taxonID	type	description	language	source
03B287EDB377FF8CFBFFFD8138EDB083.taxon	description	Dermal plates. Otothyris has a loss and fusion of several plates of the head and body. The losses include the rostral plates, subocular plate, and plates of the lateral series. Most loricariids have the anterior portion of the snout naked or with several small plates. This feature is shared by many basal members of the Hypoptopomatinae, such as Plesioptopoma Reis, Pereira & Lehmann, 2012, Gymnotocinclus Carvalho, Lehmann & Reis, 2008, and Rhinolekos Martins & Langeani, 2011. The anterior region in other taxa in the Hypoptopomatinae is covered by one to four larger rostral plates. Four rostral plates are present in Pseudotothyris and Schizolecis Britski & Garavello, 1984, which are closely related to Otothyris, that has only two plates. These two plates are equivalent in shape, size and position to the two more anterior plates in Pseudotothyris and Schizolecis (Fig. 1 a). The loss of two rostral plates in Otothyris is the most parsimonious scenario according to Martins et al. (in press). Though varying between specimens and even contralaterally, the subocular plate may be also absent in Otothyris (Fig. 1 c). Fused structures include the postrostral plates. Whereas most taxa in the Hypoptopomatinae have four postrostral plates, Pseudotothyris and Otothyris, as well as some members of the Hypoptopomatini, have only three plates. The second postrostral plate in these taxa has a similar size, shape and position as the sum of the second and third plates in the other members of the Hypoptopomatinae, which leads us to hypothesize the fusion of postrostral plates 2 and 3 (Fig. 1 b, c). According to Martins et al. (in press) these fusions in Pseudotothyris and Otothyris were independently acquired, when compared to those in some taxa in the Hypoptopomatini. Basal lineages of the Hypoptopomatinae and related subfamilies have numerous and irregularly distributed prenasal plates; usually more than ten and reaching up to 50 in Plesioptopoma and Neoplecostomus microps (Steindachner, 1877), and 55 in Hypostomus careopinnatus Martins, Marinho, Langeani & Serra, 2012. Otothyris has only three to seven pre-nasal plates. The seven small plates in O. rostrata occupy the space corresponding to the three to six larger plates in congeners. This pattern could be the result of many events of loss and / or fusion of plates. Fusion and loss events also involve the lateral body plates. Compared to other taxa in the Hypoptopomatinae, the mid-dorsal, median, and mid-ventral series of Otothyris are shorter (Fig. 2; fig. 3 in Schaefer, 1997). The mid-dorsal series has four to 13 plates; however, it never extends beyond the vertical through the end of the adpressed dorsal fin. The median series falls short of the end of the caudal peduncle, such that the posterior two or three plates of the dorsal and ventral series are in contact with each other. Furthermore, this series usually has plates missing posterior of the first perforated plates. The absence of mid-dorsal and mid-ventral series was suggested by Schaefer (2003) to represent a conservation of a juvenile feature in adults of Lithogenes Eigenmann, 1909, since these are the last series formed during ontogeny. The reduction of the number of plates in the mid-dorsal and mid-ventral series in Otothyris could be interpreted in the same way, and also related to the interruption of plate development. Infraorbital series. The species of the Hypoptopomatinae usually have five infraorbital bones. Otothyris, however, has a reduced infraorbital series of only four infraorbitals (Fig. 1). This feature, also shared with Pseudotothyris, is a result of the loss of the infraorbital 1. Laterosensory system. Otothyris has reductions in several portions of the laterosensory system, including the cephalic and lateral body canals. While most taxa in the Hypoptopomatinae have the preopercle bearing a branch of the laterosensory system, the absence of this canal was reported in Acestridium Haseman, 1911, Otocinclus Cope, 1871, Oxyropsis Eigenmann & Eigenmann, 1889, and Otothyris; the latter genus being reported as polymorphic for this feature (Schaefer, 1991, 1998). We observed the preopercular canal only in O. lophophanes and O. travassosi in the genus. However, these species are in fact polymorphic for this feature. This polymorphism is related to a loss of the canal during ontogeny, since it occurs only in juveniles smaller than 21.0 mm SL, whereas adults of all species of Otothyris lack the canal in the preopercle (Fig. 1 b, c). A reduction of the laterosensory canal system also occurs in the infraorbital series. Infraorbital 2 often lacks a laterosensory canal, mostly in adults (Fig. 1 b, c). Juveniles of approximately 15.0 mm SL have the median plate series of the body with canals extending from the compound pterotic to near to the base of the caudal fin (Fig. 2 a), whereas this canal is reduced to