Foraminiferans are Amoeba-like single-celled organisms found either
free-floating or attached to surfaces in marine ecosystems. Many build ornate
tests (shells) from calcium carbonate, and planktonic forms are
widely used in biostratigraphy (the use of small fossils to date sedimentary
rocks), but others lack the ability to produce their own biominerals, and
instead construct protective coverings by cementing together other items.
In a paper published in the journal Zootaxa on 10 June 2013, a team
of scientists led by Manuel Maldonado of the Centro de Estudios Avanzados deBlanes describe a new species of agglutinated Foraminiferan from the Seco de
Palos seamount in the Western Mediterranean.
The new species is placed in the genus Spiculosiphon, and given the specific name oceana, in honour of the non-profit organization for ocean
conservation OCEANA, which was responsible for the collection of the samples
from which the species is described. Spiculosiphonoceana
lives attached to a substrate by a long stalk, both the stalk and the main body
being covered by agglutinated Sponge spicules, though these are arranged
laterally in a slight spiral around the stalk but radiate out from the body.
(A) General view of the Spiculosiphon oceana. (B) Detail of capitate region of the holotype,
showing the globelike, central structure and the radiating tracts of spicules. Maldonado
et al. (2013).
Spiculosiphon oceana is a giant by Foraminiferan standards, reaching in excess of 4 cm
in length. It is only the second species assigned to the genus Spiculosiphon; the first species, Spiculosiphon radiata is also large, but
less so than Spiculosiphon oceana,
reaching only about 2 cm. This species was described from specimens collected
off the coast of Norway in 1964.
Maldonado et al. note that
both species of Spiculosiphon show
remarkable convergent evolution with some small species of Carnivorous Sponge,
using scavenged Sponge spicules to build a body very similar in form to the
Sponge; both organisms then trapping relatively large prey and dissolving it
externally.
(A) View of the carnivorous sponge Asbestopluma hypogea soon after trapping
a small Copepod. The sponge isdisplaying the spiny-headed morphology, which is
typical after a period of starvation in order to maximize the chances of new
prey capture. (B) View of the capitate region of Spiculosiphon oceana for a comparison with the body shape of the Carnivorous Sponge. Maldonado et al. (2013).
Maldonado et al. further
observe that many agglutinated Foraminiferans appear to have a preference for
Sponge spicules when incorporating material into their tests, while tending to
reject other sources of biogenic silica such as Diatom shells. They suggest
that this may be linked to the ancient nature of the group; the earliest Foraminiferans
are thought to have appeared about 770 million years ago, in the Middle Cryogenian
Period (about the same time as the earliest Sponges), while the Agglutinated
Foraminiferans are thought to have arisen in the late Ediacaran or early Cambrian,
about the same time as the earliest Siliceous Sponges (Sponges producing
spicules made of silica). The earliest Diatoms appeared in the Early Jurassic,
about 199 million years ago, by which time Agglutinated Foraminiferans had
evolved to use Sponge spicules wherever possible.
That said, they also acknowledge that while Sponge spicules and
Diatom tests are generally considered to be chemically identical, Sponge
spicules do persist for much longer in seawater without dissolving (which
clearly has advantages when using recycled material as a construction
material), leading Maldonado et al.
to suggest their may be different trace elements or compounds in the two
materials, which both contributes to the more durable nature of the Sponge
spicules and is detectable to the Foraminiferans.
SEM micrograph of stalk. (Tightly packed needle-like
spicule fragments, with no obvious cement betweenthem. Some debris (d) has
flocculated on the spicules. Note that the silica of some of the oldest
spicules started dissolving, asindicated by the occurrence of tiny cavities and
pits (p) at their surface. Dissolution cavities are to be distinguished
fromaccidental breakages (b) caused to the stalk during collection or
laboratory manipulation. Maldonado et al.
(2013).
Maldonado et al. also
record patches of colour on the stalk of Spiculosiphon oceana
which appear to derive neither from the mineralogy of the spicules nor any
fouling organism living external to the stalk. Instead they suggest this may be
caused by photosynthetic symbionts growing inside the stalk (beneath the
translucent spicules). Other species of Agglutinated Foraminiferans have been
recorded to host a variety of Dinoflagellates, Diatoms, unicellular
Chlorophytes (Green Algae), unicellular Rhodophytes (Red Algae) and Cyanobacteria; the colour of
the markings on the Spiculosiphon oceana
stalks tending to suggest Dinoflagellates, Rhodophytes, or Cyanobacteria might
be present, though they were unable to confirm this.
The stalk in showing a region in which the translucent
spicule wall gets a brownish to purplish coloration. Maldonado et al. (2013).
Finally Maldonado et al.
report the presence of a Calcareous Foramiferan test attached to the stem of
one of the specimens (presumably the remains of a past meal) and not that both
this test and the adjacent area of the stem show raised levels of the element tellurium.
This is a very rare element, and has never been reported in any Foraminiferan
before (nor many other organisms). It is unclear whether the source of this
tellurium is the Calcareous or the Agglutinated Foraminiferan, nor exactly what
biological process it could have been used in.
(C) Detail of a calcareous foraminifer (f) externally
attached to the wall of one ofthe collected stalks. Note that a triaene (t) has
been incorporated into the test and that some debris (d) hasflocculated on the
stalk. Maldonado et al. (2013).
See also…
Golden Algae (Chrysophyceae) are photosynthetic eukaryotic microbes
(i.e. single celled organisms that posses cell nuclei similar to those
found in the cells of animals and plants, but unlike bacteria which do
not), found throughout the world, predominantly in fresh water. The
group is mostly poorly studied, with the exception of a few species
which are toxic to Fish.
Four new species of fossil Diatom from the western United States. Diatoms are single celled algae related to Kelp and Water Moulds. They
are encased in silica shells with two valves. During reproduction the
cells divide in two, each of which retains one valve of the shell,
growing a new opposing valve, which is slightly smaller and fits flush
within the older valve. This means that the Diatoms grow smaller with
each new generation, until they... 
The oldest animals - Pre-Ediacaran Sponges from Namibia(?) Sponges are curious creatures. They are considered to be animals as they
are multicellular and some of them have fixed body shapes, however they
show no cell differentiation, and can be broken down into individual
cells (by, for example, forcing them through a sieve) and they will
re-assemble themselves without apparent ill-effect. In some ways they
are more like colonial protists than true animals. Biologists have long
regarded them as the most primitive animal...
Follow Sciency Thoughts on Facebook.
