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1.1. A review of the southern African ascidian literature
The history of the literature and a bibliographic list for the then known global
ascidian fauna from about 330 B.C. to 1882 A.D. is given by Herdman, 1882 in his
report on solitary ascidians ‘Ascidiae Simplices’ collected during the H.M.S. Challenger
expedition. The voyage can be divided into a series of comparatively short stages
covering the globe from 1873 to 1876. The 1882 report of Herdman includes references
to the preliminary report (Part 1 and 2 of Herdman (1880)) that contains the description
for Clavelina enormis Herdman, 1880 collected from Simon’s Bay, South Africa.
This species description, based on a single specimen, is short and the specimen’s
taxonomic status remains ambiguous (Monniot, C. et al. 2001). In the 1882
report by Herdman an account is given of eighty-two species arranged in (then) twenty
genera.
Herdman’s subsequent report on the colonial ascidians ‘Ascidiae Compositae’ published
in 1886 contained a supplementary list on early literature. The report gives an
account of one hundred and two species arranged in (then) twenty-five genera, which
includes descriptions on eight species collected from the South African coast. The
South African species described were viz.: Atropogaster elongata var. pallida,
Leptoclinum albidum, Goodsiria placenta (junior synonym to Gynandrocarpa
placenta), Goodsiria placenta var. fisca (junior synonym to
Gynandrocarpa placenta), Amaroucium colelloides (junior synonym to
Aplidium colelloides), Psammaplidium exiguum (junior synonym to Aplidium
exiguum), Psammaplidium subviride and Leptoclinum edwardsi.
Diplosomoides molle (junior synonym to Didemnum molle) from Arrou
Island (north of Australia) was subsequently described from the KwaZulu-Natal coast
off South Africa by Monniot et al. (2001).
Adding to our early knowledge of the southern African ascidian fauna was the work
done by Sluiter (1898a) in the report ‘Ergebrisse einer Reise van Prof. Max Weber
in Jahne 1894’. In this work he described thirty-two species, thirty new to science,
one solitary specimen (Microcosmus coalitus) from the Namibian coast, and
nine from neighbouring Mozambique. Species that had been recollected included Amaroucium
flavoliniatum (junior synonym to Aplidium flavolineatum), Polyclinum
isispingense and Distoma caeruleum (junior synonym to Eudistoma caeruleum)
(Michaelsen 1919, Michaelsen 1934, Millar 1956b, Millar 1962a, Lafargue and Vasseur
1989, Monniot, C. et al. 2001).
Michaelsen (1904a) reported on the collections made during the Steamer Valdivia’s
1989-1899 ‘Deutschen Tiefsee-Expedition’ off the Cape of Good Hope, Plettenberg
Bay, St Francis Bay and on the Agulhas Bank. This included new species such as
Halocynthia vanhöffeni (junior synonym to Pyura stolonifera), Cynthiopsis
valdiviae (junior synonym to Pyura herdmandi), Microcosmus albidusand
Monandrocarpa tritonis (for further information see Michaelsen, 1904b). The
subsequent ascidian descriptions by Dr. R Hartmeyer (1912) contributed further to
the knowledge of the group occurring off the southern African coast and led to the
description of twenty-two species of which thirteen were new to science. A subsequent
species list of ascidians from the South African coast, given by Hartmeyer in 1913,
includes new species descriptions for Trididemnum cerebriforme and Aplidium
schultzei.
Work by Michaelsen (1921a) on the Western Indian Ocean, his research in 1923 on
the South African ascidians (Michaelsen 1923c) and his study on ‘The Ascidians of
the Cape Province of South Africa’ (1934) are valuable contributions to our current
knowledge of the ascidian fauna found in southern African waters.
