ARTHROPODS and the origins of ARTHROPODA and related phyla

Phylum Annelida Gastrotricha Phylum Nematoda Phylum Phylum Phylum Phylum Phylum Phylum Tardigrada Phylum Arthropoda Phylum Annelida - segmented

Marine, freshwater, & terrestrial segmented worms. Cosmopolitan, very diverse. Polychaeta (mostly marine), Oligochaeta (earthworms etc.) and Hirudinea (leeches). 1 mm - 3 m. 15,000 . Phylum Gastrotricha

Microscopic (0.06-3 mm) unsegmented free-living, aquatic worms. Marine and freshwater. Mieofauna and periphyton. Very abundant. Microphagous . Ca. 750 species. Phylum Nematoda - roundworms

Microscopic to very long (up to 100 cm) unsegmented worms. Free-living and parasitic (intestinal roundworms, hookworms, pinworms, trichinosis), many pathogens of and (important to agriculture). Ubiquitous, very abundant. Marine, freshwater, terrestrial. Ca. 80,000 species. Phylum Nematomorpha - horsehair worms

Very long, thin unsegmented worms (1 cm - 1 m). Immature forms parasitic in insects, sowbugs; adults occur in freshwater. Ca. 350 species. Phylum Priapulida

Marine segmented worms (several mm to 15 cm), with extensible, spiny . Ca. 15 species known. Predaceous. Live in mud on bottom of shallow seas (esp. cold oceans). Phylum Kinorhyncha

Microscopic marine segmented worms. Bristly, spiny, with crown of curved spines on . Mouth bears piercing stylets. Feed on , protozoans, . Muddy bottoms and meiofauna. Ca. 150 species. Phylum Loricifera

Microscopic marine animals (1 micron -1 mm). Mieofauna. Only discovered in 1983. 25 species. Phylum Onychophora - velvet worms Terrestrial, wormlike. Elongate. Segmented, each with pair of short legs. -like papillae on head. Possess tracheae. Live on forest floor of tropical and southern temperate rainforest forest. Predaceous. Spit quick-hardening -based glue from oral papillae to ensnare prey. Feed on snails, worms, insects, sowbugs. Tear open prey with jaws, inject saliva, suck out digested tissue. Mostly on southern continents. Ca. 100 species. Phylum Tardigrada - water bears Microscopic, segmented animals (200-500 microns), with clawed legs. Found in , lichens, freshwater, marine. Feed on algae, other tiny . Can withstand very harsh or extreme environments in dormant, cryptobiotic, state. 840 species. The TRADITIONAL view (Haeckel, Snodgrass, Weygoldt, Nielsen, Brusca & Brusca and many others) ARTICULATA - segmented animals

poda

Annelida OnychophoraTardigrada Crustacea Myria (insects)

Segmented body: each segment with •coelomic cavities •neuromeres •nephridia • (=Arthropoda of some authors)

poda

Annelida OnychophoraTardigrada Chelicerata Crustacea Myria Hexapoda

Exoskeleton ( + protein) which can be molted ARTHROPODA (=Euarthropoda of some authors)

poda

Annelida OnychophoraTardigrada Chelicerata Crustacea Myria Hexapoda

• Tagmosis - regional specialization of body segments •Sclerotization or calcification of the •Exoskel. of articulated plates •Jointed appendages •Head with 5 pairs of appendages •Compound eyes •Etc. The 4 major groups of extant (EU)ARTHROPODA

Chelicerata (horseshoe crabs, , sea ) Crustacea (, crabs, etc.) Atelocerata (=Tracheata) (, ) Hexapoda (insects)

See Table 3.2 Grimaldi & Engel; Tree of for more details MANDIBULATA

poda

Annelida OnychophoraTardigrada Chelicerata Crustacea Myria Hexapoda

•Mandibles •Highly developed compound eyes ATELOCERATA

poda

Annelida OnychophoraTardigrada Chelicerata Crustacea Myria Hexapoda

•Loss of 2nd antennae •Tentorium •Tracheae •Malpighian tubules poda

Annelida OnychophoraTardigrada Chelicerata Crustacea Myria Hexapoda

PATTERN OF TAGMOSIS UNIQUE! Head: 5-6 fused segments with labrum, mandibles, maxillae, labium Thorax: 3 segments, 3 pairs of 6- segmented legs : 11-segments, no limbs except for terminal genitalia and cerci The fourth stage in the development of the body form (Fig. 24 D) differentiates the insects from all other arthropods. It is well shown in the of many insects (Fig. 23 C). In this stage the trunk segments back of the protocephalon (Prc) become segregated into three regions. The first be called the gnathal region (Gn), since its appendages are destined to become feeding organs; the second is the thoracic region (Th), set apart as the locomotor center of the by the special development of its appendages as locomotory organs; the third is the abdominal region (Ab), on which the appendages are reduced and mostly obliterated.

