. The Cambridge natural history. Zoology. ASCIDIAE SLMPLICES CLAVELINIDAE 71 Sub-Order 1. Ascidiae Simplices. Fixed Ascidians, which are solitary, and very rarely reproduce by gemmation ; it", as in a few cases, small colorues are formed, the members are not buried in a connuon investing- mass, but each has a, tlistinct test of its own. No strict line of demarcation can be drawn between the Simple and Com])ound Ascidians; and one of the families of the former group, the Clavelinidae (the " Social " Ascidians of ]\Iilne-Edwards), forms a transition from the typical Simple forms w
. The Cambridge natural history. Zoology. ASCIDIAE SLMPLICES CLAVELINIDAE 71 Sub-Order 1. Ascidiae Simplices. Fixed Ascidians, which are solitary, and very rarely reproduce by gemmation ; it", as in a few cases, small colorues are formed, the members are not buried in a connuon investing- mass, but each has a, tlistinct test of its own. No strict line of demarcation can be drawn between the Simple and Com])ound Ascidians; and one of the families of the former group, the Clavelinidae (the " Social " Ascidians of ]\Iilne-Edwards), forms a transition from the typical Simple forms which never re])roduce by gemmation, to the Com- pound forms which always do. Over 500 species of Ascidiae Simplices are now known, but there are probably very many more still undescribed. The sub-order may be divided into the follow- ing families:— Fam. 1. Clavelinidae.—Simple Ascidians which reproduce by gemmation to form small colonies (Fig. 33), in which each member, or ascidiozooid, has a distinct test, but all are connected by a common blood-system, and Ijy a prolongation of the " epicardiac tubes" (see p. 83) from the branchial sac. Buds are formed on the stolons (Fig. 33), which are vascular outgrowths from the posterior end of the body, containing prolongations from the ectoderm, mesoderm, and endoderm (the epicardium) of the Ascidiozooid. Branchial sac not folded: internal longitudinal bars usually aljsent; stigmata straight; tentacles simple. The Clavelinidae are the simplest of the Ascidiae Simplices. They are the forms that come nearest to the Compound Ascidians, and are closely related to the Distomatidae. They are probably the nearest representatives now existing of the ancestral forms from which both Simple and Compound Ascidians are descended. This family contains amongst others the following three genera :—Uctemascidia, Herdman, with internal longitudinal bars in the branchial sac; Clavclina, Savigny, with a long body and intestine extending beh
Size: 1701px × 1468px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
