L4 - Pseudo and Coelomates

Question 2

What is a Pseudocoelomate (blastocoelomate)?

Answer 2

Fluid filled body cavity; partially lined with tissue derived from the mesoderm, hence is not bounded by a peritoneum.
It consists of Body covering (from ectoderm), Muscle layer (from mesoderm), Pseudocoelom (fluid-filled space), Digestive tract (from endoderm).

Question 3

What group are Pseudocoelomate (blastocoelomate) and what are their associated features?

Answer 3

This group is an assemblage of 9 phyla, grouped into the blasto/pseudocoelomates
As a group, they are:
- pseudocoelomates
- covered by a cuticle
- no organs for gas exchange, internal transport or excretion
- poorly cephalised
- digestive tract has mouth and anus separated
- most are very small; many are microscopic and make up a large part of the interstitial fauna

Question 4

Pseudocoloelomate - What is the phylum Nematoda?

Answer 4

Extremely abundant in interstitial spaces of marine & freshwater sediments and soil water. Over 1 million species, can be free living, parasitic, predatory - there is massive diversity e.g. 4-5 million per square meter of marine sediment. Significant parasites of humans, plants, animals ; economically important. Long cylindrical & tapered at both ends with a thick, tough cuticle. Plays an important role in decomposition and nutrient cycling. Can be very difficult to identify species. Feed on animal fluids, plant juices, bacteria, fungi - some use lassos to catch prey. Usually off-white or grey in colour.

Question 5

Pseudocoloelomate - What are the parasitic species (in humans) in the phylum Nematoda?

Answer 5

Hookworms, Ascarids, Filarial nematodes

Question 6

Pseudocoloelomate - What are the parasitic species (in humans) in the phylum Nematoda - Hookworms?

Answer 6

Hookworms - e.g. Trichuris spp, Ancylostoma, Necator. Juvenile worms penetrate skin of feet, burrow into bloodstream, carried up to lungs, migrate to pharynx, swallowed and into intestine to mature to adult stage.

Question 7

Pseudocoloelomate - What are the parasitic species (in humans) in the phylum Nematoda - Ascarids?

Answer 7

Ascarids -e.g. Ascaris lumbricoides. Eggs ingested through faecal contamination. Can cause malnutrition and intestinal blockage.

Question 8

Pseudocoloelomate - What are the parasitic species (in humans) in the phylum Nematoda - Filarial nematodes?

Answer 8

Filarial nematodes, e.g. Brugia malayi, Wucheria bancroftii, Loa Loa. Vector borne, cause blockages of the lymphatic system ; elephantiasis. Elephantiasis is caused by lymphatic filariasis

Question 9

Pseudocoloelomate - What is the phylum Nematoda - How can parasitism be exploited?

Answer 9

Several thousands of species nematodes are entomopathogenic ; they kill insects and molluscs. Including pestiferous species

Question 10

Pseudocoloelomate - What is the phylum Rotifera?

Answer 10

Mostly freshwater including in films around soil. Can be very abundant. Range in size from 0.1mm to 1mm. Only contain about 1000 cells. Have trunk, often with a spiny girdle called a lorica, and a posterior foot with adhesive glands. Anterior end has a crown of cilia (called a corona) often in two discs. Circular beat of cilia look like turning wheels, hence their name of ‘wheel bearer’. Swim using cilia or crawl like a leech. Feed on protozoans and other rotifers. Only capable of sexual reproduction, but parthenogenesis (a form of asexual reproduction where growth and development of embryos occur without fertilisation) possible under favourable conditions.

Question 11

Pseudocoloelomate - What is the phylum Gastrotricha?

Answer 11

Body is bottle shaped and ventral surface is ciliated (stomach hairs). Marine and freshwater. Many interstitial, some amongst debris, algae and in soil water. Glide on surfaces propelled by their ventral cilia. Feed on bacteria, small protozoa and organic detritus. Sexually mature 3 days post hatching, lifespan is <40 days

Question 12

Pseudocoloelomate - What is the phylum Nematomorpha?

Answer 12

Mostly freshwater, long hair like bodies up to 40cm long. Closely related to nematodes. Juvenile parasitic in arthropods, adult non-feeding, free-living in water or damp soil

Question 13

Pseudocoloelomate - What is the phylum Acanthocephala?

Answer 13

Endoparasites of marine, freshwater and terrestrial vertebrate digestive system. Body <5cm with spiny proboscis. Arthropod intermediate host.

Question 14

Pseudocoloelomate - What is the phylum Kinorhyncha?

Answer 14

Anterior end of the body is spiny. Microscopic animals that burrow through marine sediments.

Question 15

Pseudocoloelomate - What is the phylum Loricifera?

Answer 15

1st identified in 1983, interstitial in marine sediments, abdomen has a cuticular girdle called a lorica, hence their name. 0.25mm long spiny anterior end

Question 16

Pseudocoloelomate - What is the phylum Priapulida?

Answer 16

Unsegmented wormlike marine animals. Burrow in sand and mud, 1mm to 20cm in size. Anterior part of the body forms an introvert which can be pushed in & out. Teeth present at the end of the introverted end, used to capture prey then pull them inside. Possess small surface spines and papillae, can be fairly common in some sediments, e.g. Priapulus cordatus

Question 17

Pseudocoloelomate - What is the phylum Entoprocta?

Answer 17

Previously grouped with the coelomate lophophorates. Unlike bryozoa, the anus is inside the ring of tentacles, hence their name. All marine, apart for 1 spp. Attached to rocks, shells etc. Grow from a creeping stolon, or commensalistic with sponges, polychaetes and bryozoans. Superficially similar to bryozoans, some solitary, most colonial. All less than 5mm in length

Question 18

What is a Coelomate (eucoelomate)?

