PHYLUM

PHYLUM

1. PORIFERA

   • SPONGES
   • Giant basket shaped sponges found in the Caribbean
   • ASCON SYCON LEUCON (GRADING)
   • No true tissues or organs. No true gut or nervous system. Cells loosely aggregated, high regenerative potential. Adults sessile, mostly marine. Asymmetrical or radially symmetrical. Body with pores, canals and chambers through which a water current flows. Chambers lined with flagellated cells (choanocytes). Possess an internal skeleton of spicules and/or organic fibres.

2. CNIDARIA

   • Mostly marine, a few freshwater species (eg. Hydra)
   • Cells well differentiated to form tissues.
   • Body wall three layered
   • Single body cavity – the coelenteron
   • Mouth generally surrounded by tentacles
   • Two main structural types – the polyp & the medusa
   • Possess nematocysts – stinging structures within cnidocyte cells
   • Nervous system is not centralised and is in the form of a network.

3. BILAERIA

   • ACELOMATES
     • Phylum Platyhelminthes
       • Bilaterally symmetric Sac-like or branched blind-ending gut Body monomeric (no segmentation, but see tapeworms) No body cavity (acoelomate); “skeleton” parenchymatous tissue No circulatory system Circular & longitudinal muscles Ciliated epidermis (free-living forms)
       • CLASS TURBERELLIA
         • REPRODUCTION: Most platyhelminths are hermaphrodites (both sexes in same individual) Eggs may be entolecithal (yolk in cytoplasm of ovum) or ectolecithal (yolk cells external to ovum) Sometimes a larva, sometimes direct development Some can reproduce asexually by fission
       • Class Trematoda (flukes) Monogenea – direct life cycles Digenea – indirect (complex) life cyles Class Cestoda (tapeworms)
         • Flatworms Simple body plan Single opening to gut No body cavity Diverse group Aquatic and terrestrial Important parasitic representatives Ciliated epidermis (free-living forms)
   • PSEUDOCELOMATE
     • Phylum Nematoda
       • Complex cuticle Complete gut No circular muscles Pseudocoel body cavity No circulatory system Usually dioecious (separate sexes)
       • Buccal cavity is variable in structure – it may be absent, present & lacking teeth, have fixed teeth or movable mandibles It is of taxonomic importance and conveys ecological information by indicating the feeding specialisation of the species
       • 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
       • Movement is characteristically serpentine No circular muscles so can not extend body – movement is by alternate contractions of dorsal & ventral longitudinal muscles working against high internal turgor pressure
       • Roundworms Complex cuticle Body cavity is a pseudocoelom Very diverse & abundant group Aquatic and terrestrial Important parasitic representatives

4. ANNELIDA

   • Class Polychaeta
     • Polychaetes are one of the major groups of marine macrofauna. Usually the main constituent of the macrofauna of marine sediments. Terrestrial oligochaetes (earthworms) feed on dead organic matter and are of enormous importance to the ecology of the soil
     • Parapodia Numerous & relatively complex chaetae Structurally diverse
     • Parapodia are a major distinguishing feature of the polychaetes They are paired lateral appendages formed by an extension of the body wall
     • Errant – free-moving e.g. Nereis spp., Nephtys spp., Phyllodoce spp. Sedentary Burrows (e.g. Arenicola marina) Tubes (tubicolous; e.g. Serpula vermicularis)
   • SUB CLASS Oligochaetes
     • Relatively few simple chaetae Often still referred to as a class Simultaneous hermaphrodites Small numbers of large eggs Protective structure (cocoon)
   • SUB CLASS HIRUNDENIA
     • No chaetae Suckers at anterior and posterior Body is single hydrostatic unit Simultaneous hermaphrodites Segmentation not seen in all organs Eggs laid in cocoons

5. MOLUSCA

   • Monoplacophora
     • ~12 species All marine & deep sea limpet-like appearance, thought to be the most primitive mollusc group
     • Aplacophora
       • ~250 species All marine Worm-like body, no shell but body covered in calcareous spicules
       • Polyplacophora
         • ‘chitons’ ~800 species All marine, mostly grazers in shallow water Shell consists of 8 overlapping plates bound together by leathery girdle
         • BIVALIA
           • Clams etc ~10,000 species Mostly marine, some freshwater, most are burrowing filter feeders Shell consists of two valves connected by a flexible ligament
             • Bivalves have completely lost the head, buccal mass and radula. The mantle cavity is much larger than in other Mollusca and has dominated bivalve evolution.
           • Gastropoda
             • Snails & slugs ~60,000 species – most diverse of the molluscan groups marine, freshwater & terrestrial, many are grazers Shell is usually spiral but may be highly modified or absent
   • One of the largest phyla of animals Include marine, freshwater and terrestrial representatives Unsegmented body includes a calcareous shell, mantle, visceral mass, foot and head Mantle secretes the 3 layered shell Mantle cavity is a chamber enclosed within the shell and houses excretory openings and the gills which are modified for filter feeding in some groups The radula is a specialised feeding structure unique to the molluscs Possess well developed digestive, circulatory, nervous, reproductive and excretory organ systems