. The Cambridge natural history. Zoology. CHAP. XIH ANTHOZOA = ACTINOZOA 327 body, attached at one end (the aboral end) to the common colonial matrix or to some foreign object. At the opposite or free ex- tremity it is provided with a mouth surrounded by a crown of tentacles. In these respects, however, they resemble in a general way some of the Hydrozoa. It is only when the internal anatomy is examined that we find the characters which are absolutely diagnostic of the group. In the Hydrozoa the mouth leads directly into the coelenteric cavity; in the Anthozoa, however, the mouth leads into a
. The Cambridge natural history. Zoology. CHAP. XIH ANTHOZOA = ACTINOZOA 327 body, attached at one end (the aboral end) to the common colonial matrix or to some foreign object. At the opposite or free ex- tremity it is provided with a mouth surrounded by a crown of tentacles. In these respects, however, they resemble in a general way some of the Hydrozoa. It is only when the internal anatomy is examined that we find the characters which are absolutely diagnostic of the group. In the Hydrozoa the mouth leads directly into the coelenteric cavity; in the Anthozoa, however, the mouth leads into a short tube or throat, called the " stomodaeum," which opens into the coelenteric cavity. Moreover, this tube is connected with the body-wall, and is supported by a series of fleshy vertical bands called the mesenteries (Fig. 146). The mesenteries not only support the stomo- daeum, but extend some dis- tance below it. Where the mesenteries are free from the stomodaeum their edges are thickened to form the im- portant digestive organs known as the mesenteric filaments (m/). It is in the possession of a stomodaeum, Fig. 146.—Diagram of a vertical section '^ , . through an Anthozoan zooid. B, Body- mesenteries, and mesenteric ^^^11; G, gonads; M, mesentery; mf, filaments that the Anthozoa mesenteric filament; St, stomodaeum; T" tPTliiELClG differ from all the other Coelen- terata. There is one character that the Anthozoa share with the Scyphozoa, and that is, that the gonads or sexual cells (G-) are derived from the endoderm. They are discharged first into the coelenteric cavity, and then by way of the mouth to the exterior. In the Anthozoa the gonads are situated on the mesenteries. ]srearly all the Anthozoa are sedentary in habit. They begin life as ciliated free-swimming larvae, and then, in a few hours or days, they become attached to some rock or shell at the bottom and immediately (if colonial) start the process of budding, which gives rise to the colonies of
Size: 1570px × 1591px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
