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A case of symmetrical conjoined twins in a bottlenose dolphin Tursiops truncatuo

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Erwin J O Kompanje at 1. Erasmus University Rotterdam and 2. Natural History Museum Rotterdam
Erwin J O Kompanje
  • 1. Erasmus University Rotterdam and 2. Natural History Museum Rotterdam
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147
Erwin J.O. Kompanje
Naturalis (Nationaal Natuurhistorisch Museum), Leiden & Natuurhistorisch Museum Rotterdam
Kompanje, E.J.O., 2005 - A case of symmetrical conjoined twins in a bottlenose dolphin Tursiops
truncatus (Mammalia, Cetacea) - DEINSEA 11: 147-150 [ISSN 0923-9308]. Published 29 December
2005
Case reports of conjoined twins (‘Siamese twins’) in wild mammals are very scarce. Most published
reports of conjoined twinning concern cases in man or in domestic mammals. In this article a case of
conjoined twinning in a wild mammal is described: a parapagus dicephalus with unilateral schistopro-
sopus in a bottlenose dolphin Tursiops truncatus stranded on the coast of the Netherlands in 1917. This
case concerns the oldest known case of a symmetrical conjoined twin in a cetacean species.
Correspondence: dr Erwin J.O. Kompanje, Natuurhistorisch Museum Rotterdam, P.O. Box 23452,
3001 KL Rotterdam, The Netherlands, e-mail: e.j.o.kompanje@erasmusmc.nl
Keywords: conjoined twins, parapagus dicephalus, double monster, Tursiops truncatus.
INTRODUCTION
Conjoined twins (‘Siamese twins’) are well
known in man, in domestic and laboratory
mammals, domestic and wild birds and in
wild and captive-bred reptiles, amphibians and
fishes, but are very rarely described in wild
mammals. The precise incidence is unknown,
most likely due to high prenatal and antenatal
mortality. Almost all known cases of con-
joined twins in wild mammals concern unborn
embryos and fetus found during dissection of
the pregnant dead female. The aim of this arti-
cle is to describe a postnatal case of symmetri-
cal conjoined twins in a wild mammal.
Case report
A dead, 125 cm long, newborn female
dicephalic bottlenose dolphin Tursiops trun-
catus (Montagu, 1824), with open umbilicus,
was found on the beach at Wijk aan Zee, the
Netherlands, on 20 July 1917. The specimen
was sold to the Rijksmuseum voor Natuurlijke
Historie (now: Naturalis, National Museum of
Natural History) in Leiden. After preservation,
three photographs were made of the monstrum
(Fig. 1). Shortly afterwards, the specimen
was given on loan to the Anatomical Cabinet
of Leiden University for further study, but
nothing was published on this case. The speci-
men is untraceable now. It is neither in the
Anatomical Cabinet nor in any other museum,
and it is - unfortunately - most probably lost
for science. It supposedly got lost after an
English air raid during the Second World War
(Kompanje 2001). The three photographs
(reproduced here in Figure 1), still present
in the archives of the National Museum of
Natural History, form the only proof of this
rare case. This case was mentioned in a review
of Tursiops strandings along the Dutch coast
(Kompanje 2001).
A case of symmetrical conjoined twins in
a bottlenose dolphin Tursiops truncatus
(Mammalia, Cetacea)
148
 DEINSEA11,2005
Figure1ParapagusdicephalusinabottlenosedolphinTursiops truncatesfromWijkaanZee,theNetherlands,20July1917.
adorsalview,bventralview,cheadsinfrontalview.[ArchivesNaturalis,NationalMuseumofNaturalHistory,Leiden]
ab
c
DISCUSSION
Conjoined twins are always conjoined in one
of only eight sites (Spencer 2001, 2003) and
are named after the site of union [see also
Kompanje (2005) - this volume - for further
details]. Normal twinning is very rare in
cetaceans. González et al. (1999) estimated
a 0.5% occurrence of multiple gestation of
all observed pregnant females in small ceta-
ceans. With the exception of the present case,
and of the case described by Cesarini et al.
