polychaetes Flashcards
name the unsegmented Marine worms
Flatworms (Phylum Platyhelminthes)
Ribbon worms (Phylum Nemertea)
Round worms (Phylum Nematoda)
name the segmented Marine worm
annelids (Phylum Annelida)
Phylum Platyhelminthes characteristics (flatworms)
Flukes, tapeworms and turbellarians
- dorsoventrally flattened
- Gas exchange via diffusion (big enough body surface)
- Well-developed reproductive system in most
- brain = clusters of nervous tissue in head
Phylum Nematoda characteristics (Round worms)
- Extremely abundant in interstitial spaces of marine + freshwater sediments and soil water
- tapered at both ends with a thick, tough cuticle
- important in decomposition + nutrient cycling
- Significant parasites of humans, plants, animals
- Can be very difficult to identify species
Phylum Nemertea characteristics (Ribbon worms)
- free living, mostly marine
- Dorsoventrally flattened
- Ciliated epidermis
- Complete digestive system with mouth and anus
- Circulatory system
- Predators - eat other invertebrates e.g. worms and crustaceans
- Proboscis = long fleshy tube - used to entangle prey or inject venom via a stylet
- Prefer shallow, coastal waters
- Mostly < 20 cm; can be much longer (e.g. bootlace worm over 30 m)
Phylum Annelida characteristics
- Well-developed nervous system (with brain)
- Segmented internally + externally
- Bristles setae / chaetae in most (except leeches) – rods formed from scleritosed chitin that extend from each segment
- Closed circulatory system + haemoglobin
- Bilateral symmetry
- Traditionally divided into 3 classes: Hirudinea, Oligochaeta and Polychaeta
Sipunculans (Peanut worms) characteristics
- all marine, relatively common
- Live in shallow waters - either in sediment or in discarded shells
- Some bore into solid rocks to make a shelter for themselves
- Deposit feeders
- Anterior retractable appendage, introvert= multi-lobed or tentacled with mouth at end
Clitellata characteristics
- Branchiobdella - formerly in Hirudinea
- Class Hirudinea + Oligochaeta
- Form cacoons
- Hemaphrodites
what classes are apart of Clitellata
Hirudinea + Oligochaeta
class Hirudineans (Leeches) characteristics
- Marine species = parasitic - prey on other invertebrates or fish
- Anterior and posterior suckers to hold prey
- Dorsoventrally flattened
- Segmentation not as distinct as in other annelids
- No setae
Class Oligochaetes characteristics
- burrow in soft sediments
- Deposit feeders
- Terrestrial earthworms are also in this group
- Mainly found in shallow coastal waters
- Hermaphroditic
- Few chaetae (oligo)
Class Polychaetes (bristle worms) characteristics
- Largest + most of the diversity of annelids
- Paraphyletic
- Gonochoristic
- Often many chaetae (poly)
- Distinct head
- Trochophore larvae
- Varied morphologies and feeding mode
- Coelom (true body cavity) - important for hydrostatic skeleton
- can regenerate lost segments
- May have natural break points if grabbed by predators (autotomy)
- 2 clades = Errantia and Sedentaria
explain Parapodia in polychaetes
- fleshly lobes supported by chaetae on the side of each segment
- important for identification of species
- vascularized parapodia often used for movement
- Act as primary respiratory surfaces
- can be thought of as kinds of external gills that are also used for locomotion
what is the Errantia clade in polychaetes
- include free-living crawlers like nereidids (ragworms) and phyllodocids (paddleworms)
- include flattened worms protected with shield-like dorsal scales like thempolynoids (scaleworms) e.g. sea mouse
- include predatory swimming worms with giant eyes like the alciopids
- Gonochoristic - gametes released into the coelom
- Many species reproduce en masse at night (broadcast spawning)
what is epigamy
worm transforms into a swarming epitoke - rises into the water column to shed its eggs + sperm (sexual reproduction)- worm dies after reproduction (e.g. Nereids)
- most metamorphose to become night-time swimmers (epitokes) to meet their mates - timing of swarmings synchronised with the phases of the moon
