Glossary Mayflies Dragonflies and Damselflies
Stoneflies True Bugs Dobsonflies & Alderflies
Water Beetles Caddisflies True Flies
Non-Insect Invertebrates

Glossary

Anterior
At or directed toward the head or front of the body.
Caudal
Pertaining to the hind end of the body.
Dorsal
Pertaining to the top or upper surface.
Larva (pl. larvae)
A developmental stage that is the first developmental stage following egg hatch in the life cycle of the insect.
Lateral filament
A long, slender, threadlike structure attached to the side of the body.
Notum (pl. nota)
The top or upper surface of a body segment, especially of the thorax.
Nymph
The young stage of an insect that undergoes incomplete metamorphosis.
Posterior
At or toward the hind or tail end of the body.
Proleg
A fleshy, unsegmented, leglike or lobelike structure, usually occurring in pairs. Prolegs are located on the thorax of some diptera larvae and on the abdomen (usually ventrally or terminally) in many different larvae.
Pronotum
The top surface of the first, most forward thoracic segment.
Prothorax
The first, most anterior thoracic segment that touches the head.
Pupa (pl. pupae)
The transitional, "resting" life stage, that is part of insect complete metamorphosis, immediately before the adult stage.
Sclerotized
Containing fingernail like plates or hardened body wall; material insect exoskeletons are made of.
Thoracic
Pertaining to the thorax or second (middle) major body region of an insect.
Ventral
Pertaining to the bottom or underside.

Diagrams of Body Parts of Invertebrates


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Mayflies

Order Ephemeroptera
Key Characteristics

  • Remember when trying to identify Ephemeroptea that they are very fragile and their gills, legs and tails break off easily.
  • Larvae possess rows of feathery or platelike abdominal gills, three pairs of well developed, segmented legs attached to the thorax and a single claw at the end of each leg.
  • The body usually ends in 3 long tails but there are a few species that have only 2 tails.
  • Mayflies have well-developed eyes, slender antennae, and chewing mouthparts. A pair of developing front wing pads are present on the thorax; hind wing pads may be present or absent.
  • Can be confused with stoneflies (Plecoptera). Stoneflies have 2 claws at the end of each leg, two tails and they usually have three thoracic plates. Can be confused with damselflies that have 3 tails, but tails on Damselfly are featherlike gills; damselflies lack abdominal gills.
  • 3 mm - 20 mm (rarely 30 mm, not including tails)
Diagrams, Pictures of Ephemeroptera

Family Heptageniidae
Flatheaded Mayflies

  • Abdominal gills are usually platelike and are often visible from above. Gills are on abdominal segments 1-7 or rarely on 1-6.
  • Distinctly flattened bodies with horizontal heads and outspread legs and eyes facing upward.
  • 5 mm to 20 mm
Family Oligoneuriidae
Brushlegged Mayflies

  • Gill tufts are present at base of the mouthparts and front legs.
  • Two rows of conspicuous, long hairs are present along the inner surface of the front legs.
  • Minnowlike in shape and movement with a vertically oriented head.
  • 8 mm to 17 mm


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Dragonflies and Damselflies

Order Odonata
Key Characteristics

  • Long, robust bodies with large eyes and chewing mouth parts; the lower extension of the mouthpart is used for grasping prey. Conspicuous antennae that vary greatly in shape.
  • 2 pairs of wing pads and 3 pairs of segmented legs are present on the thorax.
  • Gills are not present along the body; gills are either inside the end of the abdomen or on 3 featherlike gill plates attached to the abdomen.
  • 10 mm to 50 mm
Diagrams, Pictures of Odonata

Suborder Zygoptera
Damselflies

  • Same characteristics as dragonflies, but narrower and longer.
  • Abdomen ends in three featherlike gills that dragonflies do not possess.
  • 15 mm to 30 mm
Suborder Anisoptera
Dragonflies

  • No visible external gills and no tails, but abdomen ends in 3 short, flexible wedge-shaped valves that surround the opening to the internal abdominal gills.
  • The nymphs have a unique mouthpart, for catching prey, that is shaped like a long arm with hooks at its tip.
  • When not in use, the lower mouthpart is folded beneath the insect's head and the cup-shaped tip covers the face like a mask. When a prey passes by, the mouthpart shoots out within a split second, seizing the prey.
  • 20 mm to 50 mm


