Thalassophryninae
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publication ID |
https://doi.org/10.1093/zoolinnean/zlz094 |
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persistent identifier |
https://treatment.plazi.org/id/039C87B1-FF84-1F6B-9E37-FEDD61DAFA7C |
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treatment provided by |
Plazi |
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scientific name |
Thalassophryninae |
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Thalassophryninae ( Figs 15–18 View Figure 15 View Figure 16 View Figure 17 View Figure 18 ; Table 3)
Thalassophryninae has two genera, and both were examined in this study. Daector contains four species, with two of them examined in this study. Thalassophryne has six species, three of which were examined in this analysis.
The first ural and and second preural centra are slightly elongated, with the length of the centra approximately equal to their depth in Thalassophryne , but 1.3 longer in Daector . The length of the second ural centrum is roughly two-thirds that of the first ural centrum. Neither dorsal nor ventral zygapophyses are present in the ural centra of any specimen of Thalassophryninae . The second preural centrum bears a blunt or hook-like dorsal prezygapophysis that contacts the base of the neural arch of the preceding vertebra. The neural and haemal spines of the second preural centrum are 1.3–2 times longer than the more anterior spines on the caudal vertebrae.
The dorsal hypural supports five or six principal caudal-fin rays, whereas the ventral hypural supports six or seven caudal-fin rays (six principals and one procurrent). Two dorsal and one or two ventral procurrent caudal-fin rays are present in most species of this subfamily. The only exception is Thalassophryne amazonica Steindachner, 1876 , which lacks procurrent fin rays ( Fig. 18 View Figure 18 ; Table 3). The dorsal procurrent rays are supported by the epurals. The anterior (or single) ventral procurrent caudal-fin ray is supported by the distal caudal radial cartilages. The homology of these cartilages, however, is uncertain. The only specimen in which the distal caudal radials stained was of Daector dowi (USNM 206532, 79.1 mm SL; Fig. 15A View Figure 15 ), which has two small and circular distal caudal radial cartilages. The topology of these cartilages indicates that they are either distal caudal radials of the haemal spine of the second preural centrum or of the parhypural. The second ventral procurrent caudal-fin ray, if present, is supported by the ventral hypural.
The parypural flange varies from straight to strongly concave, and its articular edge is robust and may have indentations or spinations. The morphology of the articular margin of the parhypural flange is variable in Daector dowi , with some specimens having an acute articular edge that articulates loosely with the haemal spine of the second preural centrum (UF 226263, 43.1 mm SL).
The largest juvenile specimens of Thalassophryne and Daector that were examined have a short hypurapophysis-like process on the lower third of the lateral wall of the first ural centrum that projects slightly in a lateral direction to form a narrow shelf, forming additional surface area for the origin of the m. hypochordal longitudinalis ( Fig. 15E, F View Figure 15 ). The hypurapophysis-like process of Thalassophryninae develops late in ontogeny. In the smallest examined specimens ( Thalassophryne maculosa Günther, 1861 , USNM 200558, 25.0 and 36.0 mm SL), the hypurapophysis-like process is not yet developed.
The epurals have a simple rod-like shape. In most species they are convex, but in some specimens of Daector dowi the epurals are concave (see below). The distal tips of both epurals supports caudal-fin rays in Daector . In Thalassophryne , the posterior epural supports the anteriormost non-branched fin rays (which may be either procurrent or the unbranched ray of the principal series), whereas the anterior epural does not support any fin rays (although the distal tip of the anterior epural may contact the anteriormost procurrent fin ray in Thalassophryne ).
