Comparative biology and morphology of marsupial development in Leptomysis and other mediterranean mysidacea (Crustacea)

Abstract

It was possible to rear the swarming, nearshore, and benthopelagic mysid Leptomysis lingvura G. O. Sars in the laboratory with good results. This allowed the whole process of development from oogenesis to the juvenile stage to be examined. Supplementary examinations were made on five further species which belong to the subfamilies Siriellinae and Mysinae. The eggs of the first brood clutch are produced in the ovarian tubes most probably during three moult intervals; the subsequent clutches appear during one interval. The colour of the yolk differs between species and corresponds to the colour conditions of the prefered habitats. The eggs are extruded from the paired ovaries into a pair of egg sacs. Following this they are fertilized in the marsupium. Marsupial development takes on the average 14.9 days at 16 °C. The young pass through three main stages. The following terminology is proposed: embryonic stage, nauplioid stage, and postnauplioid stage. During the embryonic stage development proceeds as is characteristic for Mysidacea. The embryonic period takes 4.6 days and is terminated by hatching from the egg membrane. The freshly hatched nauplioid corresponds in its most important features to the classic nauplius stage. Following this all body segments and appendages of the adults are formed without intervention of a moult. The nauplioid stage takes 6.6 days and ends with the first larval moult. The subsequent postnauplioid stage is liberated after 3.7 days from the brood pouch with the active help of the parent. Immediately after liberation the young undergoes a second larval moult to the juvenile stage which largely represents the adults. The abdomen of the nauplioid stage bears setae and/or spines, and in some species a caudal furca. These features disappear completely at the first larval moult. In spite of the lack of the manca stage which occurs in the Isopoda and related orders, the Mysidacea have conserved plesiomorphic features which are not present in other orders of recent Peracarida: they hatch from the egg as a nauplius stage and in some species the nauplius carries a caudal furca. The embryonic time ends at a less advanced stage than in the other orders.