porifera – sponges

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  • 9393

    Porifera Sponges Philippe Willenz et al.

  • Fig. 1

    Fig. 2

    94

    Phy

    lum

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    General Introduction

    Sponges (or Porifera) are sedentary invertebrates,

    which are generally restricted to marine environments,

    except for a single suborder of freshwater demosponges

    (Spongillina). They display the simplest stage of

    metazoan organization; they possess a reduced number

    of cell types and have no epithelium, organs, true

    digestive, circulatory or nervous system. The body

    wall of sponges is perforated by a multitude of pores

    (ostia) opening into the aquiferous system (Fig. 1&2).

    A network of inhalant canals leads to flagellated cells

    (choanocytes) grouped in chambers, where particles the

    size of bacteria are filtered and digested at the cellular

    level through phagocytosis. Filtered water flows out

    through exhalant canals. These open to the outside

    through one or several large tubes visible to the naked

    eye, the oscula (Fig. 1). The water flow brings in food and

    oxygen and also removes waste.

    Currently, at least 15,000 sponge species are estimated

    to exist worldwide of which, only approximately 7,000

    are properly described in the literature. This number

    is increasing due to both SCUBA-diving explorations

    in poorly known regions and the taxonomic study of

    material that has been gathered through oceanographic

    inventories and deposited in collections around the

    world. The Phylum Porifera is subdivided into three

    classes (Hexactinellida, Calcarea and Demospongiae),

    mainly according to the composition and structure of

    their skeletal elements.

    Sponges that are assigned to the Hexactinellida possess a

    skeleton of six-rayed siliceous spicules. They occur mainly

    in deep marine waters. So far, there are no records of this

    class in the Chilean Fjord Region; although they may be

    a dominant component of the Antarctic

    benthos and in North East Pacific fjords.

    Calcarea have a skeleton comprised of

    spicules of calcium carbonate, which

    are mostly three-rayed. Demospongiae

    are by far the most abundant class of

    Porifera. They represent 8590% of the

    global sponge fauna and include all of

    the relatively few freshwater species.

    Almost all Demospongiae possess a

    skeleton of siliceous spicules, sometimes

    supplemented or entirely replaced by

    an organic collagenous skeleton. A few

    species completely lack a skeleton.

    Porifera Sponges Philippe Willenz et al.

  • 95

    Class Calcarea

    Philippe Willenz, Fernanda Azevedo, Eduardo Hajdu, Michelle Klautau

    wide distribution from tropical to polar regions and from

    shallow waters to the deep sea.

    Two subclasses are recognized in the class Calcarea:

    Calcinea and Calcaronea, with five orders, 22 families

    and 75 valid genera.

    Collecting calcareous sponges is not easy as they are

    frequently small and inconspicuous and live in cryptic

    habitats. The calcareous sponges of the Chilean coast are

    poorly known. The few species described recently by the

    authors are the first ones for the entire fjord region.

    Class Demospongiae

    Philippe Willenz, Eduardo Hajdu, Ruth Desqueyroux-Faundez, Gisele Lbo-Hajdu, Mariana de Souza Carvalho

    MorphologyDemosponges vary greatly in size. In the Chilean Fjord

    Region they vary from a few millimetres to up to half a

    meter in height. The body forms of Demosponges are

    usually irregular and exhibit massive, encrusting, erect

    or branching patterns. The type of growth pattern is

    influenced by the nature of the substratum, the velocity

    of the water currents and the wave action. The same

    species can have different shapes under different

    environmental conditions, sometimes resulting in

    taxonomic confusion. Another possible source of

    sponge misidentification is that they may be confused

    with colonial tunicates, which have a porous surface

    similar to that of sponges.

    Growth occurs at terminal points in arborescent forms,

    along growing fronts in encrusting species and all over

    the surface in massive forms. There is no definitive

    maximum size as growth is usually indeterminate. The

    same species may be represented by individuals of

    variable sizes and the larger ones are not necessarily

    the eldest.

    ReproductionAll sponges are capable of sexual reproduction and

    some have several additional types of asexual processes.

