%0 Journal Article
%A Bartolomaeus, Thomas
%D 1999
%T Structure, function and development of segmental organs in Annelida
%J Hydrobiologia
%V 402
%P 21-37
%K ANNELIDA; REPRODUCTION; HYDROBIOLOGIA402; EVOLUTION;
ANNELIDA; NEPHRIDIA; ULTRASTRUCTURE
%X The spermatozoa of clitellates are filiform cells with the acrosome situated
in the anteriormost position, followed by the nucleus, the midpiece, and the tail.
With respect to the basic plan of a 'modified' sperm type , the clitellate
spermatozoon is characterized by the presence of an acrosome tube containing
to a variable extent the (withdrawn) acrosome vesicle, by the mitochondria being
interposed between the nucleus and the tail, and by peculiar modifications of the
central apparatus of the axoneme. The oligochaetes sensu stricto are
characterized by the presence of a basal cylinder situated inside the basal body;
the branchiobdellidans by an apical, conical indentation of the nucleus and by a
helical marginal fiber coiled around the tail; the acanthobdellids by a dense
sheath and accessory fibers surrounding the axoneme; the euhirudineans by an
anterior prolongation of the acrosome tube, the anterior acrosome. Other sperm
characters are shared by various combinations of taxa. With the aim of using
sperm morphology as a tool for phylogenetic analysis, we identified 22 sperm
characters in 21 species belonging to 12 clitellate families: Capilloventridae,
Enchytraeidae, Tubificidae (with representatives of three subfamilies), Naididae,
Lumbriculidae, Branchiobdellidae, Bdellodrilidae, Cambarincolidae,
Acanthobdellidae, Piscicolidae, Erpobdellidae, Hirudinidae. By the assumption
of the monophyly of those Clitellata having atria or derivatives thereof
associated with the male ducts, and using one enchytraeid and one capilloventrid
as outgroups, we analysed the data using the computer programme PAUP. Our
results strongly support the monophyly of the hirudinean (i.e.,
acanthobdellid+euhirudinean) assemblage, as well as the close relationship
between this group and the branchiobdellidans. Although a link between the
branchiobdellidan-hirudinean clade and the Lumbriculidae is not refuted, sperm
do not provide enough evidence for establishing the exact phylogenetic position
of this clade within the Oligochaeta.
In Annelida, nearly each segment contains a pair of ducts that either are
protonephridia or metanephridia. These segmental organs function as excretory
organs and, after having been modified, they may also act as gonoducts during
maturity. In certain polychaetous annelids and especially in clitellates this
function has been adopted by additional gonoducts which generally are formed at
the begining of maturity. At the end of the last century the gonocoel theory tried
to explain the relation between gonads, coelomic cavities and nephridia. Using
the gonocoel theory axiomatically, Goodrich (1945) assumed that in annelids a
pair of protonephridia and a pair of gonoducts represent the primary condition.
Evolution of metanephridia on the one hand and the fusion of gonoducts and
nephridia on the other hand occurred within the Annelida. Based on recent
ultrastructural investigations into the development of different segmental
organs, this paper re-evaluates Goodrich's hypothesis. According to these data
the segmental organs differentiate from a single anlage. Each consists of three
or four cells which line a small lumen filled with microvilli. The duct becomes
ciliated and the most proximal cells are separated when the coelom extends by
fluid accumulation between the lining cells. During enlargement of the coelomic
cavity the proximal part of the anlage is passively opened, so that the cilia face
the coelom, to form the funnel. If separation of the proximal duct cells is
suppressed, the anlage differentiates into a protonephridium, which secondarily
may acquire a funnel during maturity by proliferation of proximal duct cells.
Thus, different pathways in nephridial development lead to completely different
segmental organs in the fertile adult. Additional gonoducts evolve in different
lineages within the annelids.
%0 Journal Article
%A Blake, James A.
%A Arnofsky, Pamela L.
