BSC 196 Lecture Notes - Lecture 11: Parapodium, Hydrostatic Skeleton, Penis Fencing
Document Summary
Most modern animal phyla appeared in the cambrian period, 542 mya (cambrian explosion). The phyla i(cid:374)for(cid:373)ally (cid:272)alled (cid:862)(cid:449)or(cid:373)s(cid:863) are (cid:374)ot all (cid:272)losely related to ea(cid:272)h other. They are all members of the clade bilateria: have mouths, digestive cavities, true organs and tissues, and bilateral symmetry. Evolved at least 555 mya: most animals are triploblastic tissues arise from all 3 embryonic germ layers (ectoderm, mesoderm, endoderm). Cnidarians have only 2 layers (they are diploblastic). The body plans of most animals are categorized based on the presence or absence of a coelom. Flatworms are acoelomate (lack a coelom): roundworms are pseudocoelomate (have only a partial cavity), most animals are coelomate (have a true coelom). Symbiosis: an ecological relationship in which two species live together and interact directly. Mutualism: both the symbiont and its host species benefit (+/+). Commensalism: the symbiont benefits while the host is not affected (+/0). Parasitism: the symbiont benefits from harming the host (+/-).
