Lophophores

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Biology 226 Home Page

THE LOPHOPHORATE PHYLA

PHYLUM Phoronida: Vermiform lophophorate tube dwellers. Only two genera: Phoronis and Phoronopsis

PHYLUM Ectoprocta (Bryozoa): Colonial zooids. Sessile

CLASS Phylactolaemata: Freshwater ectoprocts
CLASS Stenolaemata: Marine ectoprocts
CLASS Gymnolaemata: Diverse group, primarily marine
- ORDER Ctenostomata
- ORDER Cheilostomata

PHYLUM Brachiopoda: Lamp shells. Solitary, marine, benthic.

CLASS Inarticulata: Valves not hinged
- ORDER Lingulida
- ORDER Acrotretida
CLASS Articulata: Valves articulate
- ORDER Rhynconellida
- ORDER Terebratulida

SUMMARY:

Body Plan

Coelomate. Trimeric coelom (prosocoel, mesocoel, metacoel) gives rise to three distinct body regions, prosome, mesosome, metasome. Most significant syapomorphy is the lophophore, a ciliated, tentacular coelomate outgrowth of the mesosome. Phoronids and brachiopods are solitary, ectoprocts colonial. Guts U-shaped.

Locomotion

Largely sessile.

Feeding and digestion

Feeding via lophophore: cilia make current through lophophore, trap particles and move to mouth. Gut is U-shaped, with anus next to mouth but outside lophophore (ectoproct condition). Gut not strongly differentiated (more so in ectoprocts which have muscular pharynx, gizzard, etc.), only occasionally peristaltic (most movement by cilia).

Sense Organs

Few in adult: mostly chemoreceptors. Motile larvae may have photoreceptors, statocysts. One species of brachiopod has been reported to have statocysts, probably associated with orientation in the burrow.

Nervous system

Much reduced due to sessile lifestyle. Usually just a ring around pharynx under lophophore, with connections to a intraepidermal or subdermal nerve net in the body wall. Phoronids possess one or two giant fibers mediating body withdrawal. Sensory neurons innervate the lophophore and, for the brachiopods, the mantle, particularly the margin.

Respiration and gas exchange

Most gas exchange through lophophore.

Circulation

Phoronids: essentially closed, mesodermally-derived circulatory system. No "heart" as such, but most vessels are capable of peristalsis. Blood technically leaves the closed vessels in the hemal (stomacic) plexus, although the passageways are still defined. Ectoprocts have no defined circulatory system. Brachiopods have one or more "hearts" and an open circulatory system.

Osmoregulation and nitrogen excretion

With few exceptions, all are marine and osmoconformers. Phoronids and Brachiopods: Nephridia are metanephridia, with nephrostomes opening in metacoel. Nephridioducts open near lophophore in phoronids, into mantle cavity in brachiopods. Ectoprocts have no nephridia. Waste elimination seems to be via phagocytic coelomocytes and "brown bodies".

Reproduction

Phoronids and ectoprocts: both asexual (budding; ectoprocts also use statoblasts) and sexual. Brachiopods are exclusively sexual. Sexual is either gonochoristic or hermaphroditic (simultaneous [Phoronids] or sequential). No true gonads except in Stenolaematous ectoprocts. Gametes released into metacoel. In Phoronids and Brachiopods, gametes are carried out by nephridioducts.

Embryology

Deuterostomous. Cleavage is generally radial and indeterminate. Mesoderm and coelom formation is enterocoelic, with division into three regions (paired coelomic compartments: prosocoel, mesocoel, metacoel). Free-swimming larva.

Body Plan	Coelomate. Trimeric coelom (prosocoel, mesocoel, metacoel) gives rise to three distinct body regions, prosome, mesosome, metasome. Most significant syapomorphy is the lophophore, a ciliated, tentacular coelomate outgrowth of the mesosome. Phoronids and brachiopods are solitary, ectoprocts colonial. Guts U-shaped.
Locomotion	Largely sessile.
Feeding and digestion	Feeding via lophophore: cilia make current through lophophore, trap particles and move to mouth. Gut is U-shaped, with anus next to mouth but outside lophophore (ectoproct condition). Gut not strongly differentiated (more so in ectoprocts which have muscular pharynx, gizzard, etc.), only occasionally peristaltic (most movement by cilia).
Sense Organs	Few in adult: mostly chemoreceptors. Motile larvae may have photoreceptors, statocysts. One species of brachiopod has been reported to have statocysts, probably associated with orientation in the burrow.
Nervous system	Much reduced due to sessile lifestyle. Usually just a ring around pharynx under lophophore, with connections to a intraepidermal or subdermal nerve net in the body wall. Phoronids possess one or two giant fibers mediating body withdrawal. Sensory neurons innervate the lophophore and, for the brachiopods, the mantle, particularly the margin.
Respiration and gas exchange	Most gas exchange through lophophore.
Circulation	Phoronids: essentially closed, mesodermally-derived circulatory system. No "heart" as such, but most vessels are capable of peristalsis. Blood technically leaves the closed vessels in the hemal (stomacic) plexus, although the passageways are still defined. Ectoprocts have no defined circulatory system. Brachiopods have one or more "hearts" and an open circulatory system.
Osmoregulation and nitrogen excretion	With few exceptions, all are marine and osmoconformers. Phoronids and Brachiopods: Nephridia are metanephridia, with nephrostomes opening in metacoel. Nephridioducts open near lophophore in phoronids, into mantle cavity in brachiopods. Ectoprocts have no nephridia. Waste elimination seems to be via phagocytic coelomocytes and "brown bodies".
Reproduction	Phoronids and ectoprocts: both asexual (budding; ectoprocts also use statoblasts) and sexual. Brachiopods are exclusively sexual. Sexual is either gonochoristic or hermaphroditic (simultaneous [Phoronids] or sequential). No true gonads except in Stenolaematous ectoprocts. Gametes released into metacoel. In Phoronids and Brachiopods, gametes are carried out by nephridioducts.
Embryology	Deuterostomous. Cleavage is generally radial and indeterminate. Mesoderm and coelom formation is enterocoelic, with division into three regions (paired coelomic compartments: prosocoel, mesocoel, metacoel). Free-swimming larva.