Marine Science 2016 Edition

Marine Invertebrates (1) Page 277 Figure 277.1 Mouth and tentacles (Murray Waite)  Feeding The mouth is surrounded by a ring of tentacles (Figure 277.1) on which special stinging cells called nematocysts are found. Nematocysts are for feeding and defence and are the characteristic which gives the phylum its name. Figure 277.2 a and b shows how these specialised cells fire. The venom from the nematocysts of the sea wasp box jellyfish are extremely painful and fatal in many cases. (Photo courtesy Peter Harrison JCU 1988 Reproduced with permission.) Figure 277.3 Coral reproduction (Illustration Bob Moffatt) Reproduction Reproduction is complex among Cnidarians with both asexual and sexual forms. In corals, the most common asexual means is by budding where another coral polyp grows as bud from the parent polyp resulting in a new animal that is genetical identical to the parent. For genetic diversity, sexual reproduction is needed and in corals this is a spectacular event in November each year. Inside the polyp the male and female sex organs develop which produce sperm and egg (Figure 277.3). Fertilization in some corals is internal producing an egg bundle which is released through the mouth. These fertilized eggs disperse and grown into a planula which settles to the ocean floor to grow into a juvenile and finally back into an adult. Figure 277.2a Nematocyst discharged (Bob Moffatt) Figure 277.2b Nematocyst undischarged (Bob Moffatt)