The Annelids Flashcards by Shaira Ann Rueco

consists of organisms that are typically vermiform or worm shaped.

Phylum Annelida

Earthworms, leeches, and clam worms (polychaetes) belong to this group.

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true or false

basic body plan of an annelid is that of an elongated structure, often tapering at the anterior and posterior ends.

true

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structure that project outward from the epidermis to provide traction

made up of beta-chitin (which is flexible and tough), strengthened with sclerotized protein or inorganic material (e.g. calcium carbonate)

Setae

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What is the function of setae

to form temporary attachment sites and prevent backsliding during locomotion in or within the substrate or burrow

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true or false

Arthropods’ setae, and the annelid setae is morphologically similar

False

while arthropods have bristle-like structures also called setae, the annelid setae is morphologically different, especially in its ultrastructure

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How many described species of phylum annelida

15,500 described species

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true or false

All adults (except of sipunculans) phylum annelida possess at least one pair of chaetae

true

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What are the characteristics of the body segments of annelids

annulated or ring like

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Anterior segment of annelids body

prostomium

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Posterior segment of annelids body

pygidium

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body segments in between posterior and anterior

Metameric

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○ burrowing activities constantly rework the substrate in which they thrive

○ they may ingest and excrete large quantities of sediments or soils

keep soils aerated, and their castings fertilize the soil

Ecological Importance

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Flexible
Has important role on locomotion
Thinner portions can serve as surface for gas exchange (moisture is a requisite)
Epidermal cells secrete cuticle, but remains permeable to both water and gas

Body wall

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▪ Non-living layer

▪ Permeable

▪ Mainly for protection

Collagenous cuticle

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▪ Living layer

▪ Layer where the chaetae is formed and anchored

▪ Contains cells that secrete the cuticle

▪ Other cells:

supporting cells,
albumin cells,
mucus cells,
basal cells

Simple Glandular Epidermis

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How are chaetae formed

Chaetae forms from an invagination of the epidermal chaetoblast

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− outer muscular layer − adjacent to epidermis

− contraction prompts the body to elongate while reducing overall girth

Circular muscles

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− inner muscular layer
− adjacent to the gut wall
− contraction causes the body to shrink

Longitudinal muscles

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true or false

cirular and longitudinal muscles act antagonistically. When one of the layers contract, the other one relaxes

true

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Interior-most segment of the body

Equipped with sensory appendages

Prostomium

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Segments between prostomium and pygidium

Metameric (serially repeating)

Make up most of the body

Repeating organ systems ihnerent to metameric segments

Body Proper

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Posterior-most segment

Caudal end

Pygidium

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thin sheets of mesodermally derived tissue that separates the segments

Septum

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What is the importance of this compartmentalized coelomic fluid?

allows localized deformation of the body

muscle contractions in any one segment will not alter the hydrostatic pressure in other parts of the animal, making locomotion possible.

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○ Function: Take signals from various parts of the body, process them, and create new signals to coordinate actions of different body systems ○ Components: - Dorsal Brain/ Cerebral Ganglion - Ventral pair of longitudinal nerve cords (located in the prostomium)

Central Nervous System

mass of nerve cells that relay neural signals

Ganglia

True or false Each body segment bears a pair of ganglia

true

nerve fibers protruding from ventrally located ganglia; relays signals to and from the body segments

Segmental Nerves

- Homologous to vertebrate spinal cord | - Ventrally located cords that run from the front of the body to the tail end

Nerve cord

Eye spots Nuchal Organ Ciliated Lateral organs

Sensory Organs

For light reception located on the prostomium or even directed on the upper surface of the brain

Eye spots

ciliated pits or short ridges at the posterior end of the prostomium

Nuchal Organ

Tufts of cilia in shallow pits Partially chemosensory

Ciliated Lateral organs

Central Nervous System Ganglia and Segmental Nerves Nerve cord Sensory Organs

Nervous System

Protonephridia Metanephridia

Excretory System

○ Rough translation: “primitive kidneys” ○ ultrafiltration is carried out through ciliary beating present in larval and some post-larval stages

Protonephridia

○ rough translation: “second-order kidney” ○ definition: tubular excretory gland which opens at one end to the exterior, with the other end opening into the coelom or may terminate in a flame cell

Metanephridia

kidney mouth; where water is drawn through action of cilia

Nephrostome

salt, aa, water is resorbed

Convoluted tubule

where urine and other metabolic by product comes out

Nephridiopore

Takes the form of a straight tube Supported by mesenteries Partitioned into many regions, each with a certain function (foregut, midgut, and hindgut)

Digestive System Consists of the pharynx, the esophagus, the crop, the intestine, and the gizzard

Digestive process

mouth - pharynx - esophagus - crop - gizzard - intestines - blood vessels

release calcium carbonate to rid the earthworm’s body of excess calcium.

calciferous glands

Asexual modes

- Fragmentation - Budding - Fission

sexes are separate, the male and female reproductive organs being in different individuals

gonochoristic

Where are segmental gametes produced? released?

