344
ELVEZIO CHIRARDELLI
may be very good hydrologic indicators. I n some cases, as for example
in the Adriatic, environmental factors act as selective factors on the
number of the species. I n the south Adriatic there are ten: Sagitta
minima, S. inJlata, S. serratodentata, S. setosa, S. lyra, S. bipunctata, S.
decipiens, X. hexaptera, Krohnitta subtilis and Pterosagitta draco (see
Hoenigman et al., 1961 ; Vu6eti6, 1963 ; Hure, 1955) ; in the northern
Adriatic this number decreases (Scaccini and Ghirardelli, 1941) and in
the Gulf of Trieste, where there are considerable variations in salinity
and temperature, the endemic species are only three : Sagitta setosa, S.
minima, S. inJlata and perhaps only S. setosa and S. minima can
reproduce in the Gulf of Trieste. S. bipunctata and S. serratodentata are
accidentally collected in the Gulf (Ghirardelli and Specchi, 1965 ;
Ghirardelli, 1 9 6 6 ~ ) .
Some chaetognaths also have value as fishing indicators, e.g.
Sagitta lyra (Le Brasseur, 1959)) S. serratodentata, S. setosa, S. elegans,
S. crassa, etc. Sagitta crassa also is an important food for larval stages
of Ammodytes personatus and other fishes (Murakami, 1957).
I n any event, chaetognaths should be regarded as good indicators
of conditions in the sea, provided that knowledge of the distribution and
life history of each species is given more precisely in the future; and
they will be of high value in fisheries research (Murakami, 1957). This
matter is more amply dealt with by Alvarifio (1965, 196713) and
Furnestin et al. (1966) to whom one should refer for further references
and information.
We would here summarize rather the main results of research on
the cycles of sexual maturity. The number of the generations produced
in one year obviously varies according to the different species, but is
also correlated with the environment. Generally, the number of
generations increases as the distance from the poles becomes greater
(Owre, 1960). S. elegans (Kramp, 1939; Ussing, 1938; Alvarifio, 1965)
only reproduces once per year in the Arctic and Subarctic regions. The
same applies to S. gazellae (David, 1955) in the Antarctic regions. S.
elegans reproduces two to five times per year as its distribution becomes
more southerly. Tropical species reproduce throughout the whole year.
Thus, for instance, 8. elegans a t Port Erin (Pierce, 1941) has only
one maturity period, from January to April according to the data of
1936, from February to May according t o data gathered in 1937. It
appears therefore that seasonal conditions may have an influence on
the period of seuxal maturity. I n the North Sea (Wimpenny, 1937)
and off the island of Nantucked (Georges Bank), the periods of maturity
may be two, one in spring and one in autumn (Clarke et al., 1943).
Differences in length among the specimens in the third stage have been
ELVEZIO CHIRARDELLI
may be very good hydrologic indicators. I n some cases, as for example
in the Adriatic, environmental factors act as selective factors on the
number of the species. I n the south Adriatic there are ten: Sagitta
minima, S. inJlata, S. serratodentata, S. setosa, S. lyra, S. bipunctata, S.
decipiens, X. hexaptera, Krohnitta subtilis and Pterosagitta draco (see
Hoenigman et al., 1961 ; Vu6eti6, 1963 ; Hure, 1955) ; in the northern
Adriatic this number decreases (Scaccini and Ghirardelli, 1941) and in
the Gulf of Trieste, where there are considerable variations in salinity
and temperature, the endemic species are only three : Sagitta setosa, S.
minima, S. inJlata and perhaps only S. setosa and S. minima can
reproduce in the Gulf of Trieste. S. bipunctata and S. serratodentata are
accidentally collected in the Gulf (Ghirardelli and Specchi, 1965 ;
Ghirardelli, 1 9 6 6 ~ ) .
Some chaetognaths also have value as fishing indicators, e.g.
Sagitta lyra (Le Brasseur, 1959)) S. serratodentata, S. setosa, S. elegans,
S. crassa, etc. Sagitta crassa also is an important food for larval stages
of Ammodytes personatus and other fishes (Murakami, 1957).
I n any event, chaetognaths should be regarded as good indicators
of conditions in the sea, provided that knowledge of the distribution and
life history of each species is given more precisely in the future; and
they will be of high value in fisheries research (Murakami, 1957). This
matter is more amply dealt with by Alvarifio (1965, 196713) and
Furnestin et al. (1966) to whom one should refer for further references
and information.
We would here summarize rather the main results of research on
the cycles of sexual maturity. The number of the generations produced
in one year obviously varies according to the different species, but is
also correlated with the environment. Generally, the number of
generations increases as the distance from the poles becomes greater
(Owre, 1960). S. elegans (Kramp, 1939; Ussing, 1938; Alvarifio, 1965)
only reproduces once per year in the Arctic and Subarctic regions. The
same applies to S. gazellae (David, 1955) in the Antarctic regions. S.
elegans reproduces two to five times per year as its distribution becomes
more southerly. Tropical species reproduce throughout the whole year.
Thus, for instance, 8. elegans a t Port Erin (Pierce, 1941) has only
one maturity period, from January to April according to the data of
1936, from February to May according t o data gathered in 1937. It
appears therefore that seasonal conditions may have an influence on
the period of seuxal maturity. I n the North Sea (Wimpenny, 1937)
and off the island of Nantucked (Georges Bank), the periods of maturity
may be two, one in spring and one in autumn (Clarke et al., 1943).
Differences in length among the specimens in the third stage have been