Animal Bio: Nematodes (roundworms, pinworms etc.)

Phylum

Nematoda and Nematomorpha

nematode body plan

almost every environment on earth

triploblastic ecdysozoan protostomes (shed cuticle and mouth forms first)

bilateral symmetry with cephalization (head)

pseudocoelomate and cylindrical

no respiratory or circulatory systems (gas exchange across body wall)

dioecious

outer acellular cuticle

composed of collagen (no cells)

inner hypodermis

epidermis, secretes cuticle (underneath the cuticle)

hydrostatic skeleton

musculature and fluid-filled pseudocoel form hydrostatic skeleton (fluid underneath the body)

nematode muscles

longitudinal muscle fibres only (only runs length of body; whip like motion of movement)

 Muscles attached to outside of the body wall and connect to the ventral nerve cord

Pseudocoel

gut not lined with mesoderm (filled with hemolymph (blood-like but fluid-filled pseudocoel)

hydrostatic pressure much higher than in other invertebrates (allows locomotion and muscles to contract against it)

Digestive system

Mouth/buccal cavity lead to muscular oesophagus

digestive enzymes secreted from glands and break down food for absorption

intestine absorbs nutrients through microvilli

feeding habits: free-living and parasitic species

wastes and hydrostatic pressure

wastes go through anus (because hydrostatic pressure is already high, they just have to relax muscles and the waste shoots out)

Nervous system

neural tissue (ganglia) concentrated near oesophagus

two longitudinal nerve cords run length of body

sense organs: papillae and amphids

Digestive system  

tubular excretory ducts run length of body

excretion of wastes and osmoregulation

ducts join and open to exterior by excretory pore

Reproduction

Females larger than males

male: testis, vas deferens

female: ovary, oviduct, uterus

fertilisation is internal

egg, four juvenile stages, and adult

Growth

 worm sheds cuticle (ecdysis) between each stage

 growth in body dimensions occurs between moults

Ascaris lumbricoides: large intestinal roundworm

eggs eaten by human hatch in intestine (raw fruits and vegetables etc.)

larvae penetrate intestine, travel to bloodstream to alveoli

larvae pass up trachea, swallowed, and return to intestine (might have had previous host, maybe had internal cues to leave the intestine and then return)

 large numbers of adults cause allergic reactions or intestinal blockage

Wucheria Bancroti: filarial worm

Live in lymphatic system

Mosquito feeds on human blood, worms get sucked into the mosquito, feed on next host (human), worms get deposited into human, get into the lymph nodes and develop into sexual maturity

mate and give birth to offspring that migrate onto the bloodstream

blockage that worms cause results in buildup of fluid in the tissues (elephantiasis) damaged lymphatic system

Enterobius vermicularis: pinworm

adults live in intestine, come out at night to lay eggs

 adults often seen lurking in anal folds (causes anus to itch)

 eggs spread by contaminated fingers

Phylum Nemotomorpha: hair worms

 

long, slender, cylindrical, pseudocoelomate worms

how are hair worm similar to nematodes?

 acellular cuticle

 longitudinal muscles only

 ecdysozoic, dioecious

how are hair worms different than nematodes?

vestigial digestive system

 Absorb nutrient through body wall

hairworm lifecycle

eggs hatch in water

larvae ingested by insects (drink water)

larvae into juveniles in haemocoel of insect

juveniles cause insect to seek out and jump into water

adults emerge from insects in water, mate, and lay eggs