Arenicola marina 97 



observation of Dr. Groot, who, working at Helder, 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 

 forms the littoral and the Laminarian according to their habitat 

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

 (pp. 64, 65) are generally found in U-shaped burrows, 1 have bushy 

 gills (p. 58), and average 180 to 230 mm. in length; 2 but 

 occasionally larger specimens, up to 360 mm. in length, are obtained. 



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

 be readily obtained only at very low tides, are found in vertical or 

 L-shaped burrows (p. 65), and generally possess pinnate gills (p. 58). 

 Laminarian examples are more massive than those from the littoral 

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

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

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

 the subdivision of the interval between the second and third 

 chaetiferous annuli: in littoral examples this region is almost 

 invariably divided into three rings, while in Laminarian specimens 

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

 on the Lancashire coast, in the Firth of Forth, in Salcombe Estuary 

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

 Sea coast of Germany, 3 and is represented by two specimens in the 

 British Museum, from Deal. 



Beyond the statement by M. Bohn, that A. marina leaves its 

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

 of this worm when covered by the sea. Prof. Ehlers (1892) has 

 recorded the swimming of adult A. marina 4 and the capture, before 



1 Burrows of similar form, occasionally with a heap of sand or niud near 

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

 and Devonian rocks. It is believed they were made by Polychaeta, -and some 

 authors attributed them to Arenicola (A. carbonarius Binney, Mem. Lit. Phil. 

 Soc. Manchester, 2 ser., x (1852), p. 192; A. didyma Salter, Q. J. Geol. Soc., 

 Lond., xii (1856), p. 248) ; but, as the evidence for this was insufficient, the 

 generic name associated with these burrows was changed to Arenicolites. 



2 Specimens from near low- water mark are usually larger than those found 

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

 those found in purer sand. 



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

 by Oken are described as being like a mimosa leaf ; they must therefore have 

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



4 Mr. H. C. Chadwick (19th Ann. Rep. Liverpool Mar. Biol. Comm. (1905), 

 p. 13) observed a specimen make its way slowly upwards, in a large aquarium 

 tank, by strong and frequent flexions of the body. 



H 



