TBJCHOBRANCHTTS GLACIALIS. 205 



Sub-Family IV. — Trichqbranchidea, Malmgren, 1866. 



The cephalic lobe as in the Amphitriti. The branchiae are filiform. Rostrate hooks 

 (that is, with long shafts) occur in the anterior, avicular in the posterior region. The 

 stomachs of the three genera, viz. of Trichobranchus, TerebelUdes and Actobranchus, are 

 complex, dorsal folds being developed. No ventral shields are present. 



Hessle (1917) makes a separate family for the genera Trichobranchus and TerebelUdes 

 instead of the sub-family of Malmgren, and they certainly show considerable divergence. 

 He makes them intermediate forms between the Ampharetidse and Terebellidae, and he 

 gives the characters as follows : Tentacle-membrane (cephalic lobe ?) reduced ; tentacles 

 not invaginated ; branchiae simple or pectinate ; ventral shields absent; posterior region 

 not shortened; paleae absent; hooks with elongated shafts anteriorly, short shafts 

 posteriorly, and in a single row. As shown elsewhere the presence of shafts to the hooks 

 is seen in other forms, such as Rhodina, but, in any case, the advantages of this change of 

 classification are not obvious. 



Genus CLIX. — Trichobranchus, Malmgren, 1866. 



Cephalic lobe reduced and bifid, having on each side anteriorly a prominent rounded 

 boss and a flattened fan-like plate. No distinct cephalic collar, though the lobe is 

 ensheathed by the first segment. Pigment-spots (eyes) occur behind the tentacles. The 

 lobe gives origin to a dense series of grooved tentacles, filiform and fusiform, the two 

 being intermingled in front, but posteriorly the filiform are predominant. Both the 

 longer and the shorter are grooved. Nuchal organs two ciliated flat surfaces (Hessle). 

 Body terebelliform, enlarged anteriorly and tapered posteriorly. Buccal segment large 

 and turgid posteriorly (lateral lobe). The body terminates in an anus with two papillae. 

 Branchiae filiform, on segments 2, 3 and 4. The lateral lobe of the stomach provided 

 with deep folds. Setigerous processes on each side bearing simple bristles with wings, 

 and commencing on the sixth segment. Unicinigerous processes (on the tori), from 

 the sixth to the last setigerons lobe, and bear long hooks ; the posterior, on the pinnules, 

 bear minute avicular hooks with short bases and spinous crowns. All are uniserial. 

 Nephridia occur in the fifth segment and are large at the diaphragm, smaller behind, 

 the latter probably transmitting the reproductive elements (Hessle). Tube membranous, 

 coated with much 



1. Trichobranchus glacialis, Malmgren, 1866. Plate CXV, figs. 5 and 5 d — dorsal and 

 lateral view of body ; Plate CXX, figs. 2 and 2 a — body and anterior end ; 

 Plate CXXVH, figs. 4 — 4c — bristles and hook; figs. 4<cl and 4 e — anterior end. 



Specific Characters. — Cephalic lobe with the characters of the genus, and numerous 

 ocular points occur at its posterior part. Buccal segment roll-like and transversely 

 grooved. Sides of the second and third segments with small lappets. Three pairs of 



