Atlantic pygmy octopus
The Atlantic pygmy octopus ("Octopus joubini"), also known as the small-egg Caribbean pygmy octopus, is a small octopus species in the order Octopoda. Fully grown, this cephalopod reaches a mantle length of with arms up to long. They are known for being intelligent creatures with keen senses, particularly good sight. "O. joubini" often seeks shelter from predators in empty clamshells, cans or small openings, pulling the opening closed with its arms, combining sand and gravel to form a lid. It employs the two defensive mechanisms typical of all octopuses: ink sacs and camouflage. All Cephalopods have  chromatophores, special pigmented and light reflecting cells on their skin which allows them to change colour and texture quickly. They are found in the Atlantic Ocean, particularly in the tropical waters of the Caribbean and the Gulf of Mexico. The first holotype was collected in 1929 by Guy Coburn Robson and became a key factor in distinguishing between "O. joubini" and the closely related "Octopus mercatoris" (or in some cases, an unidentified species referred to as "Octopus" sp. X). Much of the information about "O. joubini" was obtained through laboratory studies of captive specimens and what little is known about  their behavior in a natural environment is inferential. Physical characteristics. "O. joubini" is red-orange in color which is caused by pigmented cells called chromatophores that are common in many animals. Compared to other species of octopus, the "O. joubini" color patterning is relatively less complex. They are capable of becoming a dark, light, or intermediate shade ranging from brown to orange. As hatchlings, their chromatophores can also appear yellow. Though research is limited, some studies suggest that "O. joubini" have a complex system of sensory cells along their lip that serve a chemotactic function. These cells are highly ciliated  and contain high concentrations of sensory neurons, some of which are thought to act as mechanoreceptors, and some as chemoreceptors. These neurons are likely chemoreceptors, considering the species’ benthic lifestyle and the advantages that come with chemotactic sensitivity. Habitat. "O. joubini" are found in the warm temperate to tropical waters of the Atlantic, thriving in temperatures ranging from 18 to 25 degrees Celsius. They are benthic and are typically found on soft, muddy substrates around 10 to 15 m deep. Many laboratory experiments have shown that "O. joubini" prefer to remain hidden or, in the case of a tank environment , close to the sides of the enclosure. This behavior is presumably for protection against outside predators, though no literature describes specific predators of the "O. joubini." In many instances, "O. joubini" observed in their natural habitat are found hidden in empty soda cans, and some researchers even obtained them by collecting soda cans from the ocean floor. Reproduction. "O. joubini" in captivity exhibit highly varied broods ranging from 140 to over 2,500 eggs. They can reach sexual maturity a very small size, though most spawning adults were at least 30 mm. Females typically began to lay a new set of  eggs when the oldest eggs began to hatch. The key characteristics that differentiate "O. joubini" from "O. mercatoris", and other unidentified pygmy octopuses, is the size of the eggs and its color. While varying in size, fully developed eggs range from 2.9 to 4.8 mm, and are overall smaller than other species that were studied, informally referring to them as the "small egg species" that is most representative of the original "O. joubini" Robson holotype. Additionally, "O. joubini" appear to have a reddish-orange color that is more distinct than the larger egged species. Life cycle. Females of this species  breed between March and June, laying elliptical, amber eggs in a sheltered place. The hatchlings are relatively small (0.04 g), but are fully formed and can hunt within hours. They reach maturity in around 182 days and weigh about 30 g at this time. Hatchlings go through a brief planktonic stage where they remain close to the surface of the water for the first 2-3 days and then eventually disperse throughout the water column. These hatchlings average 2.5 mm in size and 2.9 mg in weight. Mortality is high during the first week (up to 90%) but becomes stable  afterwards. By the third week, "O. joubini" undergo intense feeding and rapid growth, sometimes tripling in weight, and transition from the planktonic stage, becoming fully benthic. Their lifespan is temperature dependent and can range from 6-12 months. Diet. Like all octopuses, "O. joubini" is carnivorous. It is able to bore into the hard shells of small clams, crustaceans, or other creatures. It uses its radula, a small, spikey, tongue like structure, to drill a hole in the prey's shell, and proceeds to secrete poisonous saliva out of its beak to paralyze its victim. While the Atlantic pygmy octopus  feeds primarily on small crustaceans, only a few species have been recorded as prey of this species in the wild. In laboratory conditions, this diet is expanded considerably. Behavior. Though octopuses are solitary animals, they do appear to partake in various social interactions, especially when living in high densities or in limited space (as in a laboratory environment). "O. joubini" demonstrate loose dominance relationships where larger octopuses would take over a particular area. However, "O. joubini" do no isolate themselves and are often attracted to spaces where there are others and will often share spaces, suggesting that they are not  territorial. They are also more likely to fight with other species, rather than with each other, when competing for space. Threats. In addition to competition and presumed predation, "O. joubini" also have to deal with anthropogenic threats such as pollution. In 1999, a harmful algal bloom wiped out an entire population of "Octopus mercatoris" in St Joseph’s Bay, Florida. After five years only one brooding female was collected, demonstrating the long term impact these blooms can have on species. Though research indicated that only the species "O. mercatoris" was affected, the predicament of this algal bloom could foreshadow possible  threats to "O. joubini," and other species, where pollution could cause more severe and frequent algal blooms.