelated organisms descended from more than one ancestor.
POLYPODIALADJPROTISTSPronunciation:

Etymology:

Polypodial (adj.) pseudopodia describes the condition where an amoeboid cell makes multiple major pseudopodia at a time.
POLYSTELICADJPLANTSPronunciation:

Etymology:

Polystelic (adj) describes a stem that has more than one or multiple steles. Also, it is an inflorescence in which the branches do not end in a flower.
POLYTOMYNSYSTEMATICSClick here
POMENPLANTSPronunciation:

Etymology:

A fruit consisting of a core formed by several united carpels enclosed within a firm fleshy receptacle.
PRIMARY ZOOSPORENPPROTISTSPronunciation:

Etymology:

Means for asexual reproduction. Primary zoospores are formed first in zoosporangium. They are poor swimmers and encyst readily. Flagella emerge from the anterior of the spore.
PRIMITIVE CHARACTERNPSYSTEMATICSPronunciation: PRI-ma-tiv

Etymology: Primitive is derived from the Latin primitivus (derived from primus-first), which means first or earliest.

In a biological or evolutionary sense, primitive means early. Usually, it is an adjective that modifies character or state. The term does not carry any value judgment associated with it, nor does it imply a position of the Ladder of Life. Most organisms are mosaics of primitive and derived characters. For example, the primate hand (manus) of five digits is a primitive state of all extant tetrapods.
PROBOSCIS (PROBOSCISES OR PROBOSCIDES)NANIMALS, PROTISTSPronunciation:

Etymology:

A proboscis is a tube or tubular process that occurs on the head or the anterior of the gut.
PROGLOTTIDNANIMALSPronunciation:

Etymology:

A proglottid is one of the pseudosegments that make up the strobila of a tapeworm. Typically, they are hermaphroditic and are released when gravid.
PROKARYOTENBACTERIAPronunciation:

Etymology:

A prokaryote is a cell form that has no nucleus or membrane-bound organelles. They are commonly called bacteria.
PROMITOTICADJPROTISTSPronunciation:

Etymology:

Promitotic (adj.) mitosis occurs in closed mitotic systems with an intrnuclear spindle and a persistent nucleolus.
PROMYCELIUM (PROMYCELIA)NFUNGIPronunciation:

Etymology:

Short hypha that germinates from teleopores of rust, on which basidiospores develop.
PRONOTUM (PRONOTA)NANIMALSPronunciation:

Etymology:

The pronotum is the dorsal part of the insect thorax and the segment anterior to the mouth in annelids.
PROSOMA (PROSOMATA)NANIMALSPronunciation:

Etymology:

The prosoma is the cephalothorax of chelicerates and some other invertebrates.
PROSTHECA (PROSTHECAE)NBACTERIAPronunciation:

Etymology:

Prosthece are buds that arise from the cell surface. In bacteria like Caulobacter the buds develop into stalks and other structures.
PROSTOMIUM (PROSTOMIA)NANIMALSPronunciation:

Etymology:

The prostomeum is the segment anterior to the mouth in annelids.
PROTASPIDNANIMALSPronunciation:

Etymology:

The protaspid (adj.) developmental stage of trilobites was the initial larval stage at which the body is unsegmented.
PROTHALLIAL CELLNPPLANTSPronunciation:

Etymology:

Prothallial cells are remnants of the vegetative microgametophyte in pollen grains.
PROTONEMA (PROTONEMATA)NPLANTSPronunciation:

Etymology:

A protonema is the initial filamentous (sometimes thalloid) gametophyte that grows from the spore of charophytes, and non-vascular embryophytes.
PROTONEPHRIDIUM (PROTONEPHRIDIA)NANIMALSronunciation:

Etymology:

Protonephridia (protonephridium, sing.) are excretory organs that are ciliated tubules. The flame cell lies at the internal terminus ciliated tubule.
PROTOPODITENANIMALSPronunciation:

Etymology:

The protopodite is basal segment of the arthropod leg.
PSEUDOCAPILLITIUM (PSEUDOCAPILLITIA)NPROTISTSPronunciation:

Etymology:

A pseudocapillitium is a type of a myxotist sporangium that has thread-like fragments.
PSEUDOCOELOMNANIMALSClick here
PSEUDOMONOPODIAL GROWTHNPPLANTSPronunciation:

Etymology:

Pseudomonopodial growth occurs in plants that exhibit weak overtopping.
PSEUDOPARENCHYMATOUSADJPLANTS, PROTISTSPronunciation:

Etymology:

Pseudoparenchymatous (adj) describes the structure of a multicellular organism that is formed of interwoven filaments rather than parenchyma.
PSEUDOPODIUM (PSEUDOPODIA)NANIMALS, PROTISTSPronunciation:

Etymology:

A leafless branch resembling a seta, bearing the capsule in some species of bryophytes (particularly in the Sphagnopsida and Andreaeopsida). Typically, the setae in these taxa are very short. After the fertilization of the egg, the tissue at the base of the archegonium grows and bears the capsule away from the leafy gametophore. Unfortunately, these structures that really should be called “pseudosetae” were given the name pseudopodia (a term already in common usage for the cytoplasmic extensions of amoebae and rhizarians).
PSEUDORAPHENPROTISTSPronunciation:

Etymology:

A pseudoraphe is a clear region between opposing lines of striae. It produces the illusion of a raphe on a microscope.
PSEUDOTHECIUM (PSEUDOTHECIA)NFUNGIPronunciation:

Etymology:

Sexual fruiting body resembling perithecia, but lacking same level of organization.
PUNCTA (PUNCTAE)NPROTISTSPronunciation:

Etymology:

Punctae are holes in the frustules of diatoms.
PUNCTUATED EQUILIBRIUMNPEVOLUTIONPronunciation: PUNK-tu-a-ted e-kwi-LIB-ri-um

Etymology: Punctuated equilibrium is a phrase of two words derived from Latin roots. Punctuate comes from punctuare, meaning to mark with points or dots. Equilibrium is formed from two Latin roots meaning equal (aequus) and balance (libra).

Punctuated equilibrium, first proposed by Gould and Eldridge 1972, is a model of evolution in which species remain unchanged for long periods of time, followed by bursts of rapid change.
PYGIDIUM (PYGIDIUM)NANIMALSPronunciation:

Etymology:

The pygidium was the terminal tegma of trilobites; usually, a fused terminal shield, which was strong and the most common portion preserved as fossils. It is the fused terminal segments of annelids.
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