Table Of ContentA revision of the supraspecific classification
of the subclass Calcaronea
(Porifera, class Calcarea)
Radovan BOROJEVIC
Departamento de Histologia e Embriologia, Instituto de Ciências Biomédicas,
Universidade Federal do Rio de Janeiro, Caixa Postal 68021,
21941-970 Rio de Janeiro (Brazil)
[email protected]
Nicole BOURY-ESNAULT
Jean VACELET
Centre d’Océanologie de Marseille
(CNRS-Université de la Méditerranée, UMR 6540 DIMAR),
Station marine d’Endoume, F-13007 Marseille (France)
[email protected]
[email protected]
Borojevic R., Boury-Esnault N.& Vacelet J. 2000.— A revision of the supraspecific classifi-
cation of the subclass Calcaronea (Porifera, class Calcarea). Zoosystema22 (2): 203-263.
ABSTRACT
A revision of all the genera of the subclass Calcaronea (Porifera, Calcarea) is
given. In addition to the two previously described orders, Leucosoleniida
Hartman, 1958 emend. and Lithonida Vacelet, 1981, we recognize a third
one: the Baeriida. The order Leucosoleniida includes nine families, one of
which is new (the Jenkinidae), and 42 genera of which four are new
(Breitfussia, Leucandrilla, Polejaevia and Syconessa). The order Lithonida
includes two families and six genera. The order Baeriida includes three fami-
lies of which two are new (the Baeriidae and the Trichogypsiidae), and eight
genera. The Leucosoleniida seem to have evolved from the olynthus grade, a
form that is probably present in the early stages of ontogenesis of all
Leucosoleniida and subsists at the adult stage in Leucosolenia. The
Leucosoleniida comprises a diverse group with several pathways of progres-
sing complexity of form, starting with sponges of a simple sycettid organiza-
tion and leading to sponges with a complex aquiferous system and
skeleton.Increase in size from the sycettid grade of organization may occur by
two different processes: 1) the growth and elongation of radial tubes increa-
sing the thickness of the sponge body (seen in the Sycettidae-Grantiidae line
and the Heteropiidae), or 2) the growth of the central tube containing the
ZOOSYSTEMA • 2000 • 22 (2) © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. www.mnhn.fr/publication/ 203
Borojevic R., Boury-Esnault N. & Vacelet J.
KEY WORDS atrial cavity which increases the length of the sponge body (seen in the
Porifera,
Calcaronea, Jenkinidae and the simple forms of Amphoriscidae). The sponges classified in
evolution, the Baeriida and the Lithonida have very divergent forms that are represented
generic definitions,
by only a few living species. Identification keys and illustrations are provided
Baeriida,
Jenkinidae. for all the valid genera.
RÉSUMÉ
Révision de la classification supraspécifique de la sous-classe Calcaronea (Porifera,
classe Calcarea).
Une révision de tous les genres de la sous-classe Calcaronea (Porifera,
Calcarea) est faite. Le nouvel ordre Baeriida est proposé en addition aux deux
ordres précédemment reconnus, Leucosoleniida Hartman, 1958 emend. et
Lithonida Vacelet, 1981. L’ordre Leucosoleniida comprend neuf familles
dont une nouvelle (Jenkinidae) et 42 genres, dont quatre nouveaux
(Breitfussia, Leucandrilla, Polejaevia et Syconessa). L’ordre Lithonida com-
prend deux familles et six genres. L’ordre Baeriida comprend trois familles,
dont deux nouvelles (Baeriidae et Trichogypsiidae) et huit genres. Les
Leucosoleniida semblent avoir évolué à partir du stade olynthus. Cette forme
est probablement présente dans les stades précoces de l’ontogenèse chez toutes
les Leucosoleniida et subsiste à l’état adulte chez Leucosolenia. Les
Leucosoleniida sont un groupe florissant dans lequel on reconnaît plusieurs
lignées ayant un système aquifère et un squelette de complexité croissante à
partir de l’organisation de type sycettide. La croissance en taille à partir du
stade sycettide peut avoir lieu en suivant deux voies: 1) la croissance et l’élon-
gation des tubes radiaires, qui accroissent l’épaisseur du corps de l’éponge et
qui sont représentées par la lignée Sycettidae-Grantiidae et les Heteropiidae;
2) la croissance du tube central contenant la cavité atriale qui accroît la lon-
MOTS CLÉS
gueur du corps, comme chez les Jenkinidae et les formes simples des
Spongiaires,
Calcaronea, Amphoriscidae. Au contraire, les Baeriida et les Lithonida sont des groupes
évolution, très divergents, représentés seulement par un petit nombre d’espèces. Des clés
définitions génériques,
d’identification et des illustrations sont données pour tous les genres consi-
Baeriida,
Jenkinidae. dérés comme valides.
