. A manual of zoology. Zoology. III. ANNELIDA: CH^ETOPODA. 313 Nearly all PolychiBtes are diceoious and undergo a more or less pro- nounced metamorphosis; T\-ith few exceptions (Manyunkia* trom. tlie Schuylkill, jye?-ew-* in California) they are marine. They are usually divided according to their habits into fixed (Sedentaria) and free forms (Errantia), but this olassitication lacks a morphological basis. The Seden- taria feed on vegetable matter, usually form tubes of leathery organic substances, iu which foreign matter may be incorporated or which may be calcified. The worms project their an
. A manual of zoology. Zoology. III. ANNELIDA: CH^ETOPODA. 313 Nearly all PolychiBtes are diceoious and undergo a more or less pro- nounced metamorphosis; T\-ith few exceptions (Manyunkia* trom. tlie Schuylkill, jye?-ew-* in California) they are marine. They are usually divided according to their habits into fixed (Sedentaria) and free forms (Errantia), but this olassitication lacks a morphological basis. The Seden- taria feed on vegetable matter, usually form tubes of leathery organic substances, iu which foreign matter may be incorporated or which may be calcified. The worms project their anterior segments from the tubes. The Errantia often secrete gelatinous tubes in which they can hide, but they never lose their powers of locomotion, and from time to time leave their retreats and swim about preying on other animals. Correlated with habits are differences in structure. In the Errantia the head and trunk are not very different; the anterior part of the alimentary tract can be protruded as a proboscis, and, corresponding to their predaceous habits, is often armed with strong jaws (fig. 281, A). In the Sedentaria there are no such pharyngeal teeth, but, on the other hand, there is a greater difference between anterior and posterior somites. In the latter the parapodia are weakly developed, and this part resembles the Oligoohcetes in ap- pearance. The head and beginning of the trunk (thorax) are richly provided with gills and tentacles for respiration and the taking of food (fig. 382). Sub Order I. ERRANTIA. Predaceous annelids with strongly armed pharynx. The ' , mostly represented on our shores by ^-^iij -â=--=â small species, contains some species a yard in i^ ^.C^ length. Diopatra* NotUria* The Alciopid^ "'~" ^ i, are transparent pelagic forms with large, highlv â -^â '~&~y^ , , , rrt o 11 X " Tig. of Pohinoe developed eyes. The Syllid.* usually have siiinifeni (After Ehlers.) three long tentacles ; Autob/tus,'^ Myrianida
Size: 1749px × 1429px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
