Brachiopods    -    Phylum:   Brachiopoda
"Very few species have survived unchanged. There's one called Lingula, which is a little shellfish, a little brachiopod about the size of my fingernail, that has survived for 500 million years, but it's survived by being unobtrusive and doing nothing, and you can't accuse human beings of that."  
Sir David Attenborough  (b.1926).
     The word Brachiopod is derived from from two Ancient Greek words:  'brachion'  meaning  'arm'  and  'pod' (or 'pous') meaning foot. 'Arm' refers to the means by which they feed and 'foot' refers to the way in which many secure themselves to the sea-floor.  To clarify the former; the animal has a pair of arms with tentacles on the lower or brachial valve that move so as to direct a current of water, containing microscopic food, to the lophophore - a mouth-like structure used for feeding and respiration.   Generically, they are called 'Lampshells'
      Brachiopods are animals that have two valves (=shells), an upper and a lower one that are usually different in shape and size, unlike molluscs which have a left and a right shell that are the same.   Many species in the phylum also have a pedicle (=stalk) protruding from the rear of one of the valves with which it anchors itself to the seafloor.   The Brachiopoda have for a long time time been separated into two sub-phyla depending on the structure of the hinge that keeps the two shells together and allows it to open and shut.
Picture
Image 1. Inarticulate v. articulate Brachiopods. By Jaleigh Q. Pier.
      Brachiopods were once more numerous and varied than they are at present and with more than 12,000 fossil species in over 5,000 genera compared to the 330 extant species, it should come as no surprise that the taxonomic divisions are predominantly based on the fossil record.  This brings about a measure of ambiguity as the extinct animals are only know by their shells and classification is determined using primarily visual cues.  One visual difference - the structure of the hinge that keeps the two shells together - has led to the Brachiopoda being divided into two sub-phyla.  However, recent advances in molecular phylogenetics has resulted in the addition of a third. 
Picture
Image 2. Paired lophophores of Terebratalia transversa. By Alex Heyman.
       Of all animals, Brachiopods have one of the longest fossil records although their numbers have fluctuated wildly. For about 230 million years during the Ordovician, the Devonian and the Permian eras of the Palaeozoic, they were also amongst the most plentiful creatures on the sea floor.  This, plus the enormous diversity of species over time, as well as their vast range across the globe, has made the Brachiopod fossils into  reliable geological time markers.   In other words, rocks from different areas containing the same fossil species must be of the same age.  (for more on this see:  'biostratigraphy')
      All Brachiopods exclusively live in the the sea, there are no freshwater species.  Most species also prefer quiet waters without excessive wave action or currents.   They range in size from a mere 1 millimeter in length to to up to 10 centimeters long and some species are remarkably long-lived with a lifespan of about 30 years.  They are found world-wide in all but the coldest waters but are not common anywhere.  The Brachiopods are of little economic value with only some Lingulids fished for and even that on a very small scale.  As fossils however, they are a keenly sought after collector's item.
        The roughly 330 species of Brachiopods are grouped into just over 100 genera.  Of these, four genera are in the Subphylum: Craniiformea, five genera are in the subphylum: Linguliformea and the remainder belong to the subphylum: Rhynchonelliformea.  
        Brachiopods were most abundant in warm, shallow waters of the world during the Cretaceous period but over time have been displaced by the more succesful bivalves.   Most species that remain now occupy much colder and darker marine habitats.
​      All of the three subphyla have been recorded in Australian waters.  However, records of Craniiformea are particularly scarce nationwide and, whereas records of Linguliformea generally are confined to the northern half of Australia, they reach far enough south to be a better than possible encounter.  On a similar note, the Rhynchonelliformea are confined more to the southern half of the continent but, may well reach far enough north.
References  and  links:
^    Image 1.    Cropped from the original by Jaleigh Q. Pier, licensed under Creative Commons Attribution-ShareAlike 4.0 International License.
^     Image 2.   By Alex Heyman, licensed under Creative Commons Attribution-ShareAlike 4.0 International License.

^      Ax, P (2003). Multicellular Animals: Order in Nature - System Made by Man. Multicellular Animals: A New Approach to the Phylogenetic Order in Nature. Vol. 3. Springer.
^      Carlson, Sandra J. (2016) The Evolution of Brachiopoda.  Annual Review of Earth and Planetary Sciences, Univ. of California.  2016 ,44:1, 409-438. 
^      Haeckel, E. (1904).  Kunstformen der Natur,  Leipzig und Wien :Verlag des Bibliographischen Instituts, 1899-1904.

        https://www.digitalatlasofancientlife.org/
        https://www.digitalatlasofancientlife.org/learn/brachiopoda/brachiopoda-classification/
        https://www.ga.gov.au/scientific topics/disciplines/biostratigraphy#:~:text=Foraminifera%20%2D%20Globigerinella%20digitata-,What%20is%20biostratigraphy%3F,
                 characterised%20by%20certain%20fossil%20taxa.
        https://en.wikipedia.org/wiki/Lophophore
      ​https://en.wikipedia.org/wiki/Molecular_phylogenetics
        https://en.wikipedia.org/wiki/Pedicle
​​
Text:   Erik Beringen
Header photo:   Modified from the original by Professor Mark.A. Wilson , CC0  via   https://commons.wikimedia.org/wiki/User:Wilson44691
Note:  Copyright rules vary.  Please contact the editor prior to using any of the images published on this site.