SYSTEMATIC INDEX Genus *SycandraHaeckel, 1872
Genus *TeichonopsisDendy & Row, 1913
Subclass CALCARONEA Bidder, 1898 Genus Ute Schmidt, 1862
Order LEUCOSOLENIIDA Hartman, 1958 Genus *SycuteDendy & Row, 1913
Family LEUCOSOLENIIDAEMinchin, 1900 Genus *SynuteDendy, 1892
Genus LeucosoleniaBowerbank, 1864 Genus AmphiuteHanitsch, 1894
Genus AscuteDendy & Row, 1913 Genus *SycodorusHaeckel, 1872
Genus AscyssaHaeckel, 1872 Genus Leucandra Haeckel, 1872
Genus AphrocerasGray, 1858
Family SYCETTIDAEDendy, 1892 Genus Leucandrilla n.gen.
Genus SycettaHaeckel, 1872 Genus *LeucettagaHaeckel, 1872
Genus SyconRisso, 1826
FamilySYCANTHIDAELendenfeld, 1891
Family GRANTIIDAEDendy, 1892 Genus SycanthaLendenfeld, 1891
Genus GrantiaFleming, 1828 Genus *DermatretonJenkin, 1908
204 ZOOSYSTEMA • 2000 • 22 (2)
Taxonomy of Calcaronea
FamilyJENKINIDAEn.fam. Order LITHONIDA Vacelet, 1981
Genus Breitfussian.gen. Family MINCHINELLIDAE Dendy & Row,
Genus JenkinaBrøndsted, 1931 1913
Genus *LeucascandraBorojevic Genus MinchinellaKirkpatrick, 1908
& Klautau, 2000 Genus Plectroninia Hinde, 1900
Genus *AnamixillaPoléjaeff, 1883 Genus *Monoplectroninia Pouliquen &
Genus *Polejaevian.gen. Vacelet, 1970
Genus *UteopsisDendy & Row, 1913 Genus *Petrostroma Döderlein, 1892
Genus *TuleariniaVacelet, 1977
FamilyHETEROPIIDAEDendy, 1892
Genus *Syconessan.gen. FamilyPETROBIONIDAEBorojevic, 1979
Genus SycettusaHaeckel, 1872 Genus *Petrobiona Vacelet & Lévi, 1958
Genus *Grantilla Row, 1909
Genus Grantessa Lendenfeld, 1885 * Genus with only one described species.
Genus HeteropiaCarter, 1886
Genus *ParaheteropiaBorojevic, 1965
Genus VosmaeropsisDendy, 1892 INTRODUCTION
FamilyAMPHORISCIDAEDendy, 1892 In a previous study (Borojevic et al. 1990), we
Genus AmphoriscusHaeckel, 1872
revised the classification of Recent calcareous
Genus LeucillaHaeckel, 1872
sponges belonging to the subclass Calcinea
Genus ParaleucillaDendy, 1892
Bidder, 1898, in an attempt to redefine the cur-
rently recognized families and genera and to trace
FamilySTAURORRHAPHIDAEJenkin, 1908 the possible evolutionary pathways in this sub-
Genus AchramorphaJenkin, 1908
class of the Calcarea. The present study is a con-
Genus MegapogonJenkin, 1908
tinuation of this revision, extending it now to the
Recent sponges belonging to the subclass
FamilyLELAPIIDAEDendy& Row, 1913
Calcaronea Bidder, 1898.
