ANATOMY. All Strombus species share some typical anatomical characteristics. They have prominent eye stalks (eyes) and very small tentacles, a long snout called proboscis, a more or less large flared lip of the shell typical of adults. These features are well described most for Strombus gigas but are generally valid for other Strombus species.

CONCHITA. In spanish means little conch. Conchita is a veliger larva of Queen conch and it is the pet in this book and for the Queen conch Program.

COPULATION. Copulation is performed by the male which comes behind the female and inserts the penis under the female shell and mantle, up to the copulating pouch. It is possible to observe a male copulating with a spawning female. It does not mean that the eggs are immediately fertilized. The eggs have to be fertilized by sperm well before being coated by jelly coat and protecting envelopes. The male takes the opportunity of a female which does not move much as it is occupied during one day to lay eggs. And the sperm is put in the seminiferous pouch up to next spawning. Copulation is not very selective as it is possible to encounter males trying to copulate with females of a different species or even with another male. A female may be fertilized by two successive males.

CRYSTALLINE STYLE. Strombid Conchs as well as other Mollusks possess a gelatinous translucent rod, some 10 cms long, that may protrude from the visceral mass during cleaning procedure. In most Caribbean countries, this gelatinous rod is considered as aphrodisiac. In fact, it is the crystalline style which is an element of the digestive tract, secreted by the style sac which is an expansion of the stomach. It contains only digestive enzymes which are progressively dissolved in the stomach and takes part to the digestive process.

EYES. Strombid species as other Prosobranchs, (marine snails) possess a pair of eyes situated at the basis of cephalic tentacles. On the contrary, terrestrial snails possess eyes situated at the tip of the tentacles. But the eyestalks are much elongated to allow them to have a look outside from under the large flaring lip of their shell. The real tentacles are very small and look like a small expansion situated over the eye. So the more conspicuous eyestalks may be confused with tentacles. To be able to survey better for enemies, strombid species have a “stromboid notch” which is a special fold of the shell lip designed to accommodate the right eyestalk.

FOOT. The foot of Strombus gigas is large and powerful. It may slide as for other Gastropods but most often, it proceeds by jerky movements, typical of strombid species. It may use the pointed sickle-shaped operculum to anchor the foot in sediment and proceed by successive leaping movements which is not an easy task with such a heavy shell. But such disconcerting movements let Strombus species escape from natural predators.

Unfortunately such movements are of no use to escape from human predators. The muscular foot and columelar muscle which anchors the animal to its shell are the main parts to be consumed by human predators.

FEMALE GENITAL DUCT. comprises a genital glandular duct called uterus which will deposit the eggs mucous and proteinic protections. It comprises also a copulating and a seminiferous pouch to keep the sperm to next spawning and cytological fertilization. The glandular uterus is composed of a modified part of the mantle. The ultimate part of the female genital duct is the spawning groove which goes from the distal end of uterus duct down to the right border of the foot.

MALE GENITAL DUCT. is composed of a long coiled deferent duct generally called vas deferens up to the male copulating organ which is a large black penis situated on the right part of the body up to the foot and back to the head. The penis may be seen without killing the Queen Conch when it tries to upright the shell. Young, immature male have a small yellow button which is the undeveloped penis.

LIP=SHELL LIP

MANTLE. The mantle is a very special molluscan tissue responsible for synthesis of the shell. In Strombus gigas, its edge appears as an orange thick fold lining the shell aperture. It is responsible for shell growth. All the outer surface of the mantle is responsible for mother-of-pearl deposit and shell.

thickening. The mantle covers the pallial cavity which accommodates the gill filaments which allow for respiration.

METAMORPHOSIS. Metamorphosis is constituted by the wealth of anatomical and physiological modifications which allow to pass from an environment and a way of life to another during developmental stages. For Strombus gigas, the larva which hatches from egg is a veliger larva which is a swimming planctonic larva. During metamorphosis, the veliger larva loose its most important organ which is the velum and settles on the bottom in sea grass beds. It differentiates a foot which allows for moving, a gill which allows for breathing (that means use oxygen from the sea water) and a radula which allows for rasping algae to eat.

