What Are The Closest Arthropod Relatives Of Insects?

Arthropod evolution is a contentious topic, but it is generally agreed that myriapods are the closest relatives of insects, forming a group known as the Atelocerata. The closest living relatives of Anomalocaris are arthropods. Tardigrades are controversial, with some suggesting they are related to arthropods, velvet worms, and/or nematodes. Arthropods belong to the phylum Arthropoda, the largest, most abundant, and varied phylum in the world. Extant arthropods are divided into two large monophyletic groups: Chelicerata (sea spiders, horseshoe crabs, spiders, scorpions, and their relatives) and the earliest fossils of the phylum Tardigrada from northern Europe.

There are about 15 different groups of arthropods, including Arachnids (spiders, ticks, mites), Centipedes, Millipedes, and remipedes. Recent work finds Onychophora rather than Tardigrada to be the closest relatives of arthropods. Insects comprise the more diverse of two classes united together as the arthropod subphylum Hexapoda, the other being the Entognatha, consisting of the orders Diplura. Crustaceans are phylogenetically close to insects and together form the Pancrustacean clade.

Both insects and crustaceans are arthropods, with all having a common ancestor, possibly from the early Myriapoda. Modern arthropods include insects, spiders, centipedes, shrimp, and crayfish. All arthropods are descendants of a single common ancestor. The phylum Arthropoda includes insects, spiders, mites, tick, sowbugs, centipedes, millipedes, and more. They are characterized by chitinous exoskeletons.

It is now widely recognized that extant arthropods are split into chelicerates and mandibulates, with relationships within the two mandibulate. The centipedes are the closest relatives of insects due to their single pair of antennae.

Are All Insects Part Of The Same Phylum?

Most people associate various arthropods as a single group of living organisms, which is only partially accurate. While all these creatures belong to the phylum Arthropoda, they are not identical. Insects, specifically, are a distinct class within this phylum known as Insecta or Hexapoda, representing the largest class of Arthropoda. Both humans and insects share the same kingdom, Animalia. Insects are meticulously classified into numerous hierarchical categories: 33 phyla, 4 subphyla, 28 orders, 90 families, and countless genera and species. There are 29 recognized insect orders, ranging from the most primitive to the highly evolved.

In everyday language, "insect" typically refers to familiar pests and disease carriers such as bedbugs, houseflies, mosquitoes, fleas, and hornets, as well as notable groups like butterflies, moths, and beetles. However, many insects play beneficial roles in ecosystems. Insects are six-legged invertebrates characterized by a hard exoskeleton and a three-part body structure (head, thorax, abdomen). They exhibit diverse body plans, organs, and life cycles, contributing to their remarkable adaptability and success.

Arthropods, including insects, share key characteristics like jointed legs, segmented bodies, bilateral symmetry, and an exoskeleton. Insects differ from other arthropods through specific features such as the number of body segments, type of exoskeleton, number of legs, antennae structure, eye configuration, presence of wings, metamorphosis patterns, and distinct respiratory and excretory systems. These differences underscore the unique classification of insects within the vast and diverse phylum Arthropoda, which also includes crustaceans, spiders, scorpions, and other lesser-known groups.

Are All Insects The Same?

All insects belong to the phylum Arthropoda, which also includes arachnids, crustaceans, and myriapods. However, insects and other arthropods are distinct groups. The term "insect" refers specifically to members of the class Insecta, characterized by having three body parts: head, thorax, and abdomen. Despite common usage, "bug" is often used informally to describe various small creatures, leading to confusion, as not all bugs are insects and not all insects are bugs.

Scientifically, bugs are a specific subgroup of insects belonging to the order Hemiptera, known as "true bugs." True bugs are distinguished by their specialized mouthparts—a piercing and sucking "beak" or proboscis—which they use to feed on plant sap or other insects. Examples of true bugs include aphids, cicadas, shieldbugs, bedbugs, and others. This differentiates them from other insects which may have chewing mouthparts or other feeding mechanisms.

While all bugs (Hemiptera) are insects, insects encompass a much broader range, including diverse orders like Lepidoptera (butterflies and moths), Coleoptera (beetles), Diptera (flies), and many others. There are over a million described insect species, making insects the most diverse group of animals, representing more than half of all described animal species.

