Annelida

Phylum Annelida has about ______ species and consists of segmented worms living in marine, freshwater, and moist terrestrial habitats.

,About 15,000 species

body divided into a serial succession of repeated units called ______.

segments, metameres or somites

What is the significance of metamerism?

Greater complexity in structure and function; burrowing efficiency; fine control – nervous system; redundancy – safety

Metamerism independently evolved in lophotrochozoans, ______, and ______.,annelids

ecdysosomes; deuterostomes

What are annuli and septa?

Annuli – external circular grooves delimiting body segments; septa – internal delimitation of body segments

What are the two parts of the typical 2-part annelid head?

Prostomium and peristomium

The prostomium is the anterior most region of the body, ______ the mouth; the peristomium is the pre-segmental region ______ the mouth.

anterior to; surrounding

What structures may be present on annelid segments and what type of body cavity do annelids have?

Parapods – flaps may be present on each segment; coelomic cavity (eucoelomate)

The hydrostatic skeleton is a ______ filled with fluid, except for leeches.

coelom

In the hydrostatic skeleton, fluid volume is constant; contraction of longitudinal muscles ______ and ______ the body, while contraction of circular muscles ______ and ______ the body.,

shorten and expand; narrow and lengthen

Alternate waves of contraction, or ______, allow efficient burrowing; swimming annelids use ______ movements.

peristalsis; undulatory

Oligochaetes & Polychaetes have a ______ circulatory system; dorsal vessels carry blood ______ and ventral vessels carry blood ______.

closed; anteriorly; posteriorly

What ensures unidirectional blood flow, and what maintains steady pressure in the ventral vessel?

Vascular valves ensure unidirectional blood flow; aortic arches maintain steady pressure

Metanephridia are the ______ organs of the adult annelid; typically one pair occurs in each segment except the ______.

excretory; 1st 3 and last

The nephrostome is a ciliated funnel that draws in ______ and opens into the segment ______ to the metanephridium.

coelomic fluid; anterior

The nephridiopore is where the terminal end of the metanephridium ______; in some forms, nephridiopores are ______.

,opens to the outside; enteronephric

The nervous system consists of a ______, with a pair of ganglia and lateral nerves in each segment.

double ventral nerve cord

The brain consists of a pair of ______ ganglia with connections to the ventral nerve cord.

dorsal cerebral

Annelid sensory systems include tactile organs, taste buds, statocysts (in some), photoreceptor cells, and ______; polychaetes may have tentacles, palps, and eyespots.

eyes with lenses (in some)

How do Polychaeta, Oligochaeta, and Hirudinida compare in parapodia, setae, and suckers?

Polychaeta: parapodia present, setae present, suckers absent; Oligochaeta: parapodia absent, setae present, suckers absent; Hirudinida: parapodia absent, setae absent, oral and posterior suckers

Polychaeta is the ______ class of annelids with >10,000 species; they are mostly ______ and usually benthic.

largest; marine

Polychaetes have paired appendages called ______ on most segments, with many ______ arranged in bundles on the parapodia.,

parapodia; setae

Polychaetes have ______ and a well-differentiated head that often bears eyes, tentacles, and sensory palps.

no clitellum

The two polychaete morphotypes are ______

mainly tube-living

Clitellata includes ______ and ______; they form a reproductive structure called a clitellum.

Oligochaeta; Hirudinida

The clitellum is a ring of ______ cells found in a band around the body; it is permanent in oligochaetes but visible only during the ______ in leeches.

secretory; reproductive season

Oligochaetes and leeches are ______ with direct development; young develop inside a ______ secreted by the clitellum and emerge as small worms with no larval stage.

hermaphroditic (monoecious); cocoon

Oligochaetes occur from soil to freshwater; nearly all bear ______ and earthworms burrow in ______ soil.

setae; moist rich

Oligochaete locomotion uses circular muscles for metamere elongation, longitudinal muscles for metamere widening-shortening, and paired chitinous ______ to increase traction

setae

Most leeches are freshwater, a few are marine or live in moist terrestrial environments; most are flattened ______.

dorsoventrally

Leeches have a fixed number of segments but appear to have more due to superficial ______; they have no distinct coelomic compartments and no _____.

annuli; septa

In most leeches, the coelomic cavity is filled with connective tissue and spaces called ______, which may serve as an auxiliary circulatory system.

lacunae

Leeches have no ______ but have developed ______ for attachment and use them to “inchworm” along surfaces.

setae; suckers

Many leeches are predaceous and some are parasites; most are fluid feeders that prefer tissue fluids and ______ pumped from open wounds.

blood

Bloodsucker leeches have chitinous “jaws” and salivary glands that secrete an anesthetic and ______ enzymes; their gut is specialized for storage of large quantities of ______.

anticoagulant; blood