Roundworms and relatives Flashcards
How are the phylum nematoda described?
Roundworms, meiofaunal and parasitic
>20,000 spp
Many are parasitic but also many free living- wide range of environments
Major marine meiofaunal group
Species diversity high
Pseudocoelomate
Most are elongate cylindrical worms 1 to 2mm in length
How is the gut structured in the phylum Nematoda?
Anterior part of gut is a muscular oesophagus/pharynx with a pronounced oesophageal bulb- but there is some variation between species
How is movement characterised in the Nematoda?
Movement is characteristically serpentine
No circular muscles so can not extend body- movement is by alternate contractions of dorsal and ventral longitudinal muscles working against high internal turgor pressure
How is the cuticle structured in the Nematoda?
Cuticle may be smooth or have ornamentation
This may consist of transverse annulations/striations or it may be punctate
Ornamentation can be homogeneous or heterogeneous
Ornamentation may differ on the sides of the body- lateral differentiation
What sense organs exist in the Nematoda?
Papillae (small lumps) and setae (hair-like structures)- thought to be mechanoreceptors
Cephalic sensilla have a regular 6 + 6 + 4 arrangement
May also be somatic setae (on body)- cervical setae on oesophageal region, caudal setae on tail, there are commonly terminal setae on tip of tail
What are amphids?
Found in the nematoda
Amphids are thought to be chemosensory
There is one either side of the body just behind the anterior end (head)
Structure is variable but basically pocket shaped or spiral
What is the buccal cavity?
Found in Nematoda
Buccal cavity is variable in structure- it may be absent, present and lacking teeth or movable mandibles
It is of taxonomic importance and conveys ecological information by indicating the feeding specialisation of the species
What are the different feeding types of the Nematoda?
Epigrowth feeders
Omnivores/predators
Predators
How do the Nematoda reproduce?
Sexes are separate and fertilisation is internal
Female has vulva about half way along body. Male has a cloaca usually with copulatory structures.
Typically there are a pair of spicules, a gubernaculum and there may be precloacal supplements
Eggs are usually produced, there are 4 juvenile stages before the reproductive adult appears after the final moult
How is the tail structured in the Nematoda?
The tail shape is distinctive and taxonomically important
There is an adhesive organ (spinneret) on the tail tip. The caudal glands are a duo g;and system that produces the adhesive material
How are the Nematoda ecologically important?
The biomass of nematodes is generally lower than that of larger organisms but high abundance and rapid metabolism results in very high productivity
They are important in nutrient cycling by breaking down organic material and feeding on bacteria etc
They provide a food source to some macrofauna
They modify sediment structure and cohesiveness
How are the phylum Priapulida described?
Coelomate unsegmented worms
16 species, all marine, shallow and deep water
Macrofaunal- range from 0.5mm to 30cm
All benthic- burrowers in sediment
Deposit feeders, suspension feeders and carnivores
Well developed chitinous cuticle (moults periodically)
Larvae commonly occur as meiofauna
How are the Priapulida structured?
Body composed of trunk and introvert (proboscis)
Introvert is barrel-shaped and has longitudinal rows of spines (scalids)
Trunk normally has additional hooks or spines, may also have a posterior caudal appendage
How are the phylum Kinorhyncha described?
Marine
Meiofaunal
Well developed cuticle, superficially segmented
Retractile head with spines
150 species
Separate sexes
Adhesive tubes
How are the phylum Nematomorpha described?
Mostly freshwater or damp soil
325 species
Adults free living- juveniles parasitic in arthropods
Filliform worms- thread like bodies may be up to 1mm in length
