Egg Pouches and Other Reproductive Structures in Pelagic Chaetognatha 1 
Angeles Alvarino 2 
ABSTRACT: Some specimens of Eukrohnia bathyantarctica David from the col- 
lections obtained by the United States Antarctic Research Program were observed 
which had marsupial sacs full of eggs, and hanging from the opening of the ovi- 
ducts. The eggs in the sacs, in various specimens, appeared at different stages of 
development, from the gastrular stage up to the eclosion of the larvae. 
The breeding pattern in Chaetognatha either 
is seldom mentioned or is hidden in the perti- 
nent literature among other subjects related to 
the group. For this reason a review of the breed- 
ing characteristics merits specific attention. 
Norgaard (1905) was the first to indicate the 
brood sacs in Eukrohnia , when he stated: "In 
samples from the Vest Fiord there were speci- 
mens with eggbags. The wider part of the fin 
was bent downwards, this forming a hollow in 
which the eggs lay tightly pressed together.” 
Similarly, Ritter-Zahony (1910) observed: 
"Die Eier waren vollstandig aus den Ovarien 
ausgetreten und bildeten zwei pflaumenformige, 
von einer gallertigen Hiille umgebene Ballen 
am Riicken des Tieres.” He included illustra- 
tions of this sac for E. hamata (Mobius). How- 
ever, considering the extension of the laminar 
part of the fin, the species probably corres- 
ponded to E. hathypelagica Alvarino. Ritter- 
Zahony (1910) also explained: "Diese Eier- 
sackchen lagen nebeneinander zu einem am 
Rumpf-, drei Vierteln am Schwanzabschnitt.” 
Ritter-Zahony (1911), describing E. fowleri , 
stated: "Eiersackchen, die wie bei E. hamata 
von den eigentiimlich deformierten Seitenflos- 
sen umhullt waren.” He also noticed small 
brooding sacs in E. hamata from the Antarctic. 
These specimens probably belonged to E. bathy- 
antarctica David. 
1 Contribution from the Scripps Institution of Ocean- 
ography, La Jolla, California. These studies have been 
supported by the Marine Life Research Program, the 
Scripps Institution’s component of the California 
Cooperative Oceanic Fisheries Investigations; and by 
the National Science Foundation (NSF GB-2861). 
Manuscript received September 15, 1967. 
2 Scripps Institution of Oceanography, La Jolla, 
California 92037. 
Kuhl (1928) made similar observations for 
Eukrohnia. 
At Point Barrow, Alaska, MacGinitie (1955) 
observed two mature specimens of E. hamata 
40 mm long "carrying young in a marsupium 
formed by folding of the posterior lateral fins.” 
He also explained that when the material was 
brought to the laboratory "some of the young, 
which were 3 mm long, began escaping from 
the marsupium.” 
Tchindonova (1955) stated that the majority 
of the specimens of E. fowleri were sexually 
mature, with ovarian sacs that had already rup- 
tured. This probably refers to the brooding sacs. 
David (1958) indicated that one specimen of 
E. bathyantarctica had "an egg-shaped opaque 
structure appended to the oviduct.” He also 
suggested that in E. bathyantarctica and E. fowl- 
eri "the seminal vesicles function as spermato- 
phores and are attached intact to the external 
opening of the oviducts by a fine tube which is 
probably the vas deferens.” David (1958) was 
unable to find a single specimen of E. fowleri 
or E. bathyantarctica with mature seminal vesi- 
cles, and thus he considered the sacs observed 
attached to the oviducts to be remains of the 
seminal vesicles. These small sacs, which are 
also illustrated in David’s figures 2a and 3c 
might be the brooding sacs beginning to de- 
velop. 
Ghirardelli (1959^) was also able to observe 
specimens of E. bathyantarctica and explained: 
"le spermatofores hanno la forme di un fiasco, 
limitato esternamente da una membranella anista 
resistente. Questa membrana forma un prolun- 
gamento (simile appunto al collo di un fiasco) 
che si trova infilato nell’ orificio genitali fem- 
minile, i cui bordi si presentano assai rilevati. 
