TAXONOMIC STATUS OF OYSTERS
51
Oysters are members of the family Ostreacea; class Bivalvia, in the phylum
Mollusca. Under the current systematic schema, most commercially important species
are classified in three major genera: Ostrea, Saccostrea, and Crassostrea and a
number of minor genera (Carriker and Gaffney, 1996).
Fig.3.1: Morphological structure of Saccostrea cucullata shells of Mandovi - Zuari Estuary, Goa
Fig.3.2: Phenoplastic nature of Saccostrea cucullata in Chorao Island and Nerul Creek of
Mandovi - Zuari Estuary, Goa, India
52
Oyster species are a challenging group for taxonomists and phylogeneticists.
Several studies based on morphology and geographic range information have
attempted to identify characters and traits that can be used for identification and
resolving relationships among species (Stenzel 1971; Bernard 1983; Harry 1985; Brock
1990), but this process has proven problematic. For example, shell morphology, which
is commonly used as a primary distinguishing feature, is phenoplastic and greatly
affected by habitat (Tack et al., 1992). Oysters are notorious for the complex taxonomic
problems they present and the profound nomenclatural confusion regarding species
identities. The basis of early oyster taxonomy, such as the work of Cox (1883), Saville-
Kent (1893) and Iredale (1924), is entirely conchological. Later, many authors, e.g.,
Hirase (1930), Elsey (1935), Nelson (1938) and Thomson (1952), studied the anatomy
of the internal tissues, such as the gill ostia, heart, adductor muscle, mantle, pallio-
branchial fusion, promyal chamber and rectum and confirmed their generic importance
in oyster nomenclature. The malacological characters of taxonomic usefulness are,
however, limited and have been almost completely ignored by most systematists
(Thomson, 1954). In recent years several researchers have developed molecular
markers and identification keys to help resolve some of the questions surrounding
oyster identifications and taxonomic relationships. Comparative features of three Oyster
genera from Glude (1971), Ahmed (1975) and Stenzel (1971) are listed in Table 3.1
(Source: Angell, 1986).
53
Table 3.1: Comparative features of three Oyster genera based on conchological and malacological characters
Characteristics Ostrea Crassotrea Saccostrea
Chromata Present Absent Present
Promyal Chamber Absent Present Present
Umbonal Cavity Absent Moderate Deep
Sexual
Development
Protandrous
hermaphrodite Dioecious Dioecious
Spawning Mode Larviparous Oviparous Oviparous
Turbidity Tolerance Low High Moderate
Salinity Preference Stenohaline Euryhaline Stenohaline
Shape Sub circular, Flat Somewhat Elongated
and cupped
Cornucopia or
Rudistiform
Shell Margins Crenulated in some
speciesNot Crenulated Crenulated
Valves Equal Upper Valve Smaller Upper Valve
Smaller
Size Small to Moderate May be Large Small to Moderate
Range All Tropical Seas
All Tropical Seas
except Polynesia and
Melanesia
Indo-Pacific
Variations in the shape of the oyster shells are likely within the same species
from the same area due to overcrowding, orientation, substratum and ecological
conditions (Quayle and Newkirk, 1989). Such variations cause great difficulties in the
identification of oysters, leading to disagreements among researchers. Oyster shell
morphology is typically plastic and creates difficulties in classification (Gaffney and
Allen, 1993). Table 3.2 presents the taxonomic status of Saccostrea cucullata.
54
Table 3.2: Taxonomic status of Saccostrea cucullata
NAME YEAR DESCRIPTION
Oliver 1922 Saccostrea is a mono-specific genus and reports S. cucullata
in the Red Sea.
Thomson 1954 Regarded the Australian rock oyster "commercialis", which
had been earlier named as "cucullata"
Thomson 1954 Claimed S. tuberculata is very close to S. cucullata
Stenzel 1971
Believed that Saccostrea cucullata (Born, 1778) should be
regarded as the 'monotypic species" or "super species" of the
genus Saccostrea.
Some of the species named in the genera Crassostrea, e.g.,
C. commercialis and Saccostrea, e.g., S. cucullata, according
to Stenzel (1971) and Ahmed (1975), are, in fact,
synonymous.
