Chaetognaths from the Laccadives with the New Record of Spadella angulata
327
1968) there is no other record from the Indian Ocean. BURFIELD (1950) reported the
occurrence of 12 species from the Barrier Reef Expedition and all except S. lyra were
found in the present collections. The commonest forms at the Great Barrier Reef were
in order of abundance S. enflata, S. neglecta, S. robusta, S. bedoti, S. pulchra and
S. pacifica (reported as S. serratodentata). The difference noticed in the Laccadive collections is the occurrence of K. pacifica, S. ferox and Sp. angulata, the abundance of S. regularis and the scarcity of S. pulchra.
A comparative study of the present collections from the lagoons with those of the
chaetognaths reported from the Palao Islands (TOKIOKA, 1942) and New Caledonia
(TOKIOKA, 1960) also shows similarities in the species composition. In the Palao Islands
10 species were present and New Caledonia sustains 4 species already recorded from the
Palao Islands. The species include K. pacifica, S. bedfordii, S. enflata, S. ferox (reported
as S. ail, S. neglecta, S. oceania, S. pacifica (reported as S. serratodentata), S. regularis,
S. robusta and S. tropica. All these except S. bedfordii and S. tropica were encountered in
the lagoon collections of Kalpeni. The similarity between the chaetognaths of the Laccadive lagoons and the Pacific lagoons indicates the identity of the Indo-Pacific tropical
fauna, a fact already pointed out by earlier authors (TOKIOKA, 1952, 1962; HYMAN,
1959).
In almost all the collections taken outside the lagoons different maturity stages of the
dominant species were encountered; this indicates that breeding was taking place. It has
been assumed that chaetognaths die after egg laying (KUHL, 1938). However, periodic
maturation of ovaries in S. enflata has already been reported (MICHAEL, 1919; THOMSON,
1947; ALVARINO, 1965, 1967; FURNESTIN and BALAN<;:A, 1968) . We found 3 different
size groups of S. enflata in the same sample, apparently representing 3 consecutive cycles
of maturity, although it could also indicate the presence of different populations which
attain maturity at different lengths. DONCASTER considered the bigger forms of S. enflata
to be a new species: S. gardineri, but as ALVARINO (1967) concluded, our work confirms
that his specimen was S. enflata at the third maturity cycle. Differences in meristic
characters cannot be considered reliable, since they show considerable overlapping and
variation with age, season and geographic localities (JOHN, 1933; A LVARIi~o, 1967).
Compared to the samples taken outside the atoll, the lagoon samples showed a
general impoverishment in chaetognaths. There were no significant changes in salinity
and temperature in and around these atolls. Hence the lowering of the population density
of chaetognaths inside the lagoon cannot be attributed to variation in salinity and
temperature. According to TRANTER and GEORGE (1969) zooplankton is lost "in transit
across the reef into the lagoon and is probably utilized by the reef community". Corals
are believed to be specialized carnivores living primarily on zooplankton (RUSSELL and
YONGE, 1963; YONGE, 1963). This is probably the reason for the lower population
density of chaetognaths inside the lagoon.
327
1968) there is no other record from the Indian Ocean. BURFIELD (1950) reported the
occurrence of 12 species from the Barrier Reef Expedition and all except S. lyra were
found in the present collections. The commonest forms at the Great Barrier Reef were
in order of abundance S. enflata, S. neglecta, S. robusta, S. bedoti, S. pulchra and
S. pacifica (reported as S. serratodentata). The difference noticed in the Laccadive collections is the occurrence of K. pacifica, S. ferox and Sp. angulata, the abundance of S. regularis and the scarcity of S. pulchra.
A comparative study of the present collections from the lagoons with those of the
chaetognaths reported from the Palao Islands (TOKIOKA, 1942) and New Caledonia
(TOKIOKA, 1960) also shows similarities in the species composition. In the Palao Islands
10 species were present and New Caledonia sustains 4 species already recorded from the
Palao Islands. The species include K. pacifica, S. bedfordii, S. enflata, S. ferox (reported
as S. ail, S. neglecta, S. oceania, S. pacifica (reported as S. serratodentata), S. regularis,
S. robusta and S. tropica. All these except S. bedfordii and S. tropica were encountered in
the lagoon collections of Kalpeni. The similarity between the chaetognaths of the Laccadive lagoons and the Pacific lagoons indicates the identity of the Indo-Pacific tropical
fauna, a fact already pointed out by earlier authors (TOKIOKA, 1952, 1962; HYMAN,
1959).
In almost all the collections taken outside the lagoons different maturity stages of the
dominant species were encountered; this indicates that breeding was taking place. It has
been assumed that chaetognaths die after egg laying (KUHL, 1938). However, periodic
maturation of ovaries in S. enflata has already been reported (MICHAEL, 1919; THOMSON,
1947; ALVARINO, 1965, 1967; FURNESTIN and BALAN<;:A, 1968) . We found 3 different
size groups of S. enflata in the same sample, apparently representing 3 consecutive cycles
of maturity, although it could also indicate the presence of different populations which
attain maturity at different lengths. DONCASTER considered the bigger forms of S. enflata
to be a new species: S. gardineri, but as ALVARINO (1967) concluded, our work confirms
that his specimen was S. enflata at the third maturity cycle. Differences in meristic
characters cannot be considered reliable, since they show considerable overlapping and
variation with age, season and geographic localities (JOHN, 1933; A LVARIi~o, 1967).
Compared to the samples taken outside the atoll, the lagoon samples showed a
general impoverishment in chaetognaths. There were no significant changes in salinity
and temperature in and around these atolls. Hence the lowering of the population density
of chaetognaths inside the lagoon cannot be attributed to variation in salinity and
temperature. According to TRANTER and GEORGE (1969) zooplankton is lost "in transit
across the reef into the lagoon and is probably utilized by the reef community". Corals
are believed to be specialized carnivores living primarily on zooplankton (RUSSELL and
YONGE, 1963; YONGE, 1963). This is probably the reason for the lower population
density of chaetognaths inside the lagoon.