The nautilus, an ancient marine animal, navigates the deep ocean. Its unique characteristics offer a glimpse into a lineage that has persisted across vast geological time.
Identity of the Nautilus
The nautilus is a marine mollusk, specifically classified within the group known as cephalopods. This places it in the same class as more familiar ocean dwellers like octopuses, squids, and cuttlefish. However, the nautilus stands apart from its relatives due to a distinguishing feature: its prominent external shell. The nautilus belongs to the family Nautilidae, the sole surviving family of the subclass Nautiloidea, which traces its origins back hundreds of millions of years.
Distinctive Physical Features
The most recognizable feature of the nautilus is its intricately chambered, spiral shell. This shell is composed of two layers: a matte white outer layer with dark orange stripes and an iridescent inner layer. Internally, the shell is divided into multiple compartments or camerae, which increase in number as the animal grows, from about four at hatching to 30 or more in adults. The nautilus occupies only the outermost and largest chamber, while the older, vacated chambers are sealed off by septa and filled with a mixture of gas and liquid.
A tissue called the siphuncle runs through small openings in these septa, connecting all the chambers. This siphuncle plays a role in buoyancy control by regulating the gas and fluid within the chambers through osmosis, allowing the nautilus to adjust its depth. Unlike other cephalopods, the nautilus possesses numerous tentacles, up to 90, which lack suckers. Instead, these tentacles have sticky grooves and ridges that help the animal grip food and transfer it to its beak-like mouth. The nautilus’s vision is relatively primitive, utilizing simple pinhole eyes without a solid lens, which primarily sense light and dark.
Life in its Ocean Home
Nautiluses primarily inhabit the deep slopes of coral reefs in the Indo-Pacific region, spanning from 30°N to 30°S latitude. They reside at depths of several hundred meters during the day to avoid predators. At night, they undertake vertical migrations, rising to shallower waters, around 70 to 150 meters, to forage.
As opportunistic predators and scavengers, nautiluses feed on a variety of prey, including lobster molts, hermit crabs, and carrion. They locate food primarily through their highly developed sense of smell. Movement is achieved through jet propulsion, where the nautilus expels water from its mantle cavity through a funnel-like structure called a hyponome, allowing it to move backward or change direction. Nautiluses are characterized by slow growth rates, taking approximately 10 to 15 years to reach sexual maturity. They are also long-lived for cephalopods, with lifespans estimated to exceed 20 years.
Ancient Lineage and Modern Threats
The nautilus is often referred to as a “living fossil” because it has undergone minimal evolutionary change over hundreds of millions of years. Its lineage dates back approximately 500 million years, with ancestors predating dinosaurs. This evolutionary stasis makes the nautilus a survivor that has persisted through numerous mass extinctions.
Despite its long history of survival, the nautilus now faces significant modern threats, primarily from human activities. Overfishing for its shell, which is sought after for the curio trade, jewelry, and decorative items, has led to population declines in some areas. Its slow growth rate, late maturity, and low reproductive output make nautilus populations particularly vulnerable to overexploitation. In response to these threats, the entire nautilus family was listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in 2016, which aims to ensure that international trade is sustainable and monitored. Additionally, the chambered nautilus (Nautilus pompilius) was listed as a threatened species under the Endangered Species Act (ESA) in 2018.