This view has relegated (demote) many oysters that grow on
rocks and mangroves in the Indo-Pacific area, such as S.
commercialis (Iredale and Roughley, 1933), S. echinata
(Quoy and Gaimard, 1835), S. glomerata (Gould, 1850) and
S. mordax (Gould,1850), to either component species of S.
cucullata or merely its geographic ecomorphs, or variants.
Glude 1971 Proposed that S. cucullata should be considered an
ecomorph of S. mordax
Dinamani 1976
Concluded that revision of the taxonomic status of such a
multitude of oyster species could only be attempted after
more detailed studies of all the "species" of the S. cucullata
group distributed around the world had been undertaken.
Buroker et al. 1979
Saccostrea manila was identified as a sibling species of S.
malabonensis using genetic markers identified by protein
electrophoresis & Electrophoretic analysis.
Phillips 1979 The local rock oyster, S. cucullata, has been misidentified as
S. glomerata in his heavy metal investigations of the species.
Torigoe 1981
Reported the occurrence of S. glomerata, S. mordax, S.
kegaki (Torigoe & Inaba, 1981) and S. echinata in Japanese
waters.
Morris 1985 Proposed that the spinose S. kegaki (Torigoe and Inaba,
1981) from Japan (Torigoe and Inaba1981) is also included
55
as a probable synonym of S. cucullata.
Quayle and
Newkirk1989
Studied variations in the shape of the oyster shells are likely
within the same species from the same area due to
overcrowding, orientation, substratum and ecological
conditions.
O’Foighil et al. 1995
Developed a number of molecular markers to distinguish
among various species of oysters. Ostrea, Crassostrea and
Saccostrea species. Molecular markers have been variously
used to examine phylogenetic relationships, elucidate genetic
diversity, and develop molecular genetic identification tools.
Used mitochondrial markers such as 16S rRNA.
Carriker and
Gaffney1996
The genera of the Ostreidae have been reviewed by many
authors. Three major genera: Ostrea, Saccostrea, and
Crassostrea and a number of minor genera
Visootiviseth et al 1998
These oysters can be differentiated at the genus level using
the chromata. Oysters having that morphologic characteristic
are regarded as members of less economically important
Oysters genera Saccostrea or Striostrea, whereas those that
do not have chromata are Crassostrea oysters
O’Foighil et al. 1998 Used mitochondrial markers such as the cytochrome oxidase
subunit I
Yoosukh and
Duangdee1999
These oysters can be differentiated at the genus level using
the chromata. Oysters having that morphologic characteristic
are regarded as members of less economically important
Oysters genera Saccostrea or Striostrea, whereas those that
do not have chromata are Crassostrea oysters
Hedgecock et al. 1999 Used nuclear markers such as the first internal transcribed
spacer (ITS-1)
Wang et al. 2004
More recently, studies have also used nuclear markers
regions of the nuclear rRNA gene family, or some
combination of mitochondrial and nuclear markers. The most
commonly used techniques to reveal genetic variation in
these markers are sequencing.
Lam and Morton 2006
The morphologies of Saccostrea cucullata, Saccostrea
glomerata, Saccostrea kegaki, and Saccostrea commercialis,
are so variable and overlapping that is not always possible to
tell them apart by eye. The differentiation of Saccostrea
56
Saccostrea cucullata was first described by the Czech mineralogist, metallurgist,
and malacologist Ignaz von Born in 1778. They are commonly called the Natal rock
oysters and are mainly seen in the Indo-pacific oceans. One of the widely accepted
scientific classifications for Saccostrea cucullata is as follows in Table 3.3.
Table 3.3: Scientific classification of Saccostrea cucullata
Saccostrea cucullata (Born, 1778)
Kingdom Animalia
Phylum Mollusca
Class Bivalvia
Order Ostreoida
Family Ostreidae
Genus Saccostrea
Species S. cucullata
Scientists aim to describe a single 'tree of life' that reflects the evolutionary
relationships of living things. However, evolutionary relationships are a matter of
ongoing discovery, and there are different opinions about how living things should be
glomerata (Sydney Rock Oyster) from Saccostrea cucullata is
so problematic by the external characteristics at times even
for experts that oysters like this are frequently given both
names, S. glomerata cucculata.
