**2. Egg-laying: description**

First of all, they are the most mobile mollusks. They come in the form of pelagic species capable of performing large-amplitude horizontal and vertical migrations, like squid. Octopoda are in turn largely territorial and therefore sedentary, while the common cuttlefish *Sepia officinalis* exhibits a nectobenthic behavior associated with low or medium migration amplitude

Unlike other classes of molluscs, cephalopods possess a cephalopodium whose eight arms play an important role in predation but also in mating and egg-laying during the formation of the egg mass (**Figure 1**). These arms are also used for handling prey during catches by

This ability to handle prey is quite unique in the marine environment and only found in primates and in some mammals. It is probably related to the exceptional development of the central nervous system (CNS). This CNS is protected by a cartilaginous skull and is located between the

**Figure 1.** Main successive steps of the life cycle of the cuttlefish *Sepia officinalis*. (Photo credits: V. Cornet, J. Henry,

depending on the latitude.

4 Biological Resources of Water

eyes, which are capable of forming an image.

capping [1].

C. Zatylny-Gaudin).

The cuttlefish *Sepia officinalis* is a semelparous species with a life cycle that varies depending on the geographical location of the population: 15–16 months in the Mediterranean Sea versus 20–22 months in the English Channel. Spawning is associated with a stereotyped behavior. In aquaria, sexually mature females that have not spawned yet manipulate eggs laid earlier by conspecifics, while increasing their ventilation rate.

The different behavioral sequences leading to the laying of eggs are gradually repeated and eventually lead to the laying of the first egg (personal observation). A female can lay dozens of eggs at once, probably 150–200 eggs, which roughly corresponds to the storage capacity of the genital coelom, before a pause that allows it to replenish its stock of mature oocytes (stage V) through asynchronous gametogenesis. It also restores the capsular products secreted by the oviduct gland and the nidamental glands. Some females are then able to lay a second batch of eggs and probably several successive spawns. We do not know exactly how many eggs are laid before the programmed death of the animal. Fertility is probably quite variable among females and is very difficult to estimate.
