[ARTHROPODS]

Body appearing otherwise: usually divided into two distinct parts: cephalothorax and abdomen; or only the head a distinct part and a segmented region behind the head. Number of appendages variable, but more than six which are legs (include claws if present, but not leg-like mouthparts), or less than six. Without wings

Body otherwise—included here microcrustaceans: aquatic forms under 3 mm (1/8 in) in length

~ Subphylum CHELICERATA, Class ARACHNIDA

Cephalothorax with five (5) pairs of legs (counting claws but not leg like mouthparts), antennae, two eyes (usually compound and on stalks). Abdomen usually having paddle-like appendages. Prawns, shrimp, crabs
~ Subphylum CRUSTACEA, Class MALACOSTRACA

The Subphylum Crustacea is an extremely diverse group within the Phylum Arthropoda, including many forms, such as copepods, cladocerans, and ostracods (Fig. 2), which are essentially microscopic (under 2 mm) in size. Others, such as prawns and crabs are the largest invertebrates found in Hawaiian streams and estuaries. All have a chitinous exoskeleton, mandibles (chewing mouthparts), and two pairs of antennae. The thorax is usually combined with the head (forming the cephalothorax) within a common covering called a carapace. Some insect larvae (Class Insecta) may superficially resemble crustaceans. For a partial list of aquatic Crustacea known from Hawaiian fresh and brackish waters see CPIE.

[CRUSTACEANS]

Small to large crustaceans (2 to 200 mm). Body typically composed of a head and more or less equal thoracic segments (with legs); OR a cephalothorax (with mouthparts and legs) and segmented abdomen, usually with appendages

Carapace short, exposing most thoracic segments; OR carapace lacking

Carapace present, but short, leaving 4 or 5 thoracic segments not covered

With one pair of uropods. Body cylindrical or compressed top to bottom

First gnathopods chelate
~ TANAIDACEA

Body enclosed in a bilterally symmetrical wall of six calcareous plates cemented to substratum, the aperture (opening in the middle) closed by calcified valves (Fig. A7-5). { Acorn barnacle
~ Suborder BALANOMORPHA

Carapace typically covers head and thorax; not bivalved. Abdomen segmented and not enclosed by carapace [see Fig. 2 - 1)]

Carapace folded, not hinged. Head not covered by carapace, but usually separated from it by a distinct ventral notch. { Water fleas
~ Subclass CLADOCERA

These small crustaceans are not well known in Hawaiian fresh water environments, although they may be commonly encountered. Lack of reference material and small size make identification to species very difficult.

Your identification is leading to a group with NO known fresh or brackish water representatives in Hawai`i. The identification may be correct for the location where you made the collection or observation (perhaps near the ocean), but the species is marine and not covered in these keys. If the collection was made in freshwater, you should back up several couplets and reconfirm your decisions.