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bimac species?

DHyslop

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Octopus bimaculoides and Octopus bimaculatus. The two species are nearly indistinguishable, so much that biologists considered it to be a single taxon until 1949. Biologists distinguish them based upon two characters, the first being egg size ('uloides has larger eggs out of which hatch fully-formed miniature octopuses, while 'ulatus lays thousands of tiny eggs out of which hatch floating larvae); the second character is what species of mesozoan parasites they have in their kidneys.

There are a lot of other criteria floating the internet on how to tell them apart. These include size and distinctive patterns in the false-eye spots. I'm skeptical of how useful these characters are because I haven't yet found mention of them in the scientific journals (If anyone has a reference otherwise please let me know!). The size of an individual bimac seems to not depend on which species it is but rather the average adult size in the wild population it came from (bimacs seem to naturally occur in localized communities).

People have gotten bimacs in the past that grow very large and some have concluded that those particular animals were 'ulatus and not 'uloides. I think the only reason for that conclusion is the desire to believe you can keep a 'uloides in a 30 gallon tank :wink:

For the record, I don't think any hobbyist can know which bimac they have unless it lays eggs or you know it came from someone rearing eggs. Again, I beg anyone with a reference otherwise to speak up.

Dan
 

monty

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DHyslop;81046 said:
There are a lot of other criteria floating the internet on how to tell them apart. These include size and distinctive patterns in the false-eye spots. I'm skeptical of how useful these characters are because I haven't yet found mention of them in the scientific journals (If anyone has a reference otherwise please let me know!).

It's not quite a scientific journal, but Norman's Cephalopods: A World Guide also says they can be distinguished based on bimaculatus having "larger size, a different ocellus and smaller egg size."

It continues:

The ocellus in Octopus bimaculatus contains an iridescent blue ring in the form of broken chain links with spokes extending to the outer edge of the false-eye spot.

under bimaculoides it says:

The iridescent ring within the ocellus is in the form of unbroken chain links.

There are close-up pics of the 'oides eyespot, but not the 'atus. The references in Norman's book are minimal, but the pictures are from many of the usual suspects (Hanlon, Hochberg, Forsythe.)

I didn't get good results in google scholar, but regular google for "bimaculatus bimaculoides ocellus" found this page by John Forsythe and a word document by Roland Anderson, so reputable people seem to agree that this is a real criterion.
 

DHyslop

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Now we're talking. I'm perfectly content ignoring Norman, but I'll trust Forsythe for the ocellus! Roland's doc also mentions ink color--does this suggest someone has held two jars of ink next to one another? :smile:

Dan
 

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