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| Sources for definitions: Gordh & Headric 2001, Martin & Davis 2004, Lawrence 2000, Thorp& Covitch 1991, Merriam-Webster 2005, Blass 2007 and the various identification key references | |
 keel |
an elevated ridge |
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| labium |
in Insecta, lower lip which is positioned
opposite the labrum in Crustacea, a swollen structure lying next to the epistome and bordering the anterior margin of the oral opening |
| labrum | upper lip which covers the base of the mandible and forms the roof of the mouth |
| lacinia | in Insecta, the blade or toothed edge of
the maxilla in Crustacea, inner distal spiny lobe of second segment of maxillule |
| lacinia mobilis | in Insecta, a small plate-like appendage
near the extremity of the mandible in Crustacea, an enlarged, nearly articulated spine of the mandible's spine row that is adjacent to the incisor process, only on left mandible |
| lagoon | a quiet coastal backwater separated from the ocean by a physical, usually land, barrier |
| lake | a large body of standing water that ocuppies a depression in the earth's surface and is completely surrounded by land |
| lamella(e) | any plate- or leaf-like process; in Ephemeroptera, one of two paired processes (upper and lower) forming the abdominal gill (plural) |
| lamellate | sheet- or plate-like; referring to a structure composed of, or covered with, thin sheets |
| laminate | a composite structure formed of thin flat layers of variable thickness, texture, composition |
| lanceolate | spear-shaped; rectangular but tapering at ends |
| larva(e) | early or immature developmental stage of an organism (plural) |
| larval | adjective of larva |
| lateral(ly) | descriptive of a structure or action to the side (adverb) |
| laterodorsal(ly) | descriptive of a structure or action to the side and back (adverb) |
| laterotergite | a lateral sclerotization of the dorsum distinct from a principal median tergum |
| lentic | referring to standing water, such as lakes, ponds and swamps |
| life cycle | the successive stages of reproduction, growth and development of an organism between the appearance and reappearance of the same stage |
| ligula | a small strap or tongue; the median sclerite of the labium which inserts into the distal margin of the prementum |
| ligular | referring to the ligula |
| limnetic | living in marshes, lakes or open water |
| littoral | area of a waterbody associated with the bank or land's edge |
| lobe | any prominent, rounded process along a margin or surface; a lateral expansion of an abdominal segment |
| lotic | referring to flowing waters |
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| macro- |
large |
| macroinvertebrate | an invertebrate that is visible to the naked eye (>1.0 mm) |
| macrophyte | large aquatic plant |
| macropterous | long winged form; forewings reach or surpass the tip of abdomen, when folded over the back |
| mala | a lobe, ridge or grinding surface of the maxilla or mandible |
| mandible | in Insecta, first pair of oral appendages; in Crustacea, first of three pairs of cephalic appendages in Isopoda, third cephalic appendage and first mouthpart appendage |
| mandibular | descriptive of a structure associated with the mandible |
| mantle | in Gastropoda, |
| marine | descriptive of salt-water (sea) habitats |
| marsupia | plural of marsupium |
| marsupium | a pouch formed from anal sclerites, in which females carry eggs and young |
| maxilla(e) | paired, lateral accessory mouthparts located immediately behind the mandibles (plural) |
| maxillary palp | palp located on outer surface of second segment of maxilla, typically sensory in function |
| maxilliped | the three pairs of appendages following the second maxillae |
| maxillule | one of a pair of the fourth cephalic appendages, used as a mouthpart |
| mechano-reception | the response to mechanical stimuli, such as vibrations of wind or water |
| medial | descriptive of something toward the middle of a structure or midline of the body |
| median | referring to the middle |
| medusa | a free-swimming, sexually reproducing jelly-fish life cycle stage |
| membrane | any thin, transparent, flexible tissue |
| membranous | referring to tissue which is thin and semi-transparent |
| merus | fourth segment of thoracic appendage |
| mesal | descriptive of a structure that is positioned in the median plane of the body |
| meso- | middle |
| mesonotum | dorsal surface of the mesothorax |
| mesopleural | descriptive of a structure associated with the lateral part of the mesothorax |
| mesoscutellum | scutellum of the mesothorax |
| mesosternum | ventral surface of the mesothorax, positioned between the mesopleura |
| mesotarsus | tarsus of the middle leg |
| mesothorax | middle thoracic segment |
| mesotrochantin | trochantin of the midleg |
| meta- | last; used to designate any posterior part of structure |
| metafemur | femur of the hindleg |
| metamorphose | to change shape, form or substance during the development process |
| metamorphosis | a series of developmental changes that convert a larval form to an adult |
| metanotal | adjective of metanotum |
| metanotum | the dorsal surface of the metathorax |
