1	Pereopods 1–3 ambulatory with dactylus shorter than propodus (e.g., Fig. 3C)	2 [Cirolanidae]
–	Pereopods 1–3 prehensile or sub-prehensile with dactylus generally as long as, or longer than propodus and strongly curved (e.g., Fig. 3D)	8
2	Eyes absent; head immersed in pereonite 1 with posterior margin appearing deeply concave; pereon with coxae 4–7 produced beyond posterior margins of their respective pereonites, at least 2 or more visible in dorsal view; lateral margins of pleonite 5 obscured by pleonite 4 (Fig. 7G)	Natatolanacaliforniensis
–	Eyes present; posterior margin of head not appearing distinctly concave; with or without dorsally visible coxae on pereonites; lateral margins of pleonite 5 may or may not be obscured by pleonite 4	3
3	Coxae of pereonites 2–7 well-developed, typically visible in dorsal view and expanded laterally with acute posterior angles; epimeres of pleonites 2–5 well-developed, expanded laterally, with acute posterior angles; pleotelson with squarish to pointed posterior margin and a strong, middorsal longitudinal ridge; margins of pleotelson and uropodal rami notched (Fig. 7F)	Metacirolanajoanneae
–	Pereonites, pleonites, pleotelson and uropods not as above	4
4	Head with prominent spatulate rostral process separating left and right antennules (Fig. 7D, E)	5
–	Head without a prominent rostral process between antennules	6
5	Posterior margin of pleotelson broadly rounded and crenulate; antennular peduncle articles 2 and 3 subequal in length (Fig. 7E)	Excirolanalinguifrons
–	Posterior margin of pleotelson obtusely rounded and acuminate; antennular peduncle article 3 longer than article 2 (Fig. 7D)	Excirolanachiltoni
6	Antennules geniculated, with peduncle article 1 longer than articles 2 or 3, and article 2 arising at right angles to article 1; peduncle of antennae with 4 articles, antennae long and extending beyond pereonite 7; lateral margins of pleonite 5 not obscured by pleonite 4; uropodal rami truncate distally, exopod does not extend to posterior margin of pleotelson (Fig. 7C)	Eurydicecaudata
–	Antennules not geniculated; peduncle of antennae with 5 articles; lateral margins of pleonite 5 obscured by pleonite 4; uropodal rami distally rounded or acuminate, extending beyond posterior of pleotelson	7
7	Uropodal rami with apical notches and not distally rounded; peduncle articles 1 and 2 of antennules fused; coxae of pereonites 5–7 visible dorsally; pereonites, pleonites and pleotelson without dorsal tubercles, carina, or setae (Fig. 7A)	Cirolanadiminuta
–	Uropodal rami rounded distally, without notches; peduncle articles 1 and 2 of antennules not fused; coxae visible dorsally on pereonites 2–7; pleonites 3–5 with row of small tubercles on posterior margins; pleotelson of adult males with two large dorsal submedian tubercles or carinae (Fig. 7B)	Cirolanaharfordi
8	Pereopods 4–7 ambulatory (dactylus shorter than propodus)	9
–	Pereopods 4–7 prehensile (dactylus generally as long as, or longer than propodus and strongly curved); adults parasitic on fishes	19 [Cymothoidae]
9	Dorsal surface of pleon tuberculate, with small to medium tubercles present on posterior margins of at least pleonites 3–5	10
–	Dorsal surface of pleon without tubercles	13 [Aegidae]
10	Pleotelson dorsally setose, lateral margins with single incision	11 [Corallanidae]
–	Pleotelson not dorsally setose, lateral margins without incisions	12 [Tridentellidae]
11	Male head with 3 large horns or tubercles, including 1 rostral and 2 posterolateral between the eyes (female without tubercles); pereonites 2–7 without dorsal setae or tubercles; pleotelson subtriangular with rounded apex, dorsal surface setose except for median longitudinal area (Fig. 8A)	Excorallanatricornisoccidentalis
–	Head of both males and females without horns or tubercles; pereonites 4–7 with dorsal setae and row of small tubercles on posterior margin; pleotelson triangular with subacute apex, entire dorsal surface densely covered with bifid golden setae (Fig. 8B)	Excorallanatruncata
12	Body dorsal surface sculptured with low or small tubercles; head of male with 5 low tubercles, including 1 rostral, 1 pair near anterior margin, and 1 pair near posterior margin; male pereonite 1 with 2 small, median tubercles near anterior margin; female lacking tubercles on head and pereon; pleonites 3–5 with small tubercles on posterior margins; pleotelson minutely tuberculate dorsally with widely rounded, slightly crenulate posterior margin (Fig. 8D)	Tridentellaquinicornis
–	Body dorsal surface sculptured with large processes and numerous tubercles; male head with 2 dorsal posterolateral horns, frontal margin produced into large, upturned process and smaller ventrally projecting rostrum; pereonite 1 with 3 large dorsal processes; all pereonites and pleonites with numerous dorsal tubercles that increase in size and become more spine-like posteriorly; pleotelson triangular with subtruncate apex, dorsally covered with longitudinal rows of large, spine-like tubercles; females much less spinose than males, lacking large processes on head and pereonite 1 (Fig. 8C)	Tridentellaglutacantha
13	Peduncular articles 1 and 2 of antennules greatly expanded (dilated), article 2 with gradual distal process extending 25–50% the distance into article 3; posterior margin of pleotelson truncate, crenulated and fringed with setae (Fig. 8E)	Aegalecontii
