Octopus bimaculatus

O. bimaculatus gets its name "two-spotted octopus" from the blue and black ocelli under each eye. One potential function of these bright blue ocelli is to allow the octopus to appear as a different animal with large eyes as it swims swiftly through the water.[4] O. bimaculatus is often confused with Octopus bimaculoides due to the similarity in looks, however they are two different species. They both have these two distinctive black and blue ocelli beneath the eyes and above the arms, however there are a few key differences in their features to tell the two species apart. The blue ring of the ocelli for Octopus bimaculatus does not have the same distinctive chain-like pattern that the Octopus bimaculoides has. For O. bimaculatus the pattern is still chain-like but more irregular, asymmetrical, and disproportionate while for O. bimaculoides the chain-like pattern is more symmetrical and orderly. The two also differ in egg size, with Octopus bimaculatus eggs being much smaller that hatch into planktonic larvae rather than benthic hatchlings like Octopus bimaculoides. Additionally, octopus bimaculatus is generally the larger of the two species.[5]

Difference in chain-like pattern of ocelli between O. bimaculatus and O. bimaculoides

O. bimaculatus is known to prey on crustaceans, snails, chitons, limpets, and bivalves. Studies have observed the predator-prey interactions between the O. bimaculatus and the Californian Scorpionfish (Scorpaena guttata) in aquariums. Findings suggest that the Californian Scorpionfish is included in the diet of O. bimaculatus in their natural habitat, specifically juvenile scorpionfish.[6] As juveniles, the octopus tend to prey on smaller benthic, marine invertebrates which include chitons, bivalves, snails, and crabs.[7] Additionally, diet appears to be strongly influenced by location, season, and sex.[8][9]

O. bimaculatus hunt regularly by swimming along the seafloor and pouncing at their prey using their web to feel if they successfully captured their prey. After capture, they use their beak and radula to consume their prey. There has been observations of certain species of fish following the octopus into kelp forests looking for scraps from the octopus prey.[4]

O. bimaculatus lives about 12–18 months. Young are planktonic for one to several months before settling on the ground. However, in captivity, O. bimaculatus has been observed to live up to 2 years.[2]

Most matings occur in May and June when water temperatures are rising, but they may mate throughout the year. Most females then lay their eggs between April and August. Mating ranges from 10 to 60 minutes long. During this time, the male extends a modified arm called the hectocotylus which transfers spermatophores to the female.[13][14] After the eggs are fertilized, the females lay their eggs in a sheltered area protected by rocks. The amount of eggs laid depends on the size on the female, but typically the number of eggs are very high, with the average being approximately 20,000 eggs, about 100 to 250 per strand. The larger females tend to lay more eggs than the smaller females. After the eggs are laid, the females stay to care for and protect the eggs until they hatch into planktonic larvae.[15] Females tend to die during the process of watching over the eggs due to starvation and exhaustion.[2]

The stages of development on average range over a period of 50.4 days after fertilization occurs.[15] The eggs fully develop over a range of 30–90 days depending on water temperature. Studies have found development time is shortest, 31 days, when the water temperature is at 19.7 degrees C. There are two major stages in the development; the rapid initial stage and the second slower stage.[2] Newly hatched eggs are planktonic and on average are 4 mm long from the top of the mantle to the end of the arms. Much of the embryonic development is similar and can be described by the development of Octopus vulgaris.[15]