After Michaelsen’s contribution to the taxonomy of South African ascidians two decades
of inactivity was followed by the work of Dr. R.H. Millar, who in his illlustrious
career (stretching from the 1940’s to 1980’s) investigated many aspects of ascidian
biology (Millar 1949a, 1949b, 1951, 1952a, 1953a, 1963b, 1963c, 1971, 1974b), systematics
(Millar 1950, 1952b, 1954a, 1959, 1960d, 1963d, 1966a, 1970a, 1970b, 1978) and evolution
(Millar 1966b). He studied the ascidian fauna of the Scottish (Millar 1950, 1952b,
1960b, 1988d) and British coast (Millar 1970b), northern Europe including Iceland
(Millar 1966c, 1967b, 1974a), Brazil (Millar 1958, 1961b, 1977), the Caribbean (Millar
1962b, Millar and Goodbody 1974), New Zealand (1982b), the Pacific (1975, 1988b,
1988c), Atlantic (Millar1955a, 1982a) and Indian Oceans (1988a), the Antarctic (Millar
1960a, Millar 1968b) as well as the deep water ascidians from Galathea (Millar 1957a,
1964a, 1969a). In addition he investigated and contributed significantly to the
knowledge of the ascidian fauna of southern Africa (Millar 1954b, 1955b, 1956b,
1961a, 1962a, 1963b, 1964b), North Africa and the African Gold coast (Millar 1953b,
1956a, 1957b, 1960c, 1965, 1968c), the Vema Seamount (Millar 1968a) and Madagascar
(Millar 1967a).
This preceded a second period of inactivity where again very little interest was
shown in southern African ascidians and it was only in 1992 that a collection of
ascidians made by Prof. C. L. Griffiths (University of Cape Town, Cape Town) and
Dr. M. Schleyer (Oceanographic Research Institute, Durban) was sent to the internationally
renowned ascidian taxonomists, Dr. C. Monniot and Dr. F. Monniot (at the Muséum
national d’Histoire naturelle, Paris), for taxonomic identification and description.
The subsequent paper, Monniot et al. (2001) describes eighty-two species
of which twenty-two are new. The ascidians were collected mainly from shallow waters
along the coast from Saldanha Bay in the west to Sodwana Bay in the east of the
southern African coast. This publication includes a short summary of the species
previously collected from the southern African coast but not recollected, as well
as species of which the current taxonomic state is ambiguous.
The work by Monniot et al.(2001) concludes the literary contributions made
to South Africa’s ascidian knowledge with the exception of four natural product
papers that describe bioactive secondary metabolites produced by ascidians. These
secondary metabolites include new antimicrobal amines (Hooper et al. 1995)
and new nitrogenous constituents (Rashid et al. 2001) in Pseudodistoma
species from Tsitsikamma Marine Reserve and Algoa Bay off the Eastern Cape coast.
New alkaloids have also been isolated from a species of the Aplousobranchia genera,
Polycitor (family Polycitoridae) from Sodwana Bay (Rudi et al. 1994)
and Lissoclinum (family Didemnidae) from Aliwal Shoal, Umkomas off the KwaZulu-Natal
coast (Patil et al. 1997).
Ascidians are a prominent component of the intertidal and subtidal reef fauna along
the southern African coast, but despite the numerous past contributions very little
is known about these animals, their species composition, distribution and diversity.
Even less is known about their ecology and community structure. About fifty intertidal
species have been described; about ninety-four species from subtidal reefs out to
a depth of 40 m and thirty-nine species from depths of 40-150 m (Parker-Nance 2001).
The above account clearly highlights the incompleteness and sporadic nature of data
collection over the last century and the present meagre species list of the South
African fauna is clearly not a true reflection of the richness, diversity or importance
of ascidians to the structure of South African reefs. This thesis represents the
first study of the taxonomy of southern African ascidian fauna by a resident South
African scientist. The aim of this thesis is therefore to add to the paucity of
knowledge of this unique and important group of organisms.
1.2. Biogeography
Community composition and natural processes occurring along the South African coast
is better understood for the littoral zone than for subtidal habitats (Stephens
1937). Information available on intertidal communities and processes along the southern
African coast suggest that different biogeographical regions exist (Stephens 1937,
Ekman 1953, Briggs 1974, Branch et al. 1994).
The area between Ponta do Ouro (on the Mozambique border) to just north of East
London (to the south) constitutes the subtropical component of the South African
coast (Figure 1). The continental shelf fringing the coast is narrow and the warm
water from the Mozambique channel flows close to shore bringing with it a number
of more tropical Indo Pacific species. The northern part of KwaZulu-Natal is the
only area along the South African coast that has a number of coral reefs; the rest
of the coastline consists of warm temperate reefs (Figure 1).
South of East London the continental shelf increases in width pushing the warm water
away from the coast resulting in cooler water temperatures. The area is characterised
by a warm temperate reef fauna made up of a number of soft-bodied sessile invertebrates.
The main sessile components are sponges, ascidians and bryozoans. Species diversity
and composition is not known.
The area between East London and Cape Point forms a transition zone between the
warm Agulhas on the east coast and the colder Benguela current on the west coast.
