. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 10 ANNALS OF THE SOUTH AFRICAN MUSEUM (i) spiral zooids: modified hydranths without mouth or tentacles but with a gastral cavity. They are characteristic of some of the Hydractiniidae and typically perform writhing movements and tend to twist into a spiral. (ii) tentaculozooids : similar to tentacles in structure, with a solid core of endo- derm cells and no mouth or gastral cavity. More delicate and slender than spiral zooids. (iii) nematophores : highly extensile structures representing reduced hyd
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 10 ANNALS OF THE SOUTH AFRICAN MUSEUM (i) spiral zooids: modified hydranths without mouth or tentacles but with a gastral cavity. They are characteristic of some of the Hydractiniidae and typically perform writhing movements and tend to twist into a spiral. (ii) tentaculozooids : similar to tentacles in structure, with a solid core of endo- derm cells and no mouth or gastral cavity. More delicate and slender than spiral zooids. (iii) nematophores : highly extensile structures representing reduced hydranths and without mouth or tentacles. Characteristic of the Plumulariidae, where they may also be called sarcostyles, but also occurring in a number of other families. The polyps of the Hydroida are occasionally solitary, as in the families Corymorphidae and Myriothelidae, where the individuals are large and provided with various internal elaborations of structure, but they are more often colonial and consist of numerous individuals derived by asexual multiplication but remaining in cellular continuity with one another. Colonies may be stolonial, where growth is horizontal and the hydranths arise direct from a common hydrorhiza, or erect, where growth is vertical, pro- ducing an upright hydrocaulus bearing the hydranths. Such a hydrocaulus may be unbranched, and bear a terminal hydranth with or without a number of lateral ones, or it may be branched. The form of erect colonies depends primarily on the type of growth. Kiihn (1914) defined three types of growth' and these types have been accepted by modern systematists and are depicted in most textbooks. 1. MONOPODIAL GROWTH WITH TERMINAL HYDRANTH (raceme). The firsi hydranth on the hydrocaulus is terminal. Below this is a growth-zone, and below this a budding zone. Buds are formed in the budding zone and the growth zone budding zone hydranth 1 MONOPODIAL, 6 TERMINAL GROWING POINT. Please note that these images are extracted fro
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
