How did cephalopods evolve?
Cephalopods evolved during the Cambrian ($530 Ma) from a monoplacophoran-like mollusc in which the conical, external shell was modified into a chambered buoyancy apparatus. During the mid- Palaeozoic ($416 Ma) cephalopods diverged into nauti- loids and the presently dominant coleoids.
Which arm is the Hectocotylus?
Among Decapodiformes (ten-limbed cephalopods), generally either one or both of arms IV are hectocotylized. In incirrate octopuses it is one of arm pair III. Rare examples of double and bilateral hectocotylization have also been recorded in incirrate octopuses.
What did an octopus evolve from?
The cephalopods were once thought to have evolved from a monoplacophoran-like ancestor with a curved, tapering shell, and to be closely related to the gastropods (snails). The similarity of the early shelled cephalopod Plectronoceras to some gastropods was used to support this view.
What did squids evolve?
Until now the origins of cephalopods, which evolved from ancient marine molluscs with shells, have been shrouded in mystery.
Why are cephalopods advanced?
Cephalopod mollusks such as octopus, cuttlefish, and squid (coleoids) are of special interest for studying the evolution and function of learning and memory mechanisms at the system level. They are believed to have the most advanced cognitive behaviors of all invertebrates, rivaling the abilities of many vertebrates.
Does Hectocotylus regrow?
In male cephalopods, an arm called the hectocotylus is adapted to deliver sperm to the female. This arm breaks off from the male during copulation and stays lodged in the female. The hectocotylus regenerates after the mating episode.
How many hearts do squid have?
three hearts
Squid have three hearts: two branchial hearts and one systemic heart. The branchial hearts pump blood to the gills, where oxygen is taken up. Blood then flows to the systemic heart, where it is pumped to the rest of the body. The systemic heart is made of three chambers: a lower ventricle and two upper auricles.
What’s the difference between cephalopod and mollusk?
The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. They are also the only cephalopods with four gills instead of two.) Cephalopods have a more developed nervous system than other mollusks. They also have very well developed eyesight that is used in finding prey.
Which is the best definition of a hectocotylus?
Definition of hectocotylus : a modified arm of a male cephalopod that is specially and variously adapted to effect the fertilization of the eggs especially : an arm that in argonauts and some octopods receives the spermatophores, is inserted into the female mantle cavity, and then is broken free from the body of the male
Where did the hectocotyl arm get its name?
The hectocotyl arm was first described in Aristotle’s biological works. Although Aristotle knew of its use in mating, he was doubtful that a tentacle could deliver sperm. The name hectocotylus was devised by Georges Cuvier, who first found one embedded in the mantle of a female argonaut.
Where is the hectocotylus located in a seven arm octopus?
In male Seven-arm Octopuses ( Haliphron atlanticus ), the hectocotylus develops in an inconspicuous sac in front of the right eye that gives the male the appearance of having only seven arms.
What does a male hectocotyli do to the female?
Structurally, hectocotyli are muscular hydrostats. Depending on the species, the male may use it merely as a conduit to the female analogous to a penis in other animals, or he may wrench it off and present it to the female.