2 Thoracic neurosetae as long-shafted hooks starting on seg- 



ment 6. Tentacuhir lobe frilly 3 



2' Thoracic neurosetae as avicular uncini starting on segment 



5. Tentacular lobe collar-shaped 4 



3 A single median gill with four partly fused lamellated lobes 



(Tcirhcllidcs). Eighteen bundles of notosetae T. .•<()•(>(_' mi i 



3' Two or three pairs of simple cirriform gills (Trich()h)-ain-lnis). 



Fifteen bundles of notosetae. [Three pairs of gillsj T. glacialis 



4 Gills as numerous simple filaments {Tlichpiis). [Gill filaments 



on three segments. Base on uncini produced forwards with 



a terminal attachment button and a small notch below it] T. setosiis 



4' Gills branched 5 



5 Notosetae with denticulate tips. Lateral lobes either present 



or absent on segments 2-4. Over 20 segments with notosetae 6 



5' Notosetae with smooth tips. Lateral lobes present on seg- 

 ments 2-4. About 17-18 segments with notosetae 9 



6 Gills with .short basal stumps and long terminal branches; 



notosetae with short denticulate tips (Anipliit)-it( ). Small 

 lateral lobes on segments 1, 2, and 3. [Over 35 .segments 



with notosetae] A. m-iiatd 



6' Gills with well-developed trunks and short terminal branches. 

 Notosetae with long denticulate tips in posterior segments. 

 No lateral lobes on segments 2-4 ( Ti irhclht) 7 



7 Two pairs of gills. Only jjosterior third of body without noto- 



setae T. i)t(riicliai ta 



T Three pairs of gills. Notosetae continue to near end of 



abdomen 8 



8 Posterior notosetae with a spur pi-eceding the denticulate 



blade T. Uipuhn-'ni 



8' Posterior notosetae without a sjnir preceding the denticulate 



blade T. nihni 



9 Two pairs of gills (one often missing). Uncini avicular. those 



of first row often with long basal shafts (Pista) 10 



9' Three pairs of gills. Uncini pectinate, with a single vertical 



series of teeth and lack basal shafts (Loiniia) 12 



10 Gill filaments s])irally branched, forming a compact tuft oi' 



"l)om-pon" at end of trunk. [LIncini of first row with long, 



narrow shafts] Pislu ci-istnta 



10' Gill filaments dendritically branched 11 



11 Second pair of lateral lobes divided to form two tai:)ered pro- 



jections. Uncini of first row without long necks Pistn pahnatd 



11' Second pair of lateral lobes not divided. Uncini of first row 



with long necks and tapered shafts Pista tiiiadfildJmta 



117 



