Do bivalves have a larval stage?
In bivalves the veliger is sometimes referred to as a D-stage (early in its development) or pediveliger (late in its development) larva. Following metamorphosis, the foot may be used by the juvenile mollusk to move about on the seabed (in gastropods) or in the seabed (in some bivalves).
What type of larva do bivalves have?
Many brooding bivalves release their young as swimming veliger larvae while others retain them longer and release them as juveniles. Freshwater mussels (Unionoidea) have glochidial larvae that attach to fish as ectoparasites. Bivalves are most easily recognized by their two shells (hence “bi-valv-ia”).
What is the life cycle of a bivalve?
The life cycles of bivalves include metamorphosis in the majority of cases, involving larval, juvenile, and adult stages.
What is the larval stage of a mollusk called?
Veliger
Veliger, larva typical of certain mollusks such as marine snails and bivalves and a few freshwater bivalves. The veliger develops from the trochophore (q.v.) larva and has large, ciliated lobes (velum). The velum forms from the ciliary ring (prototroch), a characteristic of the trochophore stage.
What are 3 things all mollusks have in common?
Despite their diversity, mollusks share in common a three-part body plan that includes a head, a foot and a visceral mass.
How do bivalves feed?
As filter feeders, bivalves gather food through their gills. Some bivalves have a pointed, retractable “foot” that protrudes from the shell and digs into the surrounding sediment, effectively enabling the creature to move or burrow. Bivalves even make their own shells.
What are the larval stages of most Mollusca?
In some mollusks, the zygote hatches and undergoes two larval stages—trochophore and veliger—before becoming a young adult; bivalves may exhibit a third larval stage, glochidia.
What four characteristics do all molluscs share?
Some common features are :
- Unsegmented soft body with bilateral symmetry.
- Presence of an internal or external shell.
- A toothed tongue (made mostly of chitin) called the radula.
- A mantle which is a fold in the body wall that lines the shell.
- Muscular foot (and/or tentacles in some).
What main characteristic do all mollusks share?
Despite their amazing diversity, all molluscs share some unique characteristics that define their body plan. The body has a head, a foot and a visceral mass. This is all covered with a mantle (also known as a pallium) that typically secretes the shell.
Is Mollusca a trochophore?
Trochophore, also called trochosphere, small, translucent, free-swimming larva characteristic of marine annelids and most groups of mollusks. In some mollusks (such as gastropods and bivalves), the trochophore develops into a second stage, the veliger (q.v.), before metamorphosing to adult form.
Do bivalves have larvae?
Most of the bivalve larvae that hatch from eggs in the water column feed on diatoms or other phytoplankton. After about four days, they become D-stage larvae, when they first develop hinged, D-shaped valves. These larvae have a relatively small dispersal potential before settling out.
Where do most bivalves live?
Most bivalves live on the bottom in shallow water and bury themselves in sand or mud, with just the edge of their shell showing. Some of them, like oysters and ocean mussels, glue themselves to rocks. A few, like scallops, don’t bury themselves, and move around.
Mollusks have a soft body and share several characteristics, including a muscular foot, a visceral mass of internal organs, and a mantle.
How are the larvae of a bivalve cultured?
This section of the manual synthesizes the various approaches and the methods used in the culture of larvae from the fertilized egg to settlement with emphasis on some of the more commonly cultured species. Fertilized eggs are permitted to develop to the fully-shelled “D” veliger stage in tanks of the type shown in Figures 50 and 52.
How many classes of bivalves are there in the world?
Bivalves belong to the phylum Mollusca, a group that includes such diverse animals as chitons (chain shells), gastropods, tusk shells, cephalopods (squid and octopus) as well as clams, oysters, mussels and scallops. The phylum has six classes of which one is Lamellibranchia or Bivalvia.
What kind of function does a bivalve have?
It has a sensory function and can initiate closure of the valves in response to unfavourable environmental conditions. It can control inflow of water into the body chamber and, in addition, it has a respiratory function.
When does the gonad appear in a bivalve?
Sexes of bivalves can be separate (dioecious) or hermaphroditic (monoecious). The gonad may be a conspicuous, well defined organ as in scallops or occupy a major portion of the visceral mass as in clams. The gonad is generally only evident during the breeding season in oysters when it may form up to 50% of the body volume.
Which is the second larval stage of a mollusk?
The free-swimming larva that emerges from the egg in many mollusks Veliger The second larval stage of many mollusks; has large, ciliated lobes and the beginnings of a foot, shell, and mantle Chitons Animals found on rocky marine shorelines with 8 overlapping plates on their dorsal surface
This section of the manual synthesizes the various approaches and the methods used in the culture of larvae from the fertilized egg to settlement with emphasis on some of the more commonly cultured species. Fertilized eggs are permitted to develop to the fully-shelled “D” veliger stage in tanks of the type shown in Figures 50 and 52.
Is the larval stage of a veliger a feeding stage?
Feeding or non-feeding veligers are possible, depending on which species has produced them. In a feeding veliger, the larval stage is, in most cases, relatively “undeveloped” and must feed on phytoplankton for a period of weeks to months in order to develop to the point where it is able to metamorphose.
Where does the veliger stage of a gastropod take place?
Veliger of gastropods. The veliger is the second larval stage in the development of gastropods, following the earlier, trochophore, stage. In some species, including virtually all pulmonates, the veliger stage is passed within the egg capsule and the hatching stage is a juvenile rather than a free-living larva.