Genus Grantiopsis Dendy, 1892
The common characteristic of all representatives
Genus *KebiraRow, 1909
of the Calcarea is the presence of calcium carbon-
Genus *ParalelapiaHôzawa, 1923
ate spicules that have a basal diactine or triactine
Genus LelapiaGray, 1867
structure. Calcareous spicules are secreted into an
intercellular space that is delimited by two or
FamilyINCERTAESEDIS
more cells. Although molecular evolutionary
Genus Sycyssa Haeckel, 1872
studies have identified a potential early common
Order BAERIIDA n.ord. origin of the two subclasses of the Calcarea, there
FamilyBAERIIDAEn.fam. is no convincing molecular evidence for a close
Genus Baeria Miklucho-Maclay, 1870 relationship between Calcarea and other sponges
Genus *Lamontia Kirk, 1895 (Lafay et al. 1992; Cavalier-Smith et al. 1996;
Genus *Leucopsila Dendy & Row, 1913 Borchiellini et al. 1999). To our knowledge, no
Genus *EilhardiaPoléjaeff, 1883 study has been conducted on molecular phyloge-
ny within the subclass Calcaronea, and the pre-
FamilyTRICHOGYPSIIDAEn.fam. sent revision is based on morphological and
Genus Trichogypsia Carter, 1871 anatomical data.
Genus *KuarrhaphisDendy & Row, 1913 Dendy & Row (1913) conducted the first major
Genus *Leucyssa Haeckel, 1872 general revision of the Calcaronea in an attempt
to classify all the described genera into the evolu-
FamilyLEPIDOLEUCONIDAEVacelet, 1967 tionary pathways recognized at the time. Since
Genus *LepidoleuconVacelet, 1967 then there have been several modifications of that
ZOOSYSTEMA • 2000 • 22 (2) 205
Borojevic R., Boury-Esnault N. & Vacelet J.
proposal (Laubenfels 1936; Hartman 1958; pathway, but this cannot be reconstructed from
Borojevic 1979; Vacelet 1991). But despite the morphological data alone.
recent description of new species and even higher Using this approach, we have confirmed the sepa-
taxa, and the availability of new information ration of sponges that we now group in the order
gathered from cell and developmental biology, Leucosoleniida from those belonging to the
genetics, biochemistry, as well as observations of Lithonida, in agreement with the previously pro-
morphology at both the microscopic and the posed classifications (Borojevic 1979; Vacelet
ultrastructural level, there has been no overview 1991). We were also led to separate a group of
of the classification that attempts to group all the sponges considered as “aberrant” by Dendy &
described calcaronean genera so as to show the Row (1913) from the Leucosoleniida, and pro-
putative evolutionary development of the group, pose the recognition of the Baeriida as a new
with the exception of Burton’s (1963) “Revision order in Calcaronea for this group.
of the Classification of the Calcareous Sponges”. The scope of most of the genera is that proposed
The fundamental rationale of the Burton’s revi- by Dendy & Row (1913), who provided very
sion was to analyse the supposed great intraspe- detailed descriptions of the genera, and discussed
cific variability of the Calcarea that has resulted synonymy and correspondence with the previ-
in the merging of species and higher taxa, which ously described taxa extensively. The reader is
had been previously recognized as distinct phylo- referred to that revision for a detailed discussion
genetic and taxonomic units, into a small number on earlier synonymies.
