Why are annelids and mollusks closely related?
Because annelids are actually more closely related to species within the mollusk phylum than they are to their worm cousins in the flatworm and roundworm phyla. Although they look quite different on the outside, mollusks and annelids share a more recent common ancestor than roundworms and annelids.
What are mollusks most closely related to?
Mollusks are probably most closely related to organisms in the phylum Annelida, also known as segmented worms. This phylum includes the earthworm and leech. Scientists believe these two groups are related because, when they are in the early stage of development, they look very similar.
Are molluscs more closely related to arthropods or annelids?
Molluscs and annelids are more closely related to each other than either is to arthropods. This means that segmentation as observed in arthropods and annelids is homoplastic and not homologous. In contrast, the trochophore larvae present in molluscs and annelids is probably a true homology.
What do molluscs have in common?
WHAT FEATURES DO MOLLUSKS HAVE IN COMMON? As well as a shell, most mollusks have a muscular foot for creeping or burrowing. Some also have a head with sense organs. The soft body includes lungs or gills for breathing, and digestive and reproductive parts, all enclosed by a skinlike organ called the mantle.
What are annelids most closely related to?
Annelids and arthropods have long been considered each other’s closest relatives, as evidenced by similarities in their segmented body plans.
Are flatworms more closely related to the annelids or the molluscs?
Flatworms (Phylum Platyhelminthes), annelids (Phylum Annelida) and mollusks (Phylum Mollusca), while extraordinarily diverse, share a number of characteristics, which suggests they are more closely related to each other than other invertebrate phyla.
What characteristics are shared by both mollusks and annelids?
Annelids have other similarities with mollusks, including:
- A closed circulatory system (like cephalopods).
- An excretory system consisting of tubular nephridia.
- A complete digestive system.
- A brain.
- Sensory organs for detecting light and other stimuli.
- Gills for gas exchange (but many exchange gas through their skin).
Are molluscs and arthropods related?
What are the Similarities Between Mollusks and Arthropods? Mollusks and arthropods belong to two phyla of Kingdom Animalia. Both groups contain invertebrates.
What are the phylogenetic relationships between the molluscs annelids and arthropods?
The resulting tree suggests that the molluscs and annelids form a monophyletic lineage and unites the molluscan taxa to a monophyletic group. Therefore, the result supports the Eutrochozoa hypothesis and the monophyly of molluscs, and indicates early acquisition of segmented body plans in arthropods.
How do land mollusks differ from water mollusks?
Their bodies are not divided into different segments or parts. Mollusks often have a hard outer shell to protect their bodies. Mollusks live nearly everywhere on Earth. Most live in water, but some live on land, usually in damp places.
What is the same about all molluscs?
The three most universal features defining modern mollusks are: a mantle with a cavity used for breathing and excretion, the presence of a radula, and. the structure of the nervous system.
What do annelids look like on the outside?
Mollusks are invertebrates such as the common snail. Most mollusks have shells. Annelids are worms such as the familiar earthworm. They have segmented bodies. Annelids look like roundworms on the outside, but on the inside they are more like mollusks.
What kind of mollusks are in the annelid group?
The annelids traditionally include the oligochaetes, which include the earthworms and leeches, the polychaetes, which are a marine group, and two other smaller classes.
Are there any mollusks that have two shells?
Class Bivalvia (“two shells”) includes clams, oysters, mussels, scallops, and geoducks. They are found in marine and freshwater habitats. As the name suggests, bivalves are enclosed in a pair of shells (or valves) that are hinged at the dorsal side. The body is flattened on the sides.
What kind of circulatory system does a mollusk have?
Most mollusks have an open circulatory system with a heart that circulates the hemolymph in open spaces around the organs. The octopuses and squid are an exception to this and have a closed circulatory system with two hearts that move blood through the gills and a third, systemic heart that pumps blood through the rest of the body.