BENTHIC FORAMINIFERA
A. J. Gooday, Southampton Oceanography Centre,
Southampton, UK
Copyright & 2001 Elsevier Ltd.
Introduction
Foraminifera are enormously successful organisms
and a dominant deep-sea life form. These amoeboid
protists are characterized by a netlike (granuloreticulate) system of pseudopodia and a life cycle that
is often complex but typically involves an alternation
of sexual and asexual generations. The most obvious
characteristic of foraminifera is the presence of a
shell or ‘test’ that largely encloses the cytoplasmic
body and is composed of one or more chambers. In
some groups, the test is constructed from foreign
particles (e.g., mineral grains, sponge spicules, shells
of other foraminifera) stuck together (‘agglutinated’)
by an organic or calcareous/organic cement. In others, it is composed of calcium carbonate (usually
calcite, occasionally aragonite) or organic material
secreted by the organism itself.
Although the test forms the basis of foraminiferal
classification, and is the only structure to survive
fossilization, the cell body is equally remarkable and
important. It gives rise to the complex, highly mobile, and pervasive network of granuloreticulose
pseudopodia. These versatile organelles perform a
variety of functions (locomotion, food gathering, test
construction, and respiration) that are probably
fundamental to the ecological success of foraminifera
in marine environments.
As well as being an important component of
modern deep-sea communities, foraminifera have an
outstandingly good fossil record and are studied
intensively by geologists. Much of their research uses
knowledge of modern faunas to interpret fossil
assemblages. The study of deep-sea benthic foraminifera, therefore, lies at the interface between
biology and geology. This articles addresses both
these facets.
History of Study
Benthic foraminifera attracted the attention of some
pioneer deep-sea biologists in the late 1860s. The
monograph of H.B. Brady, published in 1884
and based on material collected in the Challenger
round-the-world expedition of 1872–76, still underpins our knowledge of the group. Later biological
expeditions added to this knowledge. For much of
the 1900s, however, the study of deep-sea foraminifera was conducted largely by geologists, notably J.A. Cushman, F.B. Phleger, and their students,
who amassed an extensive literature dealing with the
taxonomy and distribution of calcareous and other
hard-shelled taxa. In recent decades, the emphasis
has shifted toward the use of benthic species in
paleoceanographic reconstructions. Interest in deepsea foraminifera has also increased among biologists
since the 1970s, stimulated in part by the description
of the Komokiacea, a superfamily of delicate, softshelled foraminifera, by O.S. Tendal and R.R.
Hessler. This exclusively deep-sea taxon is a dominant component of the macrofauna in some abyssal
regions.
Morphological and Taxonomic
Diversity
Foraminifera are relatively large protists. Their tests
range from simple agglutinated spheres a few tens of
micrometers in diameter to those of giant tubular
species that reach lengths of 10 cm or more. However, most are a few hundred micrometers in size.
They exhibit an extraordinary range of morphologies
(Figures 1 and 2), including spheres, flasks, various
types of branched or unbranched tubes, and chambers arranged in linear, biserial, triserial, or coiled
(spiral) patterns. In most species, the test has an
aperture that assumes a variety of forms and is
sometimes associated with a toothlike structure. The
komokiaceans display morphologies not traditionally associated with the foraminifera. The test forms
a treelike, bushlike, spherical, or lumpish body that
consists of a complex system of fine, branching
tubules (Figure 2A–C).
The foraminifera (variously regarded as a subphylum, class, or order) are highly diverse with
around 900 living genera and an estimated 10 000
described living species, in addition to large numbers
of fossil taxa. Foraminiferal taxonomy is based very
largely on test characteristics. Organic, agglutinated,
and different kinds of calcareous wall structure serve
to distinguish the main groupings (orders or suborders). At lower taxonomic levels, the nature and
position of the aperture and the number, shape, and
arrangement of the chambers are important.
390
A. J. Gooday, Southampton Oceanography Centre,
Southampton, UK
Copyright & 2001 Elsevier Ltd.
Introduction
Foraminifera are enormously successful organisms
and a dominant deep-sea life form. These amoeboid
protists are characterized by a netlike (granuloreticulate) system of pseudopodia and a life cycle that
is often complex but typically involves an alternation
of sexual and asexual generations. The most obvious
characteristic of foraminifera is the presence of a
shell or ‘test’ that largely encloses the cytoplasmic
body and is composed of one or more chambers. In
some groups, the test is constructed from foreign
particles (e.g., mineral grains, sponge spicules, shells
of other foraminifera) stuck together (‘agglutinated’)
by an organic or calcareous/organic cement. In others, it is composed of calcium carbonate (usually
calcite, occasionally aragonite) or organic material
secreted by the organism itself.
Although the test forms the basis of foraminiferal
classification, and is the only structure to survive
fossilization, the cell body is equally remarkable and
important. It gives rise to the complex, highly mobile, and pervasive network of granuloreticulose
pseudopodia. These versatile organelles perform a
variety of functions (locomotion, food gathering, test
construction, and respiration) that are probably
fundamental to the ecological success of foraminifera
in marine environments.
As well as being an important component of
modern deep-sea communities, foraminifera have an
outstandingly good fossil record and are studied
intensively by geologists. Much of their research uses
knowledge of modern faunas to interpret fossil
assemblages. The study of deep-sea benthic foraminifera, therefore, lies at the interface between
biology and geology. This articles addresses both
these facets.
History of Study
Benthic foraminifera attracted the attention of some
pioneer deep-sea biologists in the late 1860s. The
monograph of H.B. Brady, published in 1884
and based on material collected in the Challenger
round-the-world expedition of 1872–76, still underpins our knowledge of the group. Later biological
expeditions added to this knowledge. For much of
the 1900s, however, the study of deep-sea foraminifera was conducted largely by geologists, notably J.A. Cushman, F.B. Phleger, and their students,
who amassed an extensive literature dealing with the
taxonomy and distribution of calcareous and other
hard-shelled taxa. In recent decades, the emphasis
has shifted toward the use of benthic species in
paleoceanographic reconstructions. Interest in deepsea foraminifera has also increased among biologists
since the 1970s, stimulated in part by the description
of the Komokiacea, a superfamily of delicate, softshelled foraminifera, by O.S. Tendal and R.R.
Hessler. This exclusively deep-sea taxon is a dominant component of the macrofauna in some abyssal
regions.
Morphological and Taxonomic
Diversity
Foraminifera are relatively large protists. Their tests
range from simple agglutinated spheres a few tens of
micrometers in diameter to those of giant tubular
species that reach lengths of 10 cm or more. However, most are a few hundred micrometers in size.
They exhibit an extraordinary range of morphologies
(Figures 1 and 2), including spheres, flasks, various
types of branched or unbranched tubes, and chambers arranged in linear, biserial, triserial, or coiled
(spiral) patterns. In most species, the test has an
aperture that assumes a variety of forms and is
sometimes associated with a toothlike structure. The
komokiaceans display morphologies not traditionally associated with the foraminifera. The test forms
a treelike, bushlike, spherical, or lumpish body that
consists of a complex system of fine, branching
tubules (Figure 2A–C).
The foraminifera (variously regarded as a subphylum, class, or order) are highly diverse with
around 900 living genera and an estimated 10 000
described living species, in addition to large numbers
of fossil taxa. Foraminiferal taxonomy is based very
largely on test characteristics. Organic, agglutinated,
and different kinds of calcareous wall structure serve
to distinguish the main groupings (orders or suborders). At lower taxonomic levels, the nature and
position of the aperture and the number, shape, and
arrangement of the chambers are important.
390