Arthropods Crustaceans — covered last lab Principle Classes of Arthropods – Two pairs of antennae – “Mouth field”: feeding appendages • Mandibles (jaw) • Maxillae (mouth appendages) • Crustacea • Maxillipeds (modified legs) – Gills: lateral thoracic Cephalothorax Abdomen • Upper branches of Thorax walking legs Antennae Head • Arachnida (sensory reception) • Myriopoda Swimming appendages • Insecta Walking legs Pincer (defense) Mouthparts (feeding) Arachnids – includes spiders, scorpions, ticks, and mites 50 µm (a) Scorpions have pedipalps that are pincers (b) Dust mites are ubiquitous scavengers in (c) Web-building spiders are generally specialized for defense and the capture of human dwellings but are harmless except most active during the daytime. food. The tip of the tail bears a poisonous to those people who are allergic to them stinger. (colorized SEM). Figure 33.31a–c Arachnids Myriopoda • Two tagmata: cephalothorax & abdomen Centipedes & millipedes – six pairs of appendages: • Two tagmata: head & trunk (= thorax + abdomen) • 1 pair chelicerae w/ venom fangs or claws • Head w/ 4 segments & 4 pairs of appendages • 1 pair pedipalps — sensory / food manipulation • Trunk w/ many segments — 1 pair of legs/segment • 4 pairs walking legs Intestine Digestive Stomach Heart Brain gland Eyes Ovary Poison gland Anus Book lung Spinnerets Gonopore Sperm Chelicera Pedipalp Silk gland (exit for eggs)receptacle Figure 33.34 Figure 33.33 Figure 33.32 Heyer 1 Arthropods Myriopoda Insects Centipedes & millipedes • External anatomy • Two tagmata: head & trunk The insect body has three tagmata: • Head: head, thorax, and abdomen. – 1 pair of antennae • The segmentation of the thorax and abdomen are obvious, – Mouth parts: 1 pair of mandibles (jaws) but the segments that form the head are fused. + 2 pair of maxillae Abdomen Thorax Head • Trunk: – Legs of first trunk segment = maxillipeds Compound eye • Feeding limbs • Venom claws in centipedes – Remaining segments have walking legs Antennae Figure 33.35 Insects • External anatomy Head: 6 segments Thorax: 3 segments Abdomen: 11 segments External morphology of insects http://www.insectsexplained.com/ insect wing modifications External anatomy — insect head • Elytra – front wings of Haltere – modified 2nd pair of beetles modified into wings in flies. wing cover Gyroscopic stabilization of flight. External morphology of insects http://www.insectsexplained.com/ Heyer 2 Arthropods Mouthpart variations Insects • Mouthparts & feeding behavior (A) chewing mouthparts (B) lapping mouthparts (C) siphoning mouthparts (D) piercing mouthparts Legend: a, antennae c, compound eye lb, labium lr, labrum md, mandibles mx, maxillae Xavier Vázquez Insects Insects • Mouthparts & feeding behavior • Mouthparts & feeding behavior Insects Insects • Mouthparts & feeding behavior • Mouthparts & feeding behavior Heyer 3 Arthropods Cerebral ganglion. The two nerve cords meet in the head, where the ganglia of Insects several anterior segments are fused into a Insects cerebral ganglion (brain). • Internal anatomy The antennae, eyes, and other sense organs • Mouthparts & feeding behavior are concentrated on the head. Heart. Ovary Dorsal artery Crop Anus Malpighian tubules. Vagina Excretory organs— out- pocketings of the digestive tract. Nerve cords. Tracheal tubes. Gas exchange by a system of Mouthparts. Formed from A pair of ventral nerve several pairs of modified appendages. branched, chitin-lined tubes that infiltrate the cords with several body and carry oxygen directly to cells. Opens segmental ganglia. to the outside of the body through spiracles that can control air flow and water loss by opening or closing. Figure 33.35 Metamorphic Development Holometabolous Development • Ametabolous: direct development without metamorphosis • Hemimetabolous: gradual or incomplete metamorphosis • Metamorphosis occurs during a pupal stage • Holometabolous: complete metamorphosis (a) Larva (caterpillar) (b) Pupa (c) Pupa (d) Emerging adult Figure 33.6a–e (e) Adult Fig. 33.37: Once again, Eight of the Conflicting phylogenetic data! thirty insect I. Traditional taxonomy III II I from mouth parts & orders development II. Revised taxonomy 1. Key based on mitochondrial DNA sequences 2. Feeding III. Revised taxonomy 3. Development based on comprehensive comparisons of anatomy, neurology, development & DNA. Did terrestrial arthropods arise independently? Did crustaceans derive from terrestrial arthropods? Heyer 4 .