The Annelids Flashcards
- consists of organisms that are typically vermiform or worm shaped.
Phylum Annelida
Earthworms, leeches, and clam worms (polychaetes) belong to this group.
true or false
basic body plan of an annelid is that of an elongated structure, often tapering at the anterior and posterior ends.
true
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
What is the function of setae
to form temporary attachment sites and prevent backsliding during locomotion in or within the substrate or burrow
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
How many described species of phylum annelida
15,500 described species
true or false
All adults (except of sipunculans) phylum annelida possess at least one pair of chaetae
true
What are the characteristics of the body segments of annelids
annulated or ring like
Anterior segment of annelids body
prostomium
Posterior segment of annelids body
pygidium
body segments in between posterior and anterior
Metameric
○ 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
- 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
▪ Non-living layer
▪ Permeable
▪ Mainly for protection
Collagenous cuticle
▪ 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
How are chaetae formed
Chaetae forms from an invagination of the epidermal chaetoblast
− outer muscular layer − adjacent to epidermis
− contraction prompts the body to elongate while reducing overall girth
Circular muscles
− inner muscular layer
− adjacent to the gut wall
− contraction causes the body to shrink
Longitudinal muscles
true or false
cirular and longitudinal muscles act antagonistically. When one of the layers contract, the other one relaxes
true
Interior-most segment of the body
Equipped with sensory appendages
Prostomium
Segments between prostomium and pygidium
Metameric (serially repeating)
Make up most of the body
Repeating organ systems ihnerent to metameric segments
Body Proper
Posterior-most segment
Caudal end
Pygidium
thin sheets of mesodermally derived tissue that separates the segments
Septum
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.
○ 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
