264 PART II. SYSTEMATIC ACCOUNT 



mid-ventral furrow, is rather constricted at its base (Fig. 13 1 A), and bears 

 two dense, closely adjacent rows of pinnules. The delicate, brownish keels of 

 the bridle, which lies at the front end of the mesosoma, are fused neither 

 ventrally nor dorsally, and in front of the bridle lie a pair of triangular, 

 ventral, clearly marked patches of glandular epidermis (Fig. 131^4). Behind 

 the keels, and almost parallel to them, are further glandular epidermal tracts, 

 corresponding in their antero-lateral parts to the glandular girdles of some 

 other species. Their ventral ends, however, turn backwards and extend far 

 back to the hind edge of the mesosoma as a pair of ventral glandular ribbons 

 (Fig. 131C). The fore-part of the body bears narrow mid-ventral and mid- 

 dorsal furrows, and in the hind part of the mesosoma two rows of large 

 internal sacculate glands may be seen by transparency. The dividing groove 

 between the mesosoma and the metasoma has a forward-projecting lappet 

 on either side of the mid-dorsal line. 



The long metameric part of the trunk bears numerous paired papillae, 

 numbering (in my female specimen) 153 on the right and 166 on the left side 

 of the body. The rather large, densely packed papillae run along the sides of 

 the narrow ventral sulcus (Fig. 13 1С) and each contains a single pyriform 

 gland. The narrow dorsal ciliated band begins a short way behind the front 

 edge of the metasoma (Fig. 131$). In the zone of thickened papillae lie 

 30-40 large higgledy-piggledy ventral papillae (Fig. 13 ID), many of them 

 bearing on their tips weak cuticular thickenings, whose dimensions vary 

 greatly, while there are on a few papillae oval or hoop-shaped adhesive 

 plaques reaching 30-40/x across. 



In two more or less complete individuals studied by Southward and 

 Southward, one had two and the other three girdles of toothed platelets, 

 whilst in a third specimen I found two girdles and a very weak additional 



Fig. 131. Siboglinum atlanticum: A - front end of the body of a female from the right side; В - the 

 hind part of the mesosoma and the beginning of the metasoma from the dorsal, and, С - from the 

 ventral side; D - the region of thickened papillae from the ventral side; E - the region of 

 the girdles from the ventral side; F- part of a girdle; G - toothed platelet; H- dorsal glandular 

 shield and ventral papilla of the postannular region in dorso-lateral view; I -the same from one side. 

 ag - anterior ventral glandular area of epidermis ; an - girdles ; с - cephalic lobe ; со - dorsal ciliated 

 band; da - anterior group of teeth; dp - hind group of teeth;/- keel of the bridle; g - glandular 

 part of the integument ; gt - pyriform glands seen by transparency ; ms - mesosoma ;mts- metasoma ; 

 p - cuticular plaque; pa - metameric papillae; pa 1 - papillae of the zone of thickening; 

 pa 2 - papillae in front of the girdles ; pa 3 - supplementary postannular papilla ; ps - protosoma ; 

 s 1 - groove between the protosoma and the mesosoma; s 2 - groove between the mesosoma and the 

 metasoma ; sc - dorsal glandular shield ; sv - ventral sulcus ; t - tentacle ; tg - ventral glandular 

 ribbon of the mesosoma ; tl - lateral glandular ribbon of the metasoma ; v - ventral postannular 

 papilla. 



