Amphiascus: Can a Copepod be a Friend of Mine?

Amphiascus sp., copyright Alexandra.

The animal shown in the image above is a member of Amphiascus, a cosmopolitan genus of about thirty known species of benthic harpacticoid copepods. Amphiascus is a genus of the family Miraciidae; in older texts, you will find it referred to the Diosaccidae, but this family is now regarded as a synonym of the former. Miraciids are somewhat elongate harpacticoids generally with a fusiform body shape and females with paired egg sacs; as with other copepod taxa, their specific characterisation depends on fairly fine characters of the appendage setation (Willen 2002). Wells et al. (1982) placed Amphiascus in association with a group of related genera in the miraciid family tree on the basis of its retention of a fairly extensive setation on the pereiopods, two inner setae on the endopod of pereiopod II in females, and two articulated claws on that segment in males. However, the proposed phylogeny of Wells et al. provides no apomorphies for Amphiascus itself, implying that it is characterised only by plesiomorphies relative to related genera.

The title of this post refers to the circumstances surrounding the discovery of a relatively recently described Amphiascus species, A. kawamurai Ueda & Nagai 2005. In the cultivation in Japan of nori, the edible alga used (among other things) in wrapping sushi rolls, the conchocelis phase of the life cycle is grown on oyster shells in outdoor tanks of seawater (like many algae, nori goes through an alternation of generations, with its life cycle including two very distinct forms; as well as the familiar large flat alga, the life cycle of nori includes a small filamentous shell-boring stage, initially mistaken for a distinct organism and called Conchocelis). Unfortunately, the oyster shells may also become overgrown with diatoms, retarding the growth of conchocelis. As a result, nori growers may be required to laboriously scrub the shells of diatoms several times over the conchocelis growth period. However, it was noticed in Ariake Bay in Kyushu that some form of copepod would sometimes appear in the nori tanks, presumably brought in with seawater from the bay. When this copepod was present, it would graze on the diatoms, reducing the need for other controls. Study of the nori-tank copepod revealed it to be a previously undescribed species, revealing once more that even the species we are not aware of have the potential to directly improve our lives.

REFERENCES

Ueda, H., & H. Nagai. 2005. Amphiascus kawamurai, a new harpacticoid copepod (Crustacea: Harpacticoida: Miraciidae) from nori cultivation tanks in Japan, with a redescription of the closely related A. parvus. Species Diversity 10: 249–258.

Wells, J. B. J., G. R. F. Hicks & B. C. Coull. 1982. Common harpacticoid copepods from New Zealand harbours and estuaries. New Zealand Journal of Zoology 9 (2): 151–184.

Willen, E. 2002. Notes on the systematic position of the Stenheliinae (Copepoda, Harpacticoida) within the Thalestridimorpha and description of two new species from Motupore Island, Papua New Guinea. Cah. Biol. Mar. 43: 27–42.