In species of Saccostrea such as cucullata, glomerata, and
kegaki which are all morphologically similar to each other with
an oval, deeply cupped left valve and a smaller, relatively flat
right valve with slightly plicate, raised margins, even the
phylogenetic results using some molecular markers cannot
differentiate them. Only mitochondrial 16S rDNA gene
sequence data accurately identifies S. cucullata
57
grouped and named. Encyclopedia of Life (EOL) (http://eol.org/) reflects these
differences by supporting several different scientific 'classifications'. Some species have
been named more than once. Such duplicates are listed under synonyms. EOL also
provides support for common names which may vary across regions as well as
languages. There are nearly 20 different classifications available at present for
Saccostrea cucullata and a few are mentioned below in Table 3.4 (Source:
http://eol.org/pages/449497/names)
Table 3.4: Different classifications available at present for Saccostrea cucullata
Recognized By Rank Classification
Species 2000 & ITIS
Catalogue of Life: April 2013
(http://www.
catalogueoflife.org/)
Species
58
Inventaire National du
Patrimoine Naturel
(http://inpn.mnhn.fr)
Species
BOLDS resource for
species-level taxa
Barcode of Life Data
Systems (BOLD)
(http://www.
boldsystems.org)
Environments
http://environments-
eol.blogspot.com/
59
BioLib.cz Import
(http://www.biolib.cz/en/)
Integrated Taxonomic
Information System (ITIS)
(http://www.itis.gov/)
Species
BOLDS images II
Barcode of Life Data
Systems (BOLD)
(http://www.
boldsystems.org)
Species
60
Inventaire National du
Patrimoine Naturel
(http://inpn.mnhn.fr)
Species
Inventaire National du
Patrimoine Naturel
(http://inpn.mnhn.fr)
Species
61
Inventaire National du
Patrimoine Naturel
(http://inpn.mnhn.fr)
Species
Inventaire National du
Patrimoine Naturel
(http://inpn.mnhn.fr)
Species
62
Mineralogy
OBIS depth range resource
Ocean Biogeographic
Information System (OBIS)
(http://www.iobis.org/)
NCBI Taxonomy
view in classification
(http://www.ncbi.nlm.nih.gov)
Species
63
Wikipedia
(http://www.wikipedia.org/)
Paleobiology Database
view in classification
(http://www.paleodb. org/)
Species
64
India Biodiversity Portal
Species Data
(http://indiabiodiversity.org/)
Species
Taxonomic Hierarchy of
COL-China 2012
view in classification
Species
World Register of Marine
Species (WoRMS)
view in classification
(http://www.
marinespecies.org/)
Species
65
The names in the table below presents an overview of the relationships of this
group to other groups in the tree of life, based on the classification hierarchies provided
by EOL classification partners. "Parents" are more inclusive group’s one level higher up
in the hierarchy. "Children" are the subgroups of the current group. The three related
names of Saccostrea cucullata are mentioned below in Table 3.5.
(Source: http://eol.org/pages/449497/names/related_names).
Table 3.5: Related names for Saccostrea cucullata used by different groups
Parents Sources
Saccostrea Dolfuss &
Dautzenberg 1920 Paleobiology Database
Saccostrea Dollfus &
Dautzenberg 1920
WORMS Species Information (Marine Species)
Integrated Taxonomic Information System (ITIS)
Saccostrea NCBI Taxonomy
Species 2000 & ITIS Catalogue of Life: April 2013
Taxonomic Hierarchy of COL-China 2012
Sometimes taxonomists create new names for groups that already have a name.
They may do this because they are unaware of the original name, or they may think the
organism before them belongs to a different group when in fact it does not. If two or
more names are found to apply to the same group, they are considered synonyms. In
66
most cases, the first name takes priority and is considered to be the valid or accepted
name. However, there can be exceptions, and it's not always easy to determine which
of a series of synonyms should be considered valid or accepted. Here we list the
synonyms provided to EOL by our classification partners. We also include other
versions of the name that most likely refer to the same group, for example, misspellings
in the literature or different variations of the authorship associated with the name.
