An Introduction to the Invertebrates, Second Edition - tiera.ru

214 ANIMALS WITH LOPHOPHORESFig.16.1 Examples of three phylawith lophophores: (a) longitudinalsection of Phoronis,showingthelophophore; (b) diagram ofa generalised bryozoanzooid; (c) diagram of bryozoanwith two greatly modified zooidssuperimposed; (d) a brachiopodwith the lophophore coiledinternally.fastens it to the shallow sea bottom. The lophophore is eithersimple, with rather few tentacles, or elaborate and spirally coiled.There is a closed blood system with haemoglobin in corpuscles,the nervous system is subepidermal and largely diffuse. The excretoryorgans are protonephridial in the larva, metanephridial in theadult. The animals are mostly hermaphrodites, releasing gametesthrough the excretory pores, and the fertilised eggs develop intofree-swimming ‘actinotroch’ larvae.16.2.2 BryozoaThe Bryozoa (Figure 16.1b) are very common intertidal animals.There are 20 000 species, of which 5000 are living today. They are the