KOPOID AND SWEZY: UNARMOREU DINOFLAGELLATA 291 



Gyrodinium contortum (Scliiitt) 



Text figure CC, 22 



Gymnodinium contortum Sehiitt (1895), p. 11, \A. 21, fig. CTi^^. 

 Gymnodinimn opimum Scliiitt (1895), pi. 21,.68&. 

 Spirodinium opimum, Lemmeriiiann (1899), p. 360. 



Diagnosis. — A large species with ovoidal body, its lengtli 2.68 transdiameters 

 at the Avidest part ; girdle a descending left spiral, displaced 1.4 transdiameters ; 

 sulcus extending from near the apex to the antapex ; surface striate ; color, yellow 

 ochre. Length, 134m. Atlantic or Bay of Naples. 



Description. — The body is long ovoidal, tapering anteriorly and rounded posteriorly where 

 it is widest in its posterior third, its length 2.68 transdiameters at the widest part. The epicone 

 exceeds the hypocone in length by 0.1 of its own length, but, owing to its narrower width, is not 

 greater in size. It is conical in shape (40°) with blunt apex. It has a length on the left and 

 right sides of 0.24 and 0.77 of the total length of the body. The hypocone is broader than the 

 epicone with a rounded antapex which is notched on the ventral face by the distal end of the 

 sulcus. 



The girdle joins the sulcus at a distance from the apex of 0.24 of the total length of the body. 

 It turns posteriorly at an angle of 35° from the horizontal plane in its spiral course around the 

 body, decreasing the steepness of its course in the last quarter of its length, meeting the girdle 

 distally at an angle of about 20° from the horizontal. It is displaced 1.4 transdiameters at the 

 widest part of the body. The furrow is wide, 0.08 transdiameter in width, and deeply impressed. 

 The sulcus begins below the apex and passes posteriorly with a strong left deflection, giving it a 

 torsion of about 0.5 transdiameter. It is enlarged near the antapex to about twice its width 

 anteriorly. 



The nucleus is ellipsoidal and midventrally placed. Its chromatin contents are arranged in 

 coarse strands following its long axis. Its major and minor axes are 0.74 and 0.42 transdiameters 

 in length respectively. Numerous vacuoles of varying sizes are scattered through the cytoplasm. 

 In the peripheral zone is a layer of rodlets, radially arranged. The surface is striate with 

 equidistant, longitudinal striae. 



Dimensions. — Length, 111/^ to 134/^; transdiameter, 45/^ to 50/^; axes of 

 nucleus, 37/* and 21m. 



Occurrence. — Figured by Schiitt (1895) from the collections of the 

 Plankton Expedition from the Atlantic or from tlie Bay of Naples. A single 

 individual was taken July 19, 1906, 1.5 miles oft' I^a Jolla, in a surface haul with 

 a No. 20 net. This individual was dark yellow ochre in color. 



Synonymy. — Schiitt (1895) figured as two distinct species two forms, 

 Gymnodinium contort nm and G. opimum, which we have here ])laced as synony- 

 mous. Their size differs slightly, contortum having a length of 134m and a 

 width of 50m and ojiinium 111m and 45m, a difference witliiu ordinary species 

 variation. Both are ovoidal in outline, widest posterioi'ly (Schiitt's fig. 68&, 

 pi. 21 (1895) of G. oj)iiiiiim is evidently oriented wrong end uppermost), with 

 the same or nearly the same relative pr(.])ortions and surface sti-iae as in his 

 G. contortum. 