Saccostrea cucullata has 22 synonyms which are mentioned below in Table 3.6
(Source: http://eol.org/pages/449497/names/synonyms)
Frequent synonyms / misidentifications:
Table 3.6: Frequent synonyms or misidentifications of Saccostrea cucullata by different
sources
Paleobiology Database
Name Relationship
*Saccostrea cucullata (Born 1778) Preferred
Ostrea cucullata Born, 1778 Valid
Lopha (Lopha) cucullata (Born 1778)
Ostrea (Lopha) cucullata (Born 1778)
Crassostrea cucullata (Born, 1778)
Gryphaea cucullata (Born 1778)
NCBI Taxonomy
Name Relationship
*Saccostrea cucullata Preferred
Crassostrea cucullata Synonym
Saccostrea cucculata Misspelling
Saccostrea cuccullata
Saccostrea cucullata (Born 1778) Authority
Species 2000 & ITIS Catalogue of Life: April 2013
Name Relationship
*Saccostrea cucullata (Born 1778) Preferred
Ostrea turbinata Lamarck, 1819
Ostrea forskali Gmelin, 1791
Ostrea saccellus Dujardin, 1835
Ostrea forskahlii Gmelin, 1791
67
Ostrea stellata Gmelin, 1791
Ostrea purpurea Lightfoot, 1786
Ostrea gibbosa Lamarck, 1819
Crassostrea cucullata (Born, 1778)
Dioeciostrea subtropica Orton, 1928
Saccostrea cuccullata [sic]
Saccostrea forskhalii (Gmelin, 1791)
Ostrea cornucopiae Gmelin, 1791
Ostrea cucullata Born, 1778
Food and Agriculture Organization of the United Nations (FAO)
(Source: ftp://ftp.fao.org/docrep/fao/009/w7191e/w7191e20.pdf)
FAO names: En - Hooded oyster; Fr - Huître-capuchon; Sp - Ostión capuchón.
Name Relationship
Crassostrea cuccullata (Born, 1778)
Ostrea cornucopiae (Chemnitz, 1785) (Invalid name)
O. cornucopiaeformis (Saville-Kent, 1893)
O. echinata (Quoy and Gaimard, 1835)
O. forskaelii (Chemnitz, 1785) (Invalid name)
O. forskalli (Gmelin, 1791)
O. glomerata (Gould, 1850)
O. malabonensis (Faustino, 1832)
O. mordax (Gould, 1850)
O. spinosa (Deshayes, 1836)
Saxostrea amasa (Iredale, 1939)
S. commercialis (Iredale and Roughley, 1933)
S. gravida (Iredale, 1939)
*Marks the preferred name from each source.
Many people know organisms only by the common names, or "vernacular"
names. Unlike scientific names, common names are almost always different for
speakers of different languages. They may also vary regionally within a language. The
table below shows some of the common names provided to EOL for this organism from
a variety of providers, including EOL curators. Currently we can only set one preferred
common name per language on a given EOL page, but all the names should be
searchable. Saccostrea cucullata has 7 common names in English which are mentioned
in Table 3.7.
(Source: http://eol.org/pages/449497/names/common_names)
68
Table 3.7: Common names of Saccostrea cucullata
Name Sources Status
Common rock oyster Hans-Martin Braun Trusted
Forsskål’s Oyster Hans-Martin Braun Trusted
* Hooded Oyster Hans-Martin Braun Trusted
Milky Oyster Hans-Martin Braun Trusted
Natal rock oyster Hans-Martin Braun Trusted
small rock oyster NCBI Taxonomy Trusted
Sydney cupped oyster uBio Unknown
*Marks the preferred name from each source.
Oyster species are a challenging group for taxonomists and phylogeneticists.
They are notorious for the complex taxonomic problems they present and the profound
nomenclatural confusion regarding species identities. Because of shell plasticity, the
taxonomy of Saccostrea has been problematic.
Species of Saccostrea are common oysters on Indo-Pacific rocky shores. The
taxonomy of this genus is unclear because of morphological plasticity among its
constituent species. Variations in the shape of the oyster shells are likely within the
same species from the same area due to overcrowding, orientation, substratum and
ecological conditions. Such variations cause great difficulties in the identification of
oysters, leading to disagreements among researchers. The taxonomic status of
Saccostrea genus rock oysters along the coastlines of India is unclear and poorly
known because of the morphological plasticity among its constituent species. Species of
Saccostrea from these localities have been identified solely on the basis of shell
morphology and anatomy. The malacological characters of taxonomic usefulness are,
however, limited and have been almost completely ignored by most systematists. In
recent years several researchers have developed molecular markers and identification
keys to help resolve some of the questions surrounding oyster identifications and
taxonomic relationships.