. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE PBOSOFTOIA. 373 later elongating laterally to form the coiled lophophore with its numerous tentacles. The early stages of the development of the Ecardines is not known, but in Lingula the larva is free-swimming long after the shell has formed, the peduncle being late in develop- ing. In this form also the lophophore arises as a circle of tentacles surrounding the mouth and subsequently elongates laterally. The affinities of the BracLiopods have long been an open qu
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE PBOSOFTOIA. 373 later elongating laterally to form the coiled lophophore with its numerous tentacles. The early stages of the development of the Ecardines is not known, but in Lingula the larva is free-swimming long after the shell has formed, the peduncle being late in develop- ing. In this form also the lophophore arises as a circle of tentacles surrounding the mouth and subsequently elongates laterally. The affinities of the BracLiopods have long been an open question- They were by early writers regarded as Mollusca, later as Annelida or closely related to thai group, but are now usually considered to be more nearly related to the Polyzoa than to any other forms and to be most properly associated with them, the general likeness of a young Lingula, for instance, to a Polyzoan being very striking. The presence of the mantle- lobes and the shell seem to mark the Brachiopoda as something far removed from the other members of tiie type Prosopygia, but it must be remembered that in the larval Ectoproctous Polyzoa the corona behaves in a manner closely similar to the Brachiopod mantle and it is not impossible that the two structures may have something in common. Another distinguishing feature of tha Brachiopods is the indication of a segmentation. The presence of two dissepiments and in Rhynchonella of two pairs of nephridia certainly suggests metamerism, hut objection has been raised to the dissepiments having any metameric significance, on the ground that they do not bear the proi)er r«lationsiiips to the body axis to be regarded as comparable to the dissepiments of the Annelida. It ha* been stated by some authors as a characteristic of the that tlieir body axis is bent upon itself so that the two ends are approximated and one surface, the dorsal, is almost obliterated, while the other, the ventral, is very much enlarged, as
Size: 1052px × 2376px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
