Light and Scanning Electron Microscopic Study on the Lingual Papillae in the Newborn Sea Otter Enhydra Lutris

Okajimas Folia Anat. Jpn., 73(1): 65-74; May, 1996

Light and Scanning Electron Microscopic Study on the Lingual Papillae in the Newborn Sea Otter Enhydra lutris

Taeko SHIMODA,Eiko NAKANISHI, Sentaro YOSHINO and Shigeru KOBAYASHI

Department of Home economics, Univercity of kyushuwomens, Kitakyushu, Japan, Department of Oral Pathology and Departmennt of Anatomy, Kyushu Dental College, Kitakyushu, Japan, Oita Small Hospital, Oite, Japan

-Received for Publication, March 1, 1996-

Key Words: lingual papilla, Enhydra lutris, LM, SEM

Summary: The tongue of Enhydra lutris (sea otter), died from brain contusion at the first day of its age, was investigated by light and scanning electron microscopy in this study. Three types of papillae (filiform, fungiform and circumvallate papillae) were present on this tongue. In our evaluation, the filiform papillae were divided into four shapes which were conical, club-shaped, large horny and triangular papillae. The different types of filiform papillae were located in different area of this tongue. The fungiform papillae were divided into two shapes, which were hemispherical or club-shaped, and were distributed among the filiform papillae on the dorsal and the margin of the tongue. These papillae had many taste buds in the epithelium of the dorsal aspect of them. The circumvallate papillae were present in a V-shaped row at the posterior part of the lingual body, and many taste buds lay in the epithelium of both the lateral walls facing the trench and dorsal aspect of the papillary body, and then the ducts of the serous glands opened into the floor of the trenches. The lingual mucosa of the interpapillae area at the pharyngeal part of the tongue contained taste buds and the ducts of the mixed glands opened there. Based on our examination, the lingual papillae of this newborn sea otter had many features which were described to be peculiar to young stage of mammals.

It is generally accepted that the morphology of 56 cm), which is also named as sea otter, was used lingual papillae in mammalian tongues varies with for the observation in this study. The sea otter, died species. Sontag (1920) made a report about the from brain contusion at the first day of its age, was morphology of lingual papillae, which included the fixed with 10% neutral formalin solution after anat- filiform, fungiform, circumvallate and foliate ones, omy and the tongue was sent to our laboratory. and about those variation and the difference in num- After macroscopic observation, the tongue was div- ber of circumvallate papillae by species. ided into two near the median. Although Mustelidae almost lives on land, the sea One side of this specimen was cut into several otter (Enhydra lutris) and the river otter (Lutra pieces, then dehydrated in graded ethanol and em- canadensis) live in water. The sea otter is the smallest bedded in palaffin. Then these pieces of specimens one in all marine mammals and the features appear were sectioned frontally and sagittaly in 4 tun, and to be similar to Pinnipedia, so it may be necessary to stained with hematoxylin-eosin before observation compare the tongue of this animal with that of other by light microscopy. marine mammals. There are many reports about the The other side of specimen was fixed with 1/2 sea otter, but the description about the anatomy of Karnovsky solution over night and post-fixed in its tongue is very few. phosphate-buffered 1% osmium tetroxide solution In this paper, the morphological and histological at 4°C for 2 hours. This procedure was followed by characters of the tongue of the newborn sea otter are dehydration, freezing point drying and platinum- described in detail and compared with those of other palladium ion-sputtering in order. Then they were mammals. examined under scanning electron microscope (Hitachi S-530). After the observation, this specimen was embedded in palaffin, sectioned sagitally in 8 tim , Material and Methods and stained with hematoxylin-eosin.

Enhydra lutris (body weight 1.4 kg, body length

65 66 T. Shimoda et al.