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Stoneflies

Order Plecoptera
Key Characteristics

  • Abdomen ends in two tails.
  • Well-developed legs each ending in 2 claws.
  • Fingerlike or hairlike, simple or branched, fleshy gills are present; gills may be attached to the mouthparts, thorax, the base of the legs, and/or the abdomen.
  • Elongate, somewhat flattened to cylindrical in form with developing wing pads usually present in older nymphs.
  • Head has widely separated eyes, long slender antennae, and chewing mouthparts. Both the head and top surface of the first three thoracic segments are sclerotized. Sometimes confused with Ephemeroptera whose legs end in 1 claw and often have three tails.
  • 5 mm to 35 mm (sometimes up to 60 mm, not including tails)
Diagrams, Pictures of Plecoptera


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True Bugs

Order Hemiptera
Key Characteristics

  • Mouth is shaped like a beak. It is either conelike or a piercing, sucking structure.
  • Oval to slender elongate forms, somewhat flattened. Abdomen lacks any hairlike structures. Gills can look like filaments or strawlike tails; or they are short and flaplike.
  • Head and eyes are well developed.
  • The thorax may lack wings, have fully developed wings, or have variously shortened wings or wing pads.
  • Short to long antennae and well developed thoracic legs.
  • Forewings, when at rest, are held close over the back, and the two forewings usually overlap at the tips. Forewings usually have a thickened or leathery region at base and a membranous region at end of forewing. Hind wings, when present are completely membranous.
  • Resemble adult water beetles in body shape. However, water beetles have chewing mouthparts and true bugs have mouthparts that form a single piercing and sucking tube or conelike structure; water beetles have forewings that are present in adults and do not overlap.
  • 1 mm to 65 mm
Diagrams, Pictures of Hemiptera


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Dobsonflies & Alderflies

Order Megaloptera
Key Characteristics

  • Includes some of the largest aquatic larvae which are highly active. Bodies are long and slightly flattened. Abdominal segments 1-7 or 1-8 each have a pair of lateral filaments.
  • No wing pads. Thoracic legs are present.
  • Abdomen ends either in a single unbranched filament or in a pair of prolegs each of which ends in 2 hooks and a dorsal filament.
  • The head capsule and the first three thoracic segments are sclerotized.
  • Three pairs of segmented legs on thorax.
  • 10 mm to 90 mm
Diagrams, Pictures of Megaloptera


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Water Beetles

Order Coleoptera
Key Characters

Aquatic Larvae

  • Distinct head with chewing mouth parts, thoracic legs usually present.
  • Most beetle larvae are generally oval in shape.
  • Lateral filaments can be present or absent.
  • If abdomen has well-developed lateral filaments, then it will not end in a single, undivided hairlike structure.
  • Larvae do not have a pair of terminal prolegs, each has a single hook (as in Tricoptera). Abdomen has 8-10 segments.
  • Some beetle species have larvae and adults which are both aquatic; others have aquatic larvae which leave the water when they become adults.
  • 2 mm to 60 mm

Aquatic Adults
  • Hard bodied, distinctive oval to elongate insects.
  • Head has chewing mouth parts, well-developed eyes, and variably shaped antennae.
  • Possess hardened wing covers and hind wings that are folded tightly on top of the body.
  • 1 mm to 40 mm

Diagrams, Pictures of Coleoptera

Family Elmidae
Riffle Beetle

Larvae
  • Body is long and oval to hemispherical in cross section.
  • Underside (belly) flattened or concave (to view, turn the insect sideways and on its back under the microscope).
  • Abdomen has nine segments. The last abdominal segment has a chamber with hairlike gills inside and terminal hooks underneath; these hairs can be hard to see (use high power) when they are retracted into the abdomen.
  • The underside of the last abdominal segment has a shield-shaped plate (operculum).
  • 2 mm to 10 mm

