44 
longer than proximal; lateral armature arising in proximal half, 
consisting of | pinnate and 2 bare setae; apical armature consisting 
of 5 geniculate setae (1 geniculate seta fused basally to 1 pinnate seta 
and small tube pore; see insert); distal endopod segment with row of 
spinules along abexopodal margin and 2 transverse hyaline frills 
subapically. 
Labrum with elaborate spinular ornamentation and pores as in 
Fig. 5A-B. 
Mandible (Fig. 3C) with well developed gnathobase bearing 
several fine, multicuspidate teeth around distal margin and 1 pinnate 
spine at dorsal corner; | row of spinules near base of palp. Palp 2- 
segmented; proximal segment without ornamentation; distal segment 
with 4 naked setae arranged in 2 pairs; subapical pair fused basally. 
Paragnaths (Fig. 5A) strongly developed lobes with medially 
directed hair-like setules, separated by medial lobe covered with 
dense pattern of short setules. 
Maxillule (Figs 2A, SA—B). Praecoxa without ornamentation; 
arthrite elongate, strongly developed, with 2 naked setae along outer 
margin, 2 short setae on anterior surface, and 6 spines/setae around 
distal margin; 3 distal spines unipinnate and bearing pore (Fig. SA— 
B) at base of proximal spinule. Coxa with cylindrical endite bearing 
2 naked setae and | curved, pinnate spine. Palp represented by basis 
and possibly incorporated rami, forming cylindrical segment with 5 
naked setae around distal margin. 
Maxilla (Fig. 2B) without surface ornamentation on syncoxa; 
medial margin membranous and bearing | coxal endite with 1 
pinnate spine and 2 naked setae. Allobasis drawn out into very long, 
slightly curved, unipinnate claw; allobasal claw with spinules along 
distal half of inner margin and transverse row of posterior spinules 
halfway the length; accessory armature consisting of | pinnate spine 
on posterior surface, and | tube pore along outer margin. Endopod 1- 
segmented, and located on anterior surface of allobasis; ornamented 
with 2 naked setae. 
Maxilliped (Fig. 3D) without ornamentation on syncoxa. Basis 
smooth without ornamentation. Endopod drawn out into very long, 
unipinnate claw without accessory armature; longer than basis. 
Swimming legs P1—P4 (Fig. 4A—D) with wide intercoxal sclerites 
and well developed praecoxae, both without ornamentation. Coxae 
and bases with anterior rows of surface spinules as figured. Bases 
without outer seta. Exopods 3-segmented, endopods 3-segmented 
(P1), or 1-segmented (P2—P4). 
P1 (Fig. 4A) with large coxa; with | row of spinules on anterior 
surface. Basis with | strong, bipinnate spine and long setules along 
inner margin; rows of spinules along outer distal margin, and near 
base of exopod. Exp-1 and -2 with | bipinnate slender spine; exp-3 
with | bipinnate spine, 1 long unipinnate seta and 2 bipinnate 
weakly geniculate setae. Endopod slightly shorter than exopod; enp- 
1 with 1 bipinnate inner seta; enp-2 without seta; enp-3 with 2 
geniculate setae apically. All segments of exopod and endopod 
ornamented with small spinules and setules along outer and inner 
margin as figured. 
P2—P4 (Fig. 4B—D). Coxae without ornamentation; basis with 
row of spinules along outer margin; additional spinules along inner 
margin, and on anterior surface of P3—P4; all segments with pattern 
of spinules as figured; inner and outer margins of exopod and 
endopod segments with setules or spinules. P2 exp-1 longer than 
exp-2 and -3 combined; P3 exp-1 subequal to exp-2 and -3 com- 
bined; P4 exp-1 shorter than exp-2 and -3 combined. P2—P4 with 
strong inner seta on enp-2, outer exopodal spines slender, terminal 
setae very long. Endopods minute, represented by small segment. 
Spine and setal formulae as in generic diagnosis. 
Fifth pair of legs (Fig. 2C, E) fused to supporting somite. 
Baseoendopod represented by small, outer setophore bearing basal 
W. LEE AND R. HUYS 
seta; endopodal lobe not expressed. Exopod forming minute seg- 
ment with | bipinnate apical seta. 
MALE. Body larger than in 2. Somites bearing P2—P4 wider than 
in 2. Body length 515-690 um (n=20; mean = 622 um; measured 
from anterior margin of rostrum to posterior margin of caudal rami). 
Largest width measured at P6-bearing somite: 109 um. 
Prosome (Fig. 1C) 4-segmented, comprising cephalothorax and 3 
free pedigerous somites. No distinct demarcation between urosome 
and prosome. Cephalothorax with smooth posterior margin; pleural 
areas small and rounded; sensillae and few pores present as illustrated 
in Fig. 1C. Rostrum not defined at base (Fig. 1C), with pair of tiny 
sensillae near apex. 
Pedigerous somites not covered with spinules. All prosomites 
without defined hyaline frills but separated by large membranous 
areas. Body without marked constrictions between individual 
somites; P4-bearing somite not distinctly narrower than others. 
Urosome (Fig. 1C) 6-segmented, comprising P5-bearing somite, 
genital somite and 4 abdominal somites. P5-bearing somite and 
genital somite without surface ornamentation, except for pairs of 
dorsal sensillae. Free abdominal somites, including anal somite, 
with several rows of spinules laterally and ventrally; dorsal hind 
margin smooth without any ornamentation. Hyaline frills of 
urosomites not present. Spermatophore extraordinarily large, about 
half of body length. 
Antennule (Figs 3E, 5C) 10-segmented; haplocer, with 
geniculation between segments 7 and 8. Segment | longest, un- 
armed. Some elements on segments 4, 6 and 8 (inserts in Fig. 3E; 
Fig. 5C) very small. Segment 5 not swollen. Segment 8 with | small 
fused spine in median anterior margin. Armature formula: 1-[0], 2- 
[7], 3-[6], 4-[1 + 1 small spine], 5-[4 + (1 + ae)], 6-[1], 7-[1], 8-[1 + 
1 fused spine], 9-[4], 10-[5 + acrothek]. 1 seta on fifth segment very 
small [arrowed in Fig. SC). Apical acrothek consisting of slender 
aesthetasc and 2 naked setae. 
Inner basal spine of P1 modified into robust barbed element (Fig. 
4E). P2—P4 as in &. 
Fifth pair of legs (Figs 2F—H, 5D) fused to supporting somite. 
Baseoendopod with short setophore bearing outer basal seta; 
endopodal lobe not expressed. Exopod with 2 elements; 1 apical 
tripinnate spine fused to exopod, and | small slender bipinnate seta 
on subapical outer margin (Figs 2G, 5D); abnormal exopod (Fig. 
2H) resembling female condition frequently observed on one or 
either side; only 1 out of 9 males showed normal P5 exopod on both 
sides. 
Sixth pair of legs (Figs 2F, 5D) asymmetrical; represented on both 
sides by small membranous plate (fused to ventral wall of support- 
ing somite along one side; articulating at base and covering gonopore 
along other side; dextral and sinistral configurations present); with- 
out additional ornamentation. 
ETYMOLOGY. The species is named in honour of Dr William F. 
Humphreys (Western Australian Museum, Perth), who collected the 
material. 
DISCUSSION 
Inermipes gen nov. is placed in the family Ameiridae on account of 
the morphology of the antennules, mouthparts and the sexual dimor- 
phism in the inner basal spine of leg 1. Within the group of 
freshwater ameirids it can be readily identified by the unisetose 
antennary exopod, the lack of the outer basal seta on P1—P4 the 
extreme reduction in the swimming legs (particularly the endopods) 