(2004), only four cases of conjoined twins in
Cetaceans could be traced in the literature, all
found in unborn foetusses during dissections
in the Japanese and Russian whaling industry
(Table 1). Other complex foetal anomalies
found during these dissections includes holo-
prosencephaly, schistoprosopus and anoto-
cephaly, all in baleen whales (e.g., Zinchenko
& Ivashin 1960).
The present case is the first example of
conjoined twins in a wild newborn dolphin.
A diagnosis of a parapagus dicephalus mono-
somos dibrachius with unilateral schistopro-
sopus on the left head in a full-term female
newborn bottlenose dolphin seems accurate.
A second case in a wild newborn bottlenose
dolphin is described by Cesarini et al. (2004).
Judging from the description these authors
gave (two faces, one braincase, one foramen
magnum) this pair of conjoined twins should
be diagnosed as parapagus diprosopus.
Symmetrical conjoined twins in wild terres-
trial mammals have been very rarely reported
(Table 2). Spontaneous occurrence of con-
joined twins in laboratory animals is uncom-
mon. Szabo (1989) reported one conjoined
twin out of 10.000 in the rat and one case in
4000 rabbits bred in 20 years.
Spencer (2000a, 2000b, 2003) provides con-
vincing evidence that symmetrical conjoined
twins are the result of secondary fusion of two
originally separate monovular embryonic discs,
and are not the result of incomplete fission
producing a partially separated zygote.
149
KOMPANJE:symmetricalconjoinedtwinsinabottlenosedolphin
Reference species taxonomy age
Kawamura 1969 Balaenoptera borealis thoracopagus fetus
Kawamura & Kashita 1971 Stenella coeruleoalba cephalopagus fetus
Kamiya et al. 1981 Stenella coeruleoalba parapagus dicephalus fetus
Zinchenko & Ivashin 1987 Balaenoptera acutorostrata thoracopagus fetus
Kompanje 2001 Tursiops truncatus parapagus dicephalus newborn
Cesarini et al. 2004 Tursiops truncatus parapagus diprosopus newborn
Table1PublishedcasesofsymmetricalconjoinedtwinsinCetacea.
Reference species taxonomy age
Reisel 1671 Lepus europaeus cephalopagus newborn
Jung 1671 Lepus europaeus cephalopagus newborn
Seger 1671 Lepus europaeus cephalopagus newborn
Mentzel 1686 Alces alces cephalopagus fetus
Neugebauer 1851 Lepus europaeus cephalopagus newborn
Benesch 1957 Lepus europaeus cephalopagus newborn
Fay 1960 Odocoileus virginianus parapagus dicephalus fetus
Table2Publishedcasesofsymmetricalconjoinedtwinsinwildmammals,otherthanCetacea.
150
 DEINSEA11,2005
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Jung, G.S., 1671 - Monstrum Leporinum - Miscellanea
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Received12October2005
Accepted9November2005
DEINSEA - ANNUAL OF THE NATURAL HISTORY MUSEUM ROTTERDAM
P.O.Box 23452, NL-3001 KL Rotterdam The Netherlands
... Including the present case in Phocoena phocoena, only ten cases of symmetrical conjoined twins in cetacean species have been described in the literature (Kawamura 1969;Kawamura & Kashita 1971;Zemsky & Budylenko 1973;Kamiya et al. 1981;Zinchenko & Ivashin 1987;Kompanje 2001Kompanje , 2005bDabin et al. 2004;Aytemiz et al. 2014;Tamburin et al. 2014 Conjoined twins can be separated in symmetrical and asymmetrical twins. Symmetrical conjoined twins concern two equal conjoined parts (the classic 'Siamese twins'). ...