Daector : The hypurals support 11 principal caudal-fin rays (I, 4, 5, I), with the exception of a single specimen of Daector dowi (UF 226263, 84.0 mm SL), which has six dorsal principal caudal-fin rays (formula I, 5, 5, I). The total counts of fin rays of this specimen are the same as in other specimens (15), having a single dorsal procurrent ray instead of two as observed in all other specimens of Daector dowi . The morphology of the unbranched principal fin ray observed in other specimens and the dorsalmost branched caudal-fin ray of this specimen (UF 226263, 84.0 mm SL) is similar (i.e. slightly thinner than other principal fin rays), and they appear to be homologous. Therefore, it is likely that the posterior tip of the corresponding unbranched principal fin ray of UF 226263 (84.0 mm SL) branched during ontogeny, resulting in a branched fin ray.
Daector reticulata (Günther, 1864) has one ventral procurrent fin ray ( Fig. 15B View Figure 15 ), whereas Daector dowi has two. The shape of the epurals and their support for procurrent fin rays and the shape of the parhypural flange is variable in Daector dowi ( Figs 15A View Figure 15 , 16 View Figure 16 ). The shape of the anterior epural varies from convex (UF 226263, 84.0 mm SL) to straight (UF 226263, 89.6 mm SL). From the 11 cleared and stained specimens examined, the anterior epural of seven specimens has a slender flange on the proximal portion of the anterior margin. The length of this flange varies from weakly developed (UF 226263, 84.0 mm SL; Fig. 16E View Figure 16 ) to elongate, extending to the midpoint of the anterior epural in UF 226263 (43.1 mm SL; Fig. 16A View Figure 16 ). The presence and prominence of the flange, such as the curving of the epural, do not appear to be related to ontogeny, because different conditions were observed in specimens of similar size. The anterior epural that does not bear the flange has a rod-like shape. The posterior epural is more consistently straight or slightly convex.
In most specimens of Daector dowi , both epurals support caudal-fin rays. However, in one specimen (USNM 206532, 59.7 mm SL) the first and second dorsal procurrent caudal-fin rays are supported by only the posterior epural ( Fig. 16C View Figure 16 ). The anterior epural contacts but does not support the first dorsal procurrent ray, as in Thalassophryne . Another variation observed in the caudal-fin rays is the presence of three dorsal procurrent rays, with the anteriormost positioned between the neural spine of the second preural centrum and the anterior epural (UF 226263, 74.5 mm SL); this unique occurrence is interpreted as individual variation because all other specimens of Daector dowi have two dorsal procurrent rays. A similar individual variation (i.e. one dorsal procurrent caudal-fin ray between the neural spine of the second preural centrum and the anterior epural) was observed in Opsanus beta and Opsanus pardus .
The parhypural flange in Daector is consistently concave, but the curvature of the margin varies from slight (USNM 206532, 59.7 mm SL) to highly concave (UF 226263, 84.0 mm SL). The latter specimen also has a unique elliptical invagination at the midpoint of the margin. The shape and the width of the articular edge of the parhypural flange are also highly variable. The smallest (UF 226263, 43.1 mm SL) and the largest (UF 226263, 89.6 mm SL) specimens examined have an acute anterior edge ( Fig. 16A, F View Figure 16 ). The edge is still angular but is slightly longer in specimens UF 226263 (47.9 and 82.3 mm SL; Fig. 16B View Figure 16 ) than in UF 226263 (43.1 mm SL). All other specimens examined have a long articular edge of the parhypural, in which the articular surface is also variably shaped. For example, some specimens have a straight articular edge of the parhypural (USNM 206532, 59.1 mm SL and UF 226263, 84.0 mm SL; Fig. 16C, E View Figure 16 ), whereas in others the articular surface is indented, with three or four spine-like projections [UF 226263, 60.0 mm SL ( Fig. 16D View Figure 16 ) and USNM 206532, 79.2 mm SL ( Fig. 15A View Figure 15 )]. The variations observed in the morphology of the parhypural flange are not related to ontogeny, because the distinct curvature of the parhypural flange and the width and shape of the anterior edge of parhypural flange were found in specimens of similar size across the available size range, indicating that these differences are a product of individual variation. Another individual variation that was observed in a specimen of Daector dowi (UF 226263, 43.1 mm SL) was that it has two neural spines on the second preural centrum.
