Ecomorphological, space, and mineral relations of dermal denticles in angular angel shark (Squatina guggenheim)

Abstract

Shark skin is predominantly specialized for swimming and protection, with the dermal denticle being the main structure associated with these abilities. The dermal denticle is a mineral structure with a unique morphology for each species, which allows its use as a taxonomic tool. Few studies have investigated the microscopy aspects of skin and dermal denticles, considering the high diversity of sharks. Here, we investigated the three‐dimensional morphoquantitative aspects and mineral composition of dermal denticles in different regions of the angular angel shark, Squatina guggenheim, using scanning electron microscopy and dispersive energy system. With the microscopy, we were able to observe that the dermal denticle morphology changes according to the area it is located. It was possible to describe the dermal denticles individually, from root to the crown, highlighting all of their individualities. Through the dispersive energy system, we showed the proportions of each mineral found in the denticle, by area, demonstrating the composition and the particularities of crown, body, and root, where whitlockite was described for the first time in elasmobranchs. In this way, the present study presented the specificities of the dermal denticles of S. guggenheim, as well sought to understand the different structure functions for the animal, thus assisting future research in animal morphology.

Morphological pattern of the dermal denticles of the Southern sawtail catshark Galeus mincaronei Soto, 2001

“…We observed that the dermal denticles of the caudal crest of G. mincaronei have a larger area of contact with the tegument than denticles in other areas of the body. De Lima Viliod et al (2021) reported a similar arrangement in the dorsal denticles of the Hidden angel shark Squatina guggenheim (Marini, 1936), attributing it mainly to defense. However, further histological or ecological studies are needed to identify the role and function of C1 dermal denticles in the genus Galeus or, more specifically, in the deep‐water shark G. mincaronei .…”

“…Higher densities of dermal denticles were observed in the P, D, and C2 fins of G. mincaronei , with no difference between the sexes. W. Raschi and Tabit (1992) and De Lima Viliod et al (2021) suggested that higher dermal denticle densities potentially indicate hydrodynamic functions or protection against abrasion. Larger dermal denticles, such as those we observed at the C1 site in G. mincaronei , at lower densities may confer defense or resistance.…”

“…Three dermal denticle functions have also been observed in deep‐water shark species, such as A. ampliceps , including generalized functional denticles on the dorsal edge of the tail, abrasion‐resistant denticles on the head and the rest of the fins, and photophore functions in the rest of the body (H. G. Ferrón et al, 2018). Additionally, in S. guggenheim , two functions were reported for dermal denticles: protection and defense (De Lima Viliod et al, 2021). In S. canicula , denticles were associated with abrasion strength, defense against ectoparasites, and dermal denticle antifouling to reduce fouling at certain flow speeds (Feld et al, 2019; Sullivan & Regan, 2011).…”

“…The length and width of each denticle were analyzed with ImageJ 1.53e software. Density was calculated by counting the number of denticles, including all denticles found at the edges in a square of 0.5 mm 2 , using ImageJ 1.53e software according to Feld et al (2019) and De Lima Viliod et al (2021). The normality (Shapiro–Wilk) and homogeneity (Levene's test) of the data were analyzed.…”

Relationship Between Skin Scales and the Main Flow Field Around the Shortfin Mako Shark Isurus oxyrinchus

“…In order to explore the relationship between the flow field around the shark and the adaptive growth of scales, the physical parameters of scales were measured. The morphology, riblet size, roughness, and composition of shark scales have been previously studied in fine detail ( Motta et al, 2012 ; Popp et al, 2020 ; de Lima Viliod et al, 2021 ). A sub-set of 45 skin samples of 2 cm × 2 cm were carefully dissected from the different parts of the shark using pre-made templates consisting of plastic substrates and pins ( Figure 3A ).…”