Results 2-b). These triplet papillary bodies were completely separated. And then, it was difficultto detect papillary The tongue of the sea otter was rectangular and bodies without histological observation, either be- had a shallow apical median sulcus separating it into cause they were concealed by overhanging triangular two lateral parts. This tongue was about 40 mm in filiform papillae (Fig. 4-a,b) or because they were length and about 19 — 21 mm in width. In the tongue, very small (Fig. 4-b,d). Many fissures were observed the sulcus terminals, sulcus median linguae were on the dorsal aspect of the large papillary body unclear. Lyssa and sublinguae were absent (Fig. 1). which branched (Fig. 2-b,4-c). There were many The tongue was covered with stratified squamous taste buds on the lateral walls facing the trench and epithelium. At height magnificationby scanningelec- the dorsal aspect of the papillae (Fig. 4-a,b,c). The tron microscopy, microridges were distributed over vallum were divided into many concentric circles of the whole surface of all papillae. The phenomenon lobules, which were reniform or conical appearance of thickening over margins of the cells was unclear. (Fig. 2-b). The ducts of the serous glands (of von Three types of papillae (filiform, fungiform and Ebner) opened into the floor of the trenches. circumvallate papillae) were present on the dorsal surface of the tongue, but the foliate papillae were absent (Fig. 1). Discussion The filiform papillae were divided into four shapes of which were conical, club-shaped, large horny and It is reported that the average weight and length triangular papillae (Fig. 1). On the surface of the of the sea otter at birth is from 1.4 to 2.3 kg and lingual body, conical filiform papillae (240-300 Rrn 0.55m (Kenyon 1969, Walker 1975). From these in height) were distributed and those points were reports, it may be considered that this newborn sea directed backward, or backward and inward (Fig. otter must have developed normally. 2-a,d, 3-a,d,e). At the margin of the tongue, the The morphology and the histological charactores club-shaped filiform papillae, approximately 600 on the tongue of Mustela, Lutra and other marine 800 pm in height, became higher from the posterior mammals were as follows. part to the apex of the tongue (Fig. 2-e,f, 3-a,b,c). According to Furubayashi's report (1989),filiform, Besides, the large horny filiform papillae scattered fungiform, vallate and foliate papillae were present among these club-shaped ones only at the apex. on the tongues of adult Japanese weasels (Mustela These club-shaped or large horny filiform papillae itatsi).The vallate and foliate pappillaewere furnished protruded like fringesfrom the tongue. The triangular with taste buds, but the fungiform were not. Taste filiform papillae, which were simple (Fig. 2-c), or buds on the vallate papillae were present only in the compound types with the apex divided (Fig. 2-a,b), epithelium of the lateral walls facing the trench. completely covered on the pharyngeal part of the Tuckerman (1890) described that filiform, fungi- tongue and arranged in overlapping each other like form, circumvallatepapillae are present on the tongue scaly leaf. The lingual mucosa of the interpapillae of the river otter (Lutra canadensis). Seven or eight area of the pharyngeal part contained taste buds. circumvallate papillae are observed on the tongues The ducts of the mixed glands opened there. of adult Lutra, but in the young ones, six or seven The fungiform papillae were divided into two circumvallate papillae are observed. In the young shapes which were hemispherical (Fig. 2-d, 3-d) and Lutra, the bulbs (taste buds) were present in the club-shaped (Fig. 2-e,f, 3-c,e). The former scattered epithelium of the dorsal aspect, the lateral walls of among the conical filiform papillae on the dorsal the circumvallate papillae and the outer wall of the surface of the tongue, but the latter were among the trench, whereas those which were on the dorsal club-shaped filiform papillae on the margin of the aspect were absent in adult Lutra. Besides, the fungi- tongue. The hemispherical fungiform papillae on the fot in papillae contained the bulbs on the dorsal posterior part of the dorsal surface of the tongue aspect of them. were very large (300p.m in diameter). And they had As for the pennipedia, Kubota (1968) showed taste buds on the dorsal aspect of these papillae. The that filiform,fungiform and one to fivevallate papillae club-shaped fungiform papillae were very similar in were present on the tongues of fetal or adult fur seals shape to the club-shaped filiform papillae at the (Callorhinus ursinus). Then only vallate papillae margin of the tongue, but the club-shaped fungiform were with taste buds. papillae had taste buds in the epithelium near the Unlike most of Mustaridae and other marine top of them (Fig. 2-e, 3-c). mammals, the sea otter has an unique habit of The circumvallate papillae were present in a feeding while floating on its back. The molars of V-shaped row (Fig. 1), and the three small papillary them are broad, flat, and well-adapted to crushing bodies (triplet papillary bodies) were observed (Fig. shells of crustaceans, snails, sea urchins and mussels The Lingual Papillae of the Newborn Sea Otter 67