Answer 18

Fluid filled body cavity completely lined with tissue derived from mesoderm. E.g. Earthworm. Body covering (from ectoderm), muscle layer (from mesoderm), coelom (fluid-filled space), digestive tract (from endoderm), tissue layer suspending organs (from mesoderm),

Question 19

What is the tissue lining the coelomate (eucoelomate) consist of?

Answer 19

Is a layer of epithelial cells called peritoneum. Internal organs may bulge partway into the coelom, but always lie behind the peritoneum, and are called retroperitoneal. Organs may extend so far into the coelom that they become suspended by a fold of peritoneum which is then called a mesentery.

Question 20

What are the three evolutionary lines of coelomate phyla based on their embryology?

Answer 20

Protostomes, Deuterostomes, Lophophorates

Question 21

The three evolutionary lines of coelomate phyla based on their embryology - Protostomes?

Answer 21

Molluscans, annelids, arthropods and some minor related phyla are collectively termed as Protostomes

Question 22

The three evolutionary lines of coelomate phyla based on their embryology - Deuterostomes?

Answer 22

Echinoderms, hemichordates, chordates and some minor related phyla are collectively termed Deuterostomes

Question 23

The three evolutionary lines of coelomate phyla based on their embryology - Lophophorates?

Answer 23

3rd group. Phyla - Bryozoa, Phoronida, Brachiopoda. Fit intermediately between proto and deuterostomes

Question 24

What caused the separation?

Answer 24

Based on embryology. Protostomes are said to be more primitive of the groups - not a function of their ability to survive, but more to do with when they evolved.

Question 25

Coelomate (eucoelomate) - Protostomes - Phyla Annelida?

Answer 25

15,000 spp, segmented worms, elongated body showing metameric segmentation. Segments are : in a linear series, demarcated externally by grooves, internally separated by septa. Each internal system shows segmentation, each segment contains : nervous system, excretory system, reproductive system. Coelom surrounded by longitudinal and circular muscle bands, used in hydrostatic skeleton. 3 classes : polychaetes, clitellata and sipuncula

Question 26

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class Polychaeta?

Answer 26

>5,300 spp : bristle worms, Prostomium carries sense organs, tactile antennae, chemosensory palps, eyes. Peristomeum carries tentacles/cirri, and ventral mouth on evertable probiscis. Each segment has a pair of biramous parapodia divided into - dorsal notopod, ventral neuropod. Have internal support from acicula.

Question 27

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class Polychaeta? What are more details of Polychaetes?

Answer 27

They are extremely variable in both form and lifestyle. Some taxa swim among the plankton or above the abyssal plain. Most burrow or build tubes in the sediment. Some live as commensals of other animals : a few are parasitic. There are 2 divisions of polychaetes based on mobility. Mobile forms (Errant) tend to have well-developed sense organs and jaws, sedentary forms lack them but may have specialised gills or tentacles used for respiration and deposit or filter feeding, also known as burrow or tube Polychaetes.

Question 28

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class Polychaeta - Subclass Echiura?

Answer 28

140 spp ; drab, unsegmented marine worms that live in crevices and sediments. Cylindrical body ; they are annelids that have secondarily lost their segmentation. Flat, ribbon-like proboscis, highly mobile and extendable. Eat sediment.

Question 29

Coelomate (eucoelomate) - Protostomes - Phyla - Annelida - Class - Polychaeta - Family- Siboglinidae?

Answer 29

Fewer than 200 spp ; tubeworms, beardworms and vestiminiferids marine, deep water, sessile, upright, tube dwelling worms. Lack digestive tract as adults ; posterior part of body (opisthsoma) is segmented and bears setae. 10-40cm long ; less than 1mm wide = long and skinny. Have a 'beard' of tentacles for absorbing nutrients from water

Question 30

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class - Polychaeta - Family - Siboglinidae? pt2

Answer 30

Up to 2m long and 2.5cm - 4cm wide. Most nutrients come from chemosynthetic bacteria found in a modified 'stomach' (trophosome) which oxidises hydrogen sulphide ; use resultant energy to fix carbon. Hydrothermal vents, e.g. Riftia

Question 31

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class - Clitellata - Order - Oligochaeta?

Answer 31

3,100 spp, earthworms and a few aquatic species. Reduced head, no obvious appendages, all hermaphrodite, no gills. Develop a clitellum = a thickened glandular section of the body wall that secretes a viscid sac in which the eggs are deposited. Diet of decomposing organic matter. Marine spp < 0.5mm, earthworms up to 3m. No parapodia, most have few small setae

Question 32

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class - Clitellata - Order - Hirudinea?

Answer 32

500 spp ; leeches. Mostly ectoparasites. Anterior and posterior suckers. All have 33 segments. Coelom restricted to 5 anterior segments. Feed using either : probiscus to penetrate host skin, sucking pharynx with 3 triangular jaws. Secrete various compounds in their saliva, including : anaesthetic pre-incision, anticoagulants, inc. hirudin, post-incision

Question 33

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class - Clitellata - Order - Branchiobdella?

Answer 33

An order of freshwater worms in the clitellata. Superficially similar to leeches. Ectosymbionts or ectoparasites on freshwater crustaceans. Distributed in the northern hemisphere, with a holarctic distribution in east asia, europe, with a hotspot of species diversity in North and Central America

Question 34

Coelomate (eucoelomate) - Protostomes - Phyla Annelida - Class - Sipuncula?

Answer 34

320 spp, peanut worms or sipunculids. Drab, uncoloured marine worms, 2mm - 70cm ; most around 10cm. Live in soft sediments, cracks, old shells. Possess a retractable introvert at the anterior, bears the mouth. Eats sediments and deposits, uses the introvert to collect deposits. E.g. Golfingia, Phascolion, Phascolosoma.