52 



TELETHUS^E. 



Sjphserodonim abyssorum Hansen, 1 a species from the Norwegian Northern Expedition, 

 has jointed bristles like the present species. The head is slightly hollowed in the middle, 

 with a rounded process at each side, but the foot differs from the southern form just 

 described. 2 



Family XVIIT.— Telethusje, Savigny, 1820 (Arenicotjd^). 



Arenicolea, Audouin and Milne Edwards ; Paromocrisea, De Blainville ; Dorsalees, 

 Lamarck ; Arenicoliens, De Quatrefages. 



Limivorous forms in which the head is moderately developed, devoid of appendages, 

 and bounded posteriorly by the nuchal grooves. No palps or tentacles. Eyes indistinct. 

 A pair of statocysts (otocysts) as a rule in the first segment (except in A. Glaparedii). 



The body is elongate, rounded, of three regions, with numerous pairs of branched 

 gills which are absent from the first six segments. It ends in a somewhat blunt anal 

 extremity. Four annuli occur between each setigerous ring, except in the first three or 



C.TTU 



He. 

 Fig. 106. — Transverse section of Arenicola marina, L. 



Branchia. cm. Circular muscular fibres. 



four segments. Pharynx globular, unarmed, though the papillas may have a cap of 

 chitin. The feet are sessile and little developed, the dorsal division bearing capillary 

 bristles, and the ventral, which forms a thickened pad, having a vertical row of long hooks. 



Nerve-cord non-ganglionated. 



Three diaphragms occur in the ccelom at the anterior end of the first, third, and 

 fourth segments. A pair of hearts place the gastric vessel in connection with the ventral. 



Segmental organs five, six, or thirteen pairs, the first pair opening on the fourth or 

 fifth segment. 



One or more pairs of glandular coeca at the posterior part of the oesophagus. No 

 ccelomic septa in region of stomach, but strong septa are present at the anterior part of 

 the first, third, and fourth bristled segments, and in the intestinal region. 



Externally the body-wall in the anterior (pre-branchial) region has a thin cuticle 



covering the glandular hypoderm beneath. The circular muscular coat which follows is 



of considerable strength, and anteriorly often presents thicker parts in transverse sections. 



Within is the powerful layer of longitudinal muscle forming various wedge-shaped masses 



i 'Nyt Mag. f. Naturvid./ Bd. xxiv, p. 9, Taf. vi, figs. 9—12, 1879. 



2 Mr. Southern has recorded the occurrence of Sphserodorum Glaparedii, Green , and S. minutum, 

 Webster and Benedict, from Blacksod Bay, July, 1914. 



