The glossary below includes select terminology used here, and it also includes other terms often associated with the description of aquatic invertebrates.  The source of most of these definitions are from the publications listed in the reference section. 


Abdomen: the third main division of the body; behind the head and thorax

Accessory flagellum: a small fingerlike projection or subantenna of the antenna, especially of amphipods

Anterior: in front; before

Apical: near or pertaining to the end of any structure, part of the structure that is farthest from the body; distal

Apicolateral: located apical and to the side


Basal: pertaining to the end of any structure that is nearest to the body; proximal

Bilobed: divided into two rounded parts (lobes)


Calcareous: resembling chalk or bone in texture; containing calcium

Carapace: the hardened part of some arthropods that spreads like a shield over several segments of the head and thorax

Carinae: elevated ridges or keels, often on a shell or exoskeleton

Caudal filament: threadlike projection at the end of the abdomen; like a tail

Cercus (pl. cerci): a paired appendage of the last abdominal segment

Concentric: a growth pattern on the opercula of some gastropods, marked by a series of circles that lie entirely within each other; compare multispiral and paucispiral

Corneus: resembling horn in texture, slightly hardened but still pliable

Coxa: the basal segment of an arthropod leg

Creeping welt: a slightly raised, often darkened structure on dipteran larvae

Crochet: a small hook like organ

Cupule: a cup shaped organ, as on the antennae of some beetles (Coleoptera)


Detritus: disintegrated or broken up mineral or organic material

Dextral: the curvature of a gastropod shell where the opening is visible on the right when the spire is pointed up

Distal: near or toward the free end of any appendage; that part farthest from the body; apical

Dorsal: pertaining to, or situated on the back or top, especially of the thorax and abdomen

Dorsolateral: toward the top and side


Elytra: hardened shell-like mesothoraic wings of adult beetles (Coleoptera)


Femur: the leg section between the tibia and coxa of Arthropoda, comparable to an upper arm or thigh

Flagellum: a small fingerlike or whip like projection

Furcula: the forked springtail of Collembola


Gill: any structure especially adapted for the exchange of dissolved gases between animal and a surrounding liquid

Glossae: a lobe or lobes front and center on the labium; in Plecoptera, the lobes are between the paraglossae


Hemelytra: the leathery mesothoraic wings of some Hemiptera


Labium: a lower mouthpart of an arthropod like a jaw or lip

Labrum: an upper mouthpart of an arthropod consisting of a single usually hinged plate above the mandibles

Lateral: feature or marking located on the side of a body or other structure

Lateral teeth: ridges on the inside edge of a bivalve shell, near the hinge and to the sides of the beak

Ligula: forming the ventral wall of an arthropod’s oral cavity; the “lower lip”

Lobe: a rounded projection or protuberance


Mandibles: the first pair of jaws in insects

Maxillae: the second pair of jaws in insects

Mesocoxae: the basal segments of the middle legs

Mesonotum: the dorsal surface of the mesothorax

Mesotarsi: the tarsus of the middle legs

Mesothorax: the second or middle section of the thorax bearing the middle legs

Metathorax: the third or hind section of the thorax bearing the hind legs

Metatibiae: hind tibia

Molar lobe: the ridged or roughened grinding surface of the mandible

Multi spiral: a growth pattern on the opercula of some gastropods marked by several turns from the center to the edge; compare paucispiral and concentric


Notum: the dorsal surface of any thoracic segment


Operculate: having a lid or cover

Operculum: a lid or covering structure, like a door to an opening


Palpal lobes: the grasping pinchers at the end of the Odonata lower jaw

Palpus (pl. palpi): tactile, usually segmented structure on the maxillae and labium

Papillae: fleshy protuberances

Paraglossa (pl. paraglossae): lateral lobe of the labium

Paucispiral: a growth pattern on the opercula of some gastropods marked by few turns from the center to the edge; compare multispiral and concentric

Periphyton: algae and associated organisms that live attached to underwater surfaces

Procoxae: the basal segments of the front legs

Posterior: behind; opposite of anterior

Prementum: distal portion of the lower jaw of an Odonata

Proleg: any projection appendage that serves for support locomotion or attachment

Pronotum: the upper or top part of the prothorax

Protarsus (pl. protarsi): front foot; occurring on legs arising from first thoracic segment

Prostheca: a mandibular sclerite set with hair

Prothorax: the first thoracic segment closest to the head

Protibia (pl. protibiae): tibia of the foreleg

Protrochantin: on the front leg, a small, forward projecting sclerite on the trochanter (the segment between the coxa and femur)


Rostrum: a beak or beaklike mouthpart


Sclerite: a hardened area of an insect body wall, usually surrounded by softer membranes

Scutellum: in adult coleopterans and Hemiptera, the triangular sclerite between the bases of the elytra or hemelytra

Seta (pl. setae): hair like projection

Sinistral: the curvature of a gastropod shell where the opening is seen on the left when the spire is pointed up

Spiracle: an opening to the internal respiratory system usually at the sides or end of the abdomen of insects

Sternum (pl. sterna): the entire ventral portion of a thoracic or abdominal segment


Tarsus (pl. tarsi): the leg segment or segments at the apex of the tibia usually bearing a claw

Telson: the most posterior segment of a crustacean

Thoracic: of or pertaining to the thorax

Thorax: middle portion of the body between the head and abdomen, consisting of three segments (prothorax, mesothorax, and metathorax), each of which bears a pair of articulated legs

Tibia: the segment of an arthropod leg, between the femur and tarsus, comparable to a shin or forearm of human anatomy

Tubercles: small bumps or pimple like structures


Ventral: toward the lower surface when the body is in normal walking position; opposite of dorsal

Verrucae: wart like elevations bearing several too many setae pointing in different directions

Ventrolateral: on the lower surface and to one side of the midline


Wingpads: the developing wing of an immature insect

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