Whither a seven-armed octopus? Wonder whether it’s a case of wither? So does the author of this study:

An Octopus With Only Seven Arms: Anatomical Details,” Ian G. Gleadall, Journal of Molluscan Studies, Volume 55, Issue 4. 1989, pp. 479-487.  The author, at School of Medicine Tohoku University Seiryo cho Sendai, Japan, reports:

“A male specimen of Octopus is described which has only seven arms: the fourth right arm is congenitally absent. Dissection reveals that, as in normal octopuses, eight brachial nerves arise from the brain. However, right brachial nerves 2, 3 and 4 are connected by unusually short lengths of the interbrachial commissure, distal to which right brachial nerves 3 and 4 run together, with corresponding arteries, into the third right arm. Hectocotylization of the latter confirms that it is the fourth right arm which is missing. Other abnormalities of the specimen include an obviously asymmetrical funnel organ and three pairs of conjoined suckers.”

(Thanks to investigator Kurt Verkest for bringing this to our attention.)