The reproduction of molluscs is as diverse as the different types of molluscs that exist. Reproductive strategies change depending on the type of environment in which they live, whether they are terrestrial or aquatic animals, although all reproduce through sexual reproduction.
In this article on our site we will explain in detail how mollusks reproduce, although first we will explain what mollusks really are, some important features and details about your reproductive system. Likewise, we will detail two examples of reproduction in molluscs according to their species.
What are mollusks? - Types and examples
Molluscs are a large phylum of invertebrate animals, almost as numerous as the arthropods. There is a wide variety of molluscs, but they all share certain characteristics that make them similar, although each one has its own adaptations.
These characteristics we are talking about are included in the division of its body, categorized into four regions:
- A cephalic area where the sensory organs are concentrated next to the brain.
- They have a locomotor foot very muscular for crawling. This foot is modified in some groups, such as the cephalopods, whose foot evolved into tentacles.
- In the posterior area we find the pallial cavity, where the olfactory organs and the gills (in those molluscs of aquatic life) are found. and body orifices such as the anus.
- Finally, the mantle. It is the dorsal surface of the body which secretes protection, such as spicules, the shell or venom.
Within the types of molluscs, there are some lesser-known classes, such as the Caudofoveata class or the Solenogastrea class. These molluscs are characterized by being worm-shaped and the body protected by spicules.
Some molluscs present a very primitive morphology, as is the case of the molluscs belonging to the classes Monoplacophora and Polyplacophora. These animals have a muscular foot like that of snails and their body is protected by a single shell, in the first case, or by several in the second. The former resemble a clam with a single shell, and the latter resemble a well-known arthropod, the sow bug.
Other molluscs are the fang shells which, as their name suggests, have their entire body protected by a fang-shaped shell elephant. They belong to the class Scaphopoda and are all marine animals.
And we come to the most well-known types of molluscs: bivalves, such as clams, oysters or mussels. Gastropods, snails and slugs. And finally, the cephalopods, which are the octopus, cuttlefish, squid and nautilus.
If you want to delve into the world of molluscs, you cannot miss our article "Types of molluscs - Characteristics and examples".
The reproduction of molluscs
In such a heterogeneous group of animals that, moreover, can live in very different habitats, the reproductive strategies with which they have evolved are equally diverse.
Mainly molluscs they reproduce through sexual reproduction, that is, within each species there are unisexual individuals, female molluscs or male molluscs. However, some species are hermaphrodite and, although most cannot self-fertilize (they need the presence of another individual), certain species can, such as some land snails.
The vast majority of mollusk species are aquatic and, in this environment, the main type of fertilization is external. Only some species have internal fertilization, such as cephalopods. Therefore, aquatic molluscs present external fertilization. Both females and males release their gametes into the environment, these are fertilized, develop, hatch and live as free larvae until the adult stage, which in some species is practically sessile or crawling and in others free swimmers.
Land molluscs, which are pulmonate gastropods or land snails, have a more developed reproductive system Each individual has both sexes but can only act as one in the moment of copulation. The male introduces the sperm through the penis inside the female where the eggs will be fertilized. The female will then lay fertilized eggs buried in the ground where they will develop.
Examples of reproduction in molluscs
The number of different species of molluscs complicates the synthesis of the explanation of their reproduction, for this reason we present two very representative examples of mollusc reproduction:
1. The reproduction of the common snail (Helix aspersa)
When two snails reach the adult stage they will be ready to carry out the reproduction of snails Previously, before copulation, both snails court each other. This courtship consists of a series of circular movements, friction and hormonal release that can last up to 12 hours.
When the snails are very close, they launch what is known as a " love dart". These structures are true chitinous darts impregnated with hormones that penetrate the skin of the snail and favor reproductive success. After the dart, one of the snails protrudes the penis through its genital pore and comes into contact with the partner's pore, enough so that it can deposit the sperm.
After a few days, the fertilized animal will insert its cephalic area into the moist soil and lay its eggs in a small nest. After a while, a hundred miniature snails will emerge from it.
two. The reproduction of oysters
Generally, when the warm season arrives and ocean waters exceed 24 ºC, it is time for oysters to reproduce. These animals release pheromones into the water that show their reproductive status. When this occurs, both male and female oysters release millions of gametes that will fertilize outside their bodies.
The development of the eggs is vertiginous, in a few hours they enter the state of larva. A couple of weeks later, they drop to a rocky bottom, usually guided by chemical cues from other adult oysters. They are attached to the substrate using a cement they create themselves and will spend the rest of their lives there.