Adults
  • Small, dark beetle, somewhat elongated; Antennae usually slender, and sometimes clubbed.
  • Chewing mouthparts and presence of forewings can help distinguish riffle beetles from true bugs.
  • 1 mm to 8 mm
Family Psephenidae
Water Pennies

  • Head and legs of these immature beetles are not visible from above.
  • Body disklike with plates covering head and legs.
  • Almost round in shape.
  • Could be confused with Leucotrichia (purse dwelling caddisflies) cases.
  • 4 mm to 6 mm
Family Ptilodactylidae
Ptilodactylid Beetles

  • Completely round in cross section.
  • The last abdominal segment does not have a ventral covering. Either abdominal segments 1-7 each have a pair of tufted ventral gills or only segment nine has ventral gills.
  • Often confused with Elmidae larva. Elmidae is not round in cross-section and the end of their abdomen is generally more tapered; Elmidae has a ventral covering.
  • 4 mm to 6 mm


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Caddisflies

Order Trichoptera
Key Characteristics

  • Long and caterpillar-like. Distinct head with chewing mouthparts and a hard head capsule; the thorax may also have hard, dark, sclerotized plates on the top surface.
  • Thoracic legs are well-developed; no wing pads or tails are present. End of abdomen has prolegs, each with a claw.
  • Caddisflies have small, simple eyes and reduced antennae that are hard to see. Some species are free-living, while others form cases made of silk, sand grains, pebbles or bits of plant matter in a wide variety of shapes and sizes.
  • 2 mm to 40 mm
Diagrams, Pictures of Trichoptera

Family Hydropsychidae
Net Spinners

  • Generally, strongly curved body with branched gills on the center of the second and third thoracic segments and at least on abdominal segments 1-6.
  • Anal prolegs have a tuft of long hairs and abdomen is usually covered with small hairs. Prolegs may be short or long prolegs, each has a single hook.
  • The 3 thoracic segments are covered with well-developed dorsal plates which are sclerotized.
  • When collected, they typically retreat backwards with great agility by using their abdomen and well developed anal prolegs.
  • Head is as wide as the thorax.
  • 10 mm to 16 mm (up to 40 mm)
Family Philopotamidae
Fingernet Caddisflies

  • Pronotum has just one sclerotized dorsal plate, usually pale in color, sometimes yellow or orange.
  • Anterior margin of the head capsule irregularly shaped with a distinct notch that can be seen from above.
  • Head and pronotum are brownish orange, pronotum bounded posteriorly by a pronounced black line.
  • Has three pairs of true legs, and no prolegs or abdominal gills, so as not to be confused with Chironomidae.
  • 10 mm to 12 mm (sometimes 16.5 mm)


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True Flies

Order Diptera
Key Characteristics

  • Larvae are usually elongate, soft bodied, maggot-like in form.
  • No jointed, "true" legs. The thorax does not have three pairs of segmented legs, although on some, 1 or 2 prolegs are present.
  • Wing pads are not present.
  • Head may or may not be well developed and easy to see. Eyes are often poorly developed or absent. The shape of antennae varies. Abdomen has 8-10 segments (these segments are occasionally fused into fewer apparent segments or appear to be subdivided).
  • Abdomen may have poorly developed prolegs (lobe-like legs or welts).
  • The first or last segments may have prolegs or other fleshy or hairlike processes.
  • 1 mm to 100 mm
Diagrams, Pictures of Diptera

Family Tipulidae
Craneflies

  • Some of the thickest and largest of all Diptera. Bodies are often soft and pliable and somewhat pointed or rounded with no distinct head.
  • Cylindrical body that often has small lobes or creeping welts (prolegs).
  • Abdomen of some may be bulbous. Most have 5-8 fleshy projections (spiracular disk) at the end of the abdomen used for breathing.
  • One of the more common and smallest types of Tipulidae is the genus Antocha, which has very short prolegs or creeping welts on the underside of the abdomen and ridges on the top (dorsal) part of the body. The Antocha also has dark sclertotized plates on the dorsal ridges giving it an almost stripped appearance. Antocha is different from most Tipulidae because it lacks openings used for air intake and instead have elongated gills at the end of their abdomen (they actually breath differently than most other Tipulidae).
  • 10 mm to 100 mm
Family Chironomidae
Midges

