GALATHEALINUM ARCTICUM 417 



longest tube has a maximum diameter of 1-95 mm at the anterior end, the 

 other tube is a little narrower, and both tubes taper slightly towards the 

 posterior end. The first 10 to 20 cm of each tube is made up of small funnel- 

 shaped segments 1-5 to 2 mm long, overlapping slightly (Fig. G162A). The 

 thick wall is many layered, with an outer dark-brown layer of felted fibres. 

 Individual fibres are only 1— 2/x in diameter, but they are mostly aggregated 

 into bands 50 to 500/x wide. The inner layers contain fewer fibres and are 

 not uniformly coloured. Brown rings 0-5 to 1 mm long are separated by 

 narrower colourless interspaces. The posterior part of the tube is unseg- 

 mented and all the layers of its wall are ringed, though the outer layer is 

 whitish and its rings are not very distinct." 



G. arcticum has most of the characteristics given by Ivanov in the diagnosis 

 of the genus, "except that its metameric papillae bear single adhesive plaques, 

 rather than groups of two or more (see Table A5). 



"G. arcticum is distinguished from both of the other species in having 

 single adhesive plaques on the metameric papillae and in having the keels 

 of the bridle touching on the dorsal side. It differs from G. brachiosum in 

 having a smaller number of tentacles, a differently shaped cephalic lobe (this 

 may be only an effect of fixation), smaller adhesive plaques, especially on the 

 metameric papillae and finer fibres in the tube wall. It has more in common 

 with G. bruuni, but differs from it in the absence of a mid-dorsal groove in 

 front of the bridle. All three species have been described from specimens 

 which lack posterior ends. They are apparently all very long, and it is 

 obviously difficult to collect the whole of an animal perhaps a metre long 

 if it is deeply buried in the bottom deposit. To judge from the epifauna 

 attached to the present tubes, all but the top 5 cm was buried in the 

 deposit. 



"Most pogonophores have been found in depths of more than 500 m, but 

 Siboglinum caulleryi is known from 22 m in the Sakhalin Gulf, Oligobrachia 

 dogieli occurs in 119 m in the Sea of Okhotsk and a few other species are 

 known from between 100 and 500 m, always in cold waters. Thus this new 

 record from 36 m adds to the evidence now accumulating to show that 

 members of the Pogonophora are restricted to waters of low temperature 

 than to those of great depths alone. 



"Material: two incomplete specimens, one male, one female, in their 

 tubes. 



"Locality: Thetis Bay, Herschell Island, Yukon (Canada): 69° 32' N, 

 138° 57' W. 



"Depth: 36 m."] 