The west coast of South Africa has a smaller number of species but sustains highly
productive food chains fuelled by up-welling events when cold nutrient rich water
is brought up to the surface. This has resulted in the area sustaining a lucrative
fishing industry (Lubke and de Moor 1998; Branch et al., 1994).
1.3. Collection sites off the southern African coast
1.3.1. Western Cape Province
The Western Cape Province has a coastline inclusive of the area between the Komkans
on the west coast to the Bloukrans river mouth east of Knysna. Specimens were collected
from South Paw in a depth of 17 to 20 m off Clifton beach between Bantry Bay in
the north and Camps Bay in the south. Specimens were also collected from Vulcan
Rocks situated southwest of Hout Bay, which is situated on the western side of Cape
Peninsula. The reef is composed of a number of large granite boulders and pinnacles,
which causes the surface to break. Collections were made from a depth of 20 to 27
m. Further collections were also made from False Bay, a large bay situated on the
east side of the Cape Peninsula from Cape Point in the west to Kaap Hangklip on
the east. Bakoven is situated just south of Millar’s Point between Simon’s Town
in the north and Smitswinkel Bay in the south. Specimens were collected from a depth
of between 17 to 19 m. The collection of specimens from Plettenberg Bay, situated
on the eastern border of the Western Cape Province, were made from depths of 16
m from Groot Bank and Playground reefs situated north east of Plettenberg Bay between
Plettenberg Bay and Natures Valley (Figure 1).
1.3.2. Eastern Cape Province
The Eastern Cape Province lies between the Bloukrans River mouth on the west and
Port Edward north of East London to the east. Specimens were collected from Tsitsikamma
Marine Reserve, St Francis Bay, Algoa Bay and East London. Collections were made
from Middelbank Reef at depths of 27 to 30 m and Rheeders Reef from a depth of 5
to 30 m within the Tsitsikamma Marine Reserve at the mouth of the Storms River.
Specimens were collected from Thunderbolt reef situated in the eastern side of St
Francis Bay just west of the Cape Recife lighthouse from 18 to 40 m. The area is
not protected and sea conditions may be unpredictable with a large sea and low visibility.
Intertidal collections were made from the Table Mountain sandstone rocky shore off
Cape Recife. This rocky cape divides St Francis Bay to the west from Algoa Bay in
the east (Figure 1).
Algoa Bay is a large crescent-shape bay with depths within the bay up to 66 m. The
subtidal reefs in the western part of the bay are protected and easily accessible.
The reefs that have formed part of specimen collections include Postman’s Reef situated
close inshore at 5 m, Philip’s Reef (Night Reef) from a depth of between 12 to 17
m, off shore from Shark Rock and the Old Slipway. Specimens were also collected
from White Sands Reef from a depth of 12 to 30 m and Bell Buoy at a depth of 20
m. The East London coastline was sampled at Three Sisters off Danger Point north
of Nahoon Point at a depth of between 14 to 19 m and off shore from Cintsa north
of East London at a depth of 16 to 17 m.
1.3.3. Mozambique
Three specimens from a small collection made off the coast of Mozambique by Dr.
P.S. Coetzee (the collection is currently held by the University of Port Elizabeth)
are described in this study. The Mozambique specimens belong to a new species with
a know distribution from Tsitsikamma Marine Reserve in the south to Mozambique in
the north (see Chapter 4 for species descriptions and details on the sample localities).
1.4. Materials and Methods
Ascidian specimens must be collected and preserved with the utmost care. Collected
specimens should be kept alive and be relaxed with menthol as soon as possible after
collection. If not properly relaxed specimens are very difficult to examine and
describe.
Once collected, specimens were submerged in fresh seawater and left to stand for
about an hour without disturbance. A small menthol crystal (ca. 2 mg) was
then added to each of the specimens and the collection was placed in a fridge (ca.
4°C). Samples were then left undisturbed for between 4 to 8 hours after which
sufficient concentrated formaldehyde (37%) was added to give an approximately 10%
formalin solution, without disturbing the samples. The sample containers were then
sealed once mortality had set in. A more concentrated final formalin solution in
seawater was used than the 4 % used by Monniot et al. (2001) to fix and preserve
specimens. Experience has shown that due to the large size of the majority of the
specimens collected a lower concentration sometimes leads to the degradation of
the sample due to decay. Samples left at room temperatures (22 - 30°C) died relatively
quickly and didn’t relax as well as those kept at lower temperatures.
