Amphiascus

Amphiascus tenuiremis, from Tom Chandler & Adriana Bejarano.

Belongs within: Podogennonta.

Amphiascus: can a copepod be a friend of mine?
Published 15 September 2015
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.

Systematics of Amphiascus
<==Amphiascus Sars 1905N41
    |--*A. longirostris (Claus 1863) (see below for synonymy)N41
    |--A. abyssi (Boeck 1872)N41
    |--A. accraensis (Scott 1894) [=Stenhelia accraensis]N41
    |--A. angrapequensis Pesta 1916N41
    |--A. angustipes Gurney 1927W67
    |--A. brevicornis (Thompson & Scott 1903) [=Stenhelia brevicornis]N41
    |--A. brevifurcus (Czerniavski 1868)N41
    |--A. brevis Sars 1909N41
    |--A. brucei (Scott & Scott 1901)N41
    |--A. brunneus Willey 1931N41
    |--A. catharinae Scott 1906N41
    |--A. caudaespinosus Brian 1927N41
    |--A. congener Sars 1909N41
    |--A. crassus (Giesbricht 1902)N41
    |--A. dactylifer Wilson 1932N41
    |--A. demersus Nicholls 1939N41
    |--A. dentipes (Thompson & Scott 1903) [=Stenhelia dentipes]N41
    |--A. dispar (Scott & Scott 1894)N41b [=Stenhelia dispar]N41
    |--A. elegans Brady 1918N41
    |--A. faroensis (Scott 1903) [=Dactylopus stromi var. faroensis]N41
    |--A. giesbrechti Sars 1906N41
    |--A. glacialis Brady 1910N41
    |--A. gracilicaudatus (Thompson & Scott 1903) [=Stenhelia gracilicaudata]N41
    |--A. herdmani (Scott 1896) [=Stenhelia herdmani]N41
    |--A. ignotus Brady 1918N41
    |--A. lamellifer Sars 1911N41
    |--A. limicolus (Brady 1900) [=Stenhelia limicola]N41
    |--A. littoralis (Scott 1903)N41
    |--A. longicornis (Thompson & Scott 1903) [=Stenhelia longicornis]N41
    |--A. pacificus Sars 1905W67
    |--A. pallidus Sars 1906N41
    |--A. perplexus (Thompson & Scott 1903) [=Stenhelia perplexa]N41
    |--A. pestai Monard 1935N41
    |--A. polaris Sars 1909N41
    |--A. pyroeides Monard 1928N41
    |--A. reflexus (Scott 1895) [=Stenhelia reflexa]N41
    |--A. rufescens Brian 1925N41
    |--A. similoides Monard 1928N41
    |--A. sinuatus Sars 1906W67
    |--A. tenuiremis (Brady & Robertson 1875)N41
    |--A. ultimus Monard 1928N41
    |--A. valens Gurney 1927N41
    `--A. varicolor Farran 1913N41

*Amphiascus longirostris (Claus 1863) [=Dactylopus longirostris, Stenhelia longirostris; incl. Amphiascus mixtus (Scott 1903)]N41

*Type species of generic name indicated

References

[N41] Nicholls, A. G. 1941. A revision of the families Diosaccidae Sars, 1906 and Laophontidae T. Scott, 1905 (Copepoda, Harpacticoida). Records of the South Australian Museum 7 (1): 65–110.

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.

[W67] Wells, J. B. J. 1967. The littoral Copepoda (Crustacea) of Inhaca Island, Mozambique. Transactions of the Royal Society of Edinburgh 67: 189–358.

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.

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