(Walker 1975). Other marine mammals often swallow former at the apex of the tongue. There were few the foods wholly with water without masticating. It reports on such high papillae at the apex of the is, therefore, described that the gustatory papillae tongue in young or adult mammals. The results of and glands of marine mammals such as Pinnipedia the present study indicate that the high club-shaped and Cetacea tend to degenerate (Sonntag 1923 a, and large horny filiform papillae of the newborn sea Kubota 1968). In this report, three types of papillae otter are somewhat different from the fringing pa- (filiform, fungiform and circumvallate papillae) were pillae. These filiform papillae of this tongue may present on the dorsal surface of the tongue. have important mechanical functions during suckling. The tongue of the sea otter may play more import- Possibly these structures at the apex may be helpful ant role on masticating than that of other marine for the adult sea otter to take foods. Based on our mammals. examination, the lingual papillae of this newborn sea Taste buds were present in the epithelium of the otter had several features which were described to circumvallate, fungiform papillae and the mucosa of be peculiar to young stage of mammals. The question the pharyngeal part of the tongue. The location of whether these features are evident to the sea otter or taste buds on circumvallate papillae were very similar just a stage in its development still remains. to that of the young Lutra canadensis. According to Sonntag (1925), taste buds occur on the whole aspect of the circumvallate papillae in many new-born References animals, and those on the dorsal aspect are more numerous at birth than in adult life. Afterwards, the 1) FurubayashiR et al. Histologicalpattern of the tonguein the japaneseweasels, Mustela itatsi, with specialreference to taste buds on the dorsal aspect diminish as the age the morphologyand distributionof papillae, taste buds and advances. Reports on Lutra canadensis (Tuckerman, lingualglands, Acta AnatomicaNipponica 1989; 64:210— 1890)coincide with the descriptionby Sonntag (1925). 214(in Japanese). It is necessary to compare our results with those of 2) HabermehlKH. Uber besondererandpapillen an der zunge the adult sea otter. neugeborenersaugetiere. Zeitschrift fur Anatomic und Entwicklungsgeschichte1952; 116:355-372. In the present study, it was difficult to number the 3) KenyonKW. The sea otter in the eastern pacificocean, papillarybodies of the circumvallatepapillae, because p. 352. NewYork: DoverPublication. 1969. there were several papillary bodies of different sizes 4) KubotaK. Comparativeanatomical and neurohistological in the same trench. The vallum of the circumvallate observationson the tongueof Northernfur seal (Callorhinus ursinus).Anattomical Record 1968;161:257-266. papillae were not distinguish in shape from the 5) SonntagCF. Thecomparative anatomy of the tongueof the neighbouring filiform papillae. There is a possibility marrumalia.1. Generaldescription of the tongue. Proceed- that the circumvallate papillae of the new born sea ingsof the GeneralMeetings for ScientificBusiness of the otter may be under progressive changes. ZoologicalSociety of London,pp. 115-129. London: Messrs. By previous reports (Habermehl 1952, Yamasaki Longmans,Green. 1920. 1978), the fringing papillae of the lingual margin 6) SonntagCF. Thecomparative anatomy of the tonguesof the mammalia.VIII. Carnivora,Proceedings of the General have been observed in the prenatal and newborn Meetingsfor ScientificBusiness of the ZoologicalSociety of mammals, and then they have disappeared at the London,pp. 129-153.London: Messrs. Longmans, Green. end of the suckling period. These authors assumed 1923a. that the fringing papillae might have a relation to 7) SonntagCF. Thecomparative anatomy of the tonguesof the suckling.Habermehl (1952)showed that these fringing mammalia.VII. Summary,Classification and Phylogeny. Proceedingsof the GeneralMeetings for Scientific Business papillae have no taste buds and become more minute of the ZoologicalSociety of London, pp. 701-762. London: at the apex of the tongue. Messrs.Longmans, Green. 1925. In this study, the characteristicclub-shaped filiform 8) TuckermanF. On the gustatoryorgans of some of the papillae, approximately 600-800 im in height on mammalia.Journal of Morphology1890; 4:180-181. the lingual margin and the lingual apex, were ob- 9) WalkerEP. Mammalsof the world, vol 2 (ed.J.L. Paradiso), pp. 1109-1223.Baltimore, London: The Johns Hopkins served. The became higher towards the apex of the UniversityPress, 1975. tongue, and only at the apex, large horny filiform 10) YamasakiF et al. Papillaryprojections at the lingualmargin papillae were present among them. in the stripeddolphin, stenella cocruleoalba, with special In comparing the fringing papillae with the filiform referenceto their developmentand regression.Journal of papillae of this study, the latter are higher than the Morphology1978; 157:33-48. 68 T. Shimoda et al.

