MOLLUSCA
Examples: Snails, clams, oysters, mussels, squid, octopi
There are approximately 85,000 known species of mollusks on our planet, and possibly 20,000 more that haven't been discovered. This phylum has the largest marine species we know of today. There are six classes of mollusks: Gastropoda, which emerged 600 million years ago and are classified by their spiral shell and colors; Monoplacophores, which are very small and remain on the seabed; Polyplacophores, also known as Chitons, are found anywhere between the shallow coral reefs and the abyssal zone; Scaphopods, made up of 350 species are small, curved and white; Bivalves, which indicates two plates on a hinge that protects the animal living inside; Cephalopods, such as squids are the most evolved and are carnivorous.
There are approximately 85,000 known species of mollusks on our planet, and possibly 20,000 more that haven't been discovered. This phylum has the largest marine species we know of today. There are six classes of mollusks: Gastropoda, which emerged 600 million years ago and are classified by their spiral shell and colors; Monoplacophores, which are very small and remain on the seabed; Polyplacophores, also known as Chitons, are found anywhere between the shallow coral reefs and the abyssal zone; Scaphopods, made up of 350 species are small, curved and white; Bivalves, which indicates two plates on a hinge that protects the animal living inside; Cephalopods, such as squids are the most evolved and are carnivorous.
CIRCULATORY SYSTEM
Many animals have a closed circulatory system where blood is pumped fully throughout the body to provide constant nutrients needed for vigorous activities. Mollusks on the other hand, have an open circulatory system where blood doesn't fully circulate through the organism. The blood is released from the heart to the vital areas once it has collected the oxygen that the gills have extracted from the water. Blood is released into these vital areas between the organs called hemocoels, filling the tissues with blood. The deoxygenated blood is then diffused through the cells back to the circulatory system; this process causes a slow blood flow. An open circulatory system is ideal for mollusks because they doesn't require extremely laborious motion.