New Crustacea from the Swan River Estuary. 
35 
3 — NEW CRUSTACEA FROM THE SWAN 
RIVER ESTUARY. 
By J. M. Thomson,, B.Sc. 
Hackett Research Scholar, University of Western Australia. 
Read 14th March, 1944. 
INTRODUCTION. 
The species with which this paper deals were collected during the period 
March to December, 1943, during an investigation of the fauna occurring 
amongst the algae of the estuary. The collections were taken almost entirely 
from the western side of Freshwater Bay, where the rocky nature of the 
bottom provides ample hold for the algae. 
As a faunistic environment the Swan estuary presents some peculiar 
features. The estuary is a drowned river valley but owing to the negligible 
tidal influence on the coast outside its mouth, there is no tidal influence in 
the river. Nevertheless there is a marked variation in the salinity during 
the year. The salinity is practically that of the open ocean in summer; 
whereas in winter, at least in the shallow water near the banks where the 
investigation was carried out, the water became practically fresh after heavy 
downfalls of rain. Thus in summer the fauna tends to be made up of marine 
and estuarine forms, in winter of estuarine and freshwater forms. 
This serves to explain the variation in Geologic type of Crustacea pre- 
sented here, ranging from the marine Mesochra , through the estuarine Coro- 
phium to the practically freshwater Gladioferens. 
The species here described include two Copepods, an Am phi pod, and two 
Isopods. 
DESCRIPTION OF NEW SPECIES. 
Class: COPEPODA. 
Order: CALANOIDA. 
Family: CENTROPAGIDAE. 
GLADIOFERENS, Henry (1919). 
Gladiferens imparipes sp. nov. 
Occurrence. 
Amongst algae, July to December. Large numbers. 
Female. 
Ovigerous, 1-35-1-4 mm, non-ovigerous up to 1-5 mm. Body rather 
robust, cephalothorax oval, its greatest width a little behind the middle. 
Head narrowly rounded in front and projecting below in a rostral promin- 
ence. Last thoracic segment fairly short, expanded laterally into slight lobes 
each bearing a slender seta. 