In everyday language, "bug" is often used interchangeably with "insect," but from an entomological perspective, bugs are a specific group within insects. Clarifying this distinction helps in understanding the vast diversity within the arthropods and highlights that while all bugs are insects, the insect class contains many more organisms beyond just true bugs.

How Many Types Of Arthropods Are There?

Arthropods, the largest animal phylum, are categorized into two main monophyletic groups: Chelicerata (which includes sea spiders, horseshoe crabs, spiders, scorpions, and their relatives) and Mandibulata (comprising myriapods, insects, and various crustacean lineages). Representing about 84% of all known animal species, arthropods inhabit all ecosystems, showcasing remarkable adaptations for both aquatic and terrestrial environments.

They are characterized as invertebrates with segmented bodies, jointed appendages, and exoskeletons made of chitin. The exoskeletons of some crustaceans and certain beetles incorporate calcium carbonate, providing additional structural features.

Current estimates suggest that there could be between 1. 17 million and 10 million species of arthropods, indicating their diversity far surpasses that of all other animal phyla combined. Over 800, 000 arthropod species have been formally described, with insects alone comprising the most significant number of described species among any taxonomic class. The phylum is often divided into four subphyla: Chelicerata, Crustacea, Hexapoda, and Myriapoda, which includes centipedes and millipedes.

The sheer variety of arthropods, including familiar insects like ants, flies, and beetles, underscores their dominance in the animal kingdom, accounting for approximately 80% of living animal species. Their ecological roles in parasitism and decomposition are integral to many ecosystems, making arthropods essential to biodiversity and ecological balance worldwide.

What Was The First Insect On Earth?

The Devonian insect Rhyniognatha hirsti, found in the 396-million-year-old Rhynie chert, is recognized as the oldest insect, known solely from its mandibles. Insects likely originated around 480 million years ago during the Ordovician period, coinciding with the emergence of terrestrial plants. It is hypothesized that insects evolved from a group of crustaceans. Fossil records indicate that the earliest insects, dating back approximately 412 million years, lived during the Early Devonian Period.

New genetic studies suggest that insect evolution may have occurred earlier than previously thought. The first insects were small, measuring a few millimeters, dwelling in soil, and feeding on decomposing vegetation, fungi, spores, and possibly bacteria. Notably, the first winged insects—dragonfly-like and grasshopper-like—appeared around 400 million years ago, marking a pivotal moment in entomological evolution. The evolution of wings enabled insects to take flight, making them the first creatures on Earth to do so, significantly contributing to their success.

Fossils from the Paleozoic Era reveal some insects of massive size, including giant dragonflies. Recent timelines suggest that the ancestors of today’s insects evolved earlier than once believed, around 479 million years ago, alongside the first land plants. Despite the extensive fossil record, the evolutionary relationships among insect groups remain unclear. The discovery of these ancient insects provides vital insights into the evolutionary history of terrestrial life.

Are Spiders And Insects Closely Related?

Spiders are often mistaken for insects, but they belong to a distinct group known as arachnids. Both spiders and insects fall under the phylum Arthropoda, which includes joint-legged invertebrates with exoskeletons. Despite this shared classification, arachnids and insects are categorized into separate classes: Arachnida for spiders and Insecta for insects. This distinction is evident in their physical structures.

Spiders typically have two main body segments—the cephalothorax and abdomen—whereas insects possess three segments: head, thorax, and abdomen. Additionally, spiders feature unique anatomical elements such as chelicerae and specialized leg movements, contributing to their characteristic appearance and often "creepy" demeanor.

Molecular and morphological evidence indicates that spiders are more closely related to horseshoe crabs than to insects, suggesting an earlier evolutionary divergence from a common ancestor. While both spiders and insects have exoskeletons and jointed legs, their respiratory systems differ; spiders often use book lungs for respiration. Furthermore, spiders are part of the subphylum Chelicerata, which includes other arachnids like mites, ticks, and scorpions, whereas insects belong to the subphylum Hexapoda, encompassing diverse orders such as Diptera (houseflies).

The evolutionary history traces spiders back to trigonotarbids from the late Silurian period, highlighting a long separate lineage from insects. Adult insects typically possess features such as wings and antennae, absent in spiders. The specialized leg mechanics of spiders result in movements that appear more eerie compared to the faster, varied motions of insects. Spiders' adaptability allows them to inhabit various environments without being tied to specific plants or habitats.