of “genera” and “species”. This drastic decrease in An analysis of the proposed classification will
lower systematic units has not been universally reveal that many points are still uncertain.One of
accepted (see discussion in Borojevic et al.1990). the major drawbacks of any attempt to prepare a
Recent biochemical studies of the Calcarea have general revision of calcareous sponges is the fact
shown that slight morphological differences may that our knowledge on this group is still very
correspond to large genetic differences, and that a fragmentary. The largest collection of Calcarea
full genetic separation of sympatric or allopatric ever studied is that described more than a century
populations is often associated with subtle or ago by Haeckel (1872), who analysed and
even undetectable differences as inferred by the reviewed most of the specimens collected up to
more conventional morphological criteria (Solé- his time. It is noteworthy that Haeckel proposed
Cava et al. 1991; Klautau et al. 1994). Thus the a large portion of the presently recognized genera,
classical taxonomy based on the morphological and in many cases new specimens have not since
criteria is overconservative, and many specimens been found. The Indo-Pacific, Antarctic and
that had been classified as simple variations of the Japanese Calcarea have received more attention,
previously described and often cosmopolitan mostly during the period between the end of the
species, probably represent distinct taxonomic last century and the first part of this century, but
units. the fauna of calcareous sponges in many other
In the present work we have tried to identify the regions remains very poorly known. A review of
taxonomic units that potentially represent mono- any collection, even from regions one would
phyletic groups of species within the Calcaronea, expect to be much studied such as the European
and we have tried to identify all the possible evo- coasts of the Atlantic or the Mediterranean, pro-
lutionary pathways, leading from the simplest duces many new species that frequently belong to
Calcaronea, such as Leucosolenia, to the most new higher taxa, indicating that our knowledge
complex, such as Lelapia. We present the more of the diversity of this group of sponges is very
complex types of skeletal and tissue organization incomplete. The present revision aims at gather-
as deriving from simpler ones, and follow the ing and assessing the available data so as to guide
conventional view that the simple “ascon” type of the supraspecific identification of the Calcaronea,
sponge organization is “primitive”. This does not and propose a framework for future cellular and
mean that we interpret the progressive increase of molecular studies, which should give new
complexity as necessarily the true evolutionary insights into the biology of this group. This
206 ZOOSYSTEMA • 2000 • 22 (2)
Taxonomy of Calcaronea
A B
n
FIG.1.—Syconsycandra; A, SEM view of the choanoderm; B, a choanocyte showing the typical apical nucleus (n) of the Calcaronea
(TEM). Scale bars: A, 3µm; B, 0.7µm.
approach will highlight the taxonomic questions The skeleton is composed of free diactine, triactine,
which should be addressed in future morphologi- tetractine and/or polyactine spicules, to which can be
added a solid basal calcitic skeleton with basal spicules
cal, genetic and molecular studies of the Calcarea.
either cemented together or completely embedded in
For all the terms of sponge morphology we refer
an enveloping calcareous cement. The aquiferous sys-
the reader to Boury-Esnault & Rützler (1997). tem can be asconoid, syconoid, sylleibid or leuconoid.
Members of the Calcarea are viviparous and their lar-
vae are blastulae.
ABBREVIATIONSUSED
MNHN Muséum national d’Histoire naturelle, Paris.
Subclass CALCARONEA Bidder, 1898
BMNH Natural History Museum, London.
DIAGNOSIS.— Calcarea with diactines and/or sagittal
triactines and tetractines, rarely also with regular
SYSTEMATICS spicules. In addition to the free spicules, there can be a
non-spicular basal calcareous skeleton in which basal
Class CALCAREA Bowerbank, 1864 spicules are cemented together or completely embed-
ded in an enveloping calcareous cement. In ontogeny,
DIAGNOSIS. — Marine Porifera in which the mineral the first spicules to be produced are diactines in the
skeleton is composed entirely of calcium carbonate. settled larva. No information is available for the early
ZOOSYSTEMA • 2000 • 22 (2) 207
Borojevic R., Boury-Esnault N. & Vacelet J.
spicules, which may belong to calcaronean
sponges have been reported from Early Cambrian
reefs (James & Klappa 1983) and in Ordovician
strata (Van Kempen 1978), but no unequivocal
calcaronean fossils have yet been found (Reitner
& Mehl 1995).
The aquiferous system in the Calcaronea can be
asconoid, syconoid, sylleibid or leuconoid.
Asconoid, syconoid, and sylleibid systems are
sp found only in the Leucosoleniida. The leuconoid
cc
aquiferous system, such as that seen in the
Leucosoleniida, can easily be derived from a
syconoid type of organization, as these sponges
retain traces of the radial organization of the
skeleton and the usually clearly defined central
atrium. However, the leuconoid systems in the
Baeriida and the Lithonida bear no trace of an
o
original tubular or radial organization, but are
instead quite similar to the leuconoid aquiferous
systems of the Demospongiae.
