1	Pleon composed of 3 free pleonites plus pleotelson; body broad, depressed and platter-like; dorsum with distinct medial carinae (Fig. 18A)Endnote 13	Heteroseroliscarinata [Serolidae]
–	Pleon composed of 1 or 2 dorsally visible free pleonites plus pleotelson	2
2	Pereopod 1 subchelate in both sexes, with broadly expanded propodus and prehensile dactylus (propodus at least 5 × wider than dactylus); pereopod 2 prehensile only in males	3
–	Pereopod 1 ambulatory or only weakly prehensile, propodus narrow (propodus < 2 × as wide as dactylus)	6 [Sphaeromatidae]
3	Head medially fused to pereonite 1; pleopod 5 with both rami lacking transverse pleats or folds; uropods uniramous, lacking exopods	4 [Ancindae]
–	Head and pereonite 1 not fused; both rami of pleopod 5 with transverse pleats or folds; uropods biramous, exopods slender and spine-like; first segment of pleon with 3 suture lines (fused pleonites 1–4) and 2 small triangular processes on posterior margin; pleotelson with rounded posterior border (Fig. 18B)	Tecticepsconvexus [Tecticipitidae]
4	Lateral margins of head strongly produced; pleon with 2 short posterior projections overhanging anterior margin of pleotelson; pleopod 1 biramous; uropodal ramus narrow proximally, then expands at least twofold for ~ 80% of length before tapering to acute point (Fig. 19C)	Bathycopeadaltonae
–	Lateral margins of head weakly produced; pleon without posterior projections; pleopod 1 uniramous; uropodal ramus styliform, widest proximally and tapering to an acute point	5
5	Body broad (L:W ratio ~ 1.7) with densely granulated surfaces; pereonite 1 narrower than pereonites 2–7; pleotelson inflated, distinctly wider than long with truncate apex; eyes slightly elevated on swellings; uropods strongly recurved distally (Fig. 19A)Endnote 14	Ancinusgranulatus
–	Body relatively narrow (L:W ratio > 2.0) with smooth surfaces; pereonite 1 wider than pereonites 2–7; pleotelson not inflated, longer than wide with nearly acute or narrowly rounded apex; eyes not elevated; distal tips of uropods only slightly recurved (Fig. 19B)Endnote 14	Ancinusseticomvus
6	Endopods of pleopods 4 and 5 without branchial pleats or folds	7
–	Endopods of pleopods 4 and 5 with branchial pleats or folds	8
7	In lateral view, anterior margins of coxal plates of pereonites 2–4 appear raised and posterior margins not raised, giving the coxae a somewhat S-shaped appearance; species is fully marine (Fig. 20B)Endnote 15	Gnorimosphaeromaoregonense
–	In lateral view, anterior margins of coxal plates 2–4 are not raised, and coxae do not appear S-shaped; species occurs in brackish or freshwater habitats (Fig. 20A)	Gnorimosphaeromanoblei
8	Pleopods 4 and 5 with branchial pleats on both rami	9
–	Pleopods 4 and 5 with branchial pleats only on endopods	19
9	Uropods of male highly modified, each composed of elongated, cylindrical, or flattened exopod and very short endopod fused to the protopod; both uropodal rami lamellar in females; ovigerous females with 4 pairs of oostegites on pereonites 1–4	10
–	Uropods lamellar in both sexes; ovigerous females with 3 pairs, 1 pair, or no pairs of oostegites	14
10	Pleotelson of males with pronounced posteromedial tooth that completely fills apical notch and extends posteriorly beyond level of notch opening; dorsum of pleotelson with 3 transverse elevations at base, median elevation terminating in a spine; body surface densely granulated; sexual dimorphism pronounced with female body smooth, lacking ornamentation or setae (Fig. 20C)	Discerceisgranulosa
–	Pleotelson of males with highly complex and open apical notch, internal lateral margins of notch with various numbers of teeth forming sinuses of different shapes; body surface not densely granulated; sexual dimorphism pronounced, females without complex pleotelsonic notch, terminal notch either very short and simple or absent; dorsum of pleotelson sculptured with various types of tubercles	11
11	Uropods of male with ventrolateral spines on exopods; female pleotelson stout, with 4 dorsal tubercles and wide, but shallow apical notch (Fig. 21A)	Paracerceiscordata
–	Uropods of male without spines; female pleotelson not as above	12
12	Pleotelson of males long, subequal in length to pereon, with complex medial sinus formed by 2 pairs of teeth, pleotelsonic sinus expanded basally into round foramen overhung by basal knob bearing tall acute spine (spine length ≥ 4 × diameter), sinus then narrowing distally to long thin channel; female pleotelson with small distal notch and 5 dorsal tubercles (1 large medial, 4 smaller lateral); female uropodal exopods with sharply toothed posteromedial margins (Fig. 21D)	Paracerceis sp. A
–	Pleotelson of males relatively short, ca. half length of pereon; pleotelsonic sinus not as above, without round basal foramen, with or without short spine overhanging base of notch; female uropodal exopods without sharply toothed margins	13
13	Male pleotelson with short acute spine (i.e., length subequal to diameter) on basal knob overhanging sinus, interior margins of sinus with 2 pairs of lateral teeth; pleotelson of female elongate, acuminate posteriorly, with 3 dorsal tubercles (Fig. 21C)Endnote 16	Paracerceissculpta
–	Male pleotelson with large dorsal tubercle at base of sinus, interior margins of sinus with 3 pairs of sharp teeth; female pleotelson not as above (Fig. 21B)	Paracerceisgilliana
14	Pleotelson apex entire, upturned; dorsal surface of pleotelson with 2 pairs of prominent tubercles and numerous scattered small tubercles; female sculpturing less pronounced than males (see Bruce and Wetzer 2008: fig. 1)	Pseudosphaeroma sp.