... Some share one umbilical cord, other types, like the thoracopagus, have two umbilical cords. Stenella coeruleoalba cephalopagus fetuses Kamiya et al. 1981 Stenella coeruleoalba parapagus dicephalus fetuses Zinchenko & Ivashin 1987 Balaenoptera acutorostrata thoracopagus fetuses Kompanje 2001Kompanje & 2005b Tursiops truncatus parapagus dicephalus neonates Dabin et al. 2004 Tursiops truncatus parapagus diprosopus neonates Aytemiz et al. 2014 Tursiops truncatus parapagus dicephalus neonates Tamburin et al. 2014 Eschrichtius robustus thoracopagus neonates this contribution ...
... The symmetrical conjoined twin harbour porpoises described here can be determined as parapagus dicephalus. Three other cases of parapagus dicephalus are known in cetacean species, one in Stenella coeruleoalba (Kamiya et al. 1981) and two in Tursiops truncatus (Kompanje 2001(Kompanje , 2005bAytemiz et al. 2014). ...
The first case of conjoined twin harbour porpoises Phocoena phocoena (Mammalia, Cetacea)
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The harbour porpoise (Phocoena phocoena) is the smallest and most abundant cetacean in NW European continental shelf waters. Their global abundance numbers at least ~700,000 individuals. Within the North Sea, total abundance has recently been estimated at approximately 345,000 animals. The species reproduces at a rate of one offspring every 1-2 years. In this article we describe a case of conjoined twins in the harbour porpoise: a parapagus dicephalus bycaught in the Southern North Sea in May 2017. Reports of conjoined twins in wild mammals are extremely scarce. This case concerns the second known case of twinning and the first case of conjoined twins in P. phocoena, the fourth known case of parapagus dicephalus in any cetacean species and the tenth known case of conjoined twinning in a cetacean species.
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... Researchers found the aborted twins floating in a lagoon in Baja California, and the event was widely spread in scientific circuits as well as in social media (Lee, 2014;Murphy & Malm, 2014). Reports of conjoined or Siamese twins in wild mammals are very scarce; most reports are cases known in humans, in domestic animals or laboratory mammals (Kompanje, 2005). The precise incidence in wild mammals is unknown, most likely due to high prenatal and antenatal mortality. ...
... The precise incidence in wild mammals is unknown, most likely due to high prenatal and antenatal mortality. Almost all known cases of conjoined twins in wild mammals concern unborn embryos and fetus found during dissection of the dead pregnant female (Kompanje, 2005). Some cases of museum specimens of Siamese twins in terrestrial mammals do exist and are well known and documented, but none -to our knowledge -in the case of marine mammals 4 . ...
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... Although usually associated with human populations (Mian et al. 2017), the occurrence of conjoined twins has been noted in creasingly in the animal world . Anomalies of this type occur extremely rarely in the animal world, but they have been observed in humans and in other mammals, including dolphins Tursiops truncatus (Kompanje 2005), leopard cats Prionailurus benga lensis (Kompanje & Hermans 2008), buffalo Bubalus bubalis bubalis (De La Ossa & Altahona 2010) and gorillas Gorilla gorilla (Langer et al. 2014), as well as in other groups of animals such as reptiles, including snapping turtles Chelydra serpentina (Cederstrom 1931) and crocodiles (Platt et al. 2012), as well as in fish (e.g. Von Bonde & Marchand 1929). ...
... In this study, twins of 2 major groups were found among whitefish: symmetrical, parapagus type (subtypes: diprosopus, dicephalic and dithoracic parapagus) and asymmetrical, where 1 of the twins is present as a parasitic form. The diprosopus parapagus subtype has also been observed in guppies (Moreno-Valcarcel et al. 2011, Petrescu-Mag et al. 2011) and tilapia Oreo chromis aureus (Shirak et al. 2013); the dicephalic parapagus subtype has been reported in dolphins (Kompanje 2005), turtles (Cederstrom 1931), tilapia (Owusu-Frimpong & Hargreaves 2000 and Atlantic salmon (Fjelldal et al. 2016); and the dithoracic parapagus subtype (types A and B combined) has been found in red tilapia (Huang et al. 1987), sea horse Hippocampus guttulatus (Blanco et al. 2012) and hybrid Atlantic salmon × Arctic char (Fjelldal et al. 2016). Studies conducted with human conjoined twins have confirmed that in most cases, such twins are formed in females (Mutchinick et al. 2011, Mian et al. 2017). ...
