﻿410 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



DENDROSTOMUM HEXADACTYLUM Sato 



Plate 30, Figure 2 



Dendrostoma hexadactylum Sato, 1930, p. 28, figs. 13-15; pi. 4, figs. 20-24; 1937, 

 p. 162, pi. 4, fig. 17; 1939, p. 412. 



Diagnosis. — In general appearance closety resembling Dendrosto- 

 mum pyroides; differing in having six tentacles and larger and more 

 numerous introvert hooks, among which are very numerous and 

 very small upright cylindrical papillae. 



Description. — The only available large specimen, at maxinmm 

 contraction, is 60 mm. long. It was found by E. F. Ricketts on the 

 beach at Monterej'-, Calif., diu-ing a heavy storm (January 7, 8, 1939) 

 and was taken from a fragment of gray shale rock along with boring 

 clams. The hooks are fully twice as numerous as in a Dendrostomum 

 pyroides of equal size and are obviously larger. The largest are 

 situated anteriorly, next to the smooth collar, and measure 0.5 

 to 0.68 nmi. in length by 0.3 to 0.4 mm. in diameter at base. The 

 numerous cylindrical papillae, without constricted base, are about 

 0.1 mm. high and are scattered thickly among the spines. Posterior 

 to the zone of spines they flatten into ellipsoids with convex center, 

 are close together, and often occupy a quadrilateral area defined by 

 five creases in the cuticle. At posterior end of the body certain of 

 them become low papilliform; possibly all are so in life. The major 

 axis of the flattisli papillae in Sato's types varied from 0.06 to 0.107 

 mm.; the minor, from 0.05 to 0.105 mm. In my specimen, which 

 is larger than an}'- of Sato's, the papillae are a little larger. 



The tentacles spring from 6 roots, which bi-anch either twice or 

 three times near the base so that the count of tentacular arms is 

 likely to exceed 12. The branching is similar to that of D. zoster- 

 icolum. The internal anatomy resembles that of D. pyroides, with 

 the following important exceptions: Fixing m_uscle 1 is not so far 

 forward (between F' and F^ of 'pyroides); F^ is nearer the intestinal 

 spiral and usually has 2 terminal branches, one attached to post- 

 esophagus, the otlier to ascending spii-al of intestine well back of 

 the coecum; F^ is attached to intestine posterior to F^ branch. 

 The contractile blood vessel lacks the elaborate network of the vessels 

 surrounding the esophagus, although thei'e are a few small collateral 

 loops; but the long Polian tubules are more numerous and, instead 

 of branching off toward the distal end of the main vessel as in pyroides, 

 arise all along each side from a point in front of the lateral mesenteries 

 of the esophagus. Some of them branch near the base. The origin 

 of the retractors is slraighter than in pyroides and the gonad is on 

 the muscles rather than on the body wall. 



In front of the anterior end of the nephridia are four short, trans- 

 verse, parallel muscles, resembling low dissepiments, mentioned by 

 Sato. They occur also in Dendrostomum pyroides. The posterior 

 merges with the wing muscles. 



