Aegisthidae

Habitus of male Cervinia itoi, from Park et al. (2012). Scale = 100 µm.

Belongs within: Oligoarthra.
Contains: Cerviniopsinae.

Some copepods for your reading pleasure
Published 3 December 2007
Aegisthus, from here.


The copepods are a widespread group of aquatic crustaceans, another one of those groups of minute animals that are all around us, yet attract little attention because of their tiny size. Thousands of copepod species have been described from every imaginable habitat involving a certain degree of water—thousands more doubtless remain to be described.

In the tiny world of copepods, members of the family Aegisthidae are relative giants, attaining massive sizes of more than 1.5mm in length (in contrast, the type specimen of their sister taxon, Romete bulbiseta, measures a mere 360 microns). Aegisthidae are one of the more basal members of the Harpacticoida, one of the largest orders of copepods. Basal members of the order are fusiform, but many of the more derived infaunal species have a more vermiform shape. Some three thousand harpacticoid species have been named to date, and they are second only to nematodes in abundance in the meiofauna (Seifried 2003).

The relatively large size of the Aegisthidae is probably connected to their different lifestyle from other harpacticoids. Rather than being epibenthic (living on the surface of the substrate) or infaunal (burrowing within the substrate), many Aegisthidae are hyperbenthic—that is, they live in the water column just above the surface of the substrate (there is a bit of confusion about correct terminology—other authors refer to “demersal zooplankton” or “benthopelagic plankton”. Funnily enough, the choice of terminology is generally connected to which marine setting, whether tropical, temperate or deep sea, the author is mostly working with—Mees & Jones 1997). There is also a tendency to lengthen the body shape, particularly the caudal rami, two spine-like extensions from the posterior end of the abdomen (the image of Aegisthus at top left of this section shows just how incredibly long the rami can get). A few species of Aegisthidae have gone the whole pelagic hog and become genuine members of the upper zooplankton, some of the relatively few harpacticoids (members of only three families) to have done so.

I had intended to centre this post on just one of the aegisthid subfamilies, the Cerviniopsinae. It is worth noting that Aegisthidae once referred to a much smaller collection of species, the current subfamily Aegisthinae (including the holoplanktic species). However, Seifried & Schminke (2003) argued that the ‘Aegisthidae’ of previous authors represented a derived subgroup of the previous family Cerviniidae, rendering the latter paraphyletic and calling for its sinking. The ‘cerviniid’ subfamily Cerviniopsinae was recognised as probably also paraphyletic with regard to Aegisthinae, and in particular a connection was suggested to the ‘cerviniopsine’ genus Pontostratiotes. Nevertheless, Seifried & Schminke did not formally remove the Cerviniopsinae from their classification, retaining it as a provisional grouping pending a proper phylogenetic analysis of the Aegisthidae. Most of the Cerviniopsinae do not appear to have been dealt with since Lang’s major monograph of the harpacticoids back in 1948. Members of the Aegithinae share at least one distinguishing feature of the Cerviniopsinae, having the caudal furci opposed to each other rather than divergent as in the Cerviniinae (Montagna 1979). Members of the Aegisthinae show a tendency to reduction of the mandibles in the males, with the adult males of some species such as Andromastax muricatus and Aegisthus mucronatus being entirely non-feeding.

Systematics of Aegisthidae
Aegisthidae [Cerviniidae]
|--+--CerviniopsinaeSS03
| `--AegisthinaeSS03
| |--Nudivorax Lee & Huys 2000SS03
| |--Scabrantenna Lee & Huys 2000SS03
| |--Aegisthus Giesbrecht 1891SS03
| | `--*A. mucronatus Giesbrecht 1891SS03
| |--Andromastax Conroy-Dalton & Huys 1999SS03
| | `--A. muricatus Conroy-Dalton & Huys 1999SS03
| `--Jamstecia Lee & Huys 2000SS03
| `--J. terazakii Lee & Huys 2000SS03
`--CerviniinaeSS03
|--Cerviniella Smirnov 1946SS03
| `--C. langi Bodin 1968SS03
|--Paracerviniella Brodskaya 1963SS03
| `--P. denticulata Brodskaya 1963SS03
|--Expansicervinia Montagna 1981 [incl. Brotskayaia Huys, Møbjerg & Kristensen 1997]S03
| |--*E. glaceria Montagna 1981S03
| `--E. tenuiseta (Brodskaya 1963) [=*Brotskayaia tenuiseta, Cervinia tenuiseta]S03
|--Eucanuella Scott 1900SS03
| |--E. langi Por 1964SS03
| |--E. longirostrata Ito 1983SS03
| `--E. spinifera Scott 1901SS03
`--Cervinia Norman 1878 [incl. Neocervinia Huys, Møbjerg & Kristensen 1997, Pseudocervinia Brodskaya 1963]S03
| i. s.: C. brevipes Brodskaya 1963SS03
|--C. tenuicauda Brodskaya 1963S03
`--+--C. itoi (Lee & Yoo 1998) [=Neocervinia itoi]S03
|--C. unisetosa Montagna 1981S03
`--+--*C. bradyi Norman 1878S03
|--C. langi Montagna 1979S03
|--C. magna Smirnov 1946 [=*Pseudocervinia magna]S03
|--C. mediocauda Burgess 1995S03
|--C. philippinensis Huys et al. 1997S03
|--C. pilosa Lang 1948S03
|--C. plumosa Ito 1983S03
`--C. synarthra Sars 1910S03

*Type species of generic name indicated

References

Mees, J., & M. B. Jones. 1997. The hyperbenthos. Oceanogr. Mar. Biol. Ann. Rev. 35: 221‒255.

Montagna, P. A. 1979. Cervinia langi n. sp. and Pseudocervinia magna (Copepoda, Harpacticoida) from the Beaufort Sea (Alaska, USA). Transactions of the American Microscopical Society 98 (1): 77‒88.

[S03] Seifried, S. 2003. Phylogeny of Harpacticoida (Copepoda): Revision of “Maxillipedasphalea” and Exanechentera. Cuvillier Verlag: Göttingen.

[SS03] Seifried, S., & H. K. Schminke. 2003. Phylogenetic relationships at the base of Oligoarthra (Copepoda, Harpacticoida) with a new species as the cornerstone. Organisms Diversity & Evolution 3: 13–37.

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