No common name

Rhabdopleurida normani

ORDER

Rhalodopleurida FAMILY

Rhabdopleuridae

TAXONOMY

Rhabdopleura normani Allman, 1869, Norway.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

Adults have a cephalic shield, complex collar, and trunk. They can reach 0.1 in (3 mm) long, but typically are about 0.04 (1 mm) in length. There are two tentacled arms rising from the collar. The tentacles may reach 0.06 in (1.5 mm) in length.

DISTRIBUTION

Atlantic and Arctic Oceans, Mediterranean Sea.

HABITAT

These marine hemichordates are sessile colonial organisms found in shallow water up to 33 ft (10 m) deep, clinging to the bottoms or other protected nooks and crannies of rocks, corals, and other hard underwater surfaces. They live in and are con fined to a coenecium because of their attachment to a continuous organic stem or stolon.

BEHAVIOR

Adult individuals are known as zooids. They live in separate, translucent tubes within a coenecium built out of secretions from their cephalic shields. The zooids are attached to a stolon and are unable to leave the coenecium. The larvae, on the other hand, use their cilia for swimming.

FEEDING ECOLOGY AND DIET

Individual adult R. normani worms feed by poking their proboscis, or cephalic shields, out of the coenecium and extending their two ciliated "arms" into the water. Although it has been suggested that other hemichordates use the mucus they secrete to transport food items, recent research indicates that individuals of this suspension-feeding species beat their cilia to draw food particles toward the mouth and do not rely on mucus to trap their food.

REPRODUCTIVE BIOLOGY

R. normani engages in sexual and asexual reproduction. Asexual budding occurs at the stolon, which runs along the bottoms of the tubes and forms connections among the zooids. Sexual reproduction occurs throughout the year. Females secrete tubes that are coiled at the base. The coils serve as brood chambers for one to seven eggs, which are deposited at different times, and therefore are at different developmental stages. The eggs are yolky, a creamy yellow in color, and about 0.0078 in (200 pm) in diameter. Each larva hatches and grows to a size of 0.016-0.018 in (400-450 pm). At that point, it swims past the other eggs and exits the tube. The larva continues swimming in search of its own place to settle on the bottom.

CONSERVATION STATUS

Not listed by IUCN.

SIGNIFICANCE TO HUMANS None known. ♦

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