%D 1999
%T Reproduction and larval development of the spioniform Polychaeta with
application to systematics and phylogeny
%J Hydrobiologia
%V 402
%P 57-106
%K HYDROBIOLOGIA402; Spionidae; Apistobranchidae; Longosomatidae;
Poecilochaetidae; Trochochaetidae; Uncispionidae; REPRODUCTION; REVIEW
%X The reproduction and larval development of spioniform polychaetes are
reviewed. Asexual reproduction is relatively rare, being reported for only eight
species belonging to the genus Pygospio and some polydorids. Both architomy
and paratomy are known, with the latter limited to small species of
Pseudopolydora (sometimes referred to Polydorella) and one species of
Polydora. Architomy is often the primary form of reproduction in Pygospio
elegans and contributes to the maintenance of large populations. Three types of
eggs (thin egg envelopes, thick egg envelopes, smooth or reticulated, and thick
egg envelopes, honeycombed), two types of oogenesis (extraovarian and
intraovarian), and two types of sperm (ect-aquasperm and introsperm) occur in
spioniforms. Egg and sperm type are restricted to specific clades. Eggs with
thickened egg envelopes appear to be limited to spioniforms, whereas the thin
egg envelope found in some spionids occurs in other polychaete families,
suggesting that thin egg envelopes are plesiomorphic for spionids.
Spermatophores occur in the spionid subfamily Spioninae and are formed in the
male nephridia. Spioniforms exhibit a diversity of reproductive and larval
patterns including broadcast spawning, external egg masses, brooding in capsules
in tubes of females and brooding on the bodies of females. Poecilogony is
unusually common in the Spionidae. A phylogenetic analysis demonstrates that
reproductive and larval characters, when used in combination with selected adult
characters, provide a more complete database to evaluate systematic and
phylogenetic relationships than only adult morphology. Preliminary results of
parsimony suggest that the Spionidae are paraphyletic and that its definition and
the status of related spioniform polychaetes needs to be reassessed with regard
to family level classification.
Keywords Spionidae, Apistobranchidae, Longosomatidae, Poecilochaetidae,
Trochochaetidae, Uncispionidae
%0 Journal Article
%A Dohle, Wolfgang
%D 1999
%T The ancestral cleavage pattern of the clitellates and its phylogenetic
deviations
%J Hydrobiologia
%V 402
%P 267-283
%K ANNELIDA; REPRODUCTION; HYDROBIOLOGIA402; SPIRAL
CLEAVAGE; 4D CELL; ANNELIDA; CLITELLATA; ACANTHOBDELLA;
REVIEW
%X The cleavage pattern of the ancestor of the monophyletic taxon Clitellata is
reconstructed. It resembles the complicated cleavage pattern of the
glossiphoniid leeches in nearly every detail. This can be inferred from a
comparison with the peculiar fish leech, Acanthobdella peledina, on the one
hand, and with several oligochaetes, like tubificids, enchytraeids and
branchiobdellids, on the other hand. The ancestral pattern has been profoundly
altered several times in leeches and in oligochaetes. Examples are hirudinids and
erpobdellids as well as lumbricids and naidids. The alterations occur in small
eggs with little yolk which are nourished by the surrounding fluid within the
cocoon. Comparisons with polychaetes lead to the conclusion that an early
specification of the 2d cell must be a feature of the annelid ancestor and that
equal cleavage represents the derived case in the annelids.
%0 Journal Article
%A Ferraguti, Marco
%A Erséus, Christer
%D 1999
%T Sperm types and their use for a phylogenetic analysis of aquatic clitellates
%J Hydrobiologia
%V 402
%P 225-237
%K ANNELIDA; REPRODUCTION; HYDROBIOLOGIA402; AQUATIC
CLITELLATES; PHYLOGENY; SPERMATOZOA; OLIGOCHAETA;
BRANCHIOBDELLIDA; HIRUDINEA
%X The spermatozoa of clitellates are filiform cells with the acrosome situated
in the anteriormost position, followed by the nucleus, the midpiece, and the tail.