–	Peduncular articles of antennules not dilated, article 2 without distal process; posterior margin of pleotelson rounded or subacuminate	14
14	Eyes large, close-set, nearly touching at midline; pleotelson shield-shaped with subacuminate apex and weekly serrated (notched) posterolateral margins; uropodal rami ovate with subacuminate apices (Fig. 8F)Endnote 3	Aegiochusplebeia
–	Eyes medium to large, but distinctly separated and not nearly touching medially; posterior margin of pleotelson rounded; uropodal rami with broadly rounded to truncate apices	15
15	Medial process of uropodal peduncle very long, extending at least 75% of length of endopod	16
–	Medial process of uropodal peduncle extends 50% or less of length of endopod	17
16	Propodi of pereopods 1–3 with large, broad, spine-bearing medial lobe; dactyli of pereopods 1–3 longer than propodi; frontal lamina broadly expanded anteriorly, arrowhead or spatulate shaped (Fig. 9B)	Rocinelabelliceps
–	Propodi of pereopods 1–3 without expanded medial lobe; dactyli of pereopods 1–3 subequal in length to propodi; frontal lamina thin and narrow (Fig. 9E)	Rocinelasignata
17	Medial process of uropodal peduncle extends < 40% of length of endopod; propodi of pereopods 1–3 with 4 stout, recurved acute spines; merus of pereopods 1–3 with 5–8 acute spines (3–5 distal, 2 or 3 proximal) (Fig. 9A)	Rocinelaangustata
–	Medial process of uropodal peduncle extends ~ 50% of length of endopod; propodi of pereopods 1–3 with 4–6 acute spines; merus of pereopods 1–3 with 4 acute spines (3 distal, 1 proximal)	18
18	Propodi of pereopods 1–3 with 5 thin, straight acute spines; apical article of maxillipedal palp with thin, nearly straight, acute spines (Fig. 9C)	Rocinelalaticauda
–	Propodi of pereopods 1–3 with 4–6 stout and recurved acute spines; apical article of maxillipedal palp with stout, recurved acute spines (Fig. 9D)	Rocinelamurilloi
19	Pleopods and uropods not setose	20
–	Pleopods and uropods heavily setose, adapted for swimming (juvenile cymothoids)Endnote 4	unidentified Cymothoidae
20	Body very broad and darkly pigmented; pereon at least 2× as wide as pleon with strongly convex lateral margins (widest at pereonite 5); parasite of barspot cardinalfish and Panamic fanged blenny in Eastern Pacific (Fig. 10A)Endnote 5	Renocilathresherorum
–	Body not as above	21
21	Posterior margin of head weakly to strongly trisinuate; pleon not immersed in pereon	22
–	Posterior margin of head not trisinuate; pleon partially immersed in pereon	23
22	Head not immersed in pereonite 1, posterior border distinctly trisinuate; coxal margins of all or just posterior pereonites with acute or subacute posterolateral angles, coxae may be held close to body (acuminata form) or greatly expanded laterally (aster form); uropods visible dorsally, extending clearly beyond posterior border of pleotelson; parasite of ~ 40 different species of fishes (Fig. 10B)	Nerocilaacuminata
–	Head somewhat immersed in pereonite 1, subquadrate anteriorly with weakly trisinuate posterior border; uropods not visible in dorsal view, typically held concealed under pleotelson and not extending beyond posterior border; parasite of Pacific bumper, pompanos, serranos, carangids, and other fishes (Fig. 10C)	Smenispaconvexa
23	Basal articles of antennules expanded and touching or nearly touching	24
–	Basal articles of antennules not expanded and touching	25
24	Pereopods 4–7 carinate; posterior margin of pleonite 5 trisinuate except in occasional males; parasite of pelagic fishes, including striped mullet off southern California and pompanos and herring off Baja California (Fig. 11A)Endnote 6	Ceratothoagaudichaudii
–	Pereopods 4–7 not carinate; posterior margin of pleonite 5 smooth, not trisinuate; parasite of mullets and flatfish (Fig. 11B)	Ceratothoagilberti
25	Antennules longer than antennae; parasite of California and skipper halfbeaks (Fig. 10D)	Mothocyarosea
–	Antennules shorter than antennae	26
26	Frontal margin of head broadly rounded or truncate (not produced); bases of pereopods 4–7 with distinct carinae; coxae of pereonites 6 and 7 extending to and usually beyond posterior edge of respective pereonites; pleotelson in adult females nearly 2× as wide as long; parasite of at least 30 species of fishes (Fig. 11E)	Elthusavulgaris
–	Frontal margin of head produced; bases of posterior pereopods of females without distinct carinae; coxae of pereonites 6 and 7 not reaching posterior margins of respective pereonites; pleotelson in adult females either as wide as or wider than long	27
27	Merus and carpus of pereopod 4 expanded; bases of pleopods with well-developed accessory lamellae; pleotelson in adult females broadly rounded, ~ 1.5–2.0 × wider than long; males with coxal carinae on pereopods 4–7; parasite of wooly sculpin, northern clingfish, and reef finspot (Fig. 11D)	Elthusamenziesi
–	Merus and carpus of pereopod 4 not expanded; accessory lamellae of pleopodal bases not well developed; pleotelson in adult females ca. as wide as long; males without carinae on posterior pereopods; parasite of surfperch, smelt, gobies, killifish, and grunion (Fig. 11C)	Elthusacalifornica