First report of the occurrence and different types of Siamese twins in common whitefish Coregonus maraena larvae originating from the Baltic Sea
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This paper describes for the first time various forms of conjoined twins in the common whitefish Coregonus maraena originating from the brackish waters of the Baltic Sea. The occurrence of conjoined twins was observed during the hatching of whitefish under controlled conditions. Two types of twins were identified: symmetric (parapagus) and asymmetric (parasitic form). The percentage of conjoined twins among the whitefish did not exceed 0.01% of the hatched larvae. The forms of twins observed in this study were similar to conjoined twins occurring among humans. One main type, parapagus, was identified in the group of symmetric twins with 3 subtypes: diprosopus parapagus, dicephalic parapagus and dithoracic parapagus. In its parasitic form, the parasitic twin occurred as a ‘cyclops’ or just as an eye growing out of the other twin’s head. We conclude that fish, as well as their fertilised eggs, can be used as a model system to observe how such twins are joined in humans because of the similarity with conjoined twins occurring in humans. Because of internal fertilisation in fish, as well as the size and transparency of egg cells in these animals, it is possible to observe the process of fertilisation, cell division and formation of an embryo and subsequently of twins, as a model for humans.
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... The low occurrence of parapagus is well known in humans, with the diprosopus being the rarest (Mutchinick et al., 2011). Its occurrence has also been recorded in different vertebrates, such as common whitefish, sharks, dolphins, bats, and most domestic animals, including chickens (Kompanje, 2005;Nogueira et al., 2017;Nowosad & Kucharczyk, 2019;Saini et al., 1993;Sans-Coma et al., 2017). In domestic animals, there have been various reports of bovine diprosopus and some reports of diprosopus in sheep (Bähr et al., 2004;Kerr, 2007;Mazzullo et al., 2003;Schulze et al., 2006). ...
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... Cases of conjoined twin cetaceans are very rare. The earliest report dates to 1917, when parapagus newborn female bottlenose dolphins (Tursiops truncatus) were reported in the Netherlands (Kompanje, 2005). Since then, 7 other pairs of conjoined twins have been reported in different Cetacean species: a thoracopagus fetal Balaenoptera borealis (Kawamura, 1969), one report of cephalopagus and one parapagus fetal Stenella coeruleoalba (Kawamura and Kashita, 1971;Kamiya et al., 1981), a thoracopagus fetal Balaenoptera acutorostrata (Patten, 1959;Zinchenko and Ivashin, 1987), one parapagus newborn Tursiops truncatus (Dabin et al., 2004), one thoracopagus case for the same species in Turkey (Aytemiz et al., 2014), and one case of ventropagus conjoined in Megaptera novaeangliae (Zemsky and Budylenko, 1970). ...
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... Furthermore Jonsgård (1953) reported a fin whale with six foetuses of varying sizes. Multiple foetuses are less frequent in Odontocetes than in Mysticetes (Lockyer, 1984), although they have been reported in sperm whales (Physeter macrocephalus) (Matsuura, 1940;Ohsumi, 1965;Gambell, 1972;Best et al., 1984;Clarke et al., 2011), short finned pilot whale (Globicephala macrorhynchus) (Escorza et al., 1994), striped dolphin (Stenella coeruleoalba) (Tobayama et al., 1970), bottlenose dolphin (Tursiops truncatus) (conjoined twins; Dabin et al., 2004;Kompanje, 2005;Aytemiz et al., 2014, and non-conjoined twins;Gray & Conklin, 1974;Lacave, 1991), Risso's dolphin (Grampus griseus) (Gassner & Rogan, 1997), beluga whale (Delphinapterus leucas) (Osborn et al., 2012), short-beaked common dolphin (Delphinus delphis) (González et al., 1999), Dall's porpoise (Phocoenoides dalli) (Nakamatsu, 2001) and harbour porpoise (IJsseldijk et al., 2014). Of these cases, the striped dolphin, sperm whale, common dolphin, Risso's dolphin, Dall's porpoise, harbour porpoise and conjoined twins of the bottlenose dolphins were free-living individuals that stranded dead, the others were all captive animals. ...