| metapleuron | lateral area of the metathorax |
| metasternum | the ventral surface of the metathorax |
| metathoracic | descriptive of any structure associated with the metathorax |
| metathorax | the third segment of the thorax |
| metazoan | a multi celled organism |
| micro- | small |
| microflora | organisms (not animals) less than 200 µm long, only visible under the microscope, usually referring to bacteria, diatoms and small algae |
| microhabitat | the immediate environment of an organism, distinguished by its own set of environmental conditions |
| microinvertbrate | an invertebrate which is very small, indistinct without the use of a microscope (<0.5 mm) |
| microtrichia | small sclerotized or unsclerotized, hair-like structures on body or wings |
| mid- | middle |
| midleg | middle leg of an animal with 3 pairs of legs |
| midventral | referring to the middle of the underside or lower surface |
| migratory | referring to organisms that move from one place to another |
| mola(r) | the ridged or roughened grinding surface of the mandibles; when the mandible is compund, the molar corresponds to the subgalea of maxilla |
| monofilamentous | bearing a single filament |
| monogamy | male stays with one female protecting her from other males |
| morphological(ly) | physical form or structure of an organism (referring to) |
| motile | ability to move |
| moult | to cast or shed the outer skin or integument |
| mound spring | a spring that wells up in a natural elevation in the earth's surface |
| mucilaginous | sticky; gum-like |
| mucus | a shiny, slippery, glandular secretion |
| multi cellular | consisting of two or more cells |
| multifid | cut into many segments |
| multispinose | descriptive of a structure with many spines |
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| nacre |
inner surface of mollusc shells |
| nauplii | plural of nauplius |
| naupliiar | adjective of nauplius |
| nauplius | the earliest larval stage, having only antennules, antennae and mandibles |
| nematocyst | contents of the stinging cells, ejected upon stimulation |
| neonate | newborn caducean |
| neutrally buoyant | the state being still and upright in the water, below the surface, without swimming |
| niche | the total range of climatic conditions, edaphic factors and food necessary for a population to exist and reproduce |
| noctidiurnal | being active at night and in daytime |
| nocturnal | descriptive of organisms that are active at night |
| nomadic | descriptive of an organism that moves from area to area |
| nota | the dorsal surfaces of the body segments, in particular thoracic segments |
| notopleura | a depression, more or less triangular, situated immediately before the transverse suture and behind the humeri |
| notum | the dorsal or upper surface of a body segment, particularly of the thorax |
| noxious | harmful, very unpleasant |
| nucleus | the centre of any structure, around which it grows |
| nymph(al) | juvenile, sexually immature stage, usually similar to the adult form (adjective) |
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| obligate
drifter |
an organism that can only move within a stream by drifting with the flow of water |
| obligate parasite | an organism that can only live as a parasite |
| obtuse | not pointed; descriptive of a surface with a blunt or rounded end |
| occipital genae | sclerotized areas located at the ventral posterior area of the head |
| occipital margin | the posterior margin of the head |
| ocelli | simple light receptors |
| ocular | descriptive of or referring to the eyes |
| offspring | the result of reproduction |
| oligotrophic | referring to aquatic habitats, one with insufficient nutrition |
| ommatidium | one of the numberous small cone-shaped eyes which make up the compound eye of some Arthropoda |
| omnivore | an animal that feeds on plants, animals and detritus |
| omnivorous | eating a variety of organisms and plants |
| operculate | referring to a lid-like cover |
| operculum | a lid or covering flap |
| opportunistic predator |
an animal not typically predatory but that will eat another animal if it is the immediately available food source |
| opsiblastic | eggs having a dormant period before hatching |
| oral | descriptive of any structure associated with the mouth |
| orbit | an imaginary border around the eye; narrow part of the vertex adjacent to the margin of a compound eye |
| ordinal | descriptive of taxonomic status relating to an Order |
| organism | a self contained, organic entity capable of sustaining life processes |
| orifice | any opening for a tube, sac or duct |
| oscula | small mouths; in Porifera, excurrent apertures of a sponge |
| ostia | any apertures, entrances or mouth-like openings; in Porifera, openings of the surface through which water enters the body; in Lepidoptera, external genitalia openings of the female for reception of sperm |
| ovate | descriptive of stucture that is egg-shaped |
| ovipositor | egg laying tube of females, an extension of the oviduct |
| ovisac | a receptacle for eggs |
| ovoid | egg-like in shape or appearance |
| ovum | female gamete |
| oxygenated | water that is enriched with dissolved oxygen |
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