The veliger larva ready for metamorphosis has already differentiated a foot but not a gill. It is called pediveliger. As for many molluscan species, a successful metamorphosis may be triggered by environmental cues that allow for a rapid metamorphosis reducing the mortality that is a very common problem in molluscs aquaculture. Mortality at metamorphosis is generally due to the delay between velum destruction and gill differentiation. During this time, the larvae may be subject to bacterial diseases fatal in aquaculture. For Strombus gigas, the main identified metamorphosis cue is a red algal extract but some other chemicals may be efficient too.

OPERCULUM. The operculum is a horny proteinic hard structure stuck at the posterior dorsal face of the foot of most Prosobranchs. The operculum of Strombus gigas has a very special pointed, sickle shape which is similar to some sort of claw. It is used to close up the shell aperture when the animal shelters within the shell. But its size is quite small when compared with the shell aperture to be really efficient unless the animal goes very far within its spiral shaped shell. Even like that, octopus may succeed to open the “door”. The very special function of the operculum in Strombus species is to allow for leaping movements.

PLANKTON. The plankton is composed of all small animals and small algae floating free in sea water. All the planctonic organisms drift with sea current and may travel on long distance. All the cells and organisms containing photosynthetic pigments are part of phytoplancton; all the small animals constitute the zooplankton. The zooplancton comprises as well small size animals living all their life in plankton as planctonic larval stages of benthic animals (living on the bottom) such as Strombus species and many other Molluscs. The planctonic larval stage allows for large dispersion of species before settlement. It is assumed that larvae of Strombus gigas may settle as far as 100 kms from their birth place. However, only genetic studies can discriminate the origin of settling juveniles.

The planctonic stage is subject to a very important natural mortality when compared with the rate of production of larvae from the egg masses.

Planctonic larvae undergo metamorphosis, which is a drastic anatomical change to become benthic juveniles.

PROBOSCIS. A prominent proboscis, tucked between the eye stalks, accommodate the mouth. It may be short as a calf muzzle at rest but is much elongated when searching for food, as a miniature elephant trunk. It can protrude from the shell lip, through the siphonal canal of the shell, left to the eye notch.

RADULA. The radula is a narrow ribbon located in the mouth bearing small horny teeth which allow for grazing. It is a very useful organ for herbivorous snails such as all strombid species which feed on a variety of algae. They cannot eat the coarse leaves of sea grass but may scrap the surface for epiphytic algae.

SHELL. Early shell Strombus gigas, as most Molluscs elaborates its shell very early in its life history, from the first stages of embryonic development. Strombus shell is coiled as the shell of most Gasteropods.

At the moment of eclosion, the small shell is transparent as it is still constituted only of the proteinic non calcified part of the shell but it has already 1.5 whorl. At the moment of metamorphosis, it develops 4 whorls and becomes opaque because of calcification. It is still a larval shell that will remain at the apex of the adult shell which begins to grow at metamorphosis.

Shell growth. Strombid conchs grow up, coiling their shell, during approximately 3 years, then stop growing and elaborate a large flared lip which may grow during half a year. After that step, all the shell thickens, whereas the animal becomes sexually mature. It has been demonstrated that sexual maturity is not attained before the flared lip has reached a thickness of 4-5 mm.

Shell structure. The shell is composed of three parts; the outer one is the periostracum which is a thin brownish proteinic layer growing at the mantle edge. The periostracum dries and disappears in old dead shells.
The middle part which is also growing at the mantle border is the prismatic layer which is composed of a proteinic array enclosing aragonite crystalline calcium.

The inner part is the colorful mother-of-pearl glossy layer which is growing in thickness during most of life course. It is produced by all the outer surface of the mantle which may also produce pearls if there is some foreign particle included between mantle and shell.