Preserved ascidian specimens were then washed with fresh water to remove formalin
before dissection. Organs were stained with Mayer’s hemalum stain (Humason 1979).
Specimens were dehydrated with ethyl and butyl alcohols prior to mounting on microscope
slides. Canada balsam was used in the mounting and slides were left to dry and clear.
Specimens were then examined and line drawings were made with the aid of a camera
lucida. Measurements were made with the aid of an ocular micrometer. Colour images
were taken of some specimens by means of an Image Analyser camera system.
All type specimens, holotypes and paratypes, are registered in the South African
Museum, Cape Town and have been allocated a SAM A registration number. Additional
material is stored in the Tunicate and Marine Invertebrate Collection housed at
the University of Port Elizabeth. TIC (Tunicate and Invertebrate Collection) numbers
are allocated to all specimens housed in this collection.
1.5. Collection information
Early collections were made by Dr. P.S. Coetzee and are indicated together with
the collection information for each specimen.
Collections by the Coral Reef Research Foundation (CRRF):
This research collaborative programme was made by a group of scientists representing
the Coral Reef Research Foundation under the leadership of Dr. P. Colin and collection
manager Dr. L. Bell-Colin. The CRRF collection team was also accompanied by Mr.
J. Starmer and Mr. D. deMaria, others involved in this collection programme include
Prof. M. Davies-Coleman, Dr. K. McPhail and Dr. C. Gray from the Chemistry Department,
Rhodes University and Ms. S. Parker-Nance and Mr. A. Cloete from the Zoology Department
of the University of Port Elizabeth.
Scripps Institution of Oceanography (SIO) collections:
This research collaboration was made by a group of scientists representing Dr. J.
Faulkner’s laboratory at the Scripps Institute of Oceanography represented by Ms.
C. Sincich, Dr. L. West, Dr. C. Ridley and Dr. D. Mustra by in association with
Prof. M. Davies-Coleman and Dr. C. Gray from the Chemistry Department, Rhodes University
and Ms. S. Parker-Nance and Mr. A. Cloete from the Zoology Department of the University
of Port Elizabeth.
All other collections not cited were made and photographs taken by S. Parker-Nance.
1.5.1. Acronyms used in this study
CRRF - Coral Reef Research Foundation.
SAM - South African Museum, Cape Town, registration numbers allocated to holotypes
and paratypes.
SIO - Scripps Institution of Oceanography.
TIC - Tunicate and Invertebrate Collection numbers for the collection of ascidians
and invertebrates held by the University of Port Elizabeth.
0CDN - Collection of the Coral Reef Research Foundation housed in Koror, Palau.
1.6. A brief introduction to ascidian biology
1.6.1. General body structure
The growth form of ascidians can be either solitary (Kott 1985, Monniot, C. et
al. 1991) or colonial (Kott 1990, 1992, 2001). Solitary species consist of
a single individual surrounded by a tunic (Goodbody 1974), which in the case of
Pyura stolonifera (Heller, 1878) is tough and protective and may be covered
by numerous epibiont species (Figure 2a) (Millar 1955b, Millar 1962a, Kott 1985).
Ciona intestinalis (Linnaeus, 1767) which, is common in harbours and marinas
and becomes problematic because of its fouling tendencies, has a soft, almost transparent,
outer test without epibionts (Kott 1990). Solitary species generally have a sac-like
body with the branchial sac occupying the greater part of the individual. The gut,
the gonads and the heart are situated along side of the branchial sac (Figure 3a)
(Kott 1985, Monniot, C. et al. 1991).
Colonial species are characterised by a large number of zooids that are connected
or embedded to varying degrees by or in a common test. In Pseudodistoma africanum
Millar, 1954b and P. digitum sp. nov. the zooids are completely embedded
(Figure 2b,c). In the cosmopolitan species Clavelina lepadiformis (Müller,
1776) the zooids are connected only by the basal stolons (Figure 2d) (Monniot, C.
et al. 2001). The individuals reproduce sexually but colonies grow by asexual
reproduction e.g. strobilation and, or budding (Berrill 1950, Kott 1992). For developmental
information and aspects concerning the gametes, fertilization and embryogenesis,
metamorphosis and asexual development in solitary and colonial ascidians see Berrill
(1950) and Satoh (1994).
