Porichthyinae

Porichthyinae ( Figs 11–14 View Figure 11 View Figure 12 View Figure 13 View Figure 14 ; Table 2)

Porichthyinae currently has two genera, Aphos and Porichthys , and both were examined here. Aphos is monotypic. Porichthys contains 14 species, seven of which were included in the present study.

The second preural centrum and first ural centrum are