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... Parapagus dicephalus is well documented by Aldrovandi in domesticated animals (Fig. 3.) and also in fish, bird and reptile species (Aldrovandi 1642, 416-430). The malformation is also well known and documented in recent times in both wild (Gould & Pyne n. d., 157;Dabin et al. 2004;Kompanje 2005b) and domestic animals (Hámori 1974, 345). An intresting aspect of symbolism of the two-headed animals is that in Šumma izbu the two heads mean some kind of a division, and are thus always recorded as a bad sign (Jastrow 1914, 14-15), while in Antiquity and in the Middle Ages the double-headed eagle became the symbol of unity in the iconography of many noble and royal families in Europe and Asia (Hohenlohe-Waldenburg 1871, 17). ...
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Анатомические аномалии у черноморских китообразных
Conference Paper
Full-text available
  • Mar 2025
[Citation: Korosteleva A.V., Postnikova A.N., Suvorova I.V., Krivokhizhin S.V. Anatomical anomalies in Black Sea cetaceans // Proceedings of the XIII International Scientific and Practical Conference "Marine Research and Education (MARESEDU-2024)", Volume I (IV): [collection], 2025, pp. 223-228]. In this paper, we present the first description of abnormal caudal fins in bottlenose dolphins from the northern Black Sea, the first report of soft tissue hind limb appendages in the Black Sea harbour porpoises, and a case report of a Black Sea harbour porpoise calf with congenital deformation of the caudal vertebrae and fin flukes. From 2008 to 2024, we examined 5 individuals of the Black Sea cetaceans with congenital malformations. The data were obtained as part of systematic studies of cetacean bycatch and stranding response on the coast of the Crimean Peninsula and year-round photo-identification study in its waters. Individual №1, a mature male porpoise 129 cm long, was recovered dead from fixed gill nets during monitoring of the Black Sea turbot fishery off the coast of western Crimea. In front of the anus, two leathery tubercles were located symmetrically on the right and left (Fig. 1, a). During the pathological examination, no bone formations were found under these external hind limb appendages. Specimen №2, a newborn porpoise calf, a female with a body length of 67.9 cm and a weight of 4.5 kg, stranded alive on the shore in the city of Sevastopol. Significant asymmetry of the caudal fin flukes was noted: the right fluke was caudally elongated, while the left one was laterally expanded, and a visible curvature was determined at the end of the caudal peduncle. X-ray examination visualized deformation of the caudal vertebrae (Fig. 1, б, в). The measurements of the caudal lobes are shown in Fig. 2 (a). Individual №3, an adult bottlenose dolphin of unknown sex, was encountered in the waters of Sudak in a pod of other dolphins of the same species. During photoidentification, images of its caudal fin were obtained with an additional central outgrowth between the tail flukes, elongated in shape, with smooth outlines and without any traces of trauma, while the last caudal vertebrae protruded dorsally and were probably deformed (Fig. 1, г). The animal did not demonstrate obvious problems with the speed and nature of movement and moved along with the rest of the pod. Individual №4, a dead bottlenose dolphin calf, a male, was washed ashore near Alushta. The body was in an advanced stage of decomposition. The body length was 123.4 cm, weight - 10 kg. Between the flukes of the caudal fin there was a central outgrowth forming a “third fluke” (Fig. 1, д), similar to that recorded in bottlenose dolphin №3. The last caudal vertebrae were deformed and were externally defined as a protruding tubercle above the fin and oriented dorsally. The cause of death was a fracture of the vertebral column with a dorsal displacement of 1/2 of the spinal canal, which could probably have occurred as a result of an infanticidal attack or traumatic interaction with a vessel. Given the similar nature of the developmental defect in bottlenose dolphins №3 and №4 and their