An insight into the epidemiology of dolphin morbillivirus worldwide

Serum samples from 288 cetaceans representing 25 species and originating from 11 different countries were collected between 1995 and 1999 and examined for the presence of dolphin morbillivirus (DMV)-specific antibodies by an indirect ELISA (iELISA) (N = 267) or a plaque reduction assay (N = 21). A total of 35 odontocetes were seropositive: three harbour porpoises (Phocoena phocoena) and a common dolphin (Delphinus delphis) from the Northeastern (NE) Atlantic, a bottlenose dolphin (Tursiops truncatus) from Kent (England), three striped dolphins (Stenella coeruleoalba), two Risso's dolphins (Grampus griseus) and a bottlenose dolphin from the Mediterranean Sea, one common dolphin from the Southwest (SW) Indian Ocean, three Fraser's dolphins (Lagenodelphis hosei) from the SW Atlantic, 18 long-finned pilot whales (Globicephala melas) and a bottlenose dolphin from the SW Pacific as well as a captive bottlenose dolphin (Tursiops aduncus) originally from Taiwan. The presence of morbillivirus antibodies in 17 of these animals was further examined in other iELISAs and virus neutralization tests. Our results indicate that DMV infects cetaceans worldwide. This is the first report of DMV-seropositive animals from the SW Indian, SW Atlantic and West Pacific Oceans. Prevalence of DMV-seropositives was 85.7% in 21 pilot whales from the SW Pacific and both sexually mature and immature individuals were infected. This indicates that DMV is endemic in these animals. The same situation may occur among Fraser's dolphins from the SW Atlantic. The prevalence of DMV-seropositives was 5.26% and 5.36% in 19 common dolphins and 56 harbour porpoise from the NE Atlantic, respectively, and 18.75% in 16 striped dolphins from the Mediterranean. Prevalence varied significantly with sexual maturity in harbour porpoises and striped dolphins; all DMV-seropositives being mature animals. The prevalence of seropositive harbour porpoise and striped dolphins appeared to have decreased since previous studies. These data suggest that DMV is not endemic within these populations, that they are losing their humoral immunity against the virus and that they may be vulnerable to new epidemics.     

Parasites of cetaceans stranded on the Pacific coast of Costa Rica

Information regarding parasitic fauna of cetaceans from Costa Rica is provided for the first time. A total of 25 stranded dolphins and whales were examined between 2001 and 2009, including striped dolphin (Stenella coeruleoalba) (n=19), pantropical spotted dolphin (S. attenuata) (n=2), spinner dolphin (S. longirostris) (n=1), bottlenose dolphin (Tursiops truncatus) (n=1), dwarf sperm whale (Kogia sima) (n=1) and Cuvier's beaked whale (Ziphius cavirostris) (n=1). Pathological findings associated with the parasites are also presented. In the most representative dolphin species, S. coeruleoalba, the prevalence of parasites was 89.5%; moreover, all examined specimens of S. attenuata, S. longirostris, T. truncatus and Z. cavirostris presented parasites. No parasites were recovered from K. sima. Fourteen helminth taxa were identified, including six species of cestodes (Strobilocephalus triangularis, Tetrabothrius forsteri, Trigonocotyle sp., Phyllobothrium delphini, Monorygma grimaldi, Tetraphyllidea gen. sp. plerocercoid), four digeneans (Nasitrema globicephalae, Brachycladium palliatum, B. pacificum and Oschmarinella albamarina) and four nematodes (Anisakis spp., Halocercus lagenorhynchi, Halocercus sp. and Crassicauda anthonyi). A commensal crustacean, Xenobalanus globicipitis, was also identified. All identified parasites representing new geographic records for the Pacific coast of Central America and new host records are presented. Parasitological information is valuable for conservation of cetaceans in Pacific coast of Costa Rica.     

Histopathological and immunohistochemical studies on cetaceans found stranded on the coast of Italy between 1990 and 1997

Detailed histopathological and immunohistochemical studies were carried out on 24 cetaceans, 17 of which were striped dolphins (Stenella coeruleoalba), four bottlenose dolphins (Tursiops truncatus) and three Risso's dolphins (Grampus griseus), all found stranded on the Italian coast between 1990 and 1997. The most frequently detected lesions were chronic pneumonia (73.7% of the examined lungs), focal chronic pancreatitis (71.4%), non-purulent encephalitis (50%), chronic hepatitis (42.1%), and chronic focal interstitial nephritis (31.2%). The skin and the subcutaneous panniculus were often (33.3%) affected by parasitic diseases (Phyllobothrium delphini and Pennella sp.). An appreciable percentage of animals showed lymphoid depletion in their lymphatic organs (47.2%), as well as a high rate of parasitic infestations in their alimentary tracts (25%).     

