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Almost all are free-living, although many species of agnathans (lampreys and hagfish) and several species of teleost (e.g., toothpick fish and pearlfish) are parasites to other vertebrates and invertebrates. Some males from the Lophiiformes order are sexual parasites to their female counterparts. About 1% of all bird species are brood parasites. Chordata consists of members that are usually on top of the food chain, reigning over members from other phyla across a multitude of ecosystems worldwide. Species richness peaks on the continents and in the marine environment of tropical and subtropical regions. Although distributed unevenly, chordates are found in most, if not all ecosystems on Earth.