Phylum Annelida – Phylum and Class Characteristics Lecture: Segmented Worms and Allies Phylum Annelida – Phylum and Class Characteristics Phylum Characteristics: coelomate body divided into segments (metameres) via septa; repeated arrangements of organs and structures within segments (excl. digestive system); setae (bristles) and hydrostatic skeleton (excl. leeches); closed circulatory system; paired, ventral nerve cords and cerebral ganglia; paired nephridia in each segment (excretion) Diversity and Overview of Class Characteristics Class Polychaeta: most marine (“sea worms”); parapodia (paddle-like appendages); well-developed sensory organs Class Oligochaeta: most terrestrial (earthworms); secrete cocoon from clitellum (reproduction); hermaphroditic Class Hirudinida: most aquatic (leeches); dorso-ventrally flattened body; suckers for attachment; suck blood/body fluids; clitellum forms only during reproductive season

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Lecture: Segmented Worms and Allies Class Polychaeta Diversity: approx. 10,000 species, many create burrows Clam worms: most predatory with proboscis and chitinous jaws; include Nereis and Eunice spp. (ex. bobbit worm) Scale worms: flat bodies covered with plates Fireworms: toxins secreted through hollow setae Lugworms: deposit feeders (ingest organics from sediment) Tubeworms: sedentary; composition of tubes vary (ex., CaCO3, leathery, chitinous) Featherduster worms: filter feed with extended radioles (fan); include Christmas-tree worms Spaghetti worms: capture food particles with extended tentacles Parchment worm (Chaetopterus): captures food with mucous net within tube; fan-like parapodia create water flow Pogonophorans (beardworms): discovered around deep-sea vents; no digestive tract; symbiosis with chemosynthetic bacteria (located in trophosome); chitinous tubes

Class Polychaeta (“Sea Worms”)

The Bobbit Worm (Eunice sp.)

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Earthworms and Leeches Lecture: Segmented Worms and Allies Earthworms and Leeches Class Oligochaeta: approx. 3000 species; earthworms burrow  soil turnover and aeration; loss of parapodia and pronounced heads/sense organs Setae extend from pores in body wall (muscular control) Digestive system compartmentalized (incl. crop, gizzard) Dorsal blood vessel pumps blood; aortic arches stabilize blood pressure; some with hemoglobin; gas exchange through moist skin Class Hirudinea: fixed number of segments with superficial annuli; lack setae; possess anterior and posterior suckers for attachment to host Medicinal leeches (Hirudo medicinalis): used to promote growth of capillaries and reduce congestion in veins; once used for bloodletting (fevers thought to result from excess of blood)

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Annelid/Arthropod Allied Phyla Lecture: Segmented Worms and Allies Annelid/Arthropod Allied Phyla Phylum Echiura (spoon worms): approx. 140 species, all are marine burrowing worms, widespread deposit feeders; spoon- shaped proboscis; lack segmentation, but molecular evidence suggests derived from annelids Phylum Sipuncula (peanut worms): all marine burrowing worms; eversible introvert at anterior end bearing tentacles Phylum Onychophora (velvet worms): most are predators on insects in rain forests; so-called “living fossils” with little change in morphology since Cambrian Period; some with segmented bodies (ex. Peripatus); unsegmented, paired legs with claws; nephridia and ventral nerve cord Phylum Tardigrada (water bears): minute (< 1mm) cylindrical bodies; live in film surrounding mosses or in damp soils; cuticle molted; buccal tube adapted for sucking; separate sexes; terrestrial forms can undergo cryptobiosis (state of suspended animation)

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My Squishy Friend the Tardigrade