Lecture 10: Protostomes, Gnathiferans, Entoprocta

Protostome Characteristics

• legacy name, meaning “mouth first”

  • as conventionally, the blastopore forms the mouth first then anus

  • however, we now know this is not true for all protostomes

• circumesophageal brain

• ventral nerve cords

Protostomia Division

• Spiralia

  • Gnathifera

  • Platytrochozoa

• Ecdysozoa

  • Scalidophora

  • Nematoida

  • Panarthropoda

Ecdysozoa Characteristics

• molting of the cuticle during the life cycle

• trilayered cuticle

• formation of the epicuticle from the tips of epidermal microvilli

• lack of locomotory cilia

• terminal position of the mouth

Spiralia Characteristics

• spiral cleavage

  • this is secondarily lost in some

• trochophore larva

  • seen in some, not all

Gnathiferan Phyla (given)

• Chaetognatha

• Gnathostomulida

• Rotifera

• Micrognathozoa

Chaetognatha Characteristics

• arrow worms

  • meaning bristle jaw

• important component of the food web as predators of zooplankton

• both mouth and anus forming secondarily subsequent to closure of the blastopore

Chaetognatha Body Plan

• elongate 3 part body

  • head

  • trunk

  • tail

• single head coelom, paired trunk and tail coelom

• cuticle on ventral side of head

• lateral and caudal fins

• striated longitudinal muscles, and weak circular musculature

Chaetognatha Digestive System

• complete gut, ventral anus

• mouth surrouned by sets of long moveable grasping spines and short teeth used in prey capture

Chaetognatha Respiratory System

• hemal system

  • restricted to trunk

• no discrete gas exchange

Chaetognatha Excretory System

No

Chaetognatha Reproduction

• hermaphroditic

• internal fertilization

• direct development

Chaetognatha Nervous System

• centralized nervous system

• ciliary receptors

• corona

• ocelli

Rotifera Characteristics

• meaning wheel bearers

• complex and variety of forms, which is indicative of their lifestyle

  • free-swimming, sessile, colonial, parasitic, etc.

• important components in FW and brackish waters

• cryptobiosis present in many species

  • dormant fertilized eggs can withstand dissection for months

Rotifera Body Plan

• corona

  • ciliated crown

• mastax

  • pumping pharynx

• posterior end often bearing toes and adhesive glands

• epidermis syncytial, secreting extracellular glycocalyx and intracellular skeletal lamina

  • forming a lorica in some

• unique retrocerebral organ

Rotifera Digestive System

• complete and regionally specialized gut

Rotifera Excretory System

• protonephridia present

Rotifera Reproduction

• parthenogenesis common

  • males usually reduced, or absent within species

• cryptobiosis present in many species

  • dormant fertilized eggs can withstand dissection for months

Acanthocephala

• subclass of rotifera

• retractable introverted spiny proboscis

• all parasitic in vertebrate intestines

  • intermediate host: crustacean

Entoprocta Body Plan

• differs from “ectoprocta”, endoprocta means inside anus

• cup shaped calyx with a horeshoe shaped band of ciliated tentacles carried on a stalk

  • tentacles surround the mouth, anus, gonoducts, and protonephridia

• sessile, solitary, or colonial

• nearly all shallow water marine

• commensals of many water-current-producing invertebrates

Endoprocta Reproduction

• hermaphroditic (monoecious) or gonochoristic (dioecious)

• some trochophore larvae

Commensals

• organisms that live in or on a host species, benefiting from nutrients, shelter, or support without causing harm or providing significant benefits to the host

• ex. Entoprocta acts as commensals of annelids, sponges and other water-current-producing invertebrates

Why are the ecdysozoans and spiralians grouped in the same clade?

• united in the protostome clade

  • often contain ventral nerve cord

  • fate of the blastopore, in that it forms the mouth

Name one main characteristic of ecdysozoans, and an example specimen (species, or genus, or common name)

• moulting of the cuticle

• ex. lobsters which moult their outer layer

Name one main characteristic of spiralians, and an example specimen (species, or genus, or common name)

• spiral cleavage, mosaic development, often trochophore larva

• ex. arrow worms

Compare and contrast the Phyla Chaetognatha, Rotifera, and Entoprocta (e.g., how are they similar, how are they different, including main morphological characters)

• chaetognatha: monoecious, spiralia, free-swimming

• rotifera: parthogeneis, spiralia, parasitic, free-swiming, sessile

• entoprocta: monoecious or dioecious, spiralia, sessile, colonial, or solitary

True or false. Acanthocephala are rotifers.

• TRUE

• subclass of Rotifers which are parasitic, and have a retractable, spiny proboscis

True or false. Entoprocta are bryozoans

• FALSE

• “ecto”procta are bryozoans