Malignant seminoma with metastasis, Sertoli cell tumor, and pheochromocytoma in a spotted dolphin (Stenella frontalis) and malignant seminoma with metastasis in a bottlenose dolphin (Tursiops truncatus)

Seminoma with metastasis was diagnosed in a spotted dolphin (Stenella frontalis) and an Atlantic bottlenose dolphin (Tursiops truncatus). Sertoli cell tumor and pheochromocytoma were also diagnosed in the spotted dolphin. The spotted and bottlenose dolphins were adult males that stranded and died on the coasts of northwest Florida and southeast North Carolina, respectively. Neoplasia is infrequently reported in cetaceans. This is the first report of seminoma, Sertoli cell tumor, and pheochromocytoma in a dolphin, the first report of three distinct neoplasms in a dolphin, and one of the few reports of malignant neoplasia in dolphins.     

Histological Structure of the Adrenal Gland of the Bottlenose Dolphin (Tursiops truncatus) and the Striped Dolphin (Stenella coeruleoalba) from the Adriatic Sea

The structure of the adrenal gland was studied in 11 bottlenose dolphins ( Tursiops truncatus ), and five striped dolphins ( Stenella coeruleoalba ). These species are legally protected in Croatia. All examined animals died of natural causes and were found stranded along eastern Adriatic coast. In both species the adrenal gland consists of a cortex and a medulla; the cortex is divided into three zones. Whereas in the bottlenose dolphin, there is a zona arcuata which contains columnar cells arranged in the form of arches; in the striped dolphin this zone is replaced by zona glomerulosa containing rounded clusters of polygonal cells. In both species, the zona fasciculata consists of radially oriented cords of polygonal cells, whereas in zona reticularis cells are arranged in branching and anastomosing cords. The adrenal medulla in both species contains dark, epinephrine-secreting cells and light norepinephrine-secreting cells. Epinephrine-secreting cells are localized in the outer part of the medulla, whereas norepinephrine-secreting cells are found in the inner part, arranged in clusters and surrounded by septa of thin connective tissue. The gland is surrounded by a thick connective-tissue capsule, from where thick trabeculae extend towards the interior. In the bottlenose dolphin, group of cells resembling both medullar and cortical cells can be seen within the capsule; whereas only groups of cells resembling cortical cells are found within the capsule of the striped dolphin. In the bottlenose dolphin invagination of the adrenal cortex into the medulla is obvious as well as medullary protrusions extending through cortex to the connective tissue capsule.     

A pioneering survey of deep-diving and off-shore cetaceans in the northern South China Sea

A pioneering boat-based survey was conducted in 2019, to gather baseline information regarding the presence, composition, relative abundance, and spatial distribution of deep-diving and off-shore cetaceans in the northern South China Sea (SCS). A total of 27 sightings comprising at least 8 cetacean species were recorded during the 13-day survey, including 5 deep-diving species (i.e. Risso's dolphin [Grampus griseus], short-finned pilot whale [Globicephala macrorhynchus], sperm whale [Physeter macrocephalus], Cuvier's beaked whale [Ziphius cavirostris], and an unidentified beaked whale [either the ginkgo-toothed beaked whale, Mesoplodon ginkgodens, or Deraniyagala's beaked whale, Mesoplodon hotaula]), as well as 3 off-shore dolphins (i.e. pantropical spotted dolphin [Stenella attenuate], striped dolphin [Stenella coeruleoalba], and Fraser's dolphin [Lagenodelphis hosei]). With the exception of pantropical spotted dolphins, all other species were sighted and recorded at sea in the northern SCS for the first time. The pantropical spotted dolphin was the most frequently sighted species, comprising 30% of the total sightings. Deep-diving cetaceans were mainly sighted in the northern Xisha Archipelago, whereas off-shore dolphins were distributed across the survey area. The pantropical spotted dolphin was observed in aggregations of more than 100 individuals and nearly all encountered species included calves; these findings suggested that the survey area functions as an important feeding and calving ground for various cetacean species. This pioneering survey provides fundamental information regarding cetacean fauna in the northern SCS and highlights the need to strengthen research and conservation efforts concerning these species.     

