Sources differ for vertebrate and invertebrate animals. Both terrestrial and aquatic invertebrate and vertebrates enter into estivation. "Daphnia" are prey for a variety of both vertebrate and invertebrate predators. Several species of entomopathogenic nematode are important predators of insect and other invertebrate pests. Molluscs have more varied forms than other invertebrate phyla. Some parrot species prey on animals, especially invertebrate larvae. Cyhalothrin is inherently highly toxic to many fish and aquatic invertebrate species. Hydrostatic skeletons are common among simple invertebrate organisms. Most involve studying specializations of particular animal groups, such as phycology, invertebrate zoology and ichthyology. By far the largest number of described invertebrate species are insects. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The Alleghenies provide habitat for about 54 species of common invertebrate. This has been found for both invertebrate and fish species. In general, "arabica" is the more sensitive species to invertebrate predation overall. Lamarck continued his work as a premier authority on invertebrate zoology.