With respect to the basic plan of a 'modified' sperm type , the clitellate
spermatozoon is characterized by the presence of an acrosome tube containing
to a variable extent the (withdrawn) acrosome vesicle, by the mitochondria being
interposed between the nucleus and the tail, and by peculiar modifications of the
central apparatus of the axoneme. The oligochaetes sensu stricto are
characterized by the presence of a basal cylinder situated inside the basal body;
the branchiobdellidans by an apical, conical indentation of the nucleus and by a
helical marginal fiber coiled around the tail; the acanthobdellids by a dense
sheath and accessory fibers surrounding the axoneme; the euhirudineans by an
anterior prolongation of the acrosome tube, the anterior acrosome. Other sperm
characters are shared by various combinations of taxa. With the aim of using
sperm morphology as a tool for phylogenetic analysis, we identified 22 sperm
characters in 21 species belonging to 12 clitellate families: Capilloventridae,
Enchytraeidae, Tubificidae (with representatives of three subfamilies), Naididae,
Lumbriculidae, Branchiobdellidae, Bdellodrilidae, Cambarincolidae,
Acanthobdellidae, Piscicolidae, Erpobdellidae, Hirudinidae. By the assumption
of the monophyly of those Clitellata having atria or derivatives thereof
associated with the male ducts, and using one enchytraeid and one capilloventrid
as outgroups, we analysed the data using the computer programme PAUP. Our
results strongly support the monophyly of the hirudinean (i.e.,
acanthobdellid+euhirudinean) assemblage, as well as the close relationship
between this group and the branchiobdellidans. Although a link between the
branchiobdellidan-hirudinean clade and the Lumbriculidae is not refuted, sperm
do not provide enough evidence for establishing the exact phylogenetic position
of this clade within the Oligochaeta.
%0 Journal Article
%A Fischer, Albrecht
%D 1999
%T Reproductive and developmental phenomena in annelids: a source of
exemplary research problems
%J Hydrobiologia
%V 402
%P 1-20
%K ANNELIDA; REPRODUCTION; epitoky; sexual maturation; stolonization;
positional information; Hydrobiologia special issue; HYDROBIOLOGIA402;
REVIEW
%X Specific traits of reproduction, of early and postembryonic development
and of sexual maturation in annelids are reported, and the existing and expected
contributions to this field from the study of annelids are discussed. The study of
early development, as in other spiralians, reveals the existence of canonical
cleavage patterns and the combined action of antithetical principles, namely
determination by stereotypic sorting-out of 'determinants' and determination
depending upon the interactions between the blastomeres. A high potential of
information about the processes of metameric trunk segment formation and of
segment specification has only begun to be exploited in annelids. Epitoky, the
formation of a free-swimming sexual form in polychaetes, involving tissue
transdifferentiation and conversion of metabolism, locomotory and sensory
capacities, is discussed as a mostly one-way developmental process. The study
of epitoky sheds light on the metabolic relations between soma and germ cells
and on related control mechanisms. The members of epitokous species are
synchronized by meteorological parameters and by pheromones and are adapted
to spawn under pelagic conditions. The metameric construction of the trunk
predisposes for asexual reproduction by fission into trunk fragments
regenerating into complete worms. This mode of reproduction is frequent
among polychaetes and oligochaetes. Trunk fission has been modified in many
polychaetes: posterior fragments ('stolons') are formed, which take over the
function of pelagic, epitokous sexuals and leave behind a 'stock' which lacks
somatic sexual differentiation and can bud further stolons. Naturally occurring,
as well as experimentally induced regeneration, as well as the stolonization
phenomenon, reveal the existence of morphogenetic gradients and of positional
information along the annelid trunk.
%0 Journal Article
%A Franke, Hans-Dieter
%D 1999
%T Reproduction of the Syllidae (Annelida: Polychaeta)
%J Hydrobiologia
%V 402
%P 39-55
%K HYDROBIOLOGIA402; POLYCHAETA; SYLLIDAE; REPRODUCTION;
MODES; TIMING; REVIEW
%X Polychaetes of the family Syllidae exhibit a remarkable diversity of
reproductive phenomena. The primitive mode of sexual reproduction is
characterized by epitoky (as epigamy and stolonization, respectively), swarming
and external fertilization. Deviations from the primitive type, particularly
evident in meiofaunal species, include external brooding, direct sperm transfer,
internal fertilization, viviparity, parthenogenesis, and simultaneous as well as
successive hermaphroditism. True asexual reproduction is rare. The first part of
the paper gives a survey of the various reproductive modes in syllids, with
special reference to recent results. The second part focuses on the mechanisms
of environmental and physiological control of sexual reproduction.
