interpretative value. These shells may have included considerable amounts of "dead" 
carbon in their shell carbonate and consequently date several thousand years too old. 
1964 0 
Schroeder, R. E. (1964) Ecological studies of the intestinal trematodes of the gray snapper, 
Lutjanus griseus (Linnaeus), in the vicinity of Lower Matecumbe Key, Florida. Ph. D. 
Dissertation, University of Miami, Coral Gables, FL. 165 pp. 
[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] Gray snappers were collected 
from eight stations comprising four habitats over a nine-month period, and examined 
for intestinal trematodes. The incidence of each trematode was calculated for each 
habitat at each time of year. Snails were collected in the vicinity of the various 
stations, and examined for larval trematode infections. Special attention was given to 
snails known to harbor snapper trematodes. When possible some index of infection 
levels and snail population was derived, and the behavior was investigated. It was found 
that the habitat in which the fish are caught is more important in determining the nature 
of their trematode population than fish size, sex, or season of the year. The reasons 
for this probably involve the distribution of intermediate hosts, most especially the 
snail hosts. Metadena adglobosa (Manter, 1947) is most common in fish from shallow 
Florida Bay Thalassia beds, where its snail host, Cerithium eburneum (Bruguiere) is 
most plentiful. Since fish in this area are small, it is found more often in small fish than 
large fish. M. adglobosa is usually found in the pyloric caeca of L. griseus. Metadens 
globosa (Linton, 1910) was most common at the inshore stations. Its distribution 
suggests that its snail host is different from that of M. adglobosa. M. globosa was 
remarkable for the low incidence of juvenile worms. Metadena obscura n. sp. was 
described from the pyloric caeca and intestine of L. griseus. Although superficially 
similar to M. adglobosa. it differs in a number of characters, the most important of 
which are the enlarged spines of the ventrogenital pit. Paracryptogonimus 
neoamericanus (Siddiqi and Cable, 1960) was most common in fish from the inshore 
stations. It was usually found in the intestine, but occasionally was in the pyloric caeca 
of L. griseus. Few juveniles were found. In this, and in distribution, it resembled 
Metadena globosa. Hamacreadium mutabile (Linton, 1910) also was most common at the 
inshore stations. Large populations of the snail hosts, Aetrea tecta americana 
(Solander) were found near the stations having the highest incidences of H. mutabile. 
Hamacreadium gulella (Linton, 1910) was found only briefly until late October, when it 
began to appear regularly in inshore fish. A possible explanation is that it was brought 
into the area by another definitive host. One Astraea tecta americana that was infected 
with H. gulella was collected. Helicometrina nimia (Linton, 1910) was most common in 
snapper from the offshore stations. It is very rare at other stations. H. nimia is not 
specific for snappers, and is reported from many non-Lutjanid species. The gray 
snapper probably is not an important definitive host. Helicometra execta (Linton, 1910) 
was found in the gray snapper only rarely, and only at the offshore stations. It is 
probably an accidental parasite of L. griseus, and largely dependent on other hosts. It 
may not be able to complete its life-cycle in L. griseus. Its presence in the gray snapper 
is a new host record. Stephanostomum casum (Linton, 1910) was found at all stations 
in about the same percentage of gray snappers, suggesting that its intermediate hosts 
are widely distributed. Nassarius albus (Say) or N. vibex (Say) may be the snail host. 
Nassarius species are hosts to other Stephanostomum species and N. albus and N. vibex 
are widely distributed in habitats of the gray snapper. The data indicate that seasonal 
changes in parasite populations of L. griseus near Lower Matecumbe Key are a function 
of spawning migrations and cold weather movements. Many parasites probably appear 
in unusual habitats through movements of the host. Migrating fish carry parasites into 
new habitats. In a new habitat the original parasites gradually are lost, and are 
replaced by species characteristic of the new environment. Examination of a collection 
of 178 fish of 41 species other than L. griseus indicates that all trematodes of L. 
170 