different degrees depending on the species in adults (Fig. 2 b, c). An associated loss of lateral-line canals occurs in the middle of the series, near the dorsal-fin base and on the last plates of the series. Thus, the pattern in most adults of Otothyris of the lateral line is of interspersed groups of plates bearing or lacking canal segments (Fig. 2 b). This loss is most pronounced in O. rostrata in which only the anterior group of perforated plates remains (Fig. 2 c). In all of these cases, the laterosensory canals formed early in development are ontogenetically reabsorbed resulting in the loss of many canals in adults. Vertebrae. SomeofthebasalgeneraintheHypoptopomatinae, such as Plesioptopoma and Rhinolekos, have 31 or more vertebrae. This feature is shared with the Neoplecostominae, which is the sister to the Hypoptopomatinae. Conversely, a reduction to 25 to 28 vertebrae was observed in Otothyris. Fins. Juveniles of several species of the Hypoptopomatinae have simple last, and less often, penultimate pectoral-, pelvic-, dorsal-, and anal-fin rays. Ramification of those rays occurs during ontogeny, resulting in a general pattern in the Loricariidae of a dorsal with seven, pectoral with six, and pelvic and anal fins with five branched rays. Most examined Otothyris specimens retain the last two rays unbranched in the pectoral and pelvic fins, and the last ray unbranched in the dorsal and anal fins, even in adults. A similar condition, of an unbranched terminal dorsal-, pectoral-, and pelvic-fin ray, was observed in Schizolecis and Pseudotothyris obtusa (Miranda Ribeiro, 1951), in Oxyropsis acutirostra Miranda Ribeiro, 1951 in which the last dorsal-, pectoral-, and anal-fin ray are unbranched, and in Pseudotothyris janeirensis Britski & Garavello, 1984 and Otothyropsis marapoama Ribeiro, Carvalho & Melo, 2005 in which only the last the pectoral-fin ray is unbranched. In juveniles of many hypoptopomatines, the inner portion of the pectoral-fin spine is ornamented with medial serrae, a feature completely lost during ontogeny. This was observed in Pseudotothyris, Schizolecis, some species of Hisonotus Eigenmann & Eigenmann, 1889, Otothyropsis Ribeiro, Carvalho & Melo, 2005, Otocinclus, and Parotocinclus Eigenmann & Eigenmann, 1889. In some species within this subfamily, this feature is conserved to different degrees in adults. This feature was previously observed by Schaefer (1998) in Hypoptopoma Günther, 1868, Oxyropsis, Acestridium, and Niobichthys Schaefer & Provenzano, 1998, and in this study for Otothyris, Pseudotothyris janeirensis, and Hisonotus chromodontus Britski & Garavello, 2007. Another modification of the fins in Otothyris is the reduction to 12 branched caudal-fin rays, whereas the remaining hypoptopomatines have 14 rays (except for Acestridium with 10 or 12 rays). Brain. The brain of all craniates is composed of the telencephalon, diencephalon, mesencephalon, and rhombencephalon. Generally, the rostrodorsal portion of the rhombencephalon grows to form the cerebellum, by far the most variable part of the brain of actinopterygian fishes, both in size and shape (Nieuwenhuys, 1982). The cerebellum is posteriorly continuous with a distinct portion of the rhombencephalon, the crista cerebellaris. According to Lee & Bullock (1984), the cerebellum likely acts as an integration center where sensory information from various inputs is processed and relayed to the motor centers. The cerebellum of Otothyris is greatly reduced in size compared to that in Gymnotocinclus, a basal members of the Hypoptopomatinae and even Hisonotus, a more derived taxon of the subfamily (Fig. 3). This reduction is apparent mainly in the corpus cerebelli and eminentiae granularis. These are the portions of the cerebellum that mostly involve the somatosensory and mechanoreceptive functions, respectively. Moreover, the crista cerebellaris that is also related to the mechanoreceptive system, is similarly reduced. Thus, the reduction of these parts of the brain is probably related to the loss of many portions of the laterosensory system. Morphological variability. An increase of morphological variability is usually associated with miniaturization (Hanken & Wake, 1993). Some variation in species of Otothyris could not be correlated with ontogeny or sexual dimorphism, occurring intrapopulationally or even contralaterally in the same individual. These features include: the arrangement of the abdominal plates, the presence of a subocular plate, the entry of the laterosensory canal into the infraorbital series via the sphenotic or compound pterotic, and the presence of the levator arcus palatini crest.	en	Rosa, Alaina Cristine, Martins, Fernanda de Oliveira, Langeani, Francisco (2014): Miniaturization in Otothyris Myers, 1927 (Loricariidae: Hypoptopomatinae). Neotropical Ichthyology 12 (1): 53-60, DOI: 10.1590/S1679-62252014000100005, URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-62252014000100053&lng=en&tlng=en
