Chaetognatha of the Monsoon Expedition — Alvarino 
345 
respective publications. Davids (1959) records 
of S. zetesios should have included S. planctonis. 
Fowler (1906) recorded S. zetesios and, in spe- 
cies "incertae,” S. planctonis. Schilp ’s (1941) 
records of S. planctonis may apply to S. zetesios. 
Ritter-Zahony (1911) observed 5“. planctonis 
at about 44° S in the Southwest Indian Ocean 
and in the Subantarctic-Antarctic waters of the 
Southwest Indian Ocean. Tokioka’s (1940) rec- 
ords of S. planctonis from Australian waters are 
accurate, but those of S. planctonis from Japa- 
nese waters may apply to S. zetesios. The dis- 
crepancy Tokioka refers to in relation to the 
percentage of the length of the tail segment to 
the total length between those populations indi- 
cates that he was dealing with two different 
species: S. zetesios in the Japanese waters and S. 
planctonis in the New South Wales region. This 
is also understood when observing the drawings 
that appear on page 374 (loc. cit.): Fig. 8A is 
S. planctonis (the anterior end of the anterior 
fins reaches the level of the middle of the ventral 
ganglion); and Fig. 8D is S. zetesios (the an- 
terior end of the anterior fins reaches the level of 
the posterior end of the ventral ganglion). (See 
original descriptions of Steinhaus, 1896, and 
Fowler, 1905.) 
Krohnitta subtilis populates the Equatorial 
and Central Indian Ocean, and does not reach 
the boundaries of the Subtropical Convergence. 
The Indo-Pacific populations connect through 
the Indonesian seas. Other records in the Indian 
Ocean: Burfield and Harvey (1926), Fowler 
(1906), George (1952), Rao (1958*), Ritter- 
Zahony (1910, 1911), Schilp (1941), and To- 
kioka (1940, 1955, 1956*,*). 
K. pacifca was observed only at station 8 
( north of Flores Island ) . This species is not so 
widely distributed as is its congeneric K. subtilis, 
and is for the most part restricted to the Equa- 
torial waters. This is the only equatorial-tropical 
species of chaetognath common to these regions 
in the Atlantic, Indian, and Pacific oceans. The 
presence of this species in the Equatorial -Trop- 
ical Atlantic suggested one of two hypotheses: 
either it is conveyed by the Agulhas Current into 
the Benguella Current and assimilated by the 
Equatorial Current, or the populations of K. 
pacifica at both sides of Central America, al- 
though long isolated, still somehow remain un- 
changed morphologically, but the process of 
divergence is noticed. There are no conveniently 
available samples and data from the Atlantic to 
explain this problem. However, Heydorn (1959) 
did not observe it in the Benguella region. 
Other records in the Indian Ocean: Burfield 
and Harvey (1926) under the K. subtilis syn- 
onymy; Chacko (1950), Doncaster (1903), 
Fowler (1906), George (1952), Oye (1918) 
as K. kerberti] Pillai (1945), Rao (1958^, b) 
Rao and Ganapati (1958), Ritter-Zahony 
(1910), Schilp (1941), Tokioka (1955, 1956a, *), 
and Varadarajan and Chacko (1943). 
Pterosagitta draco inhabits the Equatorial and 
Central Indian waters, and its extension south- 
ward is apparently limited by the Subtropical 
Convergence. Other records in the Indian Ocean: 
Baldasseroni (1915), Beraneck (1895), Bur- 
field and Harvey (1926), Doncaster (1903), 
Fowler (1906), George (1952), Rao ( 1958^, 
b), Rao and Ganapati (1958), Ritter-Zahony 
(1910, 1911), Schilp (1941), and Tokioka 
(1940, 1955, 1956a, b). 
Eukrohnia hamata was recorded at the sta- 
tions along the southernmost part of the region 
sampled, in hauls taken from 283 and 268 m 
deep, and the records taken in the central gyral 
were from 1878 m deep. There are two possible 
alternatives: (1) E. hamata does not progress 
northward from the boundary of the Subtropical 
Convergence in the Indian Ocean, or (2) if it 
does progress northward it is not very abundant 
and hence is missed by the sampling, or it may 
appear in layers deeper than those mostly sam- 
pled. Other records in the Indian Ocean: Bur- 
field and Harvey (1926), Fowler (1906), Ritter- 
Zahony (1911), and Schilp (1941). 
E. fowleri was recorded at the mid-water 
trawls 2, 3, 4, and 10, taken from 2121, 2179, 
1721, and 2060 m deep, respectively. In all 
probability, E. fowleri populates the deep layers 
(below 1600 m) of the Indian Ocean, as it 
does in the Pacific and Atlantic. The species E. 
fowleri was only recorded at the boundary of 
the Indian Ocean and the Indonesian seas. A 
peculiarity of this species is that it emerges to 
higher levels in the Equatorial regions than in 
others in the Pacific (author’s unpublished data), 
and that the populations extend along deeper 
levels in other parts of the oceans. Other records 
