Some histological data of bone and teeth in the Rift Eelpout, Thermarces cerberus (Zoarcidae) by François J. Meunier* (1) & isabelle ArnulF (2) abstract. – The rift eelpout, Thermarces cerberus (Zoarcidae), is a deep-sea marine fish that inhabits the vicin- ity of the hydrothermal vents of the east Pacific rise. its skeleton is mineralized to a normal degree and is constituted of acellular bone as the majority of perciforms, to which it belongs. T. cerberus feeds on amphipod crustaceans and gastropods, and has thin sharp teeth constituted of an orthodentine cone with a thin external api- cal layer of enameloid. The histological characteristics of the skeleton (jaws and vertebrae) appear normal with seasonal growth marks. There is no evidence that the physicochemical characteristics of the deep-sea hydrother- mal environment of this species play a specific role on its bone anatomy and physiology. Résumé. – Quelques données histologiques sur l’os et les dents de l’anguille des sources, Thermarces cerberus (Zoarcidae). © SFI Received: 30 Jun. 2017 Thermarces cerberus est un poisson marin de profondeur qui vit près des sources hydrothermales du rift Accepted: 7 Sep. 2017 Est-Pacifique. Son squelette, normalement minéralisé, est constitué d’os acellulaire comme la très grande majo- Editor: J.Y. Sire rité des Perciformes dont il fait partie. T. cerberus se nourrit de crustacés amphipodes et de gastéropodes, et a des dents fines et pointues, constituées d’un cône d’orthodentine coiffé d’une fine couche d’émailloïde. Les caracté- ristiques histologiques du squelette (mâchoires et vertèbres) paraissent normales, et des marques de croissance saisonnières sont visibles. les caractéristiques physico-chimiques particulières de son biotope hydrothermal Key words profond ne semblent pas influencer l’anatomie et l’histologie osseuse de cette espèce. Zoarcidae Thermarces cerberus East-Pacific Deep-sea fish Acellular bone Teeth Histology Thermarces cerberus rosenblatt & Cohen, 1986, is an et al., 1987). This anatomical study based on a staining pro- eelpout (Zoarcidae) that is a conspicuous member of deep- cedure (Alizarin red S-Alcian Blue) also demonstrated that sea hydrothermal vents of the east Pacific rise (Cohen et the skeleton “is rather well ossified, even if most of the bones al., 1985; Geistdoerfer, 1985; rosenblatt and Cohen, 1986; seems to be fragile” (Arnulf et al., 1987). Yet, a histological Biscoito et al., 2002). Hence, T. cerberus lives among the study was compulsory to confirm the possible fragility of the vestimentiferan worm communities in a hydrogen sulfid- bones owing, for example, to rickets (Bertin, 1936). The aim rich habitat. The physical characteristics of this habitat are of the present study is to confirm previous assertion using peculiar: depth 2600-2700 m, temperature 8-12°C (Geistdo- classical techniques to study the histology of mineralized tis- erfer, 1985; Voight, 2000; Biscoito et al., 2002; Sancho et sues. al., 2005), and these physicochemical environmental condi- tions may have some influence on the biology of T. cerberus (Geistdoerfer and Seuront, 1995), and/or the high hydrostat- MatERial and MEthodS ic pressure at these depths, on the strength of the skeleton (Bertin, 1936). T. cerberus is a benthic predator that feeds Material mainly on gastropods (limpets fixed on the vestimentifer The specimens were caught by the expedition “Byo- tubes) and amphipod crustaceans (Geistdoerfer and Seuront, carise” (Ifremer; mars 1984) in the East Pacific: 12°48,80 N; 1995; Sancho et al., 2005). 103°96,60 W); depth: –2620 m. Five precaudal (= abdomi- Some years ago, the osteology of this species was studied nal) and five caudal vertebrae were sampled as well as the confirming its membership to the Zoarcidae family (Arnulf two lower jaws from a specimen, 250 mm Tl. (1) uMr 7208 (CnrS-irD-uPMC-MnHn), BOreA, Département Adaptations du Vivant, Muséum national d’Histoire naturelle, C.P. 026, 43 rue Cuvier, 75231 Paris cedex 05, France. (2) Service de Biologie animale, université Paris Diderot – Paris 7, Bât. Buffon case 7072, 5 rue Thomas Mann, 75205 Paris cedex 13, France. [[email protected]] * Corresponding author [[email protected]] Cybium 2018, 42(1): 83-86. Bone and tooth histology of Thermarces cerberus Meunier & Arnulf Methods mitted natural and polarized light with a Zeiss Axiovert 35 Ground sections. The right lower jaw and the anterior microscope. part of the left one were dehydrated in graded series of alco- hol till absolute ethanol, transferred to acetone, and embed- ded in methtyl methacrylate (Juster et al., 1965; Matrajt