Calcaronean sponges have choanocytes with an
apical, ovoid or pyriform nucleus. The basal fla-
gellar roots are always in contact with the nuclear
envelope at the apical pole of the nucleus. In many
species, a glycocalyx layer is present between the
microvilli which form the collar (Fig.1). The inter-
FIG.2.— Fertilization in Leucillla. Transmission electron pretation of the localization of the nucleus within
microscopy (TEM). Abbreviations: cc, choanocyte chamber;
o,osculum; sp, spicule. Scale bar: 1µm. (Courtesy Dr M.-F. the choanocytes is often hampered by artefacts
Gallissian). caused by handling of sponge collections and their
fixation. Since this is one of the most distinctive
characters distinguishing the Calcinea from the
stages of postlarval development in the Baeriida and
the Lithonida. Choanocytes are apinucleate and the Calcaronea, sections of preserved material must be
basal system of the flagellum is adjacent to the apical interpreted with caution (Vacelet 1964).
region of the nucleus. The first stage in embryogenesis Despite the observed great diversity of body plan,
is a coeloblastula in which the flagella are internal and
our present knowledge of calcaronean biology, in
face into the central cavity. This blastula passes
through a complex inversion, turning the flagellated particular their cell and skeletal morphology,
pole of the blastomeres to the outside, and giving rise indicates that there are a number of homologies
to an amphiblastula larva, in which the anterior pole is among currently known species, and strongly
flagellated and the posterior pole is bare. After settle-
supports the hypothesis of their common origin
ment, the flagellated cells give rise to choanocytes, and
as well as a rather close relationship among all the
the large posterior aflagellated cells give rise to the
other cell categories of the sponge, pinacocytes, poro- sponges belonging to this subclass. Most notably,
cytes, sclerocytes and to the amoeboid cells that are sponges in the Calcaronea have a typical fertiliza-
found between the choanoderm and the pinacoderm. tion process and a very particular pattern of
embryogenesis and larval morphogenesis.
DESCRIPTION During fertilization, the spermatozoa are cap-
Like the calcineans, calcaroneans are extremely tured by choanocytes, which transform into a
variable in size, form, organization of the aquifer- particular spermatozoon carrier cell containing
ous system, and skeleton. Most of the representa- the spermiocyst (Duboscq & Tuzet 1937, 1942;
tives are known only from Recent seas. Isolated Vacelet 1964; Gallissian 1989; Gallissian &
208 ZOOSYSTEMA • 2000 • 22 (2)
Taxonomy of Calcaronea
A B C
D E
F
FIG.3.— Diagram of the stomoblastula showing the phenomenon of inversion; A, fertilization; B, stomoblastula with the flagellum of
the flagellated cells inside the blastocoel; C, inversion; D, amphiblatula with flagellae outside; E, mature free-swimming amphiblastula;
F, young rhagon after metamorphosis.
Vacelet 1990). These cells migrate into the sub- ing the flagella outwards. The larva closes again,
choanodermal space where they fertilize large delimiting a secondary blastocoel (Fig.3). At this
mature oocytes. The entrance point of the carrier stage the larva is a typical amphiblastula with
cell into the oocyte determines the symmetry of clearly marked poles: the flagellated pole corre-
the future larva in the Leucosoleniida, but appar- sponds to the anterior pole of the free-swimming
ently not in a sponge that we currently classify in larva, while the large aflagellated cells are restrict-
the Baeriida (Duboscq & Tuzet 1937, 1942). ed to the posterior pole (Fig.4). After settlement,
Only small differences were observed in the fertil- the large aflagellated cells give rise to pinacocytes,
ization process in different species of the cal- sclerocytes and to other amoeboid cells, while the
caronean sponges studied until now. There is flagellated cells differentiate into choanocytes
only one report of a similar fertilization process (Amano & Hori 1993). The inversion of the
in the rest of the Calcarea (Tuzet 1947) (Fig.2). early larva is unique and specific to the subclass
The amphiblastula larva has large aflagellated Calcaronea, and is reminiscent of the morpho-
cells at one end and small flagellated cells at the genesis of Volvox (Ivanov 1971). The amphiblas-
other. There are four “cellules en croix” which tula larvae of the Calcaronea differ from all other
have the presumed function of photoreceptors sponge larvae. They are only superficially similar
(Duboscq & Tuzet 1941; Borojevic 1970; to the larvae of the Homoscleromorpha, which
Amano & Hori 1992). At the early blastula stage have been described as amphiblastula, but which
the flagella are directed inwards into the primary are now termed “cinctoblastula” in order to
blastocoel. Subsequently, in the stage called the underline these differences (Boury-Esnault et al.