registration in two adjacent areas, it was assumed that they were related. The measurements of the tail flukes of individual №4 are shown in Fig. 2 (b). Individual №5, a male porpoise, was washed up dead on the shore near Alushta. The weight was 19.8 kg, the body length was 110.5 cm. During physical examination, two parallel soft tissue formations, presenting hind limb appendages, were found on the sides and in front of the anus (Fig. 1, e), which were determined by palpation as protrusions turning into pits no more than 2 mm deep. The pigmentation of the skin in the perianal area was different from normal: a clear dark-colored line ran ventrally from each tubercle to the level of the lower border of the genital slit. The sizes of each tubercle area were 5 x 5 mm. The distance between them was 65 mm. The distance from the middle of the anus to the right tubercle was 26 mm, to the left - 28 mm. There were no bone elements under them. The caudal fin of dolphins is formed early in ontogenetic development in the embryonic and prefetal periods after the reduction of the hind limb rudiments, while the caudal peduncle and caudal lobes are formed early in the fetal period [Agarkov et al., 1974]. Despite the understanding of the anatomy and morphological development of the tail flukes, the molecular signals that trigger their growth are unknown. Fin growth occurs from a small diamond-shaped outgrowth through a series of intermediate forms before it reaches the taxon-specific morphology [Gavazzi et al., 2023]. The diamond shape characteristic of bottlenose dolphins №3 and №4 has some external similarities with the rudimentary form of this locomotor organ in cetaceans during embryogenesis. The very rare tubercles near the genital area in adult cetaceans can be considered as a kind of preserved external rudiments of the hind limbs.
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Preliminary report of a conjoined bottlenose dolphin (Tursiops truncatus) calf stranded on the Aegean Sea coast of Turkey
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Full-text available
  • Oct 2014
On 4 August 2014, a male conjoined dicephalic bottlenose dolphin (Tursiops truncatus) calf was found dead on the beach of Dikili/İzmir, the Aegean coast of Turkey. This is the first case of conjoined cetacean reported in Turkey and the second in the Mediterranean Sea.
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Abnormal embryos of sharpnose sharks, Rhizoprionodon porosus and Rhizoprionodon lalandii (Elasmobranchii: Carcharhinidae), from Brazilian coast, western South Atlantic
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Full-text available
  • May 2014
This study presents the second worldwide report on abnormal embryos of the sharpnose sharks, Rhizoprionodon, based on the two species (Rhizoprionodon porosus and Rhizoprionodon lalandii) occurring on the Brazilian coast. For R. porosus two conjoined twin embryos showing complete duplication of the vertebral column, viscera and several external structures (head, first and second dorsal fins, pectoral fins), and scoliosis in both axis at the pelvic fin level are reported. The three embryos of R. lalandii exhibited numerous lordosis and kyphosis along the entire vertebral column. The possible relationship between anomalies and the human major threats to sharks is discussed based on previous reproductive, genetic and ecotoxicological studies on R. lalandii for southern Brazil.
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A multiple gestation in a Delphinus delphis stranded on the north-western Spanish coast
Article
Full-text available
  • Dec 1999
  • J MAR BIOL ASSOC UK
The present study is the first record of twinning in Delphinusdelphis. The first foetus was a female of 72 cm total length which had a curved caudal area. This animal was located in the left uterine horn, very close to the genital aperture. The second foetus was a male of 46 cm total length and its external morphology was deformed. It was located in the uterus and the nose was shorter than the female foetus. Documented incidences of twinning in cetaceans are rare.
