PART III. 



THE SYNAPTID^. 



Order PARACTINOPODA Ludwig. 



External appendages of water-vascular system arise from circular canal 

 and appear only as circumoral tentacles. While five of these are radial in posi- 

 tion, no true radial canals are present in adults. 



Family SYNAPTID^ Burmeister. 



More or less cylindrical elongated holothurians with terminal mouth, with- 

 out respiratory trees and with water- vascular system greatly reduced; cir- 

 cumoral tentacles, either simple, pinnate, or digitate, are present but lack am- 

 pullce; there are no pedicels or papillaj; circular muscles of body-wall contin- 

 uous, i. e., not broken or interrupted at radii; characteristic sense-organs 

 (positional organs) i^resent, situated beside radial nerves, near nerve ring; 

 minute ciliated funnels, apparently having an excretory function, usually pres- 

 ent in body-cavity on or near mesenteries; calcareous deposits, in form of 

 anchors and plates, wheels or sigmoid bodies usually present, but no tables or 

 phosi3hatic deposits (see i3. 142) occur. 



MOBPHOLOGY. 



Form and size. — The body is generally elongated and more or less cylin- 

 drical, but the exact shape and proportions differ in different species, and, 

 owing to its remarkable contractility, its form differs greatly in the same indi- 

 vidual under varying conditions. The largest species in the family is Synapta 

 inaculata, which reaches a length of more than 200 cm., though the diameter is 

 not commonly more than 3 cm. The smallest species is Leptosynapta minuta, 

 which is only 3 to 5 mm. long. Between these two extremes we find great di- 

 versity, but species more than 30 or less than 3 cm. when fully grown, are in- 

 frequent. 



Color. — In color there is some variety, but really bright colors are rare; 

 white, flesh-color, dull yellowish, and gray are the more usual shades, but dull 

 shades of red are common. Protankyra rodea is said to be "carmine-red" and 

 Scoliodota japonica "blood-red." Green is occasionally found in an olive, or 

 some other dull shade, but the bright shades are rare. Some species are very 

 dark-colored, and have been described as "crimson-black," "dark violet- black," 

 and "brown." The color is seldom uniform, but spots and little ])apilhe — 



42 



