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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Phylum Annelida – Phylum and Class Characteristics Phylum Characteristics: coelomate body divided into segments (metameres) via septa; repeated arrangements.
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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 organsClass Oligochaeta: most terrestrial (earthworms); secrete
cocoon from clitellum (reproduction); hermaphroditicClass Hirudinida: most aquatic (leeches); dorso-ventrally
flattened body; suckers for attachment; suck blood/body fluids; clitellum forms only during reproductive season
Fig. 17.1
Class PolychaetaDiversity: 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 platesFireworms: toxins secreted through hollow setaeLugworms: deposit feeders (ingest organics from sediment)Tubeworms: sedentary; composition of tubes vary (ex.,
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.)
Fig. 17.2
Fig. 17.6
Fig. 17.11
Fig. 17.5
Fig. 17.12
Fig. 17.15
Fig. 17.14
Earthworms and LeechesClass Oligochaeta: approx. 3000 species; earthworms
burrow soil turnover and aeration; loss of parapodia and pronounced heads/sense organsSetae 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 hostMedicinal 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)
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)