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Siamese Twins in the Sei Whale Balaenoptera borealis Lesson
Article
  • Feb 1969
ALTHOUGH there have been comprehensive biological studies of whales since 1925 when the Discovery Committee founded the research station at South Georgia, there have been no reports of Siamese twins in whales as far as I know. I now report briefly the results of morphological observations on sei whale Siamese twins found on the Japanese whaling factory ship Nisshin Maru (Taiyo Fisheries Co.) in the Antarctic whaling season 1967–68.
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Theoretical and analytical embryology of conjoined twins: Part I: Embryogenesis
Article
A review of over 1,800 publications concerning the embryology and pathologic anatomy of conjoined twins provides convincing evidence that they all result from the secondary union of two originally separate monovular embryonic discs. This “fusion” theory seems to be confirmed by the adjustments to union and the pattern and incidence of specific anomalies at the proposed sites of conjunction in more than 1,200 cases, all of which can be arranged in two uninterrupted series of cases, the one united dorsally (in the neural tube) and the other, ventrally (over a shared a yolk sac). No theoretical “fission” of the vertebrate embryo at any stage of development, in any plane, in any direction can explain (1) the selection of the observed sites of fusion, (2) the details of the union, or (3) the limitation to the specific areas in which the twins are found to be joined. Part I of this disquisition deals with the pertinent normal and theoretical embryology, the adjustments to union, and the parasitic cases, as well as conjoined triplets and quadruplets, and a comparison of oviparous and viviparous embryos. Part II (in a subsequent issue of this journal) will compare and correlate the abnormalities of the various organ systems involved in 1,200 cases. Clin. Anat. 13:36–53, 2000. © 2000 Wiley-Liss, Inc.
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Theoretical and analytical embryology of conjoined twins: Part II: Adjustments to union
Article
A previous report in this journal (Spencer, 2000) discussed the probable embryologic etiology of conjoined twins, along with a system of classification based on the embryological structures postulated to be involved in the union. Part II correlates and compares the variations in the abnormal development of the individual organ systems in more than 1,200 actual cases, revealing details of embryogenesis not considered in previous publications. The site, incidence, and range of anomalies in the conjoined structures, as well as the associated malformations, follow a definite pattern as the union proceeds from one area to another; many can be explained in relation to the proposed embryologic adjustments to union, including both temporal and spatial influences. In addition, six currently inexplicable or unclassifiable cases are briefly described (including one with 12 feet), as well as two examples of early abnormal conjoined twins. Clin. Anat. 13:97–120, 2000. © 2000 Wiley-Liss, Inc.
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Parasitic conjoined twins: External, internal (fetuses in fetu and teratomas), and detached (acardiacs)
Article
  • Nov 2001
During the course of researching the embryologic etiology of conjoined twins, more than 1260 individual cases were collected from the literature and the reported abnormal anatomy tabulated and evaluated in the light of known embryology. It soon became apparent that the association of conjoined twins and their parasites with fetuses in fetu, acardiacs, and teratomas was more frequent than could be attributed to chance. These anomalous fetuses form a continuum, strongly suggesting that they are all variations of abnormal conjoined twinning, with the site of union and the extent of damage (or defect) of one embryo resulting in (1) an externally attached parasitic twin, (2) an enclosed fetus in fetu, (3) an internal teratoma, or (4) an acardiac connected via the placenta. Common patterns among them are a family history of twinning, the predominance of females, and the frequent presence of a twin or triplet accompanying the malformation. The several reports of chromosomal abnormality suggest that perhaps, at least on occasion, it is a genetically imperfect embryo that develops into a defective fetus. Of singular importance is the fact that rarely, if ever, is either a functional heart or a competent brain found in any of these abnormal fetuses, suggesting that the etiology of all of them is a primary cardiac malformation with secondary disruption in the development of the brain.
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1957 -Lehrbuch der tierärztlichen Geburtshilfe und Gynäkologie -Urban und Schwarzenberg
  • F Benesch
Benesch, F.,1957 -Lehrbuch der tierärztlichen Geburtshilfe und Gynäkologie -Urban und Schwarzenberg, München, Germany