1	Head with enlarged forceps-like mandibles projecting anteriorly (male gnathiids)	2
–	Head not as above, without projecting mandibles; body often sac-like (female and juvenile gnathiids)Endnote 7	Gnathiidae spp.
2	Eyes present, with or without pigment; telson variable in shape	3
–	Eyes absent; frontal margin of head (frons) with 3 central processes, laterals larger than middle process; epimeres single, dorsal, laterally projected; telson distinctly triangular (Fig. 12D)	Gnathiacoronadoensis
3	Pleotelson distinctly triangular	4
–	Pleotelson arrowhead or T-shaped with base expanded	8
4	Pleonal epimeres laterally expanded, highly visible; body with few to numerous setae	5
–	Pleonal epimeres not laterally expanded, barely visible; body with relatively few setae	7
5	Frontal margin of head forming broad, transverse, minutely crenulated plate (best viewed ventrally); eyes brown to reddish brown; body setosity light, without numerous setae; pleopods without setae (Fig. 12A)	Caecognathiacrenulatifrons
–	Frontal margin of head not transverse (lobes or processes present); eyes reddish brown; body not hirsute, but with numerous setae; pleopods with setae	6
6	Body mottled with brown pigment; frontal margin of head forming centrally extended narrow lobe with crenulations; mandibles split into 2 articlesEndnote 8	Caecognathia sp. A
–	Body without pigment; frontal margin of head trilobed with 3 central subequal processes; mandibles of single article only (not split into 2 articles) (Fig. 12G)	Gnathiatridens
7	Eyes dark brown, body mottled with brown pigment; frontal margin of head with 3 processes, median process largest and shaped as stepwise pyramid; head with setae and tuberculations (Fig. 12F)	Gnathiasteveni
–	Eyes reddish brown; body without pigmentation; frontal margin of head with central 3-dimensional expansion in shape of box, with 2 large setae extending outward centrally; head with setae, but lacking tuberculationsEndnote 8	Gnathia sp. MBC1
8	Pleotelson distinctly T-shaped	9
–	Pleotelson arrowhead-shaped	10
9	Eyes sessile, dark brown, lens with tuberculations; body speckled with tiny black dots; frontal margin of head produced into single large lobe; pleopods ovate, paddle-like; body hirsute (Fig. 12B)	Caecognathiasanctaecrucis
–	Eyes on distinct ocular peduncles, unpigmented, lens without tuberculations; frontal margin of head with 2 medium–large lateral processes and 4 central subequal processes; pleopods long and narrow; body hirsute (Fig. 12C)	Gnathiaclementensis
10	Pleonal epimeres double (dorsal and ventral); eyes golden/amber in color; frontal margin of head with 3 central, subequal processes; body with numerous scattered setae, but not hirsute (Fig. 12H)	Gnathiatrilobata
–	Pleonal epimeres single (dorsal only)	11
11	Eyes golden or amber in color; head with dorsal carina present; frontal margin of head as 1 broad truncate lobe with medial carina; body hirsuteEndnote 8	Caecognathia sp. SD1
–	Eyes with red and white checkerboard pattern; head without dorsal carina; frontal margin of head with 3 central subequal processes; body not hirsute, but with numerous setae (Fig. 12E)	Gnathiaproductatridens