Porifera

Most primitive animal (sort of) grade, lacking distinct tissues, but possessing specialized cells. Sponge cells that have been separated can coalesce into new sponges, but are unable to survive for long independently. Is this a clade or a paraphyletic grade group? Recent literature is divided between molecular analyses showing Porifera to be paraphyletic (with calcareous sponges closer to Metazoa) or to be monophyletic, (with Hexactinellida and Demospongia being closer to one another than either is to Calcarea.) Thus, the cladogram above is an unsatisfactory consensus. Stay tuned. Review Lab 3 for general morphology of sponges.

Specialized cell types: Choanocytes: Line the spongocoel, propelling water toward the osculum (hence drawing it in the ostia.) Pinacocytes: line the outer surface Porocytes: Line the canals Archeocytes (a.k.a. "amoebocytes"): amoeboid cells occupying mesohyl that digest and transport nutrients. Sclerocytes: Lay down spicules Spongocytes: Lay down spongin fibers. Choanocytes closely resemble choanoflagellates Reproduction may be: by budding sexual, with ova developing from archeocytes, and sperm from choanocytes.

Major "clades" Hexactinellida: (Neoproterozoic - Rec.) Characteristics: No pinacocytes. Indeed, much cytoplasm is multinucleate w/o clear cell demarcations. Silicate spicules: six rayed, jack-like triaxons, whose rami meet at 90 deg angles. Leucon grade only. Are able to transmit eletrical impulses across their bodies quickly, Lack pinacocytes Lack the derived (?) ability of other sponges to contract slightly. Ecology: Prefer soft substrates and relatively quiet, cold waters. Common at greater depths and high latitudes. Massive hexactinellid reefs known from 180 - 250 M. depth (hence below photic zone) off British Columbia. Evolutionary trends: First known from Ediacaran. Abundant in latest Devonian, occuppying ecospace vacant after Devonian extinction. Suffered like everyone in Permian extinction. Maximum diversity during Cretaceous.

Demospongia: (Cambrian - Rec.) The majority of modern sponges All leucon grade, with siliceous spicules and/or spongin Spicules may be tetraxons, monaxons, or desmas. In tetraxons, rami form 60 deg. and 120 deg. angles. May include some oddballs including the living "sclerosponges," chaetetids, stromatoporoids Important reef framework builders in Permian.

Calcarea: Ascon, sycon or leucon, with calcareous spicules Spicule morphology may be monaxon, tetraxon, star-shaped, tuning-fork shaped. Includes sphincotozoans (C - Rec), sponges like strings of hollow beads. Significant Late Paleozoic reef organisms. At least one variety, Vaceletia, survives. Ecology: Prefer warm shallow waters. Evolutionary trends: Sphinctozoan forms were significant Permian reef builders. Maximum diversity during Permian.

Problematic fossil poriferans (?):

Archaeocyatha: (Early - Middle C) (may be sister to demosponges) Characteristics: Considered sponges based on general body plan, but had some unique features. Perforate calcareous hard tissues with double-walled cone-in-cone structure. Septa, and in some, tabulae and dissepiments. No consensus on basic affinities. Ecology: Shallow, warm carbonate shelf environments of normal salinity. Often occur together with algae, indicating good illumination Evolutionary trends: Common and speciose during Early Cambrian. Extinguished during Middle Cambrian. Ecologically replaced by recognizible sponges and cnidarians.

Chaetetids: (Ord. - Rec.) Encrusting laminar form, long thought to be tabulate corals, but had either calcareous (in Paleozoic) or silica spicules (in Cretaceous). Long thought to have died out in Miocene. Discovery of living representatives clinched the argument. They belong to Demospongia. Characteristics: Form binding laminations. Hard parts consists of upright tubes with tabulae. Ecology: Binding reef organisms, requiring hard substrate initially.

Sclerospongea including Stromatoporoids: (Ord. - Rec.) Characteristics: Layered, with tubes passing through body. Surface had swellings called mamelons, with grooves called astrorhizae> Modern sclerosponges also have astrorhizae Framework of silica & spongin, with calcareous skeleton layered on top Evolutionary trends: Significant binding reef organisms in Early Paleozoic. Indeed, Stromatoporoid-coral reefs predominated in Siluran and most of Devonian. Disappear from record at Devonian extinction. Make a comeback during the Mesozoic, but never regain former glory. Formerly thought to be extinct. No consensus on spongy nature, then living cryptic sclerosponges were discovered, leading to general consensus that stromatoporoids were closely related.