    Sexual processes are multiple. Sponges lack distinct

    gonads and gametes and most of them are sequential

    hermaphroditic; eggs and sperm are produced at different

    times. In a single individual, the sex change may occur

    Calcareous sponges represent approximately 9.5% of all

    known sponges, with over 650 recognized species. The

    calcium carbonate skeleton of extant calcareous sponges

    is composed of three main types of spicules: diactines,

    triactines and tetractines (spicules with two, three and

    four tips). In some calcareans, a solid basal calcitic

    skeleton can also be present. Calcarea is the only class

    of Porifera that shows the three basic types of aquiferous

    systems: asconoid, syconoid and leuconoid. Their mode

    of sexual reproduction is exclusively viviparous, with

    blastula larvae. They are exclusively marine and have a

    only once or it may repeatedly alternate between male

    and female. Some specimens however, are permanently

    male or female. Cross-fertilization takes place in all cases.

    Sperm usually originate from choanocyte chambers

    that transform into spermatic follicles in which clusters

    of flagellated cells undergo spermatogenesis. Oocytes

    arise either from choanocytes or from archaeocytes and

    develop surrounded by follicle cells and nurse cells. In

    some demosponges the embryo may be released shortly

    after fertilization or a long development may take place

    inside the parent sponge (viviparity). Other demosponges

    release eggs before fertilization (oviparity) and a larval

    stage ensues inside a mucus envelope that adheres to the

    substratum.

    Asexual processes are also multiple. All sponges are

    capable of regenerating new individuals from fragments

    after mechanical damage. Reduction bodies called

    gemmules are produced by freshwater sponges and

    some rare marine sponges. Gemmules are small spheres

    made of a hard shell of spongin that may be reinforced

    with spicules. They are packed with cells that contain

    food reserves and are highly resistant to freezing,

    desiccation and anoxia for long periods of time. When

    environmental conditions improve, gemmules hatch and

    give rise to young sponges. Many marine sponges also

    produce buds that form new individuals when they settle

    on the substratum after falling from the parent sponge

    surface.

    More than any other marine invertebrate, sponges

  • 99

    Clathrina fjordica Azevedo et al., 2009

    Common name: Lattice sponge (of the fjords);

    Esponja rejilla (de los fiordos)

    Description: Fragile and small (60x45x7 mm). Body

    a mesh of irregular and loosely anastomosed tubes.

    Aquiferous system asconoid. Colour in life white;

    in ethanol light brown or beige. Skeleton: Without

    organisation and composed of 2 categories of triactines.

    Spicules: Triactines-1 equiangular and equiradiate; length

    92116 m; thickness 8.3 m; actines cylindrical, rounded

    and undulated. Triactines-2 equiangular and equiradiate;

    length 76122 m; thickness 9.9 m; actines conical,

    rounded and undulated. Possibility for confusion: C.

    coriacea, which has only 1 category of triactines. The

    other clathrinas cited for Chile are C. primordialis and

    C. antofagastis. Both C. primordialis and C. fjordica have

    2 categories of triactines: one cylindrical and the other

    conical and a loosely anastomosed cormus, but the tips

    of the actines are sharp in C. primordialis and rounded in

    C. fjordica. C. antofagastis has 3 categories of triactines

    with blunt tips.

    Habitat: Hard substrates, also attached to mollusc

    shells (Crepidula sp., Mytilus chilensis). Depth: 927 m.

    Abundance: Common. Distribution: SE Pacific (NPZ

    CPZ). Chile: 42S48S. Biology: Unknown. Comments:

    When removed from the water, the tubes of the sponge

    lose water, change shape and sometimes change colour.

    Scale bars: Top, 2 cm; centre left and right, 2 cm; bottom

    left and right, 100 m.

    Main reference: Azevedo et al. (2009).

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    Crambe chilensis

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  • 126

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    Crambe chilensis Esteves et al., 2007

    Common name: Orange barnacle crust sponge;

    Esponja cubre-pico-roco naranja

    Description: Small; encrusting. Oscula small;

    inconspicuous; in centre of a starry arrangement of

    clearly visible sub-superficial exhalant canals. Surface

    smooth to slightly velvety. Consistency soft, slightly

    flexible. Colour in life rosy-orange; in ethanol beige

    or brown. Skeleton: Ectosomal skeleton composed of

    brushes of subtylostyles, arranged perpendicularly or

    tangentially to surface, isochel

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