Invertebrate paleontology deals with fossils such as molluscs, arthropods, annelid worms and echinoderms. Most trace fossils are burrows of molluscs or arthropods. Arboviruses are diseases that are transmitted to vertebrates by insects, specifically arthropods. The gregarines are generally parasites of annelids, arthropods, and mollusks. Horseshoe crabs resemble crustaceans but belong to a separate subphylum of the arthropods, Chelicerata. Chitin-producing organisms like protozoa, fungi, arthropods, and nematodes are often pathogens in other species. Vibrissae are analogous to antennae found on insects and other arthropods. They feed on insects and other arthropods. Image-resolving eyes are present in molluscs, chordates and arthropods. Arthropods and most mollusks have an open circulatory system. Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. Arthropods and annelids both have close relatives that are unsegmented. "Mesofauna" are macroscopic soil animals such as arthropods or nematodes. With the Venus flytrap, prey is limited to beetles, spiders and other crawling arthropods. Trilobites form one of the earliest-known groups of arthropods.