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Deep-Water Crustacea of the Genus Sergestes (Decapoda, Natantia) from Cook Strait, New Zealand
[Introduction]
Very few specimens of the aberrant penaeid genus Sergestes have been recorded in the literature from New Zealand waters. This typical bathypelagic group is frequently encountered whenever mid-water collections are made elsewhere in the world, but hitherto little work of this type has been done in this area. The Challenger Expedition, though working the deep-waters off our coast in 1874, was using slow-moving bottom trawls, and these are largely ineffective in collecting fast-swimming pelagic crustacea. This expedition, however, took a larval stage on the surface of Cook Strait, near Wellington, but unfortunately the specimen has been lost and its name (S. parvidens) is now not recognized. Of the other overseas oceanographical expeditions that worked in the New Zealand area, the Terra Nova in 1910 took only larval stages, the Discovery II (1932) and the Galathea (1951-52) have not had their sergestid material described, while that of the Dana (1928-30) has only had preliminary descriptions of some of the more interesting species published. Two of these, Sergestes disjunctus Burkenroad and Sergestes index Burkenroad, were from page 2
north-east of the Bay of Plenty, New Zealand, and consequently were the first adult Sergestes to be recorded from our waters. However, neither of these has been taken in Cook Strait as yet.
In 1941 Professor L. R. Richardson, of this Department, obtained a sample of 47 large shrimp from the stomachs of groper and ling caught by the Pawley brothers in the course of their commercial long-line fishing in Palliser Bay, Cook Strait. It had long been known that the stomachs of these fish, at least in certain seasons, often contained interesting crustacea, fish and squid never collected by any other method, but specimens had seldom come into the hands of zoologists. Professor Richardson identified the shrimp with a large sergested taken off South Africa and recorded by Barnard (1950) as Sergestes phorcus Faxon, a species which must now be known as Sergestes potens Burkenroad. Although constantly having this sergestid in mind from the start of the Department's study of the fauna of Cook Strait, it had not been taken by any of the mid-water hauls made between 50 and about 600 fathoms up until February this year. In that month a beam trawl struck bottom at about 550 fathoms a little south of Palliser Bay and took from the mud bottom a specimen of S. potens associated with a typical benthic shrimp of the genus Sclerocrangon. The segestid was uniform scarlet in colour and possessed a large number of purple lens-less photophores scattered over its body and appendages.
From the beginning of our work in Cook Strait an abundant small, transparent, pink Sergestes has been taken, especially at night, in the 50–150 fathom zone associated with larger numbers of Pasiphaea of the same colouring. This sergestid is the common North Atlantic species S. arcticus, already recorded from the New Zealand area as a larval stage by Gurney and Lebour (1940) and also recorded below from the Bay of Plenty, the Chatham Rise, and off the coast of Otago.
In February of this year a small specimen of the scarlet membranous S. japonicus was taken in a mid-water haul at about 500 fathoms, and several larger specimens of this same scarlet species were caught at about 600 fathoms in April. These are the first records for the Southern Hemisphere of S. japonicus, a species well known from deep water in the North Atlantic, and recorded from the northern Indopacific only twice. Also in April a single specimen of another transparent, pink species, very similar, if not identical to S. seminudus of Indonesian waters, was taken at a similar depth.
In order to identify these species it became necessary to review the systematics of the genus Sergestes. It was found that Burkenroad (1937a, 1945) had suggested a subdivision of the genus, on differences in types of luminous organs and pigmentation, into the two subgenera Sergestes s.s. and Sergia; and that he had used these without formally defining them. The reality of this subdivision was quite clear in the field as the differences in appearance and habit of the two groups could be immediately recognised. Consequently I have reviewed the records of colour and luminous organs in this genus and then formally defined the two subgenera. Following this I have given a synopsis of all the 57 species of Sergestes known to me from the literature, though synonyms have, except in a few important cases, been omitted. These species have been arranged in a number of groups as originally used by Hansen in his many publications.
Finally, all Sergestidae recorded in the literature from New Zealand waters are discussed, and a checklist of all species recognized from the area given.