346
ELVEZIO CHIRARDELLI
and 750 m, the third between 750 and 1000 m, while the individuals
of the fourth stage can only be found a t greater depths. This species
migrates vertically downwards during the winter to deep waters.
The different stages of maturity of S. decipiens have also a typical
vertical distribution in the southern Adriatic and in the Bay of Naples
(Gamulin, personal communication).
S. gaxellae is typical of Antarctic waters. During winter and spring
its length increases by 5 mm per month; growth is quicker in the
summer months, the life cycle is one year and the animal achieves 60 mm
in length in 10 or 11 months (David, 1958b, 1965). According to David
the species lives oiily in Antarctic waters: consequently, the forms
described as S. lyra gaxellae of the Mediterranean (Ghirardelli, 1950a)
must be considered as young specimens of S. lyra (Hamon, 1962). It
is, nevertheless, possible that S. gazellae has diverged from the same
stock as S. lyra at a fairly recent date as an adaptation to cold-water
conditions (David, 1965). Interesting observations are those of Reeve
(1966) on the biology of S. hispida of Biscayne Bay (Florida). This
species has one main breeding season from November to March followed
by a period of summer inactivity, after which the period of rapid
growth and maturity in the latter part of the year begins again. The
majority of the individuals of this species do not live beyond the first
year, a small proportion continue through into the second year, and a
smaller fraction still, according to Owre (1960), live t o their third year.
S . hispida were kept in the laboratory and fed living plankton,
particularly copepods over 1 mm such as Acartia or nauplii of Arternia of
the larger size ; in the experiments, they were found to have food preferences based on both size and quality and mobi1ity”of the food. This species
shows a maximum feeding activity a t a temperature of approximately
25°C. The fluctuations of populations of S. hispida are connected with
the abundance of food. When the number of adult copepods increases
in October, the population of X. hispida shows a significant gain in
size, maturity and number. The average increase in size in the laboratory, in 15 days, is 3.83 mm.
S. in$ata shows a marked polymorphism in relation with the stages
of maturity. This species is present in the Gulf of Naples in two forms
which are morphologically distinct, and in each of which two phases of
sexual maturity can be seen (Ghirardelli, 1951): this is quite similar
to the behaviour described by Thomson (1947) for S. i n$&
in the seas
south-east of Australia. The two forms of Sagitta are characterized by
the ovaries whose length in one form does not extend beyond the
anterior end of the posterior fins ; in the other they do, and their eggs
are lined up reguIarly, in contrast to the short-ovary form whose eggs
ELVEZIO CHIRARDELLI
and 750 m, the third between 750 and 1000 m, while the individuals
of the fourth stage can only be found a t greater depths. This species
migrates vertically downwards during the winter to deep waters.
The different stages of maturity of S. decipiens have also a typical
vertical distribution in the southern Adriatic and in the Bay of Naples
(Gamulin, personal communication).
S. gaxellae is typical of Antarctic waters. During winter and spring
its length increases by 5 mm per month; growth is quicker in the
summer months, the life cycle is one year and the animal achieves 60 mm
in length in 10 or 11 months (David, 1958b, 1965). According to David
the species lives oiily in Antarctic waters: consequently, the forms
described as S. lyra gaxellae of the Mediterranean (Ghirardelli, 1950a)
must be considered as young specimens of S. lyra (Hamon, 1962). It
is, nevertheless, possible that S. gazellae has diverged from the same
stock as S. lyra at a fairly recent date as an adaptation to cold-water
conditions (David, 1965). Interesting observations are those of Reeve
(1966) on the biology of S. hispida of Biscayne Bay (Florida). This
species has one main breeding season from November to March followed
by a period of summer inactivity, after which the period of rapid
growth and maturity in the latter part of the year begins again. The
majority of the individuals of this species do not live beyond the first
year, a small proportion continue through into the second year, and a
smaller fraction still, according to Owre (1960), live t o their third year.
S . hispida were kept in the laboratory and fed living plankton,
particularly copepods over 1 mm such as Acartia or nauplii of Arternia of
the larger size ; in the experiments, they were found to have food preferences based on both size and quality and mobi1ity”of the food. This species
shows a maximum feeding activity a t a temperature of approximately
25°C. The fluctuations of populations of S. hispida are connected with
the abundance of food. When the number of adult copepods increases
in October, the population of X. hispida shows a significant gain in
size, maturity and number. The average increase in size in the laboratory, in 15 days, is 3.83 mm.
S. in$ata shows a marked polymorphism in relation with the stages
of maturity. This species is present in the Gulf of Naples in two forms
which are morphologically distinct, and in each of which two phases of
sexual maturity can be seen (Ghirardelli, 1951): this is quite similar
to the behaviour described by Thomson (1947) for S. i n$&
in the seas
south-east of Australia. The two forms of Sagitta are characterized by
the ovaries whose length in one form does not extend beyond the
anterior end of the posterior fins ; in the other they do, and their eggs
are lined up reguIarly, in contrast to the short-ovary form whose eggs