Glossary of Isopoda Technical Terms

Richard Brusca
Thin-walled chemosensory seta usually found on antennular flagellum.
Antennae 1 or first antennae; anteriormost paired appendages of head (= antennula).
Antennae 2 or second antennae; second paired appendages of head.
appendix masculina
Copulatory stylet arising from medial margin of male pleopod 2 endopod, used for transfer of spermatophores in at least some species. (Pl. appendices masulinae)
Composed of two rami or branches.
A keel, or acute ridge.
Head; strictly speaking the cephalon of an isopod is a cephalothorax, as it is always fused with the first thoracomere (and also with the second thoracomere in the Gnathiidea).
Having a chela; the propodus and dactylus forming a pincerlike structure wherein the latter articulates submedially on the former to produce a "moveable and fixed finger" arrangement. (True chelae are extremely rare in isopods.)
coupling setae
When present, coupling setae (or hooks) occur on the maxillipedal endites and pleopodal peduncles, and serve to lock the opposing appendages together, allowing them to function as a single unit.
Basal article of an appendage.
coxal plates
Coxae of the pereopods laterally expanded into flattened lamellar structures extending freely (as "plates") to overhang the coxa-basis hinge of the leg.
In most (but not all) isopods the labrum consists of two pieces; the anteriormost (proximal) piece is referred to as the clypeus, the posteriormost (distal) piece as the labrum proper.
Situated away from the base or point of origin or attachment.
A lobe on the inner (medial) margin of the protopod of an arthropod limb; enlarged anteriorly directed lobe of the basis of an isopod maxilliped.
Inner (medial) ramus of an appendage.
Outer (lateral) ramus of an appendage.
Narrow distal part of antenna or antennule, usually multiarticulate, occasionally reduced to one or a few articles, without intrinsic musculature.
frontal margin
Separates the upper surface of the cephalon from the frontal lamina; anterior margin of cephalon.
frontal lamina
A sternal plate arising between the bases of the antennae and probably homologous to the epistome of other arthropods.
frontal process
The lower region of the epistomal plate or sclerite, which in some Valvifera projects outward to become visible in the dorsal aspect as a protuberance lying above the frontal lamina.
A loosely used term usually refering to chelate or subchelate pereopods associated with the head region and used for food handling. This term is rarely used for isopods.
incisor process
Grasping, piercing or slicing structure arising apically on body of mandible.
The posterior border of the buccal field; the "lower lip" (see paragnath).
Flaplike structure posterior to the frontal lamina or clypeus, usually free but occasionally fused to head; the "upper lip" (see clypeus).
lacinia mobilis
Small, usually toothed, process articulating at base of incisor of left or both mandibles; present in most isopod groups.
lamina dentata
Serrate platelike structure on the mandible of anthurideans, presumed to have been formed by the fusion of spines of the spine-row.
Young of most peracarids (including isopods), which lack the 7th pereopod at time of release from broodpouch.
Third pair of head appendages; first (anteriormost) pair of mouthparts functioning as jaws and typically sclerotized.
Structure in which eggs and embryos are retained and brooded by female; the broodpouch. Isopod marsupia are typically formed by overlapping medial plates (oostegites) arising from certain pereonal coxae in females; in a few groups the oostegites have been reduced or lost in lieu of internal brooding.
Fourth pair of head appendages, functioning as mouthparts, immediately posterior to mandibles (= first maxillae).
Fifth pair of head appendages, functioning as mouthparts, immediately posterior to maxillules (= second maxillae).
Modified first pair of thoracopods, functioning as mouthparts.
molar process
Grinding, or piercing or slicing structure, arising mid-basally on body of mandible; pars molaris.
Thin ventromedial plates, born on coxae of some pereopods in female peracarids forming the marsupium, or broodpouch.
Articulated ramus consisting of one to three articles on the mandible, and up to five articles on the maxilliped. (Palps do not occur on the maxillules or maxillae of isopods.)
In isopods the labium is usually produced and cleft into a large bilobed structure, and hence more commonly referred to as the paragnath (= hypostome, metastome, hypopharynx).
Enlarged proximal, or basalmost region of an isopod antennule, antenna, pleopod, or uropod; contains intrinsic musculature.
Paired (occasionally fused) submedian processes from vas deferens on sternum of male pereonite VII or pleonite 1. (Sing. penis)
A segment of the pereon (= pereomere).
The paired legs of each pereonite.
A segment of the pleon (= pleomere).
The biramous, paired, lamellar appendages of each pleonite.
In all isopods the sixth pleonite is fused to the telson to form a pleotelson. In anthurideans the line of fusion is often visible as a deep dorsal groove or fold.
Juvenile, immature stage of gnathiideans.
Appendages (usually pereopods) adapted for holding or clinging, the dactyl is as long or longer than the propodus, strongly developed and recurved.
In sequential hermaphroditic forms, becoming a functional male (producing spermatozoa) before becoming a functional female (producing eggs).
In sequential hermaphroditic forms, becoming a functional female (producing eggs) before becoming a functional male (producing spermatozoa).
Situated near the base or point of attachment.
Second pair of maxillipeds in gnathiids (appendages of the second thoracomere).
Anteromedial projection of frontal margin of cephalon.
A small articulate piece occurring on the antennules or antennae in some crustaceans, thought to be a remnant of the second ramus (presumably the exopod). Scales rarely occur in isopods.
spine row
Spinose lobe on the mandible, between the molar and incisor processes. The homology of these spines (or setae?) is not well understood.
Small saclike sensory organ, usually containing a granule(s), used to indicate to the animal its orientation; present singly or paired on the pleotelson of some anthurideans.
Having a subchela; forming a pincerlike structure by the dactylus folding back on the propodus.
Dorsal sclerite of exoskeleton on arthropods.
The paired biramous appendages of the isopod pleotelson, representing the appendages of the fused sixth pleonite.
About This Page

Richard Brusca
Arizona-Sonora Desert Museum, Tucson, Arizona, USA

Correspondence regarding this page should be directed to Richard Brusca at

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