Copepods from ground waters of Western Australia, I. 
internal margin with a row of small spinules, on its 
distal and subdistal margin with 4-5 rows of thin 
setules. 
Leg 5. Spinous seta about as long as the plumose 
seta; setae not reaching to the posterior margin of 
the genital segment. 
Leg 6 consisting of two small spines and one long 
plumose seta; characteristic group of small pores 
present at its basis. 
Caudal rami about 3 times longer than broad, 
without cilia on the inner margins; dorsal seta 
longer than the apical outer seta, inner seta about 
2.5 times longer than corresponding outermost. 
Male 
Smaller than females, total body length, 
excluding antennule and caudal setae, 1270 pm. 
Antennule geniculate, with integumental pits as in 
females. Spine and pit pattern on the basipodite 
and endopodite of antenna, structure of legs 1-5 
and ornamentation of fifth thoracic segment as in 
females. Leg 6 consisting of a protuberance bearing 
one stout spine and two plumose setae. 
Affinities 
Mesocyclops is a cosmopolitan and widespread 
genus found mainly in surface fresh waters, rarely 
in ground waters. It includes 66 species and 
subspecies, which are especially common in the 
tropics and subtropics, a few species also occur in 
temperate and arctic regions. 
Taxonomic understanding of the genus has 
greatly improved during recent years on account 
of recognition of formerly overlooked micro¬ 
characters, such as morphology of the hyaline 
lamella on the distal segment of the antennula, the 
presence or absence of spine patterns on the 
antennular segments, the presence or absence of 
spines on the maxillulary palp, the armature of the 
intercoxal plate of leg 4, the ornamentation of the 
spines on the distal segment of the endopodite of 
leg 4 and the presence or absence of setules on the 
fifth thoracic segments (Van de Velde 1984; Dussart 
and Fernando 1988; Reid 1993). 
Following Kiefer's (1981) excellent review of 
Mesocyclops, the closest relatives to M. brooksi are 
M. notius and M. australiensis. 
From the above species, M. brooksi is readily 
distinguishable by the shortness of the genital 
segment, the different length ratio between inner 
and outer distal spines on the endopodite 3 of leg 4 
(subequal in M. brooksi, the inner shorter than outer 
in both M. australiensis and Al. notius), the different 
serration along the margins of the inner apical 
spine of the endopodite of leg 4, and the shorter 
caudal rami. 
Additionally, a salient feature of tire new species 
is the integumental pits on the dorsal surface of the 
antennule and antenna, both in male and females. 
75 
Circular pits on some segments of the antennule in 
Mesocyclops species were firstly pointed out by Von 
Daday (1906), who interpreted them as 
integumental tubercles. Subsequently, Reid and 
Saunders (1986) reported similar structures in 
specimens of Mesocyclops aspericomis (Von Daday, 
1906) from Venezuela, considering them as sensory 
structures, advantageous in spatially restricted 
habitats. Nishida (1986) showed identical 
structures in marine cyclopoids of the genus 
Oithona, interpreting them as chemo- or 
mechanoreceptors in mating behaviour, which 
could represent "areas of increased friction during 
copulation". Reid and Saunders (1986) also 
referred to such integumental pits in species of the 
genus Thermocyclops, suggesting that closer 
investigations of these structures should be carried 
out in future species descriptions. 
Etymology 
Named after Mr R.D. Brooks, a collector of the 
new species. 
Genus Microcyclops Claus, 1893 
Microcyclops varicans (G. O. Sars, 1863) 
Material Examined 
Australia: Western Australia: 2 9 (WAM 196, 
197-94), Cashen Well, Exmouth Gulf Station (BES 
2146), 22°29'S, 114°06'E, 24 May 1993, W.F. 
Humphreys and R.D. Brooks; 1 9 (WAM 198-94), 
River Well, Ashburton River (BES 2318), 22°00'S, 
115°02’E, 26 June 1993, W.F. Humphreys and R.D. 
Brooks; 1 9 (WAM 199-94), Dry Swallet Cave (C- 
18), Cape Range (BES 2372), 22°05'S, 114°00'E, 12 
July 1993, R.D. Brooks; 1 9 (WAM 200-94), 
Number 8 Bore, Cape Range peninsula (BES 2379), 
22°45'S, 114°3TE, 20 July 1993, R.D. Brooks. 
Genus Apocyclops Lindberg, 1942 
Apocyclops dengizicus (Lepechkine, 1900) 
Material Examined 
Australia: Western Australia: 1 9 (WAM 201- 
94), Marina piezometer bore C, Exmouth (BES 
2234); 21 °57'S, 114°08'E, 16 June 1993, R.D. Brooks. 
REFERENCES 
Cvetkov, L. (1968). Un filet pheatobiologique. Bullettin 
Institute Zoologie Musee, Sofia 27: 215-219. 
Defaye, D. and Kawabata, K. (1993). Mesocyclops 
dissimilis n. sp., from Lake Biwa, Japan (Copepoda, 
Cyclopoida). Hydrobiologia 257: 121-126. 
Dumont, H.J. and Maas, S. (1985). Mesocyclops cuttacuttae 
n. sp. from a cave in Northern Australia (Crustacea: 
Copepoda, Cyclopoida). The Beagle, Occasional Papers 
