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Shellfish Assessment Program - Pathobiology: Past Research

Asterophila japonica, an internal molluscan parasite of sea stars

Photo of Leptasterias polaris parasitized by Asterophila japonica (a shell-less parasitic 
A Leptasterias polaris sea star parasitized by multiple Asterphila japonica internal parasitic gastropods

Asterophila japonica is a shell-less parasitic gastropod of sea stars and a member of the family Eulimidae, the only known gastropod group to parasitize echinoderms. A. japonica is highly modified and lives entirely within the body wall of the sea star host.

Organs unrelated to digestion and reproduction are reduced or absent in this species and a specialized epithelium encloses the entire parasite including developing veliger larvae.

A. japonica is found along the Asiatic coast and Pacific Ocean, but the complete range of this parasite is unknown.

This specimen within the sea star Leptasterias polaris was collected in 2010 near St. Matthew Island, but has been seen in Alaskan waters since 1976.

The placement of gastropods in the family Eulimidae has been based on morphological traits and the character of echinoderm parasitism.

Very few eulimids have been sequenced; a phylogenetic analysis of this family may elucidate divergent evolutionary classifications. Preliminary sequencing of a 658 bp region of the mitochondrial COI gene from 2 larvae revealed 0.46% divergence between individuals and 2 variable sites were apparent between clones of one larva. For this region, A. japonica shares 73% - 76% identity with other sequenced eulimids.

Photo of female Asterophila japonica containing developing veliger larvae. Click image to 
			enlarge.           Photo of Asterophila japonica veliger
			larvae (approximately 0.5 mm across). Click image to enlarge.
A female Asterophila japonica (approx. 2 cm across) containing developing veliger larvae. Click image to enlarge.           Asterophila japonica veliger larvae (approx. 0.5 mm across). Click image to enlarge.

Juvenile Walleye Pollock

Walleye pollock, Gadus chalcogrammus (formerly Theragra chalcogramma), support a major North Pacific fishery and undergo population fluctuations. The causes of these episodes are poorly understood and likely associated with multiple contributory factors.

From 1978 to 2004, the Shellfish Assessment Program pathobologists investigated the diseases of juvenile walleye pollock as a means of attempting to understand how disease affects recruitment. Several parasites and diseases were identified, but, at the time, only a microsporidan infection appeared important.

The undescribed microsporidan, Pleistophora sp., infects the skeletal muscle of both juveniles and adults with likely different effects. In juvenile walleye pollock, mortalities are possible but it is more likely that affected fish will have increased difficulty in capturing prey or evading predators. In adults, Pleistophora sp. is likely to affect fecundity.

Photo of histological slide preparation of Pleistophora infected walleye pollock tissue. Area of 
			infection indicated by asterisk.
Histological slide preparation of Pleistophora sp.-infected walleye pollock tissue (area of infection indicated by asterisk)

Shellfish Assessment Program - Pathobiology Research CURRENT RESEARCH

Related Publications

  • BECKMEN, K. B., K. A. BURAK, T. GELLATT, F. MORADO, S. NADLER, and E. T. LYONS. 2005. Hookworms in Steller sea lions (Eumetopias jubatus) in Alaska. Presented at the 16th biennial meeting of the Society for Marine Mammalogy. San Diego, CA, Dec 2005.

  • MORADO, J. F., and A. K. SPARKS. 1990. Preliminary report on the diseases and parasites of juvenile walleye pollock, Theragra chalcogramma, from the Gulf of Alaska, p. 201-213. In F. O. Perkins and T. C. Cheng (editors), Pathology in marine science, Academic Press, Inc., San Diego.

See the publications and poster databases for additional listings.

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