Leptostracans: Phyllocarida

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LEPTOSTRACANS: Phyllocarida

NO COMMON NAME (Dahlella caldariensis): SPECIES ACCOUNT

PHYSICAL CHARACTERISTICS

Most leptostracans are 0.19 to 0.59 inches (5 to 15 millimeters) in length, but the largest species measure up to 1.96 inches (50 millimeters). Their transparent bodies are covered by a loose whitish shield, or carapace, that is folded over their backs. The carapace (CARE-eh-pes) is flattened from side to side and covers the thorax or midbody, leaving the head and long abdomen exposed. At the front of the carapace is a beaklike projection, or rostrum (RAH-strem), that extends out over the head.

The head has red compound eyes set on stalks. The first pair of antennae is usually branched, or biramous (BY-ray-mus). The second pair of antennae is uniramous (YU-neh-RAY-mus) and not branched. The mandibles (MAN-dih-bulz), or biting mouthparts, are uniramous. Maxillipeds (mack-SIH-leh-pe-hds), the leglike appendages associated with the mouth, are absent. The thorax and abdomen are distinct. The thorax has eight pairs of leaflike limbs that are all similar to one another in appearance. The seven-segmented abdomen or tail section has six pairs of limbs called pleopods (ple-o-pawds). The first four pairs are biramous. Each pair is hooked together so that they work together when swimming. The last two pairs of pleopods are small and uniramous. The tail segment at the tip of the abdomen is tipped with a long, forked projection.

GEOGRAPHIC RANGE

Leptostracans are found in all the world's oceans.

HABITAT

Most leptostracans are found from seashores to depths of 1312.32 feet (400 meters), but one species lives in deep-sea waters at depths of more than 6,561 feet (2,000 meters). Although some species prefer open waters, most live on mud bottoms that have very little oxygen.

DIET

Leptostracans stir up materials from the bottom and filter out bits of food suspended in the water. Some species are scavengers and feed on accumulations of dead organisms that have settled on the ocean floor.

BEHAVIOR AND REPRODUCTION

Adult males sometimes swim long distances in search of mates using the first four pairs of pleopods. Young individuals and adult females rest on the bottom for hours. Their leaflike limbs beat rhythmically to move oxygen-carrying water through the carapace. In captivity leptostracans burrow in mud and often remain motionless. Inactivity and slow heartbeat allow them to live in environments with very little oxygen.

The eggs of most leptostracans are thought to be carried in a special chamber located beneath the carapace. The young develop within the eggs. They hatch resembling adults, but are distinguished by having a small fourth pair of pleopods. Water temperature has a tremendous influence on growth rates of immature leptostracans. Males develop gradually as they molt, or shed their external skeletons. Females continue to resemble immature leptostracans until they are ready to reproduce.

LEPTOSTRACANS AND PEOPLE

Nebalia bipes is an important food for live fish raised in captivity.

A BLAST FROM THE PAST

In 2003, five fossil phyllocarids were described from detailed impressions left in 425 million-year-old rocks found in England. The fossils measured no more than 0.0236 inches (6 millimeters). A single fossil was cut into four blocks using a microscopic saw blade. Each block was then ground down 0.0000012 inches (30 millimicrons) at a time and digitally photographed. The images were fed into a computer to create a remarkable three-dimensional colorized reconstruction of an ancient organism.

CONSERVATION STATUS

No leptostracans are considered endangered or threatened.

NO COMMON NAME (Dahlella caldariensis): SPECIES ACCOUNT

Physical characteristics: The largest individuals of Dahlella caldariensis (abbreviated to D. caldariensis) measure approximately 0.31 inches (8.1 millimeters) long from the base of the rostrum to the tip of the tail. The rostrum is three times longer than wide and almost half as long as the carapace. The eyes lack color; eyestalks are banana-shaped with tiny, toothlike bumps along the front margin.

Geographic range: This species lives near deep-sea geysers, known as hydrothermal vents, near the Galápagos Islands and the East Pacific Rise.

Habitat: D. caldariensis is found in vent openings and clumps of mussels and vestimentiferans at depths of 8,040 to 8,595 feet (2,450 to 2,620 meters).

Diet: Not much is known about their feeding habits. However, it has been suggested that the rough eyestalks might be used to scrape surfaces to loosen bits of food, such as encrustations of bacteria and other organisms.

Behavior and reproduction: Nothing is known about their behavior or reproduction.

Dahlella caldariensis and people: Nothing is known.

Conservation status: This species is not considered endangered or threatened. ∎

FOR MORE INFORMATION

Books:

Brusca, R. C., and G. J. Brusca. Invertebrates. Second edition. Sunderland, MA: Sinauer Associates, 2003.

Hessler, R. R., and F. R. Schram. Leptostraca as Living Fossils. In Living Fossils, edited by N. Eldredge and M. Stanley. Berlin: Springer-Verlag, 1984.

Periodicals:

Briggs, D. E. G., M. D. Sutton, and D. J. Siveter. "A new phyllocarid (Crustacea: Malacostraca) from the Silurian Fossil-Lagerstätte of Herefordshire, UK." Proceedings of the Royal Society: Biological Sciences 271, no. 1535 (2004): 131-138.