On a collection of hydroids (Cnidaria, Hydrozoa, Hydroidolina) from the west coast of Sweden, with a checklist of species from the region 3171 Author Calder, Dale R. text Zootaxa 2012 2012-01-24 3171 1 1 77 https://biotaxa.org/Zootaxa/article/view/zootaxa.3171.1.1 journal article 10.11646/zootaxa.3171.1.1 1175­5334 5247704 Halitholus cirratus Hartlaub, 1913 Fig. 13 Halitholus cirratus Hartlaub, 1913: 274 , figs. 225–233 (medusa), 234 (hydroid). Type locality. Northeast Atlantic ; type material from several locations ( Svalbard , Barents Sea , Baltic Sea , North Sea ) ( Schuchert 2007: 342 ) . FIGURE 13. Halitholus cirratus : part of colony with three hydranths, ROMIZ B3918. Scale equals 0.5 mm. Museum material. Kosterhavet, 58°52.424’N , 11°06.178’E , 160– 30 m , 09.ix.2010 , biological dredge, R / V Nereus , three colonies, on Yoldiella philippiana , up to 0.5 mm high, without gonophores, ROMIZ B3918. Remarks. These specimens corresponded with descriptions of Halitholus cirratus Hartlaub, 1913 by Hartlaub (1913) , Kramp (1935b) , and Schuchert (2007) in their tiny size, distinctly tapering pedicels, opaque and grit-covered perisarc, limited numbers of tentacles (usually about six), and substrate (a species growing on shells of the bivalve genus Yoldiella ). Kramp (1935b) also noted that medusae of the species are exceedingly common in the Baltic and Belt seas and the Kattegat, suggesting that hydroids must also be common in these waters. The identification is nevertheless considered provisional because of insufficient knowledge of its medusa stage. Perigonimus yoldiaearcticae Birula, 1897 is similar and sometimes considered conspecific with H. cirratus (e.g. Naumov 1960 ; Schönborn et al . 1993 ). Schuchert (2001a) provisionally assigned that species to the genus Halitholus Hartlaub, 1913 , but kept H. yoldiaearcticae as distinct because of a lack of information about its life cycle. More recently, Schuchert (2007 , 2011 ) has continued to question whether the two are conspecific. If they prove identical, the name H. yoldiaearcticae has priority. Birula (1897) established the specific name as yoldiae - arcticae , now corrected under the code (Art. 32.5.2.3) to yoldiaearcticae . In terms of distribution, both H. cirratus and H. yoldiaearcticae are generally reported from high latitudes, including northern seas of the Russian Federation , Spitzbergen, and Greenland ( Schuchert 2001 a , 2007; Voronkov et al . 2010 ). Medusae of Halitholus cirratus extend southwards to the North and Baltic seas ( Schuchert 2007 ) as well as the Kattegat ( Kramp 1935b ). Hydroids identified as Halitholus cirratus have been reported from the Baltic Sea ( Kramp 1935b ) but not from western Sweden or the Oslofjord ( Rees & Rowe 1969 ; Jägerskiöld 1971 ; Christiansen 1972 ). Reported distribution. West coast of Sweden .—Hydroid not previously recorded. Elsewhere.—In the North Atlantic, the medusa stage has been reported from northern seas of the Russian Federation to the Baltic and North seas in the east, and from western Greenland and the Canadian Arctic to Newfoundland ( Kramp 1961 ; Shih et al . 1971 ) in the west.