–	Pleotelson without upturned apex, sculpturing not as above	15
15	Pleotelson of males with deeply slit apical notch or expanded foramen, notch may be reduced to small depression or dorsally visible slit in females; uropodal rami subequal in length, typically extending beyond posterior margin of pleotelson; ovigerous females with 1 or 3 pairs of oostegites	16
–	Pleotelson of males and females with shallow terminal notch; uropodal exopod shorter than endopod, rami not extending beyond posterior border of pleotelson; ovigerous females without oostegites	17
16	Pleotelsonic sinus (foramen) distinctly heart shaped with median point in males, but greatly reduced in females; dorsum of pleon with 2 rounded submedian tubercles just lateral to midline on pleonite 5, and 4 similarly spaced tubercles on pleotelson; uropodal rami with crenulated margins (at least in males) (Fig. 22B)	Paradelladianae
–	Pleotelsonic sinus long and narrow, with prominent rounded tubercle barely overhanging anterior base, sinus walls straight sided and finely crenulate; dorsal surface of pleotelson covered with small tubercles; uropodal rami without crenulated margins (Fig. 22A)	Dynoideselegans
17	Frontal margin of head produced as a quadrangular process; antennular articles 1 and 2 dilated; dorsal surface of pleotelson sculptured with 3 longitudinal ridges (Fig. 22C)Endnote 17	Dynamenelladilatata
–	Frontal margin of head not produced; antennular articles not dilated; dorsal surface of pleotelson smooth or tuberculate	18
18	Dorsal surface of pleotelson with many tubercles (Fig. 22E)	Dynamenellasheareri
–	Dorsal surface of pleotelson smooth, without tubercles or ridges (Fig. 22D)Endnote 17	Dynamenellaglabra
19	Uropodal exopods with distinctly serrated outer margins	20
–	Uropodal exopods with smooth or lightly crenulated outer margins	21
20	Dorsal surface of pleotelson lightly sculptured with 2 longitudinal rows of small tubercles, posterior margin with prominent transverse elevation (Fig. 20D)	Sphaeromaquoianum
–	Dorsal surface of pleotelson heavily sculptured with many longitudinal rows of small to large heavy tubercles, posterior margin without prominent transverse elevation (Fig. 20E)	Sphaeromawalkeri
21	Dorsal surface of pereonites, pleonites and pleotelson smooth, without tubercles or other ornamentation; apex of pleotelson rounded and truncate (Fig. 23C)Endnote 18	Exosphaeromainornata
–	Dorsal surface of body with ornamentation; apex of pleotelson acumi­nateEndnote 18	22
22	Pleotelson with produced rhomboid-shaped apical process and concave lateral margins, sides folded inward, forming kind of funnel-like opening when viewed ventrally; dorsum of pleotelson sculptured with 2 basal tubercles, which are continuous with 2 longitudinal ridges that converge posteriorly into a single median ridge; uropods distinctly shorter than pleotelson (Fig. 23E)Endnote 19	Exosphaeromarhomburum
–	Pleotelson triangular, dorsum without parallel ridges; uropods subequal in length to pleotelson	23
23	Dorsal sculpturing subtle, starting on pereonites 6 and 7; pereonite 6 with row of 7 weak tubercles along posterior margin; pereonite 7 with posteriorly directed median process and weak lateral tubercle on each side along posterior margin; pleon with 2 medium tubercles, 1 on each side of midline; pleotelson with 1 strong anteromedial tubercle and 2 weak tubercles lateral to midline (Fig. 23B)	Exosphaeromaaphrodita
–	Dorsal sculpturing distinct on most or all pereonites, comprising either low, weak tubercles or taller, more pronounced tubercles	24
24	Dorsal surface of pereonites with low, weak tubercles along posterior margins; pereonite 1 with 1 very weak median tubercle; pereonites 2–4 with 3 tubercles, 1 median and 2 laterals (1 per side); pereonites 5 and 6 with row of 7 tubercles, 1 at midline and 3 laterals per side; pereonite 7 with weak median process and paired lateral tubercles; pleotelson with 2 small anterior tubercles (Fig. 23A)	Exosphaeromaamplicauda
–	Dorsal surface of all pereonites sculptured with heavy, strong tubercles giving body appearance of 7 prominent longitudinal rows of tubercles; pereonite 1 with 2 transverse rows of tubercles; pereonites 2–7 each with 1 transverse row of 7 tubercles; pereonite 7 with strong median process and 3 lateral tubercles per side; pleotelson with 3 strong medial tubercles on either side of midline, plus numerous smaller tubercles scattered over dorsal surface (Fig. 23D)	Exosphaeromapentcheffi