FIG. 24 Diagrams suggesting the evolution of the definitive insect structure from that of a theoretical wormlike ancestor. Ab, abdomen; Gn, gnathal segments; H, definitive head; Lm, labrum; Mth, mouth; Prc, protocephalon (prostomium and at least one somite), or procephalic part of definitive head; Prpt, periproct; Prst, primitive head, or archicephalon (prostomium); Th, thorax.

In the fifth stage (Fig. 24 E) the body of the insect attains its final form. The gnathal segments are now united with the protocephalon in the definitive head (H), which thus comprises. the prostomium and four succeeding segments and carries the gnathal appendages as well as the protocephalic appendages. In the the thorax acquires wing rudiments in the form of paranotal lobes, two pairs of which eventually become wings, and is finally evolved into a highly perfected locomotor mechanism. The abdomen loses most of its appendages, becoming principally a container of the more important viscera and the seat of respiratory and reproductive activities. ARTHROPOD EVOLUTION: The NEW view (Aguinaldo, Zrzavy, and others) - molting animals Panarthropoda

Gastrotricha Priapulida LoriciferaKinorhynchaNematomorphaNematodaOnychophoraTardigradaARTHROPODA

•Absence of locomatory cilia ? •Trilayered (epicuticle, exocuticle, endocuticle) molted via ecdysteroids The 4 major groups of extant ARTHROPODA (= Euarthropoda)

Chelicerata (horseshoe crabs, arachnids, sea spiders) Mandibulata Crustacea (shrimps, crabs, etc.) Atelocerata (=Tracheata) Myriapoda (centipedes, millipedes) Hexapoda (insects)

See Table 3.2 Grimaldi & Engel; Tree of Life for more details Chelicerata Pycnogonida - sea spiders - horseshoe crabs +Eurypterida - sea Arachnida - microwhip scorpions Aranea - spiders Amblypigida - whip scorpions (= Uropygida) - vinegaroons - short-tailed whip scorpions - , - harvestmen Scorpiones - scorpions Pseudoscorpiones - pseudo scorpions Solfugida - sun scorpions, camel spiders - hooded tickspiders

See Table 3.2 Grimaldi & Engel; Tree of Life for more details Crustacea - cladocerans, brine Cephalocaridae - horseshoe shrimp - , Ostracoda - - isopods, doodle bugs, roly-polies Amphioda - amphipods, scuds - shrimp, crabs, Stomatopoda - shrimp Mysida - mysids Euphausiacea -

and several other orders Myriapoda

Chilopoda - centipedes Diplopoda - millipedes Diplopoda

Symphyla Pauropoda Chilopoda MANDIBULATA

Traditional hypothesis

Atelocerata Atelocerata Myriapoda Hexapoda Crustacea MANDIBULATA

New hypothesis

Pancrustacea

Myriapoda Hexapoda Crustacea Atelocerata vs Pancrustacea

Traditional hypothesis Atelocerata Myriapoda Hexapoda Crustacea Pancrustacea

New hypothesis

MANDIBULATA Paradoxopoda Mandibulata

Pancrustacea Hexapoda Pancrustacea Crustacea Mandibulata

Myriochelata Myriapoda Chelicerata

– Friedrich, M. & Tautz, D. 1995. rDNA phylogeny of the major extant arthropod classes and the evolution of myriapods. Nature 376, 165–167.

– Hwang, U.-W., Friedrich, M., Tautz, D., Park, C. J. & Kim, W. 2001. Mitochondrial protein phylogeny joins myriapods with chelicerates. Nature 413, 154–157.

– among other papers Pancrustacea, Mandibulata “The latest word. . .”

Reiger et al. 2010. Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences. Nature, 463: 1079-1084. • 41 kilobases from 62 single copy nuclear protein-coding • 75 arthropod taxa representing every major lineage • 5 outgroup taxa (, onychophorans) • 3 independent analyses (parsimony, likelihood, Bayesian)

Results • Strong support for Pancrustacea, Mandibulata • “Crustacea” paraphyletic • Xenocarida (Remipedia + ) to Hexapoda Mandibulata, Myriochelata “The latest word. . .”

Rota-Stabelli et al. 2010. A congruent solution to arthropod phylogeny: phylogenomics, microRNAs and morphology support monophyletic Mandibulata. Proceedings of the Royal Society (B):doi: 10.1098/rspb.2010.0590. Pages 1-9

• 198 protein-coding genes, new sequences for myriapods • micro RNA complements from all major arthropod taxa • 393 morphological characters

Results • Strong support for Mandibulata • Myriochelata is a tree-reconstruction artifact caused by saturation and long-branch attraction • common origin of Arthropoda (tardigrades, onychophorans and arthropods) Remipedia Cephalocarida from Reiger et al. 2010