No common name

Paravortex scrobiculariae

ORDER Rhabdocoela

FAMILY Graffillidae

TAXONOMY

Paravortex scrobiculariae (Graff, 1903), Great Britain.

OTHER COMMON NAMES None known.

PHYSICAL CHARACTERISTICS

Elongate worm approximately 0.08 in (2 mm) long, lacks adhesive organs; mouth anterior with subterminal opening that passes through small ciliated buccal cavity into muscular pharynx and then into simple saccate gut; testis sacciform, ovary single.

DISTRIBUTION

Its host, the intertidal bivalve Scrobicularia plana, occurs in northeast Atlantic, Mediterranean, and West Africa. It is unknown if it occurs throughout its host's range.

HABITAT

Lives inside gut and digestive gland of host. BEHAVIOR

Adult worms migrate within host based on the tidal cycle that relates to feeding cycle of host. Worms use cilia to swim forward from intestine through stomach to digestive gland during the ebb tide and return to intestine during the flood tide.

FEEDING ECOLOGY AND DIET

Feeds on semi-digested components of host food and residual cells released by digestive glands, which it ingests through muscular pharynx, as it makes its migrations from intestine to digestive gland. It appears that it is not capable of producing all the enzymes necessary to digest food and relies on ability to

H Kronborgia amphipodicola H Paravortex scrobiculariae

acquire enzymes along with food during its migrations to digestive gland. This strategy reduces the need to expend energy on producing these enzymes.

REPRODUCTIVE BIOLOGY

Hermaphroditic and viviparous (releases juvenile worms); up to 40 capsules, each containing two embryos and numerous vitelline cells, which enter parenchyma from female atrium, fully developed embryos leave the capsules and move freely in parenchyma until they escape parent through mouth.

CONSERVATION STATUS Not threatened.

SIGNIFICANCE TO HUMANS

One species of Paravortex commonly called tang turbellaria or black ich are pathogenic on skin of several species of marine ornamental fishes commonly kept in aquaria. ♦

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