LOPHOGASTRIDS: Lophogastrida

PHYSICAL CHARACTERISTICS

Lophogastrids (loh-foh-GAS-trids) are long, shrimplike, and usually measure 0.39 to 3.15 inches (10 to 80 millimeters) in length, but one species reaches 13.78 inches (350 millimeters). Both pairs of antennae are branched, or biramous (BY-ray-mus). The outer branches of the second pair of antennae, or exopods, are short and flaplike. The compound eyes are set on stalks. Each eye has multiple individual lenses. The first pair of jaws, or mandibles, is biramous. The larger branch is used to crush food. The smaller branch is used for handling food and for cleaning. The second pair of branched jaws is called the maxillae (mack-SIH-lee). They are bristly and used to filter particles of food from the water.

A shieldlike carapace covers the head and segmented thorax. The carapace is loosely attached to the body and extends forward out over the head in a beaklike projection. It also covers the sides of the body down to the bases of the thoracic limbs. The thoracic limbs, or pereopods (PAIR-ee-oh-pawds), are biramous. Special plates form the marsupium (mar-SOUP-ee-uhm), a special brood pouch for carrying eggs.

Both males and females have well-developed biramous limbs, or pleopods (PLEE-oh-pawds), on the underside of the abdomen. The tip of the abdomen has a pair of long appendages called uropods (YUR-oh-pawds). The uropods are found on either side of a long, pointed tail-segment, or telson. The uropods and telson of this species are distinct and do not form a fanlike tail.

GEOGRAPHIC RANGE

Lophogastrids live in all oceans except the Arctic. Most species are found in the Pacific and Indian oceans.

HABITAT

Lophogastrids usually swim in deep, open waters down to depths of 3,280 feet (1,000 meters). Some species are found in waters as shallow as 164 feet (50 meters).

DIET

Most lophogastrids are thought to be predators. They prey on free-floating animals called zooplankton. Only one species, Gnathophausia, seems to use its bristly mouthparts as filters to strain large particles of food from the water.

BEHAVIOR AND REPRODUCTION

Little is known about the behavior of lophogastrids. They are very difficult to observe in the wild. Recently they have been raised in captivity at the Monterey Bay Aquarium in California. Lophogastrids spend all their time swimming and use their pleopods to propel through the water. They use their pereopods to keep oxygen-carrying water flowing through their gills.

It is likely that both males and females are required for reproduction, but mating has never been observed. The eggs are kept in the brood pouch until they hatch. The hatchlings have a complete set of thoracic limbs.

LOPHOGASTRIDS AND PEOPLE

Lophogastrids are probably an important food source for many fish that are eaten by people.

DEEP-SEA DEFENSES

The brilliant red color of giant red mysids appears black in the dim light that penetrates the waters of their deep-sea home. This makes them virtually invisible to many predators. But if they are discovered, they can spit out a glowing fluid. The sudden splash of light startles and distracts predators, giving the mysid a chance to escape. If all else fails, their hard, spiny carapace will discourage even the hungriest of predators.

CONSERVATION STATUS

No lophogastrids are considered endangered or threatened.

GIANT RED MYSID (Gnathophausia ingens): SPECIES ACCOUNT

Physical characteristics: The giant red mysid is the largest crustacean that lives in open water. It measures up to 13.78 inches (350 millimeters) in length. The carapace has a very long, beaklike projection that extends almost to the end of the first pair of antennae, or antennules. The flaplike exopods of the second pair of antennae are long with sharply pointed tips. The back of the carapace is extended as a spine that reaches back to the second abdominal segment. The carapace is folded inward underneath the body to form a partially enclosed gill chamber.

Geographic range: Giant red mysids live in deep waters below the tropical and subtropical waters of the Atlantic, Pacific, and Indian oceans.

Habitat: They live in deep, open waters, usually at depths of 1,300 to 4,920 feet (396 to 1,500 meters).

Diet: Giant red mysids eat large particles filtered from the seawater, as well as small dead organisms found in the water.

Behavior and reproduction: Little is known about the behavior of this species. Gnathophausia ingens has a very long period of larval development that is estimated to be about 530 days. Adult females probably have more than one brood and live for almost 3000 days. From hatching to adult, an individual giant red mysid molts 13 times.

Giant red mysids and people: This species is probably eaten by larger fishes that are fished commercially and sold as human food.

Conservation status: Giant red mysids are not considered endangered or threatened. ∎

FOR MORE INFORMATION

Books:

Schram, F. R. Crustacea. Oxford, U.K.: Oxford University Press, 1986.

Periodicals:

Childress, J. J., and M. H. Price. "Growth Rate of the Bathypelagic Crustacean Gnathophausia ingens (Mysidacea: Lophogastridae). I. Dimensional Growth and Population Structure." Marine Biology 50 (1978): 47-62.

Web sites:

Giant Red Mysid (Gnathophausia ingens). http://www.mbayaq.org/efc/living_species/default.asp?hOri=0&hab=9&inhab=179 (accessed on February 22, 2005).