Tantulocaridans: Tantulocarida

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TANTULOCARIDANS: Tantulocarida

NO COMMON NAME (Itoitantulus misophricola): SPECIES ACCOUNT

PHYSICAL CHARACTERISTICS

Tantulocaridans (tan-too-loh-KAR-ee-dans) are very strange-looking animals that are external parasites on other deep-sea crustaceans. External parasites spend most of their lives attached to the bodies of their hosts. The larvae (LAR-vee), or young animal form, are very, very small, measuring from 0.00335 to 0.00709 inches (0.0085 to 0.0018 millimeters) in length. The head does not have any appendages, except for a pair of antennae that are present only during one larval stage. The mouthparts are platelike in appearance. The body trunk has six thoracic and two abdominal segments. There are six pairs of thoracic limbs that are used for swimming. The first five pairs are branched, or biramous (BY-ray-mus). The sixth pair is not branched, or uniramous (YU-neh-RAY-mus). The abdomen does not have any appendages underneath, but does have a pair on the very tip.

Adult females come in two distinct forms. Forms that do not mate to reproduce measure up to 0.08 inches (2 millimeters) long and have a small, narrow head with a small projection, or rostrum. They use their suckerlike mouthparts to attach themselves to the external skeletons (exoskeletons) of their hosts. The sacklike thorax is filled with eggs or developing larvae and does not have any limbs. There are no body openings. To escape the sacklike thorax, the larvae must break out through the adult female's body wall.

Females that mate to reproduce are smaller, less than 0.02 inches (0.5 millimeters) in length. Their bodies have two distinct body regions. The head and thorax are tightly joined, or fused, into a single body region called the cephalothorax (SEH-feh-lo-THOR-acks). The cephalothorax has a pair of antennae and a reproductive opening, but does not have any mouthparts. Small numbers of eggs are carried inside the cephalothorax. A five-segmented body follows the cephalothorax. The first two segments of the trunk each have a pair of biramous thoracic limbs that are used for grasping. The fifth and last segment has a pair of long, slender appendages. Adult males are similar in size and appearance to the adult females that mate to reproduce. They have six pairs of biramous limbs used for swimming.

GEOGRAPHIC RANGE

Very little is know about the distribution of these animals because of their small size. They are currently known to live in the North and South Pacific, North and South Atlantic, Arctic, and Antarctic oceans.

HABITAT

Tantulocaridans spend most of their lives attached to other marine crustaceans living on the ocean floor. Their hosts include cumaceans, tanaids, isopods, amphipods, copepods, and ostracods. Some larval stages are also found in mud or sand on the ocean bottom.

DIET

Tantulocaridans are external parasites and feed on the body fluids of their hosts.

BEHAVIOR AND REPRODUCTION

Very little is known about the behavior of tantulocaridans, especially about how they find and attach themselves to their hosts. After leaving their mothers, larvae spend some time burrowing on the sea bottom before attaching themselves to a crustacean living on or near the ocean bottom.

FOR TANTULOCARIDANS, LESS IS MORE

Different kinds of parasites often resemble each other. Compared to non-parasites, blood-sucking parasites are usually smaller and have fewer body segments and appendages, if they have appendages at all. Whether the parasite is a tick, louse, or tantulocaridan, small body size reduces its chances of being picked off by an irritated host. And, there is little need to walk, swim, or fly. Once the parasite settles, it's all it can eat, all the time!

Tantulocaridans have a very strange double life cycle. Part of the life cycle involves sac-shaped females that can produce larvae without mating. These larvae are released into the sea fully formed and are capable of attaching themselves to a new host. As the larvae develop, they lose all of their thoracic and abdominal segments and become adult females that also reproduce without males. Their now sacklike bodies expand to make room for the eggs and larvae developing inside.

In the life cycle that requires mating, the larvae attach themselves to their host with their mouthparts. As they feed and grow, a sacklike structure begins to grow near the rear of the body. In this sac, the larva will become an adult male or female. Mature adults escape into the sea when the sac breaks open. These males and females have never been observed alive, but it is believed that males are good swimmers and actively search for females. Fertilized eggs are thought to develop inside the expandable cephalothorax of the female.

TANTULOCARIDANS AND PEOPLE

Tantulocaridans do not impact people or their activities.

CONSERVATION STATUS

No tantulocaridans are considered threatened or endangered.

NO COMMON NAME (Itoitantulus misophricola): SPECIES ACCOUNT

Physical characteristics: The larvae have long appendages on the tips of their abdomens. The thoracic limbs are used for swimming; the last pair has a long, curved spine on each tip. The sac where adult males or females develop is formed behind the sixth thoracic segment. Males have an unsegmented abdomen with distinct appendages on the tip.

Geographic range: Itoitantulus misophricola (abbreviated I. misophricola) are found from the southern Japanese island of Okinawa, south to the Philippines.

Habitat: I. misophricola are external parasites on copepods living on or near the ocean bottom, at depths of 550 to 6,725 feet (167 to 2,050 meters).

Diet: I. misophricola eat the body fluids of certain groups of copepods.

Behavior and reproduction: Nothing is known about their behavior. The unusual double life cycle of tantulocaridans was first described in this species.

Itoitantulus misophricola and people: This species does not impact people or their behaviors.

Conservation status: I. misophricola is not considered threatened or endangered. ∎

FOR MORE INFORMATION

Periodicals:

Boxshall, G. A., and R. J. Lincoln. "The Life Cycle of the Tantulocarida (Crustacea)." Philosophical Transactions of the Royal Society of London. B315 (1987): 267-303.

Huys, R., G. A. Boxshall, and R. J. Lincoln. "The Tantulocaridan Life Cycle: The Circle Closed?" Journal of Crustacean Biology 13 (1993): 432-442.