Smaller Ecdysozoans - General Zoology - Lecture Slides, Slides of Zoology

Download Smaller Ecdysozoans - General Zoology - Lecture Slides and more Slides Zoology in PDF only on Docsity! Smaller Ecdysozoans Chapter 18 Docsity.com Ecdysozoans  Many protostomes possess a cuticle.  Non-living outer layer secreted by epidermis.  Cuticle restricts growth and must be molted via ecdysis.  Regulation of molting achieved by the hormone ecdysone.  Members of Ecdysozoa molt cuticle as they grow. Docsity.com Phylum Nematoda: Roundworms  About 25,000 species of nematodes are described, but as many as half a million may exist.  Many prefer the name Nemata for this phylum.  Found in virtually all habitats in all biomes.  Topsoil may contain billions per acre. Docsity.com Phylum Nematoda: Roundworms  Free-living nematodes feed on bacteria, yeasts, fungal hyphae, and algae.  Predatory nematodes eat rotifers, tardigrades, small annelids, and other nematodes.  Important as food for mites, insects, larvae, and fungi. Docsity.com Phylum Nematoda: Roundworms  Caenorhabditis elegans is an important model for studies of genomics and cell development and differentiation. Docsity.com Phylum Nematoda  The cylindrical bodies of nematodes are covered by a tough coat called a cuticle. Docsity.com Phylum Nematoda  Complete digestive system.  Circulatory and respiratory systems are lacking.  Ring of nerve tissue and ganglia around the pharynx lead to dorsal and ventral nerve cords. Docsity.com Phylum Nematoda  Nematodes have separate sexes.  Dioecious, females are larger.  Fertilization is internal.  Eggs are stored in uterus until deposited.  Cuticle is shed between each of four juvenile stages. Docsity.com Phylum Nematomorpha  Phylum Nematomorpha, the horsehair worms, are free living as adults, and parasites in arthropods as juveniles.  Currently placed as the sister taxon to nematodes  About 320 species are known.  Occur worldwide  Pseudocoelomate  Triploblastic Docsity.com Phylum Nematomorpha  Adults utilize stored nutrients.  Recent studies reveal that they can absorb organic molecules through vestigial gut and body wall.  Circulatory, respiratory and excretory systems are absent.  Nematomorphs are dioecious.  Females discharge eggs into water in long strings. Docsity.com Phylum Nematomorpha  Juveniles may encyst on vegetation and are eaten by an arthropod such as a grasshopper.  Larval stages have hooks that may be used to bore into a host.  May also cause infection via drinking water.  Larvae encyst within host.  Marine nematomorphs infect hermit crabs and other crabs. Docsity.com Phylum Kinorhyncha  Spines (scalids) function in locomotion, chemoreception, and mechanoreception.  Retractile head has a circle of spines and a retractile proboscis (introvert).  Body wall made of a cuticle and syncytial epidermis. Docsity.com Phylum Priapulida  The phylum Priapulida contains 16 species of marine worms that occur in colder waters.  Found from intertidal zones to deep ocean floors, several thousand meters deep.  Some are tube dwellers and feed on detritus. Docsity.com Phylum Priapulida  Cylindrical bodies under 15 cm long.  Burrow by body contractions and orient mouth at the surface.  Retractable introvert has papillae and rows of curved spines to sample and capture prey.  Chitinous cuticle covers body and is molted regularly.  Sexes are separate. Docsity.com Phylum Onychophora  About 70 living species of “velvet worms” in the phylum Onychophora.  1.4 to 15 cm in length.  Limited to moist, leafy rain forest habitat in tropical and subtropical regions.  Changed little over 500 million years.  Fossil Aysheaia similar to modern forms.  Share traits with annelids and arthropods and were considered a “missing link”.  Most are predaceous, some live in termite nests. Docsity.com Phylum Onychophora  No external segmentation except for paired appendages.  Skin is soft - cuticle contains protein and chitin but does not harden as in arthropods.  Body covered with tiny tubercles bearing sensory bristles.  Minute scales on tubercles impart an iridescent and velvety appearance.  Head has one pair of large antennae and an annelid-like eye at base. Docsity.com Phylum Onychophora  14 to 43 pairs of unjointed legs.  Legs move by waves of body contractions.  Slime glands on each side of body cavity open on oral papillae.  Mouth leads to a straight digestive tract.  Each segment contains a pair of nephridia, each containing a vesicle, ciliated funnel, and duct. Docsity.com Phylum Onychophora With exception of one parthenogenetic species, all are dioecious with paired reproductive organs.  Males deposit spermatophores on back of female.  White blood cells dissolve the skin and sperm migrate to ovaries. May be oviparous, ovoviviparous, or viviparous. Docsity.com Phylum Tardigrada  Tardigrades, or water bears, are less than a millimeter in length.  Freshwater or marine  Live in spaces between sand grains. Docsity.com Phylum Tardigrada  Trunk bears four pairs of short, stubby, unjointed legs, each with four to eight claws.  Body covered by non-chitinous cuticle that is molted four or more times during lifetime.  Mouth leads to a muscular pharynx adapted for sucking.  Two stylets protrude to pierce integument of nematodes or walls of plant cells and allow them to suck juices. Docsity.com Phylum Tardigrada  Sexes are separate.  In parthenogenetic freshwater and moss-dwelling species, males are unknown.  Egg-laying, like defecation, occurs at molting.  Eggs may be highly ornate. Docsity.com Phylum Tardigrada  Tardigrades can enter a state called cryptobiosis, where metabolism is imperceptible.  Tardigrades can dehydrate from 85% water to only 3% water.  In this state they can resist extreme temperatures, ionizing radiation, oxygen deficiency, etc. for years.  When water is available, they become metabolically active again. Docsity.com Phylogeny  Evolutionary relationships among ecdysozoans are not well-understood. Members of this clade do not share a common cleavage pattern:  Nematodes and nematomorphs - cleavage is unique, not spiral or radial.  Cleavage in kinorhynchs, lorificiferans, and tardigrades has yet to be studied.  Priapulid cleavage is nearly radial. Docsity.com Phylogeny  Sequence analysis supports placement of Onychophora in clade Panarthropoda.  Tardigrades and arthropods also share arthropod-type setae and muscles inserted on the cuticle. Docsity.com Adaptive Diversification  Nematodes show impressive adaptation – they are found in almost every habitat available to animals.  Body structure is plastic enough to allow adaptation.  Life cycle ranges from simple to complex.  Have been known to survive in suboptimal conditions. Docsity.com