Acute and chronic gas bubble lesions in cetaceans stranded in the United Kingdom

The first evidence suggestive of in vivo gas bubble formation in cetacea, including eight animals stranded in the UK, has recently been reported. This article presents the pathologic findings from these eight UK-stranded cetaceans and two additional UK-stranded cetacean cases in detail. Hepatic gas-filled cavitary lesions (0.2-6.0 cm diameter) involving approximately 5-90% of the liver volume were found in four (two juvenile, two adult) Risso's dolphins (Grampus griseus), three (two adult, one juvenile) common dolphins (Delphinus delphis), an adult Blainville's beaked whale (Mesoplodon densirostris), and an adult harbour porpoise (Phocoena phocoena). Histopathologic examination of the seven dolphin cases with gross liver cavities revealed variable degrees of pericavitary fibrosis, microscopic, intrahepatic, spherical, nonstaining cavities (typically 50-750 microm in diameter) consistent with gas emboli within distended portal vessels and sinusoids and associated with hepatic tissue compression, hemorrhages, fibrin/organizing thrombi, and foci of acute hepato-cellular necrosis. Two common dolphins also had multiple and bilateral gross renal cavities (2.0-9.0 mm diameter) that, microscopically, were consistent with acute (n = 2) and chronic (n = 1) arterial gas emboli-induced renal infarcts. Microscopic, bubblelike cavities were also found in mesenteric lymph node (n = 4), adrenal (n = 2), spleen (n = 2), pulmonary associated lymph node (n = 1), posterior cervical lymph node (n = 1), and thyroid (n = 1). No bacterial organisms were isolated from five of six cavitated livers and one of one cavitated kidneys. The etiology and pathogenesis of these lesions are not known, although a decompression-related mechanism involving embolism of intestinal gas or de novo gas bubble (emboli) development derived from tissues supersaturated with nitrogen is suspected.     

Novel gastric helicobacters and oral campylobacters are present in captive and wild cetaceans

The mammalian gastric and oral mucosa may be colonized by mixed Helicobacter and Campylobacter species, respectively, in individual animals. To better characterize the presence and distribution of Helicobacter and Campylobacter among marine mammals, we used PCR and 16S rDNA sequence analysis to examine gastric and oral samples from ten dolphins (Tursiops gephyreus), one killer whale (Orcinus orca), one false killer whale (Pseudorca crassidens), and three wild La Plata river dolphins (Pontoporia blainvillei). Helicobacter spp. DNA was widely distributed in gastric and oral samples from both captive and wild cetaceans. Phylogenetic analysis demonstrated two Helicobacter sequence clusters, one closely related to H. cetorum, a species isolated from dolphins and whales in North America. The second related cluster was to sequences obtained from dolphins in Australia and to gastric non-H. pylori helicobacters, and may represent a novel taxonomic group. Dental plaque sequences from four dolphins formed a third cluster within the Campylobacter genus that likely represents a novel species isolated from marine mammals. Identification of identical Helicobacter spp. DNA sequences from dental plaque, saliva and gastric fluids from the same hosts, suggests that the oral cavity may be involved in transmission. These results demonstrate that Helicobacter and Campylobacter species are commonly distributed in marine mammals, and identify taxonomic clusters that may represent novel species.     

Morphology of the lymph nodes in bottlenose dolphin (Tursiops truncatus) and striped dolphin (Stenella coeruleoalba) from the Adriatic Sea

Morphology of the lymph nodes was examined in six bottlenose dolphins (Tursiops truncatus) and three striped dolphins (Stenella coeruleoalba) from the Adriatic Sea. All animals had been found dead in nature. One group of the nodes was taken from the tracheal branching area and was marked as bifurcational lymph node, and the other group was taken from the mesenteric root and was marked as mesenteric lymph node. Microscopic analysis showed that the lymph nodes in both dolphin species were surrounded by a connective tissue capsule comprising smooth muscle cells. The parenchyma of the mesenteric and bifurcational lymph nodes in bottlenose dolphin was divided into the peripherally situated cortex with the lymphatic nodules and diffuse lymphatic tissue, and the centrally situated medulla structured of the medullary cords separated by the medullary sinuses. These lymph nodes structurally correspond to the lymph nodes in the majority of terrestrial mammals. The mesenteric lymph node of striped dolphin also had a peripherally situated cortex and a centrally positioned medulla as the majority of terrestrial mammals. In the bifurcational lymph nodes of striped dolphin, there was a central dense lymphatic tissue with the lymphatic nodules and a peripheral less dense lymphatic tissue structured of the cell cords and sinuses. The bifurcational lymph node in striped dolphin resembled porcine lymph nodes and belonged to the inverse lymph nodes.     

