September 19, 2016

A sea spider is a terrifying beast. It has frighteningly long legs connected to a tiny body. It possesses no teeth or gaping jaws. Instead, it has a long tube called a proboscis, which it uses to suck the fluids out of its prey. Fortunately, sea spiders are too small to threaten humans. Furthermore, the largest ones live at the bottom of the ocean near the North and South poles, far away from people.

Sea spider.
Credit: © Dray van Beeck, Shutterstock

Sea spiders are ocean animals and most of them have eight legs. But they are not true spiders. Instead, sea spiders belong to a unique group of arthropods. Arthropods are animals with jointed legs and no backbones. Many sea spiders are slender and delicate. Others are chunky and robust. Most sea spiders are small, especially those found in shallow waters. They can be less than 1/10 inch (3 millimeters) across, including the legs. Sea spiders live in all the oceans, from the shallows to depths greater than 20,000 feet (6,000 meters).

Sea spiders feed by grabbing prey with their mouthparts. They then pierce the prey and suck out the fluids with their proboscis. Sea spiders feed on invertebrates (animals without backbones), especially those that are slow or fixed in place. Many sea spiders have colors and patterns that help them blend in with algae or other life on the ocean floor. Some are brightly colored, possibly to warn away predators (hunting animals).

The body of a sea spider is so small that there is little room available for its internal organs. As a result, some of the organs extend into the creature’s long limbs. Furthermore, sea spiders lack respiratory systems. Instead, the oxygen they need simply diffuses (flows) from the ocean water into their bodies.

Most sea spiders are quite small, but those near Antarctica and the North Pole can grow to more than 30 inches (75 centimeters) in diameter. In those areas, there are fewer critters that hunt sea spiders, and there are greater concentrations of what sea spiders like to eat. The frigid waters may also play a role in their giant proportions near the poles. Cold water holds more oxygen, so more of the gas can diffuse into a sea spider’s body, allowing it to grow larger.

Like most organisms, sea spiders are vulnerable to the effects of global warming, but the polar habitats of giant sea spiders increase their risk. As polar ice melts, giant sea spiders lose their protection from such predators as birds and marine mammals. Also, because warm water holds less dissolved oxygen, warming seas reduce the range of giant sea spiders. Scientists have identified more than 1,000 species (kinds) of sea spiders, but many more probably remain undiscovered. Because of the effects of global warming, scientists fear a large number of those unknown species will disappear before they can be identified.

February 13, 2014

The discovery of a site in Canada containing hundreds of ancient fossils is being heralded as one of the most important discoveries in paleontology in the past 100 years. The huge fossil site, located in Marble Canyon in Kootenay National Park in southeastern British Columbia, contains hundreds of magnificently preserved fossils of early animals from the Cambrian, a period in Earth’s history that lasted from about 543 million to 490 million years ago. So far, scientists have found the fossils of more than 50 invertebrate (animals without backbones) species, about a dozen of which have never been seen before. The site rivals the famous Burgess Shale formation, a 505 million-year-old site discovered in 1909 in Yoho National Park about 26 miles (42 kilometers) northwest of Marble Canyon. For now, the exact location of the fossil deposit is being kept secret to protect the delicate fossils from collectors. The Marble Canyon site was discovered in 2012 by scientists fromt the Royal Ontario Museum, the Universities of Toronto and Saskatchewan in Canada, Pomona College in California, and Uppsala University in Sweden.

During the Cambrian Period, the region lay at the bottom of a shallow ocean. Fine-grained mud that accumulated over time preserved in exquisite detail the soft-bodied invertebrates that lived and died in this ocean over millions of years, giving paleontologists an excellent view of their anatomy. Many of the animals can be identified as types of worms and arthropods (animals with jointed legs). Among them are trilobites, an extinct group of arthropods related to modern crabs and lobsters. Some of the fossil animals appear similar to invertebrates alive today, while other are unique and are new to science.

A mold preserved the three-dimensional form of a trilobite after its body decayed. ((c) Sinclair Stammers, Science Photo Library; Photo Researchers)

The Cambrian Period was an important time in the history of life on Earth. Many major types of animals first appear in fossils from the early Cambrian Period. Scientists often refer to this sudden, dramatic increase in the variety of animal fossils as the Cambrian Explosion. During the Cambrian Explosion, animals evolved (developed gradually) into many new forms and spread throughout Earth’s oceans. They also began interacting with one another and their environment in more complex ways. Animals began eating other animals, growing skeletons for protection, and burrowing into sea-floor sediments for food and shelter.

The fossils unearthed from the Marble Canyon site will help researchers better understand the conditions of the marine ecosystem that spurred the rapid diversification of animal forms during the Cambrian Period. For example, some of the invertebrate species found at Marble Canyon are also known from fossil sites in Asia about the same age. This indicates that some species had spread throughout the world, while others may have been limited to particular habitats.

Additional World Book articles:

• Earth (History of Earth)
• Prehistoric animal
• How the Ocean Came to Be (a Special Report)
• Paleontology (1991) (a Back in Time article)

March 29, 2012

On March 25, Canadian-born filmmaker and undersea explorer James Cameron became the first person to dive solo to the deepest-known part of the world’s ocean. Cameron, who has directed such films as Aliens (1985), Titanic (1997), and Avatar (2009), descended to a canyon called the Mariana Trench, which lies nearly 7 miles (11 kilometers) below the surface of the western Pacific Ocean. The area, the lowest-known point of Earth’s crust, is located near the United States Territory of Guam.

James Cameron became the first person to dive solo to the deepest part of the ocean. (Courtesy Jason LaVeris, FilmMagic/Getty Images)

Cameron reached the Mariana Trench in a submersible called Deepsea Challenger. Submersibles are research vessels built to withstand the crushing pressures and near-freezing temperatures found in ocean depths. Deepsea Challenger is a 26-foot- (7.9-meter-) high capsule that descends upright.

According to Cameron, he found the seafloor to be “devoid of sunlight, devoid of any heat, any warmth.” He reported that it was “completely featureless and uniform” and that the only organisms he saw were tiny, shrimp-like arthropods (animals with jointed legs and no backbone). Cameron planned to create a television special for National Geographic and a 3D film for commercial release about his journey. Before Cameron, the only persons to descend into the Mariana Trench were U.S. Navy Lieutenant Don Walsh and the late Swiss oceanographer Jacques Piccard, who explored the trench together in the submersible Trieste in 1960.

Although Cameron is best known as a filmmaker, he has made more than 70 ocean dives over the years, including a dozen during the filming of Titanic, a movie about the sinking in 1912 of the largest and most luxurious ocean liner of the day. The Titanic struck an iceberg during its maiden voyage from England to the United States, causing the deaths of more than 1,500 people. The exact whereabouts of the ship remained unknown for decades until a team of French and American scientists led by Jean-Louis Michel and Robert D. Ballard found the wreck in the north Atlantic near Newfoundland and Labrador, Canada, in 1985 at a depth of about 2.4 miles (3.8 kilometers).

Additional World Book articles:

• Deep into the Past (a special report)
• Deep sea
• Archaeology 1985 (a Back in Time article)
• Ocean 1960 (a Back in Time article)