stomoblastula, the aflagellated cells form an 1995). In the order Leucosoleniida, after the set-
opening through which the flagellated blastula tlement of the larva, an asconoid tubular sponge
wall evaginates, inverting the larval wall and turn- is formed, which can remain at this stage of orga-
ZOOSYSTEMA • 2000 • 22 (2) 209
Borojevic R., Boury-Esnault N. & Vacelet J.
a
FIG.4.— An amphiblastula larva (a) in the parental sponge. FIG.5.— Young Syconsycandrain the sycettid stage. Scale
Scanning electron microscopy (SEM). Scale bar: 8µm. bar: 1.7 mm.
nization (e.g. Leucosolenia) or form radial out- homogenous group of sponges, in which are
growths which give rise to the radial tubes of the found all the possible modifications of the funda-
syconoid grade of organization (Fig. 5) (Schulze mental pattern of the sponge body organization,
1875). The postlarval development of the other from asconoid to leuconoid, and including most
two orders of the Calcaronea is not known. of the intermediate stages of the progressive mod-
ifications of the associated skeleton. Conse-
quently, we consider that the Leucosoleniida
Order LEUCOSOLENIIDA Hartman,
represents a single taxonomic unit that cannot be
1958 emend.
divided into two groups, according to homocoel
DIAGNOSIS.—Calcaronea with a skeleton composed of or heterocoel grade of organization as proposed
exclusively free spicules, without calcified non-spicular by Hartman (1958).
reinforcements. The aquiferous system is asconoid, The simplest forms correspond to the olynthus
syconoid, sylleibid or leuconoid. In the latter case, the
grade of organization, with a single tubular cen-
radial organization around a central atrium can gener-
ally be detected by a well-formed atrial skeleton tan- tral cavity lined by choanocytes (family
gential to the atrial wall, and/or a subatrial skeleton Leucosoleniidae) (Fig. 6). However, whereas in
consisting of subatrial tri- or tetractines with the paired the Clathrinida, the olynthus form has given rise
actines tangential to the atrial wall and the unpaired
to several independent evolutionary lineages (see
actine perpendicular to it. The post-larval development
Borojevic et al. 1990) in the Leucosoleniida, the
passes (presumably always) through an olynthus stage.
major and, as far as we are aware, sole evolution-
ary line from the homocoel to the heterocoel
DESCRIPTION grade of organization passes through a sycettid
Like the calcinean order Clathrinida (Borojevic et grade of organization.Sycetta is characterized by a
al., 1990), the Leucosoleniida represents a single central tube devoid of choanocytes, which
210 ZOOSYSTEMA • 2000 • 22 (2)
Taxonomy of Calcaronea
o
ps ps
ch
a
FIG.6.— Diagram of an asconoid aquiferous system, such as is FIG.7.—Diagram of the Sycettatype of organization of the
found in Leucosolenia. Abbreviations: ps, pinacoderm and the sponge wall. Abbreviations: ps, pinacoderm and the skeletoge-
skeletogenous layer; ch, choanoderm. The arrow shows the nous layer; a, atrium; o, osculum. The arrow shows the direction
direction of water flow. of water flow.
corresponds to the atrium, from which tubes rate. At this stage they have an inarticulate
with a choanoderm radiate (Fig. 7). This sponge choanoskeleton, i.e. the central atrial tube has a
has only an exhalant aquiferous system; the distinctive tangential skeleton, but the radial
incurrent water flows directly into the radial tubes perpendicular to the atrium are primarily
tubes through inhalant pores (Figs7; 8). supported by subatrial triactines whose paired
The first group of morphological characters used actines are adjacent to the atrial skeleton, and the
to define the Leucosoleniida is the overall shape unpaired ones support the radial tube walls. The
and the underlying skeletal support of the tubes. distal cones have peculiar small triactines.