Hepatic lesions in cetaceans stranded in the Canary Islands

This article describes the gross, histopathologic, and ultrastructural findings of the livers of cetaceans stranded on the coast of the Canary Islands between 1992 and 2000. A total of 135 cetaceans were included in the study, among which 25 were common dolphins (Delphinus delphis), 23 Atlantic spotted dolphins (Stenella frontalis), 19 striped dolphins (Stenella coeruleoalba), and 15 other species of dolphins and whales. The most common lesion observed in these animals was a nonspecific chronic reactive hepatitis (47/135), followed by hyaline intracytoplasmic inclusions in hepatocytes (33/135). Parasitic cholangitis was detected in 8/135 animals, whereas hepatic lipidosis was presented in 7/135 animals. The ultrastructure of hyaline hepatocytic cytoplasmic inclusions is described, and possible causes of these inclusions are discussed.     

Microbial diversity and structure in the gastrointestinal tracts of two stranded short-finned pilot whales (Globicephala macrorhynchus) and a pygmy sperm whale (Kogia breviceps)

Information on the gut microbiome composition of different mammals could provide novel insights into the evolution of mammals and succession of microbial communities in different hosts. However, there is limited information on the gut microbiome composition of marine mammals, especially cetaceans because of sampling constraints. In this study, we investigated the diversity and composition of microbial communities in the stomach, midgut, and hindgut of 2 stranded short-finned pilot whales (Globicephala macrorhynchus) and hindgut of a stranded pygmy sperm whale (Kogia breviceps) by using 16S rRNA gene amplicon sequencing technology. On the basis of the 50 most abundant operational taxonomic units, principal coordinate analysis, and non-metric multidimensional scaling analysis, we confirmed that the gut microbial communities of the 3 whales were different. Our results revealed that the gut microbiome of 1 stranded short-finned pilot whale GM16 was dominated by Firmicutes (mainly Clostridium) and Fusobacteria; whereas that of the other pilot whale GM19 was composed of Gammaproteobacteria and Bacteroidetes (mainly Vibrio and Bacteroides, respectively), probably caused by intestinal disease and antibiotic treatment. The gut microbiome of the pygmy sperm whale was dominated by Firmicutes and Bacteroidetes. Moreover, different gastrointestinal tract regions harbored different microbial community structures. To our knowledge, this is the first report of the gut microbiome of short-finned pilot whales, and our findings will expand our current knowledge on microbial diversity and composition in the gastrointestinal tract of cetaceans.     

Prevalence of Bartonella infection in wild African lions (Panthera leo) and cheetahs (Acinonyx jubatus)

Bartonella species are emerging pathogens that have been isolated worldwide from humans and other mammals. Our objective was to estimate the prevalence of Bartonella infection in free-ranging African lions (Panthera leo) and cheetahs (Acinonyx jubatus). Blood and/or serum samples were collected from a convenience sample of 113 lions and 74 cheetahs captured in Africa between 1982 and 2002. Whole blood samples available from 58 of the lions and 17 of the cheetahs were cultured for evidence of Bartonella spp., and whole blood from 54 of the 58 lions and 73 of the 74 cheetahs tested for the presence of Bartonella DNA by TaqMan PCR. Serum samples from the 113 lions and 74 cheetahs were tested for the presence of antibodies against Bartonella henselae using an immunofluorescence assay. Three (5.2%) of the 58 lions and one (5.9%) of the 17 cheetahs were bacteremic. Two lions were infected with B. henselae, based on PCR/RFLP of the citrate synthase gene. The third lion and the cheetah were infected with previously unidentified Bartonella strains. Twenty-three percent of the 73 cheetahs and 3.7% of the 54 lions tested by TaqMan PCR were positive for Bartonella spp. B. henselae antibody prevalence was 17% (19/113) for the lions and 31% (23/74) for the cheetahs. The prevalence of seropositivity, bacteremia, and positive TaqMan PCR was not significantly different between sexes and age categories (juvenile versus adult) for both lions and cheetahs. Domestic cats are thus no longer the only known carriers of Bartonella spp. in Africa. Translocation of B. henselae seronegative and TaqMan PCR negative wild felids might be effective in limiting the spread of Bartonella infection.     

