Categories
vol-1THE SPAWNING AND DEVELOPMENT
OF TROOHUS (TEOTUS) DENTATUS FORSKAL
By
A. M. EISAWY, (Pa. D.)
1mt. ofOcean. Ulnd Fisherie8, Al-Ghardaqa, U.A.H.
INTRODUCTION AND HISTORICAl.
TIle Trochidae of the Red Sea have been fairly thoroughly treated by
systemat;sts but only the egg-masses and developnent of Trochus erythraeus
Brocclli were studied (Gollar and Eisawy 1963). Trochus (Tectus) dentatus Forskal
is the largest and most important member of the family in the Eed Sea. The
meat is valued as food and the shell is utilized for botton manufacture, and is
therefore of commercial importance.
Several authors studied the spawning and development of different species
of Trochidae in oHler regions of the world. From them the following can be mentioned : Grant 1827, Jeffreys 1865, Salensky 1872, Haeckel 1875, Eobert 1898,
1901 and 1902, Boutan 1899, LR.my 1928, MeorllOuse 1932, Thorson 1935, 1940
aud 1946, Gersch 1936, Lebour ]936 and 1937, Gaillard 1952 and 1963, Ducros
]957, Hahe 1960, Vinogradova 1960, Kojima 196] and 1962 and others. They
worked on tllc following species : Trochus sp., Tr. obe~iscus, Tr. ni~oticus, Tr.
turbinatus, Tr. varius; Gibbula ma,gus, G. albida, G. divericata, G. cinera,ria,
G. pennanti, G. tumida, G. umhilicalis = Tr. oh~iquatus; Monodonta lineata;
Margrites helicinus, Mar. cineren; Oalliostoma papillosum = Tr. granulatus, Oal.
zizyphinum = Tr. conuloides; OanthMidus striatus, Oan. exasperatus, Oan. cleondi =
Tr. milligranus = Oal. miliare, Oan. montagui, Oan. japonicus, Oan. callichroa
jessoensis; Skenea surpu~oides and other species.
Thc&) r-;pecie8 can he divided, according to tllc type ofthcir spawns into two
groUp8. The first group includes: thc deep-sea type of Tr. varius, Tr. obeliscus,
Tr. erythraeus. Mar. helicinus, Oal. zizyphium, Oa~. papillosum, Oa,n. striatus, Oan.
exasperatus, Oan. japonicus, Oan. callichroa jessoensis, G. tumida and other species.
The eggs which are laid in an accumulated mass, are usually large ranging between
140-300 /1 (except in Tr. erythraeus about 75 /1 across), and the developmental
period is mostly long (72-180 hours). In all species, except the deep-sea variety
of Tr. varius and Tr. erythraeus, the vcliger stage is pasEed within the egg-case and
the young hatched in the crawling stage. The second group includes: the coastal
form of Tr. variu,s, Tr. niloticus, Gibbula magus, G. cineraria, G. umbilicus, G.
pennanti, Monodonta lineata and other species. In this group, the eggs are shed
singly into the surrounding water and are usually small (105-250/1). The developmental period is comparatively short (about 20 hours) and the larvae corne out as
free swimming veligers.
