Ecology of the burrowing amphipod, Pontoporeia affinis, in Lake Michigan / by Wayne Paul Alley.

R ESULTS

LIFE HISTORY AND REPRODUCTION
The development of Pontoporeia affinis is direct through the
immature instars. Sexes become distinguishable in later instars on the
basis of obstegite formation in the females and increased length of the
antennal flagella of the male (Fig. 9).
The characteristics of the adult male are morphological modifications that are considered adaptions for a pelagic existence. The
elongation of the pleopods and the setation of the last uropods increase
its swimming capabilities. SegerstrRle (1950) felt that the adult male
seldom lives longer than one week, and apparently does not feed as its
alimentary canal is invariably empty and its mandibles are reduced in
size. The adult male ranges from 7 to 9 mm in length in Lake Michigan.
The thoracic region of the adult female becomes more robust in
appearance with the development of the large marsupial plates, or
oUstegites, that form on the inner surface of the coxal plates of the
second to fifth pereiopods. The adult female ranges from 6 to 9 mm in
length in Lake Michigano Juday and Birge (1927) found the number of
eggs carried by each adult female ranged from 13-28 with a general
average of 20.
The female dies after producing its brood. The body begins to
degenerate during the course of the incubatory period, becoming trans

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