Thalassophryne : All specimens examined of this genus have the first and second dorsal procurrent fin rays supported by the posterior epural (or the unbranched
Columns ‘Dorsal hypural’ and ‘Ventral hypural’ indicate the number and type of fin ray supported by each hypural. Columns ‘Epural 1’ and ‘Epural 2’ represent the number of procurrent fin rays supported by the anterior and posterior epurals, respectively.
Abbreviations: Br, branched caudal-fin ray; N, number of specimens examined; NBr, caudal-fin rays not branched (includes principal and procurrent). *Occurrence in a single specimen.
principal fin ray in Thalassophryne amazonica ), with the anterior epural not supporting any caudal-fin rays. The only exception is one specimen of Thalassophryne nattereri Steindachner, 1876 (MZUSP 47262, 114.8 mm SL), in which the first procurrent fin ray is supported by the anterior epural.
In Thalassophryne maculosa , the epurals are robust but simple, rod-like elements in large specimens, without flanges. The parhypural flange varies from straight (USNM 199524, 64.4 mm SL) to concave (USNM 199524, 84.2 mm SL) ( Fig. 17C–F View Figure 17 ), and in most specimens it is smooth. USNM 220558 (36.1 mm SL; Fig. 15D View Figure 15 ) has a short indented articular edge of the parhypural flange. The articular surface of a larger specimen (USNM 199524, 84.2 mm SL; Fig. 17E View Figure 17 ) is longer than in all other examined specimens (approximately half the length of the parhypural flange) and is slightly irregular in its outline. In most specimens, the length of the articular surface of the parhypural flange is approximately one-quarter of the length of the flange.
Thalassophryne nattereri has a straight parhypural flange, although its length is highly variable. For example, in specimens USNM 302333 (69.4 and 113.0 mm SL; Fig. 17A, B View Figure 17 ) the articular edge is short and does not extend beyond the foramen from which the caudal vessels exit, whereas in other specimens [MZUSP 47262, 114.8 mm SL ( Fig. 15C View Figure 15 ) and MZUSP 47283, 70.4 mm SL] the articular edge the parhypural flange is long and extends to the middle of the ventral hypural. The robust epurals are rod-like and do not bear any flanges. In one specimen, MZUSP 47262 (114.8 mm SL; Fig. 15C View Figure 15 ), the epurals are fused proximally, although the two elements remain distinct. Most specimens of Thalassophryne nattereri have the first and second procurrent fin rays supported by the posterior epural, as in other species of Thalassophryne ; the only exception is MZUSP 47262, which has the anterior epural supporting the first procurrent fin ray (see Table 3).
Thalassophryne nattereri has a total of 16 caudal-fin rays, with I, 5, 5, I as the most frequently observed principal formula. One specimen ( MZUSP 47283 View Materials ) was observed to have 14 principal caudal-fin rays (I, 6, 6, I), although the total count of fin rays is the same. This specimen has a single dorsal and ventral procurrent ray, in contrast to two pairs of both dorsal and ventral procurrent rays in other specimens of Thalassophryne nattereri .
Thalassophryne amazonica has a unique caudal skeleton among all Batrachoidiformes in that it does not have any procurrent caudal-fin rays ( Fig. 18 View Figure 18 ; Table 3). The overall arrangement of the skeleton is robust, particularly the epurals, which are thicker than the dorsal-fin rays. Furthermore, Thalassophryne amazonica is distinguished from the other species of Thalassophryne by the presence of five dorsal principal caudal-fin rays (I, 4, 5, I), in contrast to six dorsal principal fin rays. The parhypural flange has a wide articular edge that extends to the posterior margin of the first ural centrum and has a concave flange. One specimen (ANSP 178103, 76.9 mm SL) bears a unique spear-like process, which arises from the anterior region of the parhypural flange ( Fig. 18A View Figure 18 ).
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