no. 4 hartman : polychaetous annelids 427 



Key to Species 



1. Without filamentous branchiae 2 



1. With palmately arranged, filamentous branchiae after the 

 thirtieth abdominal segment . . . . H. filobranchus 



2, Inhabiting freshwater H. similis Southern 



2. In marine habitats H. filiformis 



Heteromastus filiformis (Claparede) 

 Plate 52, Figs. 1-4 



Notomastus filiformis Verrill, 1873, p. 611. 

 Areniella filiformis Verrill, 1874, pp. 386-387. 

 Ancistria capillaris Verrill, 1874, pp. 385-386. 

 Ancistria minima Webster, 1879, p. 258. 

 Notomastus laevis Webster, 1886, p. 152. 



Eisig, 1887, pp. 839-846, pi. 1, fig. 4, pi. 27, figs. 15-21, pi. 28 figs. 1-17, 

 pi. 32, figs. 15-18; Fauvel, 1927, pp. 150-152, fig. 53; Hartman, 

 1942, p. 70. 



Collections. — Numerous individuals come from central California, 

 Florida, North Carolina and Massachusetts; all are from intertidal 

 zones. 



In its grosser details this species is well known through numerous 

 accounts. The details of the hooded hooks in the thorax and abdomen 

 are shown in plate 52, figs. 1-4. Thoracic hooks measure about 0.3 mm 

 long and 0.005 mm wide; the width/length ratio is thus approximately 

 1/60. Similar proportions of abdominal hooks are about 1/15. The 

 thoracic hooks are thus proportionately far longer than are the abdominal 

 hooks, but in the details of their structure they are similar. Both have 

 the characteristic parts consisting of shaft with node, shoulder, neck, 

 beak with crest and fang and overhanging hood. In the thoracic hooks 

 the node, shoulder, neck and hood are diffused over a far greater length 

 than in abdominal hooks; it is only by microscopic measurement that 

 neck, shoulder and node can be detected. By careful measurement of 

 thickness along the shaft from tip to base one encounters a slender por- 

 tion below the beak (=neck) followed by a thicker region (^shoulder) 

 continuing into a region which is again slender and then a thicker region 

 (=node) embedded in the tissue of the parapodium; the basal end term- 

 inates in a gradually tapering, slender end. 