et RESultS-diScuSSion al., 1967). Transverse and longitudinal sections (150-200 µm thick) of the right and the left jaws, respectively, were cut eelpout teeth form two longitudinal rows on the jaws with an isomet sawing machine and ground to 50-75 µm in (Fig. 1). The teeth are sharp, lightly curved, and show a thickness. The sections were radiographed in a CGr Sigma dentine core with a thin external well-mineralized enam- generator X-ray machine, and then observed under trans- eloid layer (Figs 2-4). Dentine is crossed by canaliculi that Figure 1. – Thermarces cerberus. Horizontal section (transmitted polarized light) of the lower left jaw showing numer- ous teeth sections aligned on two rows. The arrowhead points to the tooth detailed in figures 2, 3, 4. Scale bar = 500 µm. Figures 2, 3, 4. – Thermarces cerberus. left lower jaw. Detail of a cross section of a tooth (see arrowhead in Fig. 1), natural transmitted light, polarized light and microradiography, respectively. The arrowhead points to the superficial hypermineralized layer of enameloid (Fig. 4). de: dentine; pc: pulp cavity. Scale bar = 100 µm. Figure 5. – Thermarces cerberus. Transversal section of the right lower jaw showing an axial section of a tooth. The tooth is fixed on the vascularized supporting bone (sb) by an unmineralized ligament (li). The dentine core is surrounded by a thin hypermineralized enameloid layer well seen at the tip of the tooth (en). At the base of the tooth, on the right, there is a tooth bud (arrowhead) in a lateral alveola of the dentary. Mc: Meckel cartilage. Scale bar = 250 µm. Figure 6. – Thermarces cerberus. Detail of a sagittal section of a vertebra. a: Polarized light; B: Microradiography. note the fibrillary component of the vertebral bone (arrowhead). The mineralization of the vertebral bone is heterogeneous, and three weakly hypermineralized growth zones are seen (arrows). Scale bar = 100 µm. 84 Cybium 2018, 42(1) Meunier & Arnulf Bone and tooth histology of Thermarces cerberus are orthogonal to the wall of the pulp cavity and that char- the results of the anatomical study by Arnulf et al. (1987) acterize this tissue as orthodentine. The walls of the pulp that concluded that the flimsy aspect of the skeleton seems cavity are slightly irregular (Fig. 4). Teeth are fixed on the to result only of the bones being thin. Our findings do not jaw through unmineralized ligaments (Fig. 5) and are thus support the hypothesis that deep marine environments may slightly mobile on their bony support; they belong to the induce rickets (Bertin, 1936), at least in T. cerberus. type two of Fink (1981). The bony tissue localized below the tooth is slightly less mineralized than the surrounding jaw acknowledgments. – We thank Dr Clara lord for the improve- bone (Fig. 5). This corresponds to the bone turnover in rela- ment of the English and for scientific discussions and the anony- tion to tooth replacement. mous reviewers for their valuable scientific inputs. The various bones of T. cerberus we have studied look slender and their tissue is totally deprived of osteocytes. REfEREncES There are no osteoblastic processes penetrating the bony tissue either, contrary to certain acellular bony fishes (Sire ArnulF i., Meunier F.J. & GeiSTDOerFer P., 1987. - and Meunier, 2017). The bony tissue of the dentary contains Ostéologie de Thermarces cerberus rosenblatt & Cohen 1986, Zoarcidae des sources hydrothermales du Pacifique Est, suivie large vascular cavities surrounded by thin bone trabeculae d’une discussion sur sa classification. Cybium, 11(2):141-158. (Fig. 5). 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In: Ageing of Fish (Bagenal T.B., ed.), pp. 13-27. unwin Brothers ltd, The vertebral bone shows narrow well-mineralized zones england. and wider, less mineralized, ones (Fig. 6). This alternate pat- CASTAneT J., FrAnCillOn-VieillOT H., Meunier F.J. & tern characterizes cyclical growth (Meunier, 1988; Castanet riCQlèS A. (De), 1993. - use of bone growth in aging indi- et al., 1993). These successive growth marks suggest that viduals. In: Bone (Hall B.K., ed.), Vol. 7, pp. 245-283. CrC Press, Florida. the rift eelpout is subjected to a degree of seasonality of its COHen D.M., rOSenBlATT r.H. & HAeDriCH r.l., 1985. - metabolic rate (e.g. Meunier and François, 1992; Castanet et identity of thermal vent fishes in the eastern Pacific: an interim al., 1993). This result is rather surprising because the deep- report. Biol. Soc. Wash. Bull., 6, 229-230. sea environment is generally considered as relatively stable. 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