%0 Journal Article
%A Sella, Gabriella
%A Ramella, Liliana
%D 1999
%T Sexual conflict and mating systems in the dorvilleid genus Ophryotrocha
and the dinophilid genus Dinophilus
%J Hydrobiologia
%V 402
%P 203-213
%K ANNELIDA; REPRODUCTION; HYDROBIOLOGIA402; DINOPHILUS;
EGG TRADING; LOCAL MATE COMPETITION; SEXUAL CONFLICT; SIZE
ADVANTAGE HYPOTHESIS; OPHRYOTROCHA; REVIEW
%X Predictions of mating system and sexual conflict theory are applied to
mating systems of the best studied among the simultaneously hermaphroditic,
sequentially hermaphroditic and gonochoric species of the dorvilleid genus
Ophryotrocha and of two species of dinophilids. In the hermaphroditic
Ophryotrocha species, the mating system is characterized by pair mating,
absence of sperm competition and exchange of sexual roles between partners
(egg trading). Features that stabilize the pair bond are analyzed (i.e. breeding sex-
ratio, biparental care, mechanisms against cheating). Male-male competition and
female preference for small males differentiate the mating system of a
sequentially hermaphroditic species from that of a gonochoric species, where
females prefer large males as mates. In the gonochoric species of Dinophilus
different population structures (either panmictic or with sib-mating) select
either for absence of sexual dimorphism and a 1:1 sex ratio or for strong sexual
dimorphism and female biased sex ratio.
%0 Journal Article
%A Hardege, Jörg D.
%D 1999
%T Nereidid polychaetes as model organisms for marine chemical ecology
%J Hydrobiologia
%V 402
%P 145-161
%K HYDROBIOLOGIA402; NEREIS; SEX-PHEROMONES; SPAWNING;
NEREITHIONE; HETEROSPECIFICITY; REVIEW
%X Nereidid polychaetes and indeed many marine invertebrates use chemical
signaling via sex pheromones to coordinate their reproductive behaviour. Sex
pheromones attract the sexual partner and ensure the coordinated release of
gametes by both sexual partners. In the current paper nereidids are used as model
organisms to describe the chemical and behavioural basis of chemical
communication in marine invertebrates. Structure-activity relationships can be
used to chemically classify signals according to their biological function and
suitable purification strategies are described. Pheromones in nereidids include
diverse molecules such as volatile lipophilic 5-methyl-3-heptanone and 3,5-
octadiene-2-one, uric acid and small glutathione derived peptides. A prominent
question in chemical signaling is the species specificity of chemical cues and
the scale of their distribution in the marine environment. This evolves when one
considers the wide overlap in multispecies and multiphyla spawning such as in
coral reefs. Behavioural and electrophysiological assays with several nereidid
species, confirm the existence of heterospecific activity of body fluids from
various phyla. The 'nuptial dance' reproductive behaviour, as well as the release
of gametes, are elicited when individuals are exposed to coelomic fluid of
another nereidid species and also from lugworms, starfish, and sea urchins. The
function of sex pheromones in nereidid polychaetes and their role in the timing
of reproduction in relation to other environmental cues is discussed. Future
research will focus on biosynthesis and reception of nereidid pheromones as
well as their molecular basis and possible interactions with pollutants such as
endocrine disrupters and fuel oil derivatives.
%0 Journal Article
%A Henry, Jonathan J.
%A Martindale, Mark Q.