Annotated checklist and fisheries interactions of cetaceans in Togo,with evidence of Antarctic minke whale in the Gulf of Guinea

Based on strandings and captures, 9 cetacean species, including 6 odontocetes and 3 mysticetes, are documented (photos and specimens) in Togo's coastal waters (newly‐recorded species marked with an asterisk): Antarctic minke whale (Balaenoptera bonaerensis*), Bryde's whale (Balaenoptera brydei or B. edeni), humpback whale (Megaptera novaeangliae), sperm whale (Physeter macrocephalus), pygmy sperm whale (Kogia breviceps*), short‐finned pilot whale (Globicephala macrorhynchus*), pantropical spotted dolphin (Stenella attenuata*), common bottlenose dolphin (Tursiops truncatus) and common dolphin Delphinus sp. An anecdotal sighting record for killer whale (Orcinus orca) is considered reliable. The lack of Sousa teuszii records in Togo is consistent with its apparent contemporaneous absence in Ghana. The B. bonaerensis specimen, entangled in a purse seine set on small pelagics, is a first record for the Gulf of Guinea. The occurrence of this Southern Ocean species north of the equator underscores the severe gaps in our understanding of cetacean distribution off western Africa. The majority of artisanal fishermen operating in Togolese coastal waters are of Ghanaian origin and are thought to promote trade and consumption of cetacean bushmeat. Because captures are illegal, enforced with some success in the main fishing centers, covert landings of cetaceans are exceedingly difficult to monitor, quantify or sample. Concern is expressed about pollution of Togo's coastal waters with heavy metals due to phosphorite mining and export from the coastal basin near Hahotoé and Kpogamé.     

Cetacean occurrence and diversity in whale-watching waters off Mirissa,Southern Sri Lanka

Scientific information is vital to the conservation of cetaceans and the management of whale-watching activities. The southern coastal waters of Sri Lanka are near a narrow continental shelf and biologically abundant in cetacean species. Although the occurrence of cetaceans has been investigated in certain waters of Sri Lanka, few surveys have been conducted along the southern coast. To fill this gap, we conducted boat-based surveys from January to May 2017 to investigate the occurrence, diversity, and behavior of cetaceans in the waters off Mirissa, covering a survey area of 788.9 km². During 55 survey days, we recorded a total of 242 cetacean sightings and identified at least 9 species (3 mysticetes and 6 odontocetes). The blue whale was the most common mysticete species (167 of 174 mysticete encounters), followed by the Omura's whale (4 of 174) and Bryde's whale (3 of 174). The spinner dolphin was the most common odontocete species (28 of 68 odontocete encounters), followed by the sperm whale (18 of 68), common bottlenose dolphin (13 of 68), short-finned pilot whale (5 of 68), melon-headed whale (2 of 68), and killer whale. Blue whales and sperm whales exhibited a clear preference for outer shelf and high slope areas, and blue whales were observed feeding along these waters. The present study provides near-baseline information on cetacean occurrence and diversity in whale-watching waters off southern Sri Lanka, and highlights the urgent need for proper management strategies for whale-watching activities.     

Bottlenose dolphin (Tursiops truncatus) papillomaviruses: vaccine antigen candidates and screening test development

Papillomaviruses (PVs) have been shown as being the etiologic agents of various benign and malignant tumours in many vertebrate species. In dolphins and porpoises, a high prevalence of orogenital tumours has recently been documented with at least four distinct novel species-specific PV types detected in such lesions. Therefore, we generated the immunological reagents to establish a serological screening test to determine the prevalence of PV infection in Atlantic bottlenose dolphins [(Tursiops truncatus (Tt)]. Using the baculovirus expression system, virus-like particles (VLPs) derived from the L1 proteins of two TtPV types, TtPV1 and TtPV2, were generated. Polyclonal antibodies against TtPV VLPs were produced in rabbits and their specificity for the VLPs was confirmed. Electron microscopy and enzyme-linked immunosorbent assay (ELISA) studies revealed that the generated VLPs self-assembled into particles presenting conformational immunodominant epitopes. As such, these particles are potential antigen candidates for a TtPV vaccine. Subsequently, the VLPs served as antigens in initial ELISA tests using sera from six bottlenose dolphins to investigate PV antibody presence. Three of these sera were derived from dolphins with genital tumour history and showed positive PV ELISA reactivity, while the remaining sera from lesion-free dolphins were PV antibody-negative. The results suggest that the developed screening test may serve as a potential tool for determining PV prevalence and thus for observing transmission rates in dolphin populations as the significance of PV infection in cetaceans starts to unfold.     

Use of computer tomography for imaging of Crassicauda grampicola in a Risso's dolphin (Grampus griseus).

