Arenicola : Historical 31 



The earthworm was left in the old genus Lumbricus, and the 

 lugworm removed to a new genus Arenicola, 1 because, as Lamarck 

 observed in 1818, the presence of external gills rendered impossible 

 its retention in the genus Lunibricus. Lamarck then (1818) gave a 

 fuller diagnosis of the genus Arenicola, based on the single species 

 (A. piscatorum = marina) known to him, in the following terms : 

 " Corpus rnolle, longum, annulatum, cylindricum, postice nudum ; 

 setarum fasciculi biseriales in parte media anticaque. Branchiarum 

 externarum arbusculae ant penicilli ad basim fasciculorum dorsalium. 

 Os terminale nudurn. Oculi nulli." 



Audouin and Edwards (1833) described, from specimens which 

 were doubtless ecaudate, a species, A. branchialis, which differs 

 from the lugworm in the number and arrangement of its gills, and in 

 1835 Johnston described the species A. ecaudata. The discovery of 

 this species, in which the feet and gills extend to the posterior end 

 of the worm, necessitated an emendation of Lamarck's diagnosis of 

 the genus, the statement " postice nudum " being no longer 

 applicable to the genus as a whole. But a considerable number of 

 writers, including Johnston (1865), continued to define the genus 

 Arenicola by stating the characters of the lugworm only, neglecting 

 completely the existence of the ecaudate species. 



Suggestions for a subdivision of the genus have been put forward 

 by Liitken and Prof. Mesnil. Liitken 2 proposed that A. antillensis 

 ( = cristata) should be placed in a sub-genus Pteroscolex, because of 

 the feathered or pinnate nature of the gills. He made this proposal 

 evidently with some diffidence, for he remarked that, in regard to its 

 other external features, this worm was a typical " Sandorm." 

 Claparede (1868) promptly rejected this sub-genus on the ground that 

 a similar form of gill to that occurring in " Pteroscolex " had been 

 found by Williams in examples of the common lugworm. 3 



Prof. Mesriil 4 proposed to retain in the genus Arenicola those 

 species with a small number of segments seventeen to nineteen 

 and a long achaetous tail, namely, A. marina, claparedii ( = pusilla) 

 and cristata, but to erect a new genus Arenicolidcs for the two species 

 hrancliialis and ecaudata having a large number of chaetiferous 

 segments and no tail. The writer, while not prepared to go so far as 

 Prof. Mesnil suggests, admits that there is something to be said in 



1 Arena, sand ; colere, to inhabit. 



2 Vid. Medd. Naturh. Foren. Kjobenhavn, 1864 (1865), p. 121. 



3 The gills of some specimens of A. marina are almost as highly pinnate 

 as those of A. cristata. 



4 Bull. Sci. France Belg., xxxii (1899), p. 326. 