§ Segmental gametes are produced in the peritoneal tissue (not in gonads) and are released in coelomic cavities where they mature

Gametes are spawned through

metanephridia

true or false Fertilization is internal

false Fertilization is external

true or false Embryo exhibits linear cleavage

false Embryo exhibits spiral cleavage

small, translucent, free-swimming larva of marine annelids and most groups of mollusks spherical or pear-shaped and are girdled by a ring of cilia produced by echiurans and sipunculans but not by clitellates

trochophore larva

Animals with a trocophore larval stage in their life cycle are grouped under the taxon

Trochozoa

trocophore larva is defined by its taxonomy rather than its characteristic morphology

false trocophore larva is defined by its characteristic morphology rather than taxonomy.

o G: first wheel o located around the equator of the animal o anterior to the future mouth of the annelid o larva’s main locomotory organ

Prototroch

o G: tail wheel o located posteriorly on what will become the terminal portion (pygidium)

Telotroch

in between the 2 bands of cilia

Metatroch

• Includes approximately 70% of all annelids, predominantly marine • Possess at least 1 pair of eyes and a pair of sensory appendages (tentacles) on the prostomium Have proboscis with incomplete or perforated septa at the anterior

CLASS POLYCHAETA

series of thin, flattened outgrowths where the body wall extends laterally

parapodia ○ Plays an important role in polychaete identification ○ Increase the animal’s surface area ○ Highly vascularized ○ Has important function in gas exchange ○ Has locomotory function - Bear chitinous acicula and siliceous, chitinous or calcareous setae/chaetae

chitinous support rods

Acicula

series of overlapping protective plates that covers the body

Elytra

Class POLYCHAETA's primary mode of reproduction is through

epitoky process in which a segment of a sexually immature worm (atoke) transforms into a mature one (epitoke) then detaches to undergo sexual reproduction

anterior portion of the original animal immature worm

Atoke

○ A sexually mature being ○ Reproductive module that detach from posterior of an atoke ○ Will comingle with other epitokes then discharge their sperm and egg

Epitoke

* Active, mobile species * Move through the action of the parapodia, which are operated in complex patterns as oars * Longitudinal muscles antagonize the longitudinal muscle on the other side → results into a rapid-eel-like movement

Subclass Errantia E.g. Fireworm (Erythroe sp.)

* Spend their entire lives in simple burrows in the sediment or in simple rigid tubes – they live sedentary lives * Tubes are made up of calcium carbonate, proteins and polysaccharides * Parapodia and acicula are greatly reduced

Subclass Sedentaria E.g. Christmas tree worm (Spirobranchus sp.)

○ Formerly categorized as Phylum Pogonophora (G: beard bearers) ○ Defining Characteristics: ▪ gut tissue forms an organ (trophosome) that becomes filled with chemosynthetic bacteria ▪ segmentation at the posterior portion of the body called opisthosoma ○ Deep tube dwelling worms - Some Siboglinids (esp. vestimentiferans) are well adapted to live near hydrothermal vents

Family Siboglinidae

* G: viper tail * Common Name: Spoon worms * Recently classified as a group within Phylum Annelida, and now considered to be a subclass of Sedentaria, within the polychaete • Defining Characteristics ○ Muscular organs (anal sacs) outpocketing from the rectum into the coelomic space bearing numerous funnels that discharge coelomic fluid through the anus - Unique sex determination

Subclass Echiura

How many described species of subclass Echiura?

○ 150 described in shallow waters

○ few mm to 50cm with extreme sexual dimorphism ○ deposit feeders with highly muscular proboscis which can be extended 25x the length of body ○ no segmentation or metamerism in extant species (only in fossil records and larval segmented nervous system)

Subclass Echiura E.g. Green spoon worm (Bonellia viridis)

• Defining Characteristics ○ pronounced cylindrical glandular region (clitellum) that plays important roles in reproduction - permanent gonads

CLASS CLITELLATA

* G: few setae * ~ 3,500 species * Mostly freshwater and terrestrial; few marine * Septa dividing coelomic cavity into semi-isolated compartments * Moves by peristaltic waves * well-segmented worms and most have a spacious body cavity (coelom) used as a hydroskeleton * 10,000 known species * Group where Earthworms belong

Subclass Oligochaeta

* G: leech * 500-630 described species * Mostly freshwater and terrestrial; few marine * With anterior (fused 1-4 segments) and posterior suckers (fused 25-33 segments) * No septa; no setae * Moves by looping * Simultaneous hermaphrodite (mutual sperm exchange) • Internal fertilization through copulation, jabbing packets of spermatophores (for those lacking penis), or through penetration of the body wall by the spermatophores themselves

Subclass Hirudinea

* G: little tube * Common name: peanut worms * Recent molecular data suggests that they are directly linked to Annelids but the position (i.e. taxonomic rank, sister taxa, etc.) is still debated ○ Lack setae and show no trace of segmentation ○ All marine in shallow waters ○ Mostly deposit-detritus feeders ○ Gonochoristic ○ Do not secrete tubes, just form burrows or live in empty mollusc shells or polychaete tubes, in rock crevices, and calcareous substrates of coral reefs

THE SIPUNCULANS • Defining Characteristics ○ Anterior part of body forming eversible and fully retractable introvert, with mouth at its end ○ Anterior tentacles connected to series of muscular sacs (compensatory sacs) that pump fluid into the tentacles. Multicellular bodies (urns) in the coelomic fluid specialized for accumulating wastes

How many species in THE SIPUNCULANS

About 350 species

The Annelids Flashcards

(73 cards)