Shell lip. When Queen Conch is 3 years old, the growing edge of its shell stops coiling and forms a large flared lip. At the beginning, the lip is thin and easy to break. Then it will not enlarge more and thickens during all adult life. Research work on reproduction has demonstrated that animals are not mature before they have a 4 mm thick shell lip. A 5 mm thick lip is considered as a cue for adulthood and is requested to allow for fishing. It is quite difficult to measure the lip thickness, while collecting the animals but it is easy to see that the lip thinner than 5 mm is easily broken on its border and that a lip thicker than 5 mm is not easily broken. Such a cue for adulthood has to be included in regulations of every Caribbean country.

SPAWN. It is the act of laying eggs and protecting structures and it is the egg mass as well. The egg mass is laid by the female during several hours and left in sand well covered by sand grains. The egg mass is a complex

structure which constitutes an efficient protection for the eggs during the first 5 days of development. Most larvae will hatch within 5 days.

SYSTEMATICS. Strombus gigas is the most thoroughly studied species of Strombus to date. It occurs in the tropical and sub tropical waters of the wider Caribbean region north to Bermuda and south to Brazil.

It belongs to the phylum Mollusca (which comprises soft bodied animals generally protected by a hard shell) and to the Gastropod class (which means “animals with the stomach near the foot”). As most Gastropods, the strombid species have undergone a coiling of the shell, then a swinging round of the visceral mass with the covering mantle and shell (called torsion) very early during the larval development so that the mantle cavity comes to face forwards, opening above the head. It belongs to the Order Prosobranchia (which means that the gill is situated in anterior position).

The larval torsion has other important consequences such as the fact that there is only one gill, one kidney, one gonad. Anyway there is also only one foot but it is the same in other Molluscs which do not undergo the embryonic torsion such as the Bivalves. In the new phylogenetic classification, the Gastropods sub orders Mesogastropoda and Neogastropoda have been substituted for Caenogastropoda but the family Strombidae remains unchanged and for our purpose, it does not change much.

Other caribbean Strombus species. Strombus gigas is one of the 72 species of the family Strombidae, and one of 55 species of the genus Strombus which all live in tropical and subtropical seas of the world. Strombus gigas is the largest species in the Caribbean region.Four other much smaller Strombus species live in the Caribbean region. The most common are the milk conch Strombus costatus, which has a very thick milky white labium, the elegant rooster tail conch, Strombus gallus and the delicate bloody red shelled Strombus pugilis. The hawk wing conch, Strombus raninus is less frequent and Strombus alatus is restricted to Florida. South to the Caribbean region, Strombus goliath is a Brazilian species, larger than Strombus gigas. For more details, it is necessary to refer to Abbott (1974) American sea shells.

TENTACLES. Strombus species have very small true cephalic tentacles located above the eye. They must not be confused with the very elongated eyestalks bearing the eyes which constitute a typical character of strombid species. Cephalic tentacles are sense organs bearing many sensory receptors that may detect chemicals which allow for identification of food or predators or mates.

They may also detect movements through mecanoreceptors. There is no particular study of sense organs in strombid species but behavioral studies show that Strombus gigas does not always identify properly the sexual partners as males have been observed to try to mate with other males or with females of other species.

VELIGER LARVA. The first free larval stage of Strombus gigas is a veliger larva which is a swimming planctonic larva which most important organ is the velum. At the moment of eclosion, the veliger larva has already a small transparent shell, large enough to accommodate the larva for shelter. However, many plankton feeding animals engulf large quantities of planctonic organisms; therefore the natural mortality is very high during planctonic life which is about three to four weeks.

VELUM The velum is a larval organ which allows for respiration, swimming and feeding. Planctotrophic feeding of veliger larvae is constituted of microalgae and small other particles including bacteria.

Strombus larvae do not filtrate much water to eat but engulf the small particles orientated toward their mouth by the ciliated velar lobes. They are microfagic larvae.