Increase in size from the sycettid grade of organi- The evolutionary lineages of the Sycettidae-
zation may occur by two different processes: the Grantiidae and Heteropiidae bifurcate from this
growth and elongation of radial tubes which point. Whereas in the Sycettidae, this type of
increases the thickness of the sponge body, or the inarticulated organization is found only in very
growth of the central tube containing the atrial young specimens of Sycon and Sycetta, in the
cavity, which increases the length of the sponge Heteropiidae, the inarticulate choanoskeleton is
body. Both processes can be observed in the found in Syconessa and in Sycettusa, which also
Leucosoleniida: has distal cones that are fused into a continuous
A) the first process has given rise to two evolu- tangential cortical layer. In both families the
tionary pathways. The first is well-depicted by elongation of radial tubes and their progressive
very young specimens of Sycon, as well as adult coalescence result in a compact body that has a
Sycetta, where the radial tubes are short and sepa- strictly radial organization, such as is found in
ZOOSYSTEMA • 2000 • 22 (2) 211
Borojevic R., Boury-Esnault N. & Vacelet J.
ps
ec a
dc
cx
ic
a
ch
ic
ch
FIG.8.—Diagram of Sycontype of sponge wall organization. FIG.9.— Diagram of the sylleibid type of aquiferous system
Abbreviations: ps, pinacoderm and the skeletogenous layer; ch, organization, such as observed in Polejaevia, Paralelapia,and
choanoderm; a, atrium; dc, distal cones; ic, inhalant canals. The Leucilla. Abbreviations: cx, cortex; ch, choanoderm; a, atrium;
arrow shows the direction of water flow. ic, inhalant cavities; ec, exhalant cavities.
typical adult representatives of Sycon (Fig. 8) and ilar triactine spicules. In the first subatrial row, the
Grantessa. The radial tubes are intercalated with paired actines are adjacent to the atrial skeleton and
narrow inhalant canals with an inhalant pore- the unpaired actine is perpendicular to it, lying in
bearing membrane devoid of skeleton. the wall of the radial tube. This is the most com-
Progressively, a common cortex covers the external mon form of subatrial skeleton, and is easily rec-
part of the radial tubes and the openings of inhalant ognized in all heterocoel Leucosoleniida. Although
canals, i.e. the inhalant pores move to the cortical the spicules of the choanoskeleton can be irregu-
surface, and the cortex becomes supported by a spe- larly scattered in massive sponges with a leuconoid
cific skeleton.Such corticalization has given rise to aquiferous system such as Leucandra, the original
a wide range of sponges with a solid body and with orientation of many triactines with the unpaired
elaborate skeleton.The aquiferous system changes angle turned to the atrium and the unpaired actine
from long choanocyte chambers arranged radially pointing distally, is frequently preserved. As indi-
around the central atrium, characteristic of the cated earlier, this evolutionary line has bifurcated
syconoid system (Fig. 8), to shorter elongate or quite early into two pathways that are distin-
ovoid choanocyte chambers arranged around guished by the presence or absence of pseu-
radial exhalant cavities, such as observed in the dosagittal spicules in the distal part of the radial
sylleibid aquiferous system (Fig. 9), and to ovoid tubes. In both pathways, there is both increased
or spherical choanocyte chambers arranged corticalization, and progressive evolution of the
between the inhalant and exhalant canals, such as syconoid organization into the leuconoid one (see
observed in sponges with a typical leuconoid aquif- descriptions of the families Grantiidae and
erous system (Fig. 10). Sponges belonging to the Heteropiidae).
latter evolutionary pathway usually have a typical B) The second process has also given rise to two
articulate choanoskeleton, i.e. several rows of sim- evolutionary pathways. The first one is analogous
212 ZOOSYSTEMA • 2000 • 22 (2)
