- 1 How are mollusks and annelids similar?
- 2 Why are annelids and mollusks closely related?
- 3 What structure in the clam is homologous to the tentacles of the squid?
- 4 Why are squid and octopus mollusks?
- 5 Is Metamerism present in Mollusca?
- 6 Are mollusks Metameric?
- 7 Do mollusks have a digestive system?
- 8 What is the main function of the mantle?
- 9 Are flatworms mollusks?
- 10 How many hearts does a squid have?
- 11 What is the squid mantle?
- 12 What ancestral structure and lineage did the pen in squid come from?
- 13 What are 4 defense mechanisms that squid have?
- 14 Why did the octopus lose their shell?
- 15 What are the 7 classes of mollusks?
How are mollusks and annelids similar?
Most mollusks have tentacles for feeding and sensing, and many have a muscular foot. Mollusks also have a coelom, a complete digestive system, and specialized organs for excretion. Annelids have a coelom, closed circulatory system, excretory system, and complete digestive system. They also have a brain.
Molluscs include such familiar creatures as clams, oysters, snails, and octopi. They share a distant common ancestor with the annelid worms, an evolutionary heritage suggested by their larval form, called a trochophore larva, found in all molluscs and in certain marine annelids called polychaete worms.
What structure in the clam is homologous to the tentacles of the squid?
Interestingly, genetic evidence suggest that the squid’s arms and tentacles are homologous with the foot portion that we see in bivalves and snails. Squid arms are basically just specialized versions of the muscular part of snails and clams that allow them to move.
Why are squid and octopus mollusks?
The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. Octopuses do not have shells at all, while squids have a small internal shell. They are also the only cephalopods with four gills instead of two.)
Is Metamerism present in Mollusca?
Metamerism is absent in echinoderms, molluscs and platyhelminthes.
Are mollusks Metameric?
Are molluscs metameric organisms? The body of molluscs is not divided into segments. Considering just this aspect, they appear to be evolutionarily closer to nematodes than to annelids.
Do mollusks have a digestive system?
Mollusks have a radula for grinding food. A digestive gland is connected to the stomach. The tissue beneath the shell is called the mantle. The digestive system includes a gizzard, a stomach, a digestive gland, and the intestine.
What is the main function of the mantle?
Introduction. Earth’s mantle plays an important role in the evolution of the crust and provides the thermal and mechanical driving forces for plate tectonics. Heat liberated by the core is transferred into the mantle where most of it (>90%) is convected through the mantle to the base of the lithosphere.
Are flatworms mollusks?
Mollusks are soft-bodied coelomates that generally have a head, a shell containing most of their internal organs, and a muscular foot. Flatworms, roundworms, mollusks, and annelids are all protostomes.
How many hearts does a squid have?
Squid have three hearts: two branchial hearts and one systemic heart. The branchial hearts pump blood to the gills, where oxygen is taken up.
What is the squid mantle?
The main body of the squid is called the mantle, which fits like a sheath over the internal organs. This colossal squid’s mantle is about 2.5 metres long and about 982 millimetres wide, almost the same diameter as a truck tyre. The mantle is made up of muscle and skin.
What ancestral structure and lineage did the pen in squid come from?
Some have hard, internal structures, like the cuttlebone in the cuttlefish and the pen in the squid, that evolved from the hard, outer shells of their ancestors, but in many octopuses the hard structure is completely lost. Only the chambered nautiluses have an external shell.
What are 4 defense mechanisms that squid have?
When hiding from predators doesn’t do the trick, a squid has several other defense mechanisms at its disposal. It can startle an oncoming predator, physically attack it, move erratically to confuse it, play dead, flee, or, in the case of the deep-sea squid Octopoteuthis deletron, sever ties with a body part.
Why did the octopus lose their shell?
The evolutionary pressures favored being nimble over being armored, and cephalopods started to lose their shells, according to Mr. Tanner. The adaptation allowed them to outcompete their shelled relatives for fast food, and they were able to better evade predators. Today most cephalopods are squishy and shell -less.
What are the 7 classes of mollusks?
Mollusks can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. These classes are distinguished by, among other criteria, the presence and types of shells they possess.