%D 1999
%T Conservation and innovation in spiralian development
%J Hydrobiologia
%V 402
%P 255-265
%K ANNELIDA; REPRODUCTION; HYDROBIOLOGIA402; EVOLUTION;
SPIRAL CLEAVAGE; SPIRALIA; CELL LINEAGE; REVIEW
%X It is clear that the spiralian developmental program represents a highly
flexible platform for the generation of diverse larval and adult body plans. The
widespread occurrence of this pattern of early development attests to its
tremendous evolutionary success. Despite the large degree of conservation in
the spiral cleavage pattern and other basic aspects of early development, changes
in cell fate maps and in the mechanisms of blastomere specification have arisen.
While we have learned a great deal about this mode of development, a number of
important questions remain to be answered. To what extent do these conditions
apply to the lesser studied spiralian phyla? What constraints have led to the
preservation of the early spiral cleavage program? How has this developmental
program been adapted for the construction of the various spiralian body plans
(e.g. the segmental body plans of annelids or to the potential secondary loss of
segmentation)? Are most changes associated with the elaboration of these
different larval and adult body plans restricted to the late period of development?
What molecular/genetic processes underlie this developmental program?
Clearly, the spiralian phyla represent an important group of organisms for
further studies on development and evolution.
%0 Journal Article
%A Hoeger, Ulrich
%A Rebscher, Nicole
%A Geier, Gunter
%D 1999
%T Metabolite supply in oocytes of Nereis virens: role of nucleosides
%J Hydrobiologia
%V 402
%P 163-174
%K ANNELIDA; REPRODUCTION; HYDROBIOLOGIA402; POLYCHAETES;
NEREIS VIRENS; OOCYTES; ELEOCYTES; METABOLISM; INOSINE
%X Gamete development in Nereis virens and other nereidid polychaetes is
organized in a simple way. Follicular tissues are absent and the germ cells
develop floating freely in the coelomic fluid, which thus serves as the vehicle
for the supply of substances required for oocyte growth. This overview focusses
on the role of exogenous purine nucleosides for the growing oocytes.
Eleocytes, a coelomic cell type which is proliferated in large amounts at the
beginning of sexual maturation, supply purine nucleosides to support nucleic
acid synthesis in the oocytes. Eleocytes can store large amounts of purine
nucleotides (up to 50 mmol ml^-1 cell vol.) in the form of AMP and ADP.
During oogenesis, these nucleotide stores are degraded. A transient increase in
the intracellular concentration of inosine found in eleocytes at the time of
nucleotide degradation and a release of inosine and guanosine measured in
cultivated eleocytes suggests that the stored adenine nucleotides are catabolized
to inosine (INO) and guanosine (GUO) which are exported to the coelomic
fluid. Oocytes of all stages can take up ^{14}C-INO and -GUO by an ATP
dependent, saturable uptake system. The uptake rates are highest at the beginning
of the rapid growth phase; this event corresponds in the eleocytes with the time
of nucleotide breakdown, nucleoside production and nucleoside release. In
uptake experiments with oocytes using physiological concentrations of ^{14}C-
INO, the specific radioactivity of the intracellular INO pool reached that of INO
in the incubation medium after 48h suggesting that the INO pool in the oocytes
would be fed mainly via the coelomic fluid under in vivo conditions. Both
^{14}C-INO and -GUO are converted to adenine and guanine nucleotides in
oocytes with a further incorporation into the nucleic acid fractions. Utilization
of INO for nucleic acid synthesis shows two maxima during oocyte growth: in
the early phase of slow growth, both INO and GUO are almost exclusively
incorporated into the RNA fraction. In the subsequent, rapid growth phase, both
nucleosides are incorporated into both RNA and DNA fractions. During the
latter phase, INO concentrations in the oocytes are at a minimum reflecting an
increased consumption for nucleic acid synthesis. Metabolism of exogenous
INO and GUO by oocytes is relatively slow under natural temperature
conditions. At 12 °C, up to 25% of the totally incorporated ^{14}C-nucleosides
were found in the nucleic acid fractions after 24h. Our data provide evidence for
the utilization of eleocyte-derived exogenous purine nucleosides by the growing
oocytes of Nereis virens. However, pyrimidine nucleosides are equally required
for nucleic acid synthesis but are not released by eleocytes. Oocytes store large
concentrations of the pyrimidine nucleotide precursors cytosine and cytidine.
