Copepods from ground waters of Western Australia, I. 
Caudal rami, 3.6 (holotype), 3.5-3.7 (6 paratypes) 
times longer than broad; lateral seta inserted at 
distal half of ramus; dorsal seta shorter than 
ramus; terminal inner seta slightly longer than 
outermost. 
Antennule 11-segmented, shorter than first 
prosomite; basipodite armed with 9 rows of small 
spinules, three dorsal, well-developed plumose 
setae and 7-8 lateral setae; remaining setation as in 
Figure 2. 
Antenna 4-segmented; basipodite with well 
developed exopodal seta reaching about tip of the 
second segment, and one inner, subdistal plumose 
seta [type 3a, according to Reid (1991)]; first 
segment with one seta, second segment with eight 
setae, terminal segment with seven setae; no spine 
pattern was observed on both frontal and caudal 
side of the basipodite. 
Maxilliped 4-segmented, comprising syncoxa, 
basis and 2-segmented endopodite; syncoxa armed 
with 3 inner plumose setae representing vestigial 
endites and a row of small spinules; basis with two 
inner plumose setae and numerous long spinules; 
first endopodal segment bearing a single spinulose 
seta and a row of 5-6 spinules, second endopodal 
segment with a spinulose seta and two shorter 
naked setae. 
Mandible, maxillule and maxilla without 
particular characteristics as compared to those of 
congeners. 
Swimming legs 1-4 with 2-segmented rami. 
Spine and setae formula of distal segments of 
exopodites 3.4.4.2 and 5.5.5.5, respectively. 
Couplers of all legs lacking ornament. Spine on the 
basipodite of leg 1 well developed, reaching about 
tip of distal segment of endopodite. 
Leg 4, coxa with four rows of spinules, arranged 
as in Figure 15; distal segment of the endopodite 
about 2 times longer than broad, armed with one 
apical spine, slightly longer or about as long as the 
segment. 
Leg 5 consisting of one free segment, slightly 
longer than broad; spine slightly shorter than 
segment. 
Male (Allotype) 
Length 530 pm. Habitus slender. Antennule 
geniculate, 17-segmented. Leg 5 similar to that of 
female. Leg 6 consisting of two spiniform setae, 
ventral seta shorter and stouter than dorsal one. 
Caudal rami sexually dimorphic, shorter (L/l = 
2.9-3.1) than those of female. 
Affinities 
Tine genus Metacyclops (sensu Lindberg 1961) is 
widespread in tropical and temperate regions. At 
present it includes 52 named species and 
subspecies, only two, M. arnaudi and M. arnaudi 
platypus, are recorded from Australia. 
71 
Lindberg (1961) established two species-groups 
within the genus, viz. the minutus-group and the 
gracilis-group, embracing species characterized by 
one or two distal spines on the endopodite 3 of leg 
4, respectively. M. mortoni is a member of the 
minutus-group, but it does not match any species 
in either Lindberg's (1961) or Herbst's (1988, 1990) 
keys of Metacyclops, because of the combination of 
the following characters: antennula 11-segmented, 
with first segment spinulose; basipodite of the 
antenna with 2 setae; legs 1-4 spine formula 3.4.4.2, 
endopodite 3 of leg 4 with one apical spine; 
couplers of legs 1-4 lacking ornament; inner caudal 
seta longer than outermost, male leg 6 consisting of 
2 setae. 
The spine formula 3.4.4.2 of legs 1-4 is a striking 
feature of the new species; within the genus 
Metacyclops deviation from the characteristic 
formula 3.4.4.3 has been reported only in M. 
trispinosus Dumont, 1981, from West Africa, which 
has a spine formula 3.3.3.3. 
Etymology 
The species is dedicated to Mr D.W. Morton in 
recognition of his recent valuable contributions to 
the knowledge of Australian copepods. 
Genus Mesocyclops G. O. Sars, 1914 
Mesocyclops brooksi sp. nov. 
Figures 16-28 
Material Examined 
Holotype 
9 (WAM 193-94), Bobs Well, Ashburton River, 
Western Australia, Australia (BES 2333), 22°29'S, 
115°23'E, 28 June 1993, W.F. Humphreys and R.D. 
Brooks. 
Paratypes 
Australia: Western Australia: 1 9,1 <5, same 
data as holotype (WAM 194, 195-94). 
Description 
Female 
Total body length 1350 pm (holotype), 1320 pm 
(paratype). Fifth thoracic segment with few setules 
laterally. Genital segment about as long as broad. 
Owing to the preparation the seminal receptacle is 
partially obscured in both specimens, pore canal 
recurved. 
Antennule 17-segmented, reaching the distal 
margin of the third thoracic segment; spinule 
patterns are present on segments II-X; segments 
IV-V with two (IV) or one (V) crenelate Iamellas; 
segments I-IV with several rows or groups of small 
integumental circular pits on dorsal surface; distal 
