Veliger

Veliger is the name for the larval form of molluscs, specifically from Scaphopoda, Bivalvia and Gastropoda. Veligerlarven are part of the free-floating plankton. A distinguishing feature of the Veligerlarve are the Vela, flap-like appendages occupied by cilia. These contribute to the nutrition and locomotion.

• 2.1 oviposition
• 2.2 In the egg
• 2.3 Free swimming phase
• 2.4 metamorphosis

Nutrition

The diet of Veligerlarven has a great influence on the life of the larvae. The larval begin to lay eggs and lasts until the metamorphosis into the adult. Food is taken with the help of Velarlappen to himself, with the individual Velarlappen take on different tasks. Different Vela be used to guide the food to the mouth and to keep out contaminants. Veliger are not very specific for the food can be maintained in the laboratory but also with many different types of food. Basically, two different food types are distinguished in the Veligarlarve that planktotrophe and lecithotrophic. If both types can be produced from an individual of a species is called Poecilogonie. Both Ernährungs-/Entwicklungstypen lead to morphologically and ecologically same animals. Individuals of different larval feeding types can mate normally. The planktotrophe diet of the larva is considered original and leads to a longer larval phase. A longer larval is unfavorable because the mortality of larvae is very high and decreases only through the metamorphosis to the adult animal. Through a shorter larval mortality probability can be greatly reduced. The reduction of this time at lecithotrophen Veligerlarven is considered further.

Planktotroph

Planktotrophe diet means that the animal feeds as a free- swimming larva from plankton. Planktotrophe larvae hatch from smaller eggs and basically there are more eggs in each egg-laying.

Lecithotroph

Lecitotrophe larvae feed during their larval of the past in the egg or outside the egg yolk mitgegebenen and must take no other food until metamorphosis. Although larvae usually follow only one of the two diets, there are also lecithotrophic veliger which may optionally feed planktotroph, eg Phestilla sibogea. That still lecithotrophic larvae are due to the fact that they also can go to metamorphosis without the extra food.

Development

The development to adult food is heavily dependent and is mainly to increase in size and organ development that is faster or slower depending on diet

Oviposition

The development begin to lay eggs. The size of the ice cream plays an important role especially in lecithotrophen larvae. The time to hatching is dependent on whether there are lecitotrophe or planktotrophe oviposition. Although there are only these two diets, there are three different types of egg-laying. In addition to pure lecitotrophen and planktotrophic egg-laying, there is also remixed shelves, but they are very rare. These consist of both lecitotrophen as well as from planktotrophic eggs. The number of eggs per tray is for -mixed between the number of planktotrophe and lecitotrophe for oviposition. The same conditions also apply to the size of the hatching Veligerlarven.

In the egg

During the phase in which the larva is located in the egg and can not look for food, it is dependent on the yolk reserves that have been left behind by the mother. This is one way for the parent to influence the development of the larvae. During the time in the egg development of the embryo takes place to Veligerlarve. The type of egg-laying substantially determines the length of time spent an average of the egg. Planktotrophe oviposition usually have less yolk and therefore planktotrophe Veliger must sooner look for food and, accordingly, earlier slip as lecitotrophe Veliger. This matches the observation that starving adult animals, where they are poecilogon, tend to take planktotrophe lecitotrophen oviposition and oviposition -mixed to produce. In -mixed egg-laying all Veligerlarven slip more or less simultaneously. General Veliger hatch from eggs outside in front of the lying further inside.

Originally Veligerlarven have a shell, although this need not necessarily be present in the adult animals, for example in Nudibranchia. The development of this shell runs depending on the type and family differently. In bivalves, the shell originally dorsally lying divides in half and both parts then enclose the body of the larva. Wherein the shell Scaphopoda development is similar to that of the extended but bivalves.

Free swimming phase

In the free-swimming stage, the Veligerlarven subject to the strongest growth in size. In addition to the general body size grow gametes and left midgut gland during the entire time outside of the egg. The other institutions grow species-specific approach in the larval. For the Gastropoda is during the larval and the twist well covered, which takes the visceral sac of the screw.

Metamorphosis

The metamorphosis may take up to 2 days, causes a greater morphological transformation and usually represents a final adjustment to the benthic habitat dar. During the metamorphosis going organs such as the Front sensory organ, the Velarlappen and the shell (only Nudibranchia ) lost, or. they are absorbed. Signs of conversion, when the Velarlappen beat irregularly and thereby solve the Ciliarzellen. After that, the Vela is absorbed. In addition to the reduction of larval features, the final form of the species is assumed and it also formed depending on the type missing organs in the metamorphosis. The metamorphosis is triggered by a species-specific signal in all Veligerlarven ( Scaphopoden, bivalves and gastropods ). While it is mostly traces of the biofilm in the Bivalvia, which can be found on the shell of the adult animals of this species, the metamorphosis in the gastropod is usually triggered by traces of food that take the animals in the adult stage to himself.

• Larva
• Malacology