Odobenus rosmarus (divergens)
1) General Zoological Data
Walruses are large, gregarious animals with both sexes having tusks. Males are larger (1,500 kg) than females (900 kg) and occur in Northern parts of Atlantic and Pacific oceans. Mating is said to take place in January/February and is followed by a 4-5 months delay in implantation (Nowak, 1999). Birth occurs 10-11 months thereafter, with the neonate weighing 50-63 kg. Several subspecies are nominated: Odobenus rosmarus rosmarus for the Atlantic animal and O. rosmarus divergens for the Pacific species; others are less well defined. The name (Odobenus) derives from the Greek for tooth and walking, as the animals have been observed to pull themselves over ice with their modified canines (tusks); and rosmarus derives from the Scandinavian denomination of the animal (Gotch, 1979). Longevity is 30 years according to Nishiwaki (1972). From his extensive study of pinniped chromosomes, Arnason (1974b) suggested a monophyletic origin of Pinnipedia. Different points of view were discussed by Duffield (1972). In their wide-ranging study of carnivore genomes, O'Brien et al. (1999) deduced that pinnipeds split from other carnivores approximately 30 MYA. Phylogenetic relations among the pinnipeds were strongly supported by the mitochondrial rRNA study of Ledje & Arnason (1996). Andersen et al. (1998) studied the population structure of Atlantic walruses with mtDNA fragments and found one animal with a Pacific walrus haplotype, thus proving a connection between the two populations.
General Gestational Data
General Characterization of the Placenta
This is a typical zonary placenta weighing 5,900 g and measuring 85 cm in greatest length. The "ring" of placental tissue was 25 cm wide. It was complete and the circle was 100 cm in circumference. The villous tissue was 2-2.3 cm thick and darkly congested. At the sides there was the characteristic, irregular, brownish old hematoma, the so-called hemophagous organ. The maternal surface had much fresh clot attached and was irregular on its yellowish surface. There were no subdivisions of the placental tissues. The fetal surface was smooth although a focus of white, nodular squamous metaplasia of amnion was found (5x2 cm). The umbilical cord was mostly absent and less than 10 cm remained.
Another placenta was kindly made available by Dr. Carlos Rodriguez of the New York Aquarium. It weighed 4,980 g, had a similar zonary shape and the same ‘hemophagous’ peripheral region.
A third placenta, coming from a stillborn calf, was made available by Diana Procter (Vallejo, CA). It weighed 6,700 g, its cord was 36 cm long, 4.5 cm in circumference and 2.6 cm in diameter.
Details of fetal/maternal barrier
The trophoblast at the base is mostly syncytial in nature and the quite inapparent cytotrophoblast in the labyrinth appears to give rise to the syncytium. The syncytium is superficially invasive into the endometrium, destroys some of the stroma and opens some glands, but it does not grow into the maternal vascular lumens or into their walls.
The other placentas available all had the same microscopic appearance. The colored material at the edges was crystalline (square crystals) and iron stain negative.
Trophoblast external to barrier
Other remarks - What additional Information is needed?
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