Zooids of the Aplousobranchia have the gut loop below the branchial sac. The body
of the zooid can be divided in two or three regions. Zooid of e.g. the family
Didemnidae has no posterior abdomen with the thorax containing the branchial
sac and an abdomen that contains the gut and gonads (Kott 2001). Zooids of e.g.
the genus Pseudodistoma and Polyclinum have a posterior abdomen in
which the gonad and heart are situated (Berrill 1950, Monniot, C. et al.
1991, Kott 1992). The posterior abdomen is continuous with the abdomen in Pseudodistoma
but is constricted off the abdomen in Polyclinum species. The structure of
the branchial sac, the gut and the position and structure of the gonads are all
important characteristics in identifying the various genera and species (Kott 1992).
The branchial opening forms the inhalant aperture and leads to the branchial sac.
Water is pulled into the branchial sac by the action of the cilia on the stigmata
within the branchial sac wall. The atrial opening is the exhalant aperture through
which the filtered water and faecal matter leaves the zooid. Depending on the species
the atrial aperture may open directly to the surface of the colony (as is in the
genus Euherdmania and Pseudodistoma), alternatively, a number of zooids
may open into a chamber within the colony as found in the genera Polyclinum
and Polysyncraton (Kott 1990, 2001). This chamber is connected to the exterior
by a single opening. These structures are known as common cloacal systems and the
zooids may be arranged in simple circular systems or the systems may be extensive
and elaborate.
1.6.2 The branchial sac
Ascidians are filter feeders inhaling water through the branchial aperture into
the branchial sac, which is a sac-shaped filtering device with perforated walls.
These perforations, or stigmata, are lined with cilia. The synchronously beating
of the cilia on the stigmata generates the current necessary for the movement of
water into the branchial sac (Berrill 1950, Goodbody 1974, Monniot, C. et al.1991).
The internal surface of the branchial sac is lined with a thin net-like mucus lining,
which is secreted by cells in the endostyle, situated along the mid-ventral line
(Figure 3a(3)). The mucus net moves over the branchial sac dorsally and posteriorly
in the direction of the oesophagus. The food particles suspended in the incoming
water are caught in this mucus layer or net and the filtered water leaves the branchial
sac through the stigmata. From the branchial sac the filtered water moves into the
peribranchial or atrial cavity. The mucus net is rolled into a strand dorsally by
the dorsal languets, then the strand moves posteriorly into the oesophagus. This
strand is laden with captured food particles and is pulled gradually towards the
oesophagus to the stomach where the food particles are digested.
1.6.3. The gut loop (digestive tract)
The gut loop is situated along side (as in solitary ascidians Figure 3a) or beneath
the branchial sac (as in colonial species Figure 3b) and divided into a number of
sections (Goodbody 1974, Kott 1990, Monniot, C. et al. 1991). Food particles
are digested in the stomach, which in turns leads into a mid-intestinal region and
a post-stomach. The faecal matter in the rectum is deposited in the peribranchial
cavity (also known as the atrial cavity) via the anus. From the peribranchial cavity
the faecal matter is removed from the animal by filtered water flowing out of the
branchial sac and pumped to the exterior via the atrial aperture.
1.6.4. Larvae
Ascidian larvae of the Aplousobranchia are generally the shape of tadpoles and can
be divided into the larval trunk and a tail. The trunk contains adhesive papillae
(usually three) at its anterior end while interiorly there is a cerebral vesicle
(containing an ocellus and a unicellular otolith) as well as the developing branchial
sac and gut. The larvae are non-feeding and the tail is used for mobility aiding
in the dispersion of the larvae. The tail muscles are arranged on each side of the
single row of around forty cells that represent the notochord (Berrill 1950). After
dispersal and settlement the larvae undergoes metamorphoses and becomes a feeding
and reproducing zooid. Larvae have a number of characteristics (Berrill 1950) that
may be helpful with the identification and classification of an ascidian specimen.
These characteristics include the position of the adhesive organs, the shape number
and position of the ampullae and vesicles as well as the size of the larvae. In
the colonial ascidians the larvae are incubated in the peribranchial cavity, oviduct
or in an incubation pouch constricted off the zooid (Monniot, C. et al. 1991).
Larvae are not always present in material collected and in a large percentage of
species currently described the larval structure is unknown.
