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Biology 456 – Chapter 15: Gnathiferans and Smaller Lophotrochozoans Latest Reviewed Study, Study notes of Biology

Rasmussen College - FloridaBiology

Biology 456 – Chapter 15: Gnathiferans and Smaller Lophotrochozoans Latest Reviewed Study Notes: This document provides revised study notes for Biology 456, Chapter 15, focusing on gnathiferans and smaller lophotrochozoans. It covers key zoological concepts including taxonomy, evolutionary relationships, body organization, feeding adaptations, reproductive strategies, and distinguishing anatomical features of these invertebrate groups. Special emphasis is placed on their ecological roles, developmental patterns, and significance in understanding animal diversity and evolution. The material is designed to support structured revision and strengthen understanding of invertebrate zoology concepts.

Typology: Study notes

2025/2026

Available from 06/18/2026

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BIOLOGY 456 CHAPTER 15 GNATHIFERANS AND SMALLER
LOPHOTROCHOZOANS STUDY NOTES LATEST REVIEW
Phylum Gnathostomulida
• From the Greek roots gnathos (mouth) and stoma (opening).
• Small, delicate wormlike animals.
• Live in fine sediments near coastlines, but can tolerate deep water.
• Can glide and swim.
• Have monociliated epidermal cells.
• Acoelomate, no circulatory system
• Jaws that lead to a simple, blind gut
• Internal, cross fertilization
Jaw worms….
Phylum Micrognathozoa
• Monotypic, Limnognathia maerski
• Discovered in 1994, described in 2000!
• Three pairs of jaws
• Only female reproductive organs, poorly understood
• Move by cilia, unique ventral ciliary pad that produces glue
• Live in sediment
Phylum Rotifera
• From the Latin roots rota (wheel) and fera (bearing)
• Unique organ, the corona, or wheel organ
• Lots of variation in life history traits
• Some can desiccate and live for years
External features of rotifers
• Ciliated corona, body nonciliated
– Mouth on corona on midventral side
• Cuticle – fibrous layer sometimes forming a caselike lorica
• Foot is narrow and has one to four toes
– Contains pedal glands that secrete adhesive
• Move by creeping, swimming with the coronal cilia, or both
Internal features of rotifers
• Synctial epidermis – underneath cuticle
• Large, fluid filled pseudocoel
• Digestive system complete, mastax with hard jaws called trophi, have salivary and gastric
glands
• Protonephridial tubules with flame cells that empty into a bladder, empty into cloaca
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Download Biology 456 – Chapter 15: Gnathiferans and Smaller Lophotrochozoans Latest Reviewed Study and more Study notes Biology in PDF only on Docsity!