  • Have well sclerotized head capsule, rest of body is soft. Body is usually curled.
  • Chironomidae have anterior and posterior prolegs. The prolegs project forward from front of thorax. Terminal prolegs are often less visible.
  • Some species are highly pollution tolerant, found in areas too polluted for other kinds of life. Some species, that are bright red in color, have evolved an iron based pigment that helps them to tolerate low levels of oxygen.
  • Sometimes live in loosely built tube cases of fine sand grains, mineral debris, or plant material lined with silk. These, however, are rarely found in samples because they break apart so easily or larvae abandon these retreats when collected.
  • Can often be confused with Oligochaeta which have a many segmented, limp body and no head and prolegs.
  • 2 mm to 20 mm
Family Simuliidae
Blackflies

  • Head has distinct fanlike mouth brushes.
  • Cylindrical and club shaped; slightly bulbous at the end.
  • The larvae are equipped with a disklike sucker on the rear of the abdomen which is used to anchor them to rocks.
  • Prothorax has prolegs.
  • 3 mm to 12 mm


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Non-Insect Invertebrates

Phylum Platyhelminthes, Class Turbellaria
Planarians

  • Soft-bodied, elongate wormlike forms, usually flattened ventrally.
  • Bodies lack segments and head area is commonly arrowhead shaped.
  • 2 eyespots are usually present.
  • Sometimes the tubelike pharynx is visibly protruding from the middle.
  • 1 mm to 30 mm
Diagrams, Pictures of Planarian

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Phylum Annelida, Class Oligochaeta
Aquatic Earthworms

Diagrams, Pictures of Annelida

Phylum Annelida, Class Hirudinea
Leeches

  • Dorsoventrally flattened and segmented.
  • Has both anterior and posterior ventral suckers.
  • Usually much wider than Oligochaeta.
  • 5 mm to 100 mm
Diagrams, Pictures of Leech

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Phylum Mollusca, Class Gastropoda
Snails, Limpets

Diagrams, Pictures of Mollusca

Phylum Mollusca, Class Pelecypoda
Clams and Mussels

  • These have a two-piece (bivalve) shell, with the two opposing valves connected.
  • Shells are variously shaped and sized (can be very small), but are commonly oval, and have concentric growth lines.
  • 2 mm to 250 mm
Diagrams, Pictures of Mollusca (Scallop, Chiton)

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Class Crustacea, Order Isopoda
Aquatic Sow Bugs

Diagrams, Pictures of Isopod

Class Crustacea, Order Amphipoda
Scuds

  • Body enclosed in calcium carbonate exoskeleton.
  • Look like small shrimp (often called fresh water shrimp). Eyes are well developed.
  • Body compressed sideways and first thoracic segment fused with the head; 7 pairs of legs.
  • 5 mm to 20 mm
Diagrams, Pictures of Amphipod

Class Crustacea, Order Decapoda
Crayfish

  • Head and thorax covered by hardened shield.
  • Looks like a small lobster with large front claws.
  • 10 mm to 150 mm

Diagrams, Pictures of Decapod

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LINKS

Megaloptera
(University of Arizona) 		Odonata
(University of Arizona) 		Coleoptera
(University of Arizona)
Ephemeroptera
(University of Arizona) 		Plecoptera
(University of Texas) 		Hemiptera
(University of Arizona)
Trichoptera
(University of Arizona) 		Diptera
(North Carolina State University) 		Crustacea
Mollusca
(University of Arizona) 		Platyhelminthes
(University of Arizona) 		Annelida
(University of Arizona)
Insect Drawings
(University of Illinois U-C) 		Iowa State University Entomology Image Gallery Electronic Zoo/NetVet - Animal Image CollectionÉ
Stein's Virtual Insectary UD Entomology Home Page NMNH Entomology Page
Insecta: Glossary
Aquatic Ecology Page
Environmental Organization WebDirectory!
Animals
Welcome to UCMP!
University of California Museum of Paleontology

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