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Each zooid grows from an individual embryo, one cell, in the same kind of process of division and cell specialization all multicellular animals go through. Fo

by retrac 4y ago

Each zooid grows from an individual embryo, one cell, in the same kind of process of division and cell specialization all multicellular animals go through. For humans, or sven jellyfish, the embryo develops into an independent adult form. But in siphonophores, these individuals are completely specialised to one role within a colony, and can't survive without the colony.

lisper 4y ago
> in siphonophores, these individuals are completely specialised to one role within a colony, and can't survive without the colony Again, I fail to see the distinction between what you are describing here and true multicellular organisms. My body can be viewed as a colony of individual cells. That colony consists almost exclusively of cells that are completely specialized to one role within the colony, and which cannot survive outside without the colony. (But there are exceptions, like HeLa cells.)
- retrac 4y ago
  Because you start from only one embryo. Almost all animals start from one embryo. These animals are formed from thousands to millions of embryos. From a feature categorization perspective, I guess you have a point. They look a lot like non-clonal jellyfish in practice! But the implied underlying question is: how did that mechanism evolve? Two organisms may look similar but have completely different evolutionary histories and mechanisms to arrive at that appearance. Like eyes, which seem to have evolved independently multiple times. This is a completely different mechanism to construct a multicellular organism. Not stem cells, but embryos, cloning a specialized twin, each of which undergoes embryonic development into a sort-of-organ. In almost all other animals, all genetically identical specialized cells come from a single embryo, which splits into stem cells, which then specialize. That's why it's interesting and stands out, at least to me.

by retrac 4y ago

lisper 4y ago

> in siphonophores, these individuals are completely specialised to one role within a colony, and can't survive without the colony Again, I fail to see the distinction between what you are describing here and true multicellular organisms. My body can be viewed as a colony of individual cells. That colony consists almost exclusively of cells that are completely specialized to one role within the colony, and which cannot survive outside without the colony. (But there are exceptions, like HeLa cells.)

retrac 4y ago
Because you start from only one embryo. Almost all animals start from one embryo. These animals are formed from thousands to millions of embryos. From a feature categorization perspective, I guess you have a point. They look a lot like non-clonal jellyfish in practice! But the implied underlying question is: how did that mechanism evolve? Two organisms may look similar but have completely different evolutionary histories and mechanisms to arrive at that appearance. Like eyes, which seem to have evolved independently multiple times. This is a completely different mechanism to construct a multicellular organism. Not stem cells, but embryos, cloning a specialized twin, each of which undergoes embryonic development into a sort-of-organ. In almost all other animals, all genetically identical specialized cells come from a single embryo, which splits into stem cells, which then specialize. That's why it's interesting and stands out, at least to me.