BIOLOGY 456 CHAPTER 15 GNATHIFERANS AND SMALLER

LOPHOTROCHOZOANS STUDY NOTES LATEST REVIEW

Phylum Gnathostomulida

  • From the Greek roots gnathos (mouth) and stoma (opening).
  • Small, delicate wormlike animals.
  • Live in fine sediments near coastlines, but can tolerate deep water.
  • Can glide and swim.
  • Have monociliated epidermal cells.
  • Acoelomate, no circulatory system
  • Jaws that lead to a simple, blind gut
  • Internal, cross fertilization Jaw worms…. Phylum Micrognathozoa
  • Monotypic, Limnognathia maerski
  • Discovered in 1994, described in 2000!
  • Three pairs of jaws
  • Only female reproductive organs, poorly understood
  • Move by cilia, unique ventral ciliary pad that produces glue
  • Live in sediment Phylum Rotifera
  • From the Latin roots rota (wheel) and fera (bearing)
  • Unique organ, the corona, or wheel organ
  • Lots of variation in life history traits
  • Some can desiccate and live for years External features of rotifers
  • Ciliated corona, body nonciliated
  • Mouth on corona on midventral side
  • Cuticle – fibrous layer sometimes forming a caselike lorica
  • Foot is narrow and has one to four toes
  • Contains pedal glands that secrete adhesive
  • Move by creeping, swimming with the coronal cilia, or both Internal features of rotifers
  • Synctial epidermis – underneath cuticle
  • Large, fluid filled pseudocoel
  • Digestive system complete, mastax with hard jaws called trophi, have salivary and gastric glands
  • Protonephridial tubules with flame cells that empty into a bladder, empty into cloaca
  • Bilobed brain, paired eyespots, sensory bristles, ciliated pits, dorsal antennae Rotifer reproduction
  • Rotifers dioecious, males unknown in class Bdelloidea. In class Monogonata they occur only a few weeks of the year.
  • High levels of reproductive variation
  • Sexual and asexual
  • Mictic eggs: fertilized to form a diploid embryo
  • Amictic eggs: already diploid, develop parthenogenetically
  • Read about rotifer reproduction in your book. Rotifer taxonomy
  • Class Seisonidea – Marine, elongate, cornoa vestigial, sexes similar
  • Class Bdelloidea: swimming or creeping, anterior end retractile, corona with two trochal disks, males unknown, parthenogenetic
  • Class Monogonata: swimming or sessile, single gemovitellarium, males reduced in size, three types of eggs (amictic, mictic, dormant) Phylum Acanthocephala
  • From the Greek roots akantha (spine or thorn) and kephale (head).
  • Cylindrical, invaginable, proboscis with rows of spines for attachment in the intestine of host.
  • Cosmopolitan, lots of species, all parasitic Acanthocephalan form and function
  • Body somewhat flattened, body wall synctial, lots of little trenches to increase surface area (part of the lacunar system), most substances cross body wall by diffusion
  • Proboscis can be retracted inside body
  • Very reduced nervous system and sense organs, no digestive tract
  • Dioecious
  • Larvae called acanthors develop into juveniles called cystacanths in insect. Ingested by final host. Can cause perforation of intestine! Phylum Cycliophora
  • Discovered in 1995.
  • Mouthparts of decapod crustaceans
  • Eat bacteria or bits of dropped food
  • Acoelomate with a u-shaped, complete gut
  • Sexual and asexual phases, chordoid larvae which can swim to a new host

Polyzoa and Kryptrochozoa – Detailed Notes

  • A crown of ciliated tentacles
  • Used for: o feeding o respiration

Structure

  • Tentacles are arranged around the mouth
  • Interior cavity is part of the coelom
  • Filled with coelomic fluid

Function

  1. Cilia create water currents.
  2. Food particles are captured.
  3. Gas exchange occurs across thin walls.

Behavior

  • Lophophore can: o extend during feeding o retract for protection.

4. Trochophore Larva

Definition

A trochophore larva is:

  • A free-swimming larval stage
  • Found in many lophotrochozoans.

Key Structure

Prototroch

  • Ring of large ciliated cells
  • Located in front of the mouth
  • Used for: o locomotion o sometimes feeding.

Trochophore found in:

  • Molluscs
  • Annelids
  • Sipunculans

5. Polyzoa

Definition

Polyzoa is a clade including:

  1. Cycliophora
  2. Entoprocta
  3. Ectoprocta (Bryozoa) These animals share:
  • ciliated tentacles
  • similar feeding structures.

6. Phylum Cycliophora

Discovery

  • Discovered 1995
  • First species: Symbion pandora

Habitat

  • Live on mouthparts of lobsters
  • Specifically: o Norway lobster ( Nephrops norvegicus )

Body Size

  • Extremely tiny
  • ~0.35 mm long

Reproduction:

  1. male larva produces secondary males
  2. secondary male fertilizes female.

Chordoid Larva

  • develops inside mother
  • consumes mother
  • swims away to new lobster host
  • forms new feeding individual.

7. Phylum Entoprocta

General Characteristics

  • ~150 species
  • tiny sessile animals
  • usually microscopic

Habitat

Mostly marine:

  • coastal waters
  • brackish waters One freshwater species:
  • Urnatella gracilis

Body Structure

Body consists of:

- Calyx o Cup-shaped body containing organs. - Stalk

o Attaches animal to substrate.