Understanding these differences is crucial for biological classification and appreciating the diversity within the arthropod phylum. This distinction underscores the importance of both molecular studies and morphological traits in clarifying evolutionary relationships among arthropod groups, highlighting the complexity and specialization within invertebrate life.

Is Arthropoda A Sister Group?

Arthropoda, in this context, refers to a definition commonly used in English, excluding Onychophora, and aligning with what is known as "Euarthropoda" in European literature. Understanding the sister group of arthropods is crucial for assessing characteristic evolution at the base of this phylum. Traditionally, Onychophora (velvet worms) is seen as Arthropoda's sister group, although some German literature combines Onychophora with Euarthropoda.

A differing perspective arose in 2003 by Jan Bergström and Hou Xian-guang, suggesting that Tardigrada (water bears) might be the closest relatives of arthropods, while Onychophora could be a sister group to both Arthropoda and Tardigrada. Arthropoda stands out within the Ecdysozoa clade, exhibiting a unique morphology, notably a segmented body formed from fused segments. In some analyses, Tricholepidion is considered closely related to Dicondylia (Zygentoma + Pterygota), while other studies indicate it shares a relationship with Zygentoma.

Among arthropods, the clade Pancrustacea includes major groups such as crustaceans and insects. Pycnogonids are considered a sister group to Euchelicerata, while within Euchelicerata, Xiphosura is related to Arachnida. Recent molecular analyses have consistently found relationships among various arthropod groups, including inclusion of Onychophora and Tardigrada as sister clades to Arthropoda. Additionally, some interpretations regard arthropods as part of a spiralian or protostome group, contradicting older views that placed them as sister taxa to other phyla.

What Is An Arthropod Animal?

Arthropoda is a vast phylum of invertebrate animals that encompasses insects and their relatives, including spiders, crabs, ticks, centipedes, and millipedes. Representing approximately 84 percent of known animal species, arthropods have segmented bodies, jointed limbs, and an exoskeleton made primarily of chitin, a polymer of N-acetylglucosamine. Some groups, such as certain crustaceans and beetles, also have calcium carbonate in their cuticles. The term "arthropod," derived from Greek, means "jointed foot," reflecting their defining features.

Arthropods play a significant role in various ecosystems as pollinators, nutrient recyclers, and more. This phylum includes over a million recognized species, making it the largest in the animal kingdom. Characteristics defining arthropods are their segmented bodies, jointed appendages, and an open circulatory system. They inhabit virtually all ecosystems on Earth, from terrestrial to aquatic environments, with minute species like copepods being exceedingly abundant in marine waters.

In summary, arthropods are critically important in maintaining ecological balance. Their diverse forms include familiar species such as lobsters, crabs, and insects. They are a major component of the animal kingdom and contribute significantly to the functioning of various habitats worldwide. Other invertebrate groups include annelids, nematodes, and mollusks, but arthropods remain the most diverse and numerous.

What Is The Closest Relative To Insects?

Recent molecular evidence indicates that crustaceans may be polyphyletic, originating from multiple ancestors. Consequently, certain crustaceans in Class Malocostraca are more closely related to insects than to some other crustaceans. Despite the complexities in the relationships among these groups, there has been a long-standing agreement on the closest relatives of vertebrates, which is considered unusual given the lack of significant similarities with our closest non-vertebrate relatives.

For over a century, the consensus has pointed to a group that appears quite distinct from vertebrates. Notably, insects, the most diverse organisms, are nested within the crustaceans, which are among the most abundant marine animals. Although there is still no conclusive consensus on this taxonomy, fossil evidence indicates that early insects, such as the Devonian Rhyniognatha hirsti, may share a lineage with myriapods. Insects, all belonging to the clade Arthropoda, have a close relationship with crustaceans.

Specifically, a phylogenetic analysis places insects within the Hexapoda, linking them closely to Diplura (bristletails). In addition, trends indicate that all insects descended from a common ancestor shared with crustaceans and other arthropods, including arachnids and myriapods. The shared evolutionary lineage illustrates the connection between these diverse classes, with crustaceans and insects evolving distinct characteristics from a common ancestor, reinforcing the close relationship among them and other arthropods.