Invertebrate Animals: Lophophorates & Syndermata

### Lophophorates

• Lophophorates have a lophophore, a crown of ciliated tentacles used for feeding.
• Two phyla belong to the lophophorates: Ectoprocta and Brachiopoda.
• Ectoprocta consists of about 4,500 species.
• Brachiopoda consists of about 335 species.

Rotifers and Acanthocephalans

• Rotifers and Acanthocephalans are classified under the phylum Syndermata.
• Syndermata contains about 2,900 species.

Rotifers

• Rotifers are tiny animals inhabiting freshwater, marine, and damp soil environments.
• They are smaller than many protists but are truly multicellular and have specialized organ systems.
• They are pseudocoelomates and have a gut with a mouth and anus
• Rotifers reproduce by parthenogenesis, where females produce offspring from unfertilized eggs.
• Some species lack males entirely.

Gastrotricha

• Gastrotricha are also known as "hairy-belly" worms.
• They live on the bottom of oceans or lakes and feed on decayed organic matter.

Cycliophora

• Cycliophora was discovered in 1995.
• This phylum lives on the mouthparts of lobsters.

Nemertea

• Nemertea lack a coelom, but have a gut.
• They have blood in vessels, but no heart.
• They are known as ribbon worms.

Mollusca

• Mollusca includes snails and slugs, oysters and clams, and octopuses and squids.
• Most molluscs are marine, although some inhabit freshwater and some snails and slugs are terrestrial.
• They are soft-bodied animals, but most are protected by a calcium carbonate shell.

Mollusca Reproduction

• Most molluscs have separate sexes with gonads located in the visceral mass, but many snails are hermaphrodites.
• The life cycle of many molluscs includes a ciliated larval stage called a trochophore.

Mollusca Classes

• Polyplacophora (chitons)
• Gastropoda (snails and slugs)
• Bivalvia (clams, oysters, and other bivalves)
• Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)

Chitons

• Chitons are oval-shaped marine animals encased in an armor of eight dorsal plates.
• They use their foot like a suction cup to grip rocks and their radula to scrape algae off the rock surface.

Gastropods

• Gastropods account for roughly three-quarters of all living molluscs.
• Most are marine, but many freshwater and terrestrial species also exist.
• They move slowly by a rippling motion of the foot or by cilia.

Bivalves

• Bivalves are aquatic and include many species of clams, oysters, mussels, and scallops.
• They have a shell divided into two halves drawn together by adductor muscles.
• Some bivalves have eyes and sensory tentacles along the edge of their mantle.

Cephalopods

• Cephalopods are active marine predators with beak-like jaws surrounded by tentacles.
• They immobilize prey with poison found in their saliva.
• Their foot is modified into a muscular excurrent siphon and part of the tentacles.
• Most species have a reduced and internal or missing shell, with the exception of chambered nautiluses.

Cephalopod Characteristics

• They have a closed circulatory system, well-developed sense organs, and a complex brain.
• Some Cephalopods are intelligent and can learn.
• Shelled cephalopods, called ammonites, were common but went extinct at the end of the Cretaceous period, 65.5 million years ago.

Ecdysozoans

• Ecdysozoans are the most species-rich animal group.
• Ecdysozoans are covered by a tough coat called a cuticle.
• The cuticle is shed or molted through a process called ecdysis.
• The two largest phyla are nematodes and arthropods.

Loricifera

• Loricifera are tiny animals that live buried in sediment, eating bacteria.
• The name "lorica" means "corset" referring to their hard outer covering.

Priapula

• Priapulans burrow in the sea floor sediments and have been around since the Cambrian period.
• They are named after the Greek God of fertility.

Onychophora

• Onychophora are also called “velvet worms”.
• They originated in the sea but now live only in humid forests.
• They have no known aquatic species.

Tardigrada

• Tardigrada are also known as “water bears.”
• They are very small, most being less than 0.5 mm in size.
• They can survive freezing and complete desiccation.

Nematodes (roundworms)

• Nematodes are found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals.
• They have an alimentary canal but lack a circulatory system.
• Their body wall muscles are all longitudinal, and their contraction produces a thrashing motion.

Nematode Examples

• Some nematode species are important parasites of plants and animals, but many are free-living in moist soil and aquatic habitats.
• Trichinella spiralis is a parasite that can be acquired from undercooked pork.
• Caenorhabditis elegans is a soil nematode that has become a model research organism.

Arthropoda

• Zoologists estimate that there are about a billion billion (10^18) arthropods living on Earth.
• More than 1 million species have been described, and two out of every three known species of animals are arthropods.
• Members of the phylum Arthropoda are found in nearly all habitats of the biosphere.

Arthropod Origins

• The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages.
• This body plan dates to the Cambrian explosion (535–525 million years ago).
• Early arthropods show little variation from segment to segment.
• Arthropod evolution shows fusion and specialization of segments.

Chordata

• Phylum Chordata consists of two basal groups of invertebrates, as well as vertebrates.
• Chordates are bilaterally symmetrical coelomates with segmented bodies and a notochord.
• Chordates did not evolve from echinoderms but have evolved separately for at least 500 million years.

Echinoderms

• Sea stars and most other echinoderms are slow-moving or sessile marine animals.
• A thin epidermis covers an endoskeleton of hard calcareous plates.
• They have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion and feeding.
• Males and females are usually separate, and sexual reproduction is external.

Echinoderm Characteristics

• Most adult echinoderms appear to have radial symmetry with multiples of five.
• Echinoderm larvae have bilateral symmetry.
• Living echinoderms are divided into five clades:
  • Asteroidea (sea stars and sea daisies)
  • Ophiuroidea (brittle stars)
  • Echinoidea (sea urchins and sand dollars)
  • Crinoidea (sea lilies and feather stars)
  • Holothuroidea (sea cucumbers)

Asteroidea

• Sea stars have multiple arms radiating from a central disk.
• The undersurface of each arm bears tube feet, which grip a substrate with adhesive chemicals.
• They feed on bivalves by prying them open with their tube feet, everting their stomach, and digesting their prey externally with digestive enzymes.
• They can regrow lost arms.

Ophiuroidea

• Brittle stars have a distinct central disk and long, flexible arms that they use for movement.
• Some species are suspension feeders, while others are predators or scavengers.

Echinoidea

• Sea urchins and sand dollars have no arms but have five rows of tube feet.
• Sea urchins use their spines for locomotion and protection.
• They feed on seaweed using a jaw-like structure on their underside.
• Sea urchins are roughly symmetrical while sand dollars are flat disks.

Crinoidea

• Sea lilies live attached to the substrate by a stalk.
• Feather stars can crawl using long, flexible arms.
• Both use their arms in suspension feeding.
• Crinoidea are the most basal echinoderms, and have changed little over the course of evolution.

Holothuroidea

• Sea cucumbers lack spines, have a very reduced endoskeleton, and do not look much like other echinoderms.
• They have five rows of tube feet, some of which are developed as feeding tentacles.
• Sea cucumbers have lost the 5-part symmetry as adults that most echinoderms have.
• They are a sister clade to Echinoidia.

Test your knowledge on various invertebrate animals, including Lophophorates, Rotifers, and Acanthocephalans. This quiz covers key characteristics, classifications, and reproductive methods of these fascinating organisms. Discover the diverse life forms that exist in aquatic and damp environments.