A mature male Risso's dolphin (Grampus griseus) stranded along the coasts of Friuli Venezia Giulia, northeast Italy, in May 2001. Parasitic infection with Crassicauda grampicola is often found in the tympanic bullae and pterygoid sinuses in many of the Risso's dolphins examined from the same area. For this reason, it was decided to perform computed tomography of the head to assess this imaging technique for the diagnosis of crassicaudosis in dolphins. A full postmortem examination confirmed the pathologic findings of the computed tomography scan. This technique can be considered a useful adjunct in the diagnosis of cranial crassicaudosis in live dolphins.     

Detection of Bartonella henselae in the blood of 2 adult horses

BACKGROUND: Bartonella spp. are emerging zoonotic agents that have been found in a wide variety of domestic animals and wildlife and cause a number of clinical syndromes. Bartonella sp. infection has been identified in a growing number of animal species, including cats, rodents, porpoises, and canids, but has not been reported in horses. OBJECTIVE: To document the presence of Bartonella sp. in the blood of horses. ANIMALS: One horse with chronic arthropathy and 1 horse with presumptive vasculitis. METHODS: Blood samples were tested for the presence of Bartonella sp. by a combination of multiplex real-time polymerase chain reaction and enrichment culture technique. RESULTS: Bartonella henselae was isolated or detected in the blood of both horses. CONCLUSION AND CLINICAL IMPORTANCE: Bartonella henselae infection should be investigated as the cause of disease in horses.     

Determination of the immunotoxic potential of heavy metals on the functional activity of bottlenose dolphin leukocytes in vitro

Heavy metals may affect the immune system of cetaceans. But no information exists on their effects on the bottlenose dolphin (Tursiops truncatus) immune system, although this species is a coastal top predator which can bioaccumulate high concentrations of them. This work studies the effects of Hg (1, 5 and 10mg/L), Al (2,5, 25 and 50mg/L), Cd (1, 10, 20 and 40mg/L), Pb (1, 10, 20 and 50mg/L) and Cr (1 and 10mg/L), on the function of phagocytes and lymphocytes isolated from the peripheral blood of bottlenose dolphins under in vitro conditions. Cell viability, apoptosis, lymphocyte proliferation and phagocytosis were evaluated. Viability and lymphoproliferation were measured with Alamar Blue assay, and apoptosis and phagocytosis were evaluated with flow cytometry. Apoptosis was detected as mechanism of cell death after cadmium and mercury exposure. A significant reduction in the lymphoproliferative response was registered by exposure to 1mg/L of mercury, 10mg/L of cadmium and 50mg/L of lead. Decreased phagocytosis was also observed at 5mg/L of mercury, 50mg/L of aluminium and 10mg/L of cadmium. Chromium did not present any effects on any immune assay at the concentrations tested. The concentrations of heavy metals that were found to affect the functional activity of bottlenose dolphin leukocytes are within the environmental ranges reported in the tissues of bottlenose dolphins. These results support the hypothesis that exposure to these contaminants, particularly mercury and cadmium could lead to a reduction in host resistance to disease in these animals.     

Comparative histological study of the mammalian facial nucleus

We performed comparative Nissl, Klüver-Barrera and Golgi staining studies of the mammalian facial nucleus to classify the morphologically distinct subdivisions and the neuronal types in the rat, rabbit, ferret, Japanese monkey (Macaca fuscata), pig, horse, Risso's dolphin (Grampus griseus), and bottlenose dolphin (Tursiops truncatus). The medial subnucleus was observed in all examined species; however, that of the Risso's and bottlenose dolphins was a poorly-developed structure comprised of scattered neurons. The medial subnuclei of terrestrial mammals were well-developed cytoarchitectonic structures, usually a rounded column comprised of densely clustered neurons. Intermediate and lateral subnuclei were found in all studied mammals, with differences in columnar shape and neuronal types from species to species. The dorsolateral subnucleus was detected in all mammals but the Japanese monkey, whose facial neurons converged into the intermediate subnucleus. The dorsolateral subnuclei of the two dolphin species studied were expanded subdivisions comprised of densely clustered cells. The ventromedial subnuclei of the ferret, pig, and horse were richly-developed columns comprised of large multipolar neurons. Pig and horse facial nuclei contained another ventral cluster, the ventrolateral subnucleus. The facial nuclei of the Japanese monkey and the bottlenose dolphin were similar in their ventral subnuclear organization. Our findings show species-specific subnuclear organization and distribution patterns of distinct types of neurons within morphological discrete subdivisions, reflecting functional differences.