Metazoa: (Or is is "Eumetazoa?") (Ediacaran - Rec.) Includes Cnidaria, Ctenophora, and Bilateralia. Synapomorphies: Nerves Muscles Organs Cells with determinant histories Endoderm: Inner germ layer Ectoderm: Outer germ layer Major taxa: Cnideria: (Ediacaran - Rec.) corals, jellyfish, etc. Ctenophora: Comb-jellies, with nearly no fossil record Bilatera: (Ediacaran - Rec.) Animals with bilateral symmetry, and distinct mouth and anus.

Cnidaria

Characteristics:

• Diploblastic - having endoderm and ectoderm only, separated by gelatinous mesoglea.
• Typically alternate between asexually reproducing polyp and sexually reproducing medusa generations.
• Radially symmetrical body plan (primitive) with single opening to the gut, termed the "mouth" for the sake of politeness.
• Prey capture by Nematocysts (cnidae, stinging cells) born on tentacles surrounding mouth

Major cnidarian groups:

Scyphozoa: Jellyfish (Ediacaran (?) - Rec.) Characteristics: Body plan shows four-fold radial symmetry. Although generations alternate in most studied taxa, the polyp stage is reduce and medusa predominates. Fossil record: Restricted to shallow-marine conservat-lagerstätten such as Ediacara hills (Ediacaran), Burgess Shale (C), Holtzmaden (J), and Solnhofen (J).

Cubozoa: Box jellies (Penn (?) - Rec.) Characteristics: Body plan shows four-fold radial symmetry with four tentacles or groups thereof. Medusa profile is square when viewed from above. Four eyes facilitate more active pursuit of prey. Fossil record: Restricted to two conservat-lagerstätten, Mazon Creek (Penn) and Solnhofen (J).

Hydrozoa: Hydras, fire coral (Cretaceous - Rec.) Characteristics: Marine and fresh-water. The freshwater Hydra is typical. Generations altrnate, but medusa stage is reduced. Solitary or colonial. but marine colonial forms include blade fire coral (see above), which secretes calcareous skeleton. Major groups: Hyrdoida: Solitary or colonial unspecialized polyps. Hydrocorals: Possibly polyphyletic marine colonial forms include blade fire coral, which secretes calcareous skeleton. Siphonophora: Pelagic (free-swimming) colonial marine forms, such as Portuguese Man-o-War, showing radical specialization of zooids (both polyp and medusa in one colony) into: Pneumatophores: Bell or sail for floatation. Nectophores: For swimming. Gastrozoids: For feeding. Etc. Fossil record: Fire corals known from Cretaceous onward.

Anthozoa: (Ord.- Rec.). Characteristics: Medusa stage is totally suppressed. Typically secrete some sort of hard coralite. Solitary or colonial. In colonial forms, regardless of nature of coralite, individual polyps are connected by sheets of living tissue.

Major groups:

• Zoanthiniaria: (No record) Polyploid, solitary or colonial forms without fossil record.

  Octocorallia:(No record, save questionable Ediacaran "sea-pens") Gorgonians, sea-whips, etc. Characteristics: Colonial, typically secreting durable framework of protein gorgonin. In some, gorgonin is lost and polyps sprout from matrix of soft tissue - soft corals. Polyps have eightfold radial symmetry - hence name.

  Rugosa: (Ord - Permian) (Aka "horn-corals") Characteristics: Generally solitary, some colonial Display prominent septa, often also tabulae and dissepiments. Characteristic sequence of septum growth yields calyx (NOT "calice." ) with distince cardinal and alar fossulae. Not major reef formers, but often pioneers of soft sediments, forming a "hard ground" for later encrusters Evolutionary trends: Major components of Silurian - Devonian reefs, but suffered greatly in Devonian extinction. Persisted at lower abundance and diversity to the Permian extinction. Paraphyletic with respect to Scleractinia? Possible, although equally likely that scleractinian skeleton is convergent.

  Tabulata: (Ord.(?) - Permian) Characteristics: Major reef formers, particularly in Silurian and Devonian Always colonial Individual polyps small, occupying tubular coralites with numerous tabulae but NO septa or dissepiments. Evolutionary trends: Major component of Silurian-Devonian tabulate-rugosan-stromatoporoid reefs. Greatly reduce by Devonian extinction. Extinguished by Permian extinction.

  Scleractinia: (Late Triassic - Recent) Characteristics: Minor reef formers in Mesozoic. Primary reef-builders of Cenozoic. Almost all colonial Distinguished from rugosans by sixfold-symmetrical septal arrangement. (Hence old name "hexacorals.") In living members, the ability to form large reefs depends on zooxanthellae. Thus, major reefs limited to photic zone of tropics. Major reef building corals (with zooxanthellae) termed hermatypic. Non-reef builders termed ahermatypic. In many scleractinians, the polyp and calyx, in oral view, becomes greatly elongate, forming convoluted colonies. E.g. "brain-coral."

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