Explanation of Figures

Plate I

Fig. 1. Diagram of the distribution of the lingual papillae of the new born sea otter Enhydra lutris. The Lingual Papillae of the Newborn Sea Oiler 69 Plate I

ep , epiglottis la , lingual apex Pfc conical filiform papilla Pfcs , club-shaped filiform papilla Pfh horny filiform papilla Pft , triangular filiform papilla Pfuc , club-shaped fungiform papilla Pfuh , hemisphrical fungiform papilla Pv , circumvallate papilla 70 T. Shimoda et al.

Plate H

Fig. 2. Scanning electron micrographs of the dorsal surface of the right side of the tongue. a. Compound type of triangular filiform papillae (Pft) at the posterior part of the margin. b. Two types of the circumvallate papillae. Pv3; triplet papillary bodies. C. Simple type of the triangular papilla (Pft) at the fore part of the Fig. 2a. dl. Hemispherical fungiform papilla (Pfuh) among the conical filiform papillae (Pfc). d2. Higher magnification of the dorsal aspect of the hemispherical fungiform papilla. Taste pore (arrows). e. Club-shaped fungiform papillae (Pfuc) among the club-shaped filiform papillae (Pfcs) at the anterior part of the margin. f. Club-shaped filiform papilla (Pfcs) and large horny filiform papilla (Pfh) at the apex region. The Lingual Papillae of the Newborn Sea Otter 71 Plate II 72 T. Shimoda et al.

Plate III

Fig. 3. Light micrographs of the frontal section through the lingual papilla with hematoxylin-eosin staining. a. The middle part of the tongue. The different types of lingual papillae are located in different area of this tongue. x2.5 b. The large horny filiform papilla (Pfh) at the apex of the tongue. x 13.2 C. Club-shaped fungiform papilla (Pfuc) on the anterior part of the margin. Taste buds (arrow) are present in the epithelium near the top. x16 d. Hemispherical fungiform papilla (Pfuh) with taste buds (arrow). x33 e. Club-shaped fungiform papillae (Pfuc) with taste buds (arrows). x25 The Lingual Papillae of the Newborn Sea Otter 73 Plate Ill 74 T. Shimoda et at

Plate IV

Fig. 4. Light micrographs through the circumvallate papilla with hematoxylin-eosin staining. a. Sagittal section through the circumvallate papilla on the part of the Fig. 2b. The circumvallate papilla (Pv) are concealed by overhanging triangular filiform papillae. x25 b. Oblique section through the circumvallate papillae (Pv). Two papillary bodies in the same trench (arrows). The ducts of von Ebner's glands (Eg) open into the floor of the trenches. x 10 c. Sagittal section through the circumvallate papilla on the part of the Fig. 2b. The circumvallate papilla with branches. Taste buds (arrows) on the lateral walls facing the trench and the dorsal aspect of the papillae. x25 d. High magnification of the trench (Tr). Papilla-like structure with taste buds (arrow) at the inner side of the vallum is very small. Eg; von Ebner's glands. x33