1.6.5. Systematics
The class Ascidiacea can be divided into three orders: Aplousobranchia, Stolidobranchia
and Phlebobranchia (Berrill 1950, Monniot, C. et al. 1991, Kott 1992). The
Aplousobranchia are represented by colonial forms and the Stolidobranchia and Phlebobranchia
mainly by solitary species. The present study focuses on four Aplousobranchia families;
Euherdmaniidae, Polyclinidae, Pseudodistomidae and Didemnidae (as defined by Kott
1992, 2001).
The family Euherdmaniidae Ritter, 1904 emend. Kott, 1992 is represented by
a single genus Euherdmania (Ritter, 1904). This small genus has twelve known
species worldwide with a tropical or warm temperate distribution. Only one species,
Euherdmania divida Monniot, F., 2001 (Monniot, C. et al. 2001) an
intertidal species collected from Algoa Bay, Eastern Cape Province and Isipingo,
KwaZulu-Natal has thus far been described from South Africa (Chapter 2).
The family Polyclinidae Milne Edwards, 1842 emend. Kott, 1992 is represented
by six genera: Aplidium Savigny, 1816; Aplidiopsis Lahille, 1890;
Morchellium Giard, 1872; Polyclinum Savigny, 1816; Sidneioides
Kesteven, 1909 and Synoicum Phipps, 1774. Aplidiopsis is a small genus
with fifteen known species worldwide. Only one species is known to occur along the
South African coast (Monniot, C. et al. 2001). New collections of A. tubiferus
Monniot, F., 2001 (Monniot, C. et al. 2001) extends the previous known distribution
of the species (Chapter 3). The genus Polyclinum is represented by forty
species, P. isipingense Sluiter, 1898a and P. arenosum Sluiter, 1898a
have been recorded from the Western Cape Province to the east coast of KwaZulu-Natal.
P. neptunium Hartmeyer, 1912 has been recorded only for the Western Cape
Province and P. constellatum Savigny, 1916 is only known to occur off the
KwaZulu-Natal coast. In the present study, two new species are described, one collected
off Tsitsikamma Marine Reserve and the second from Tsitsikamma Marine Reserve and
Algoa Bay within the Eastern Cape Province, South Africa (Chapter 3).
The Pseudodistomidae Kott, 1992 is represented by the genus Pseudodistoma
Michaelsen, 1924; Anadistoma, Kott, 1992 and probably the monotypic genus
Citoclinum Monniot, F., et al. 1988. The genus Pseudodistoma
has thirty-one known species, of which two are known from the South African coast.
Current research has shown that this is a genus commonly encountered and specimens
are abundant along the South African coast. Most of the species, with the exception
of P. delicatum Monniot, C. et al. 2001, are large robust colonies.
A number of new species have been found of which two are described in Chapter 4.
The family Didemnidae Giard, 1872 has eight genera; Atriolum Kott, 1983;
Didemnum Savigny, 1816; Diplosoma MacDonald, 1859; Clitella
Kott, 2001; Leptoclinides Bjerkan, 1905; Lissoclinum Verrill, 1871;
Polysyncraton Nott, 1892 and Trididemnum Della Valle, 1881. Atriolum
has only six known species worldwide (Kott 2001) but only one has been recorded
from the southern African coast (Chapter 5). Although this species has been recorded
from the Mozambique Channel, New Caledonia and the Coral Sea this is the first recorded
occurrence from South African. The genus Polysyncraton is extensive with
sixty-eight known species worldwide. Five species are known to occur around the
South African coast (Chapter 5). One new species is described for this genus; currently
the only recorded Polysyncraton species, from the Eastern Cape Province.
The following section is divided in to five chapters and two Appendices. Chapters
2 to 5 each concerns one of four families. Chapter 2 examine the family Euherdmaniidae
and the genus Euherdmania, Chapter 3 examine the family Polyclinidae and
the genera Aplidiopsis and Polyclinum, Chapter 4 examine the family
Pseudodistomidae and the genus Pseudodistoma and Chapter 5 examine the family
Didemnidae and the genera Atriolum and Polysyncraton. Each chapter
is divided into a short introduction, a discussion and a literary overview of all
the species known globally within the selected genus. This includes a summary of
taxonomic characters relevant to the identification of the species and a short discussion
on the global distribution of the species within the genus. This is followed by
species descriptions for the relevant taxa. The species description is divided into
three sections: a distribution, description and remarks section. Chapter 6 contains
a conclusion.
Appendix A lists the species recorded for specific geographical areas world wide
for the six genera discussed in Chapters 2 to 5. Appendix B gives the synonymy for
all species in the selected genera focussed on in this study.
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