However, it is not known at present whether these compounds are taken up from
exogenous sources or are synthesized within the oocytes.
%0 Journal Article
%A Olive, Peter J. W.
%D 1999
%T Polychaete aquaculture and polychaete science: a mutual synergism
%J Hydrobiologia
%V 402
%P 175-183
%K HYDROBIOLOGIA402; REVIEW; POLYCHAETA; AQUACULTURE;
PHOTOPERIOD; REPRODUCTION; SEMELPAROUS; NUTRITION
%X In 1984, the commercial aquaculture of the polychaete Nereis virens was
initiated in NE England, at about the same time similar developments took place
in the Netherlands, both establishing alternative sources of this animal as a
means of supplying existing markets for marine worms to be used as bait by sea
anglers. The industry established in NE England has shown a sustained pattern of
growth, and aquaculture has become an accepted means of supplying this niche
market. The industry in NE England has fostered particularly close contacts with
the academic sector having arisen as a transfer of Intellectual Properties from an
institute of higher education (HEI) to a start up private company. The industry
has subsequently sponsored a series of investigations that have stimulated
fundamental research into the growth and reproduction of Polychaeta. This has
resulted in development of techniques for the cryopreservation of the larvae of
marine polychaetes, for photoperiodic manipulation of the time of breeding and
optimisation of the growth process. The information derived from these studies
also suggests a re-interpretation of the life cycle of the Nereididae. The ongoing
development of commercial culture of Polychaeta is likely to give rise to
further developments of a fundamental nature, emphasising the importance of
effective links between centres of academic research and commercial
exploitation.
%0 Journal Article
%A Petersen, Mary E.
%D 1999
%T Reproduction and development in Cirratulidae (Annelida: Polychaeta)
%J Hydrobiologia
%V 402
%P 107-128
%K HYDROBIOLOGIA402; asexual reproduction; brood care; epitoky;
hermaphroditism; life history; TAXONOMY; REVIEW
%X Reproduction and development in 10 genera of Cirratulidae (Annelida:
Polychaeta) are reviewed on the basis of the literature and personal observations
on living and preserved material. Most species are gonochoristic and spawn
freely, but parthenogenesis (Dodecaceria) and hermaphroditism (Aphelochaeta,
Caulleriella, Chaetozone, and perhaps Dodecaceria), sometimes with viviparity
(Caulleriella, Chaetozone, Cirratulus(?) and Dodecaceria), occur in several
genera. Some species of Caulleriella, Cirratulus, Dodecaceria, Protocirrineris,
Timarete, and perhaps Chaetozone, reproduce asexually by architomic
fragmentation, later developing into sexual individuals with or without epitoky.
Asexual regenerates of the first five genera (including types of the bitentaculate
Cirratulus gayheadius) are figured, most species for the first time. Epitoky is
discussed, some features are figured, and the only known male epitoke of
Dodecaceria saxicola is illustrated. Failure to recognize reproductive stages,
especially asexual regenerates, has often led to taxonomic confusion. Cirratulid
gametes are poorly investigated; most observations are anecdotal comments on
presence, color or size of oocytes, less frequently sperm, and are based on light-
microscopical studies; sperm ultrastructure has been described for only one
species of Cirriformia; cirratulid oocytes have not been studied ultrastructurally.
Light microscopical observations show cirratulid sperm to be aquasperm of both
the long-headed (ent-aquasperm, e.g. some species of Aphelochaeta) and short-
headed (ect-aquasperm, all genera?) types. The karyology of cirratulids has been
studied in only three species. Planktonic larvae occur but have not been reported
from the plankton; most observations on larval development are based on
species with direct development, often with brood care in the tube or burrow of
the adult (Aphelochaeta, Dodecaceria), in a jelly mass on the bottom or in the
burrow (Cirratulus, Dodecaceria), or in jelly on the body or among tentacles and
branchiae of the adult (Cirratulus). Some larval stages of Caulleriella (the
hermaphroditic C. parva) are figured for the first time. Sexual dimorphism has
been found in Aphelochaeta and the genus of 'Cirratulus' branchioculatus.
Poecilogony is known for one laboratory culture of Cirriformia. 'Intraspecific'
differences in life histories of 'well known' species probably indicate unjustified
synonymization or failure to recognize distinct elements of species complexes.
Types of Chaetozone setosa Malmgren, 1867, have been examined; a lectotype
is designated herein.
%0 Journal Article
%A Qian, Pei-Yuan
%D 1999
%T Larval settlement of polychaetes
%J Hydrobiologia
%V 402
%P 239-253
%K HYDROBIOLOGIA402; REVIEW; LARVAL SETTLEMENT;
SETTLEMENT CUES; LARVAL; INDUCERS; JUVENILES;
METAMORPHOSIS
%X Many benthic marine invertebrate species have a dispersive larval stage in
their life histories. Larvae typically spend hours, weeks, or months developing in
plankton before they become competent to settle and metamorphose.
Recruitment to benthic populations depends on the numbers of competent larvae
transported to sites and/or the interaction between larvae and the surface of
substratum. While there is considerable evidence that on large spatial scales, the
number of competent larvae transported to sites is determined primarily by
hydrodynamics, success of larval settlement on small spatial scales is mediated
by biotic and abiotic characteristics of substratum. Larvae of many marine
polychaetes require specific cues to settle and metamorphose. Cues can
originate from conspecific or congeneric individuals, microbial films, sympatric
species, food items, or habitat. Larval settlement in an individual species can be
controlled by a single cue or a mixture of cues. Larval settlement of multiple
species can be mediated by a common cue or a mixture of cues. Although a
variety of chemicals, including proteins, free fatty acids, polysaccharides,
inorganic ions, and neurotransmitters, have been suggested as inducing larval
settlement of marine polychaetes, few natural cues have been isolated and
structurally identified.
%0 Journal Article
%A Rouse, Greg W.
%D 1999
%T Polychaete sperm: phylogenetic and functional considerations
%J Hydrobiologia
%V 402
%P 215-224
%K HYDROBIOLOGIA402; REVIEW; SYSTEMATICS; COMPARATIVE
METHOD; PRIMITIVE; SPERM; AQUASPERM; SPERM TRANSFER;
%X The terminology used to describe the sperm of aquatic animals is discussed.
It is argued that the use of the terms 'primitive' and 'modified' sperm confuse
functional associations between sperm morphology and reproductive mode with
perceived phylogenetic patterns. Therefore, terms describing sperm based on
function should be preferred. This terminology is designed to avoid any a priori
judgement of phylogenetic pattern. The various modes of sperm packaging and
transfer in polychaetes are reviewed with regard to the morphology of the
sperm. An example using an explicit phylogenetic hypothesis on the polychaete
family Sabellidae is used to suggest ways to study the evolution of sperm
structure, and to assess functional associations between sperm and reproductive
mode.
%0 Journal Article
%A Sato, Masanori
%D 1999
%T Divergence of reproductive and developmental characteristics in Hediste
(Polychaeta: Nereididae)
%J Hydrobiologia
%V 402
%P 129-143
%K HYDROBIOLOGIA402; REVIEW; REPRODUCTION; EARLY
DEVELOPMENT; GAMETE MORPHOLOGY; LIFE HISTORY; NEREIDIDAE;
HEDISTE; SIBLING SPECIES; SPECIATION
%X Comparative studies on reproductive and developmental features in brackish
water nereidid polychaetes of the genus Hediste (especially two Asian species, a
small- and a large-egg form) are reviewed. General characteristics of the gamete
ultrastructures of the two forms are very similar, though some minor
differences were detected between them. The mode of reproduction, body size
of mature adults, egg size, fecundity and mode of development are markedly
different between the two forms. Not surprisingly, the two forms have
contrasting life histories: the small-egg form with planktonic development
migrates between brackish waters and the sea, while the whole life history of the
large-egg form is usually completed in brackish waters within a river. The
different life histories are reflected in different levels of genetic differentiation
between geographically separated populations of the two forms. The life history
characteristics of the above two Asian forms are compared with those of three
other Hediste species with special reference to a relationship between
developmental pattern and speciation.
%0 Journal Article
%A Southward, Eve C.
%D 1999
%T Development of Perviata and Vestimentifera (Pogonophora)
%J Hydrobiologia
%V 402
%P 185-202
%K HYDROBIOLOGIA402; REVIEW; POGONOPHORA; EMBRYO; LARVA;
SETTLEMENT; JUVENILE GROWTH
%X Existing knowledge of the embryonic and larval development of perviate and
vestimentiferan pogonophorans is reviewed. A form of spiral cleavage has been
reported from both groups, but further clarification is desirable. The perviates
studied have large yolky eggs, incubated in the maternal tube to a ciliated
settlement stage. Others with smaller eggs are still unstudied, but may have
pelagic larvae. Vestimentiferans have small eggs and pelagic, non-feeding larvae.
Comparisons of the development of perviates with that of vestimentiferans lead
to the conclusion that the two groups belong to one higher taxon. An annelidan
relationship is indicated because the ciliated settlement stages of both are like
annelid trochophores in their ciliation and in the way they develop chaetae
initially on two segments.
%0 Journal Article
%A Weisblat, David A.
%D 1999
%T Cellular origins of bilateral symmetry in glossiphoniid leech embryos
%J Hydrobiologia
%V 402
%P 285-290
%K ANNELIDA; REPRODUCTION; ANNELIDA; LEECHES; SPIRAL
CLEAVAGE; BILATERAL SYMMETRY; REVIEW; HYDROBIOLOGIA402
%X In the embryos of glossiphoniid leeches, as in other spirally cleaving
embryos, there is ambiguity as to how the early cleavages in the embryo relate to
the bilateral symmetry of the adult. Traditionally, we have aligned the B-D axis
of the 4-cell stage with the anterior-posterior (A-P) axis of the adult. This
requires that the first cleavage be skewed with respect to the A-P axis. Here, we
re-examine the fates and behaviours of early blastomeres and conclude that a
more accurate representation of the embryo is to have the first cleavage plane
transverse to the A-P axis.
%0 Journal Article
%A Westheide, Wilfried
%A McHugh, Damhnait
%A Purschke, Günter
%A Rouse, Greg
%D 1999
%T Systematization of the Annelida: different approaches
%J Hydrobiologia
%V 402
%P 291-307
%K ANNELIDA; REPRODUCTION; PHYLOGENY; ANNELIDA;
POLYCHAETA; CLITELLATA; POGONOPHORA; ECHIURA;
HYDROBIOLOGIA402
%X Different approaches and different data sets are used to address questions
about the phylogenetic relationships of the polychaete family taxa, the position
of the Clitellata, the monophyletic nature of the Polychaeta and the Annelida, as
well as the position of the Pogonophora and Echiura. In part, the authors of this
contribution come to different conclusions regarding these questions: (1) The
analysis of G. W. Rouse minimizes assumptions about any process concerning
evolution in annelids and makes a detailed series of homology assessments,
based on morphology, across the entire range of taxa concerned. A
monophyletic taxon Polychaeta is found but there is no evidence of a sister
group for the Clitellata among the polychaetes. The Pogonophora are positioned
as members of the Polychaeta. A new classification of the polychaete families is
provided. Problems with coding morphology for cladistic analysis are outlined
and discussed. (2) D. McHugh uses the sequence of a nuclear gene, elongation
factor-1a, for phylogenetic analysis by the parsimony and neighbour joining
methods. The main message from phylogenetic analyses of molecular data is
that there is no evidence for a monophyletic Polychaeta; instead, placement of
the clitellates, pogonophorans and echiurans within the polychaete clade is
supported, rendering the Polychaeta paraphyletic. (3) The phylogenetic system
of W. Westheide and G. Purschke is based on Hennigian reasoning, and their
character weighting is based on diverse, mainly functional considerations. Their
annelid tree shows the Clitellata as a highly evolved monophylum and the
polychaetes as paraphyletic. Special emphasis is placed on the demonstration
that the Clitellata are of terrestrial origin. Advantages and disadvantages of the
different approaches and open questions are discussed.
