Arciiicola marina 97 



observation of Dr. Groot, who, working at Holder, dug out in the 

 sand a rectangle, two metres by one metre, to a depth of three 

 decimetres, and found in this quantity of sand ninety-three specimens 

 of A. marina. 



Specimens of A. marina may be separated into two kinds or 

 rovins — the littoral and the Lanunarian — according to their habitat 

 and the nature of their gills. Specimens taken in the littoral zone 

 (pp. G4, 05) are generally found in U-shaped burrows,^ have bushy 

 gills (p. 58), and average 180 to 230 mm. in length;'- but 

 occasionally lai'ger specimens, up to ;5G0 mm. in length, are obtained. 



Specimens from the upper part of the Laminarian zone, which can 

 l)e readily obtained only at very low tides, are found in vertical or 

 L-shaped ])urrows (p. Go), and generally possess pinnate gills (p. 58). 

 Laminarian examples are more massive tiiau those from the littoral 

 zone, and attain a length of 400 mm., and a girth, at the \\idest part, 

 of about 70 mm. Besides the difference in tlie character of the gills, 

 noted above, the Laminarian differs usually from the littoral form in 

 the subdivision of tlie interval between the second and tliird 

 chaetiferous annuli: in littoral exami)les this region is almost 

 invariably divided into three rings, wliile in Laminarian specimens 

 only two rings are indicated. The Laminarian form has Ijeen found 

 on the Lancashire coast, in the Firth of Forth, in Salcoml)e Estuary 

 (S. ])evon), in Jersey, on the north-west coast of France, the North 

 Sea coast of Germany,'' and is re] (resented by two specimens in the 

 Ib'itish Museum, from Deal. 



])eyoud the statement l)y .M. Jlohii, that A. marina leaves its 

 burrow at night to swim in the sea, nothing is known of the habits 

 of this worm when covered liy the sea. Prof. Elders (1892) has 

 recorded the swimming of adult A. marina^ and the capture, before 



' Burrows of siinilar fonu, occasionally with a heap of sand ov mud near 

 one of the apertures, are abundant in Cambrian, and not unconnnon in Silurian 

 and Devonian rocks. It is believed they were made by I'olycliaeta, and some 

 authors attributed them to Arcnicola (A. curhonarius IJinney, Mem. Lit. Pliil. 

 Soc. Mancliester, 2 ser., x (1852), p. 192; A. didi/ina Salter, Q. J. Geol. Soc, 

 Loud., xii (18.56), p. 248) ; but, as tlie evidence for tliis was insufficient, the 

 generic name associated with these burrows was changed to Arniicolilcs. 



■ Specimens from near low-water mark ai-e usually larger than those found 

 near liigli-water mark ; those from sand rich in organic matter are larger than 

 those found in purer sand. 



^ This locality is included because the gills of the specimens collected there 

 by Oken ai"e described as being like a mimosa leaf; they must therefore have 

 been markedly pinnate, as is evident also from Oken's figures. 



* Mr. H. C. Chadwick (19th Ann. Eep. Li\erpool Mar. Biol. Comm. (1905), 

 p. 1.^) observed a specimen make its way slowly upwards, in a large aquarium 

 tank, by strong and frequent flexions of the body. 



H 



