New copepods - taxonomic gold nugets

Sophie Conroy-Dalton

Natural History Museum, Cromwell Road, London, SW7 5BD, UK

Members of the copepod order Harpacticoida are primarily free-living, marine and benthic, although a few species are ectoparasitic, commensal or planktonic. Their body form, shape and size can vary considerably according to the micro-environment they inhabit. The Ancorabolidae is one of the most visually striking families in the Harpacticoida. Most ancorabolids are instantly recognisable by their conspicuous outgrowths that arise from the dorsal and lateral surfaces of the body, ranging from simple thorns to highly elaborate branched processes. Ancorabolids have frequently been recorded from European waters and they have traditionally been thought of as a rare and not very diverse group, assuming a limited distribution in the North Atlantic. Investigations over the last two decades have not only more than quadrupled the number of described species, but have also considerably extended the geographical distribution of the family, which now stretches from the Arctic to the Antarctic, and from the intertidal to the deep-sea, including hydrothermal vents. The apparent scarcity of ancorabolids was obviously merely a reflection of sampling bias and logistic problems involved in sampling deep-sea benthos. However, investigating remote and unusual environments is not necessarily a prerequisite for the discovery of sensational new taxa. Even in European waters extensive surveys and renewed attention to previously undersampled habitats can still unveil exciting taxonomic gold nuggets.

A recent intertidal survey along the west coast of Scotland led to the discovery of a new ancorabolid genus from a sandy beach on the stunningly beautiful, tiny Isle of Iona (just off the island of Mull). Lobopleura ambiducti Conroy-Dalton, 2004, is small, less than 0.5 mm in length and is strongly flattened. The generic name refers to the highly ornate body, which possesses a series of lobate processes on each side. The species is unique within the Ancorabolidae because of its presence of fully functional paired genital systems in both sexes (and the species name refers to this), a condition rarely observed in other harpacticoids. From the morphology of the mouthparts, it seems that this species is probably a surface feeder/grazer, scraping and collecting food particles off the sand grains. As is common to most ancorabolids, the body of L. ambiducti was completely covered by a layer of gunk (= detritus and other material), through which only the tips of sensory structures like sensillae and elongate tube-pores protrude. Unusually L. ambiducti was collected from the low water mark on a sandy beach, but most ancorabolids typically live in the flocculent, upper layer of muddy sediments. Clearly, without the development of body processes it would be impossible to maintain sensory function under this cloak of material and so it seems that the function of these processes is to enhance or at least maintain the animal's sensory performance in detritus-laden environments. Like most ancorabolids, Lobopleura ambiducti occurs in low densities: only 3 specimens were collected from Iona; additionally 11 individuals have been recorded from Co. Clare (West coast of Ireland) and 1 female from Co. Dublin (East coast of Ireland).