Affinities 159 



A. marina. The close resemblance of the chaetae of A. assimilis 

 and A. marina is also noteworthy. A assimilis is probably an old 

 species, perhaps as old, or nearly so, as A. marina. A. pusilla has 

 undergone considerable specialisation, for instance, in its crotchets, in 

 the high degree of development of its prostomium, and in the absence 

 of statocysts. In other respects A. pusilla presents characters similar 

 to A. assimilis and is clearly derived from the same stem. 



Brancliiomaldane, which is most nearly related to the ecaudate 

 species of Arenicola (see pp. 155, 156), appears to have branched 

 off near the base of the primitive stem of the family, and, while 

 retaining some primitive characters, has undergone certain retro- 

 gressive changes associated with its tubicolous mode of life. 



The relationships discussed above are indicated in the diagram 

 given on p. 158. 



THE AFFINITIES OF THE ARENICOLIDAE. 



The first satisfactory suggestion respecting the relationship of 

 Arenicola l was that of Blainville (1828), who, noticing that the 

 Telethuses and the Maldanies agree in possessing both subulate 

 chaetae and crotchets, placed these two families in one order, 

 although one contains branchiate and the other non-branchiate 

 worms (see p. 15). It is difficult to understand on what grounds 

 Milne Edwards (1838) united Arenicola and Chaetopterus in the 

 tribe Arenicolides, nor is it evident why he and, later, Oersted 

 (1843), suggested the affinity of Arenicola with the Ariciae. The 

 schema given by Grube in his classical paper (1850) shows that 

 he regarded the Telethusa 2 as related on the one hand to the 

 Maldania and on the other to Scalibregma and Eumenia, a view 

 which subsequent work has confirmed. Dr. Levinsen (1883) 

 ranged the Telethusae with the Scalibregmidae, but united these 

 with the Amphinomidae to form a sub-order Amphinomiformia. 

 The Amphinomidae differ from Arenicola in so many important 

 features that there is no basis in support of the association 

 suggested. - 



Prof. Benham placed the Arenicolidae in the sub-order Scoleci- 

 formia along with the families Opheliidae, Maldanidae, Scalibregmidae, 

 Chlorhaemidae and Sternaspidae, and Prof. Hatschek included the 



1 Arenicola marina was the only species then known. 



2 In which family Grube at first included Arenicola and Dasybranchus, but 

 later (1862) he removed the latter genus to a new family Capitellacea. 