- Tentacle Crown - 8 – 30 ciliated tentacles - used for feeding. Important difference from ectoprocts:

  • mouth AND anus inside tentacle ring Feeding Entoprocts are ciliary suspension feeders. Process:
  1. water flows between tentacles
  2. cilia capture particles
  3. particles move to mouth. Food types:
  • protozoa
  • diatoms
  • detritus. Digestive System
  • U-shaped gut
  • mouth and anus inside tentacle crown. **Other Systems
  • Nervous system**

o nerve ganglion near stomach.

- Excretory system

o flame bulb protonephridia

- Circulation

  • ~4500 living species
  • mostly marine
  • some freshwater. Common name: moss animals Colonial Animals Ectoprocts live in colonies.

Each individual is called a: Zooid

Zooids live inside a protective chamber: Zoecium

- Secreted exoskeleton made of:

  • chitin
  • calcium carbonate
  • gelatinous material. Colony Forms Colonies may be:
  • encrusting
  • branching
  • shrubby
  • fuzzy
  • tree-like. Body Structure Zooid has two parts:

Polypide

Living portion containing:

  • lophophore
  • digestive tract
  • muscles
  • nerves.

Cystid

Body wall plus exoskeleton. Feeding Zooids extend lophophore to feed. Process:

  1. tentacles form funnel
  2. cilia draw water inward
  3. food captured by cilia
  4. food moves to mouth. Digestive System
  • U-shaped digestive tract
  • digestion begins in stomach. Special Zooids Some colonies contain modified zooids.

Avicularia

  • bird-beak shaped
  • snap at predators.

Vibracula

  • long bristle
  • sweep debris away.

Reason:

  • larval forms have modified or hidden trochophore features.

10. Clade Brachiozoa

Includes:

  1. Brachiopods
  2. Phoronids Shared feature:
  • lophophore

11. Phylum Brachiopoda

Common name: Lamp shells

Evolution

  • extremely abundant in Paleozoic era
  • now reduced to ~325 species. Example living fossil: Lingula

Body Structure

Brachiopods have:

  • two shell valves
  • dorsal valve
  • ventral valve. Important difference from clams: Brachiopods Bivalves dorsal + ventral shells left + right shells Attachment Many attach using: pedicel A fleshy stalk extending through shell. Feeding Use lophophore. Steps:
  1. water flows between shell valves
  2. cilia create feeding currents
  3. tentacles capture particles
  4. food moves to mouth. Food types:
  • detritus
  • algae. Internal Systems

Circulatory system

  • open system
  • contractile heart.

Excretory system

Lophophore Shape: horseshoe-shaped Tentacles:

  • hollow
  • ciliated. Feeding Cilia create water currents. Food types:
  • plankton
  • detritus. Food captured in mucus → transported to mouth. Circulatory System
  • closed system
  • blood contains hemoglobin. Development Larval stage: actinotroch larva
  • free swimming
  • later settles and forms tube.

13. Phylum Nemertea (Ribbon Worms)

Species

~1000 species.

Habitat

Mostly marine.

Body Structure

Long ribbon-like worms. Some extremely long: Lineus longissimus

  • up to 60 meters long.

Unique Feature

Eversible proboscis

  • located in cavity called rhynchocoel.

Feeding Mechanism

  1. proboscis rapidly everts
  2. wraps around prey
  3. stabs prey with stylet
  4. injects toxin
  5. prey swallowed whole. Some toxins include: tetrodotoxin (same toxin in pufferfish).

14. Key Characteristics of Nemertea

  1. Eversible proboscis
  2. Bilateral symmetry
  3. Triploblastic
  4. Complete digestive tract
  5. Closed circulatory system
  6. Flame cell excretory system
  7. Ciliated epidermis
  8. Mostly free-living predators.

15. Evolutionary Issues

Two major debates:

1. Origin of Lophophore

Possibilities:

  • evolved twice independently
  • evolved once in common ancestor.

2. Nemertean Body Cavity

Rhynchocoel may be:

  • a true coelom
  • or a modified structure unrelated to coelom. Still debated.

16. Adaptive Diversification

Example: Ectoprocts Colonies vary widely:

  • encrusting
  • branching
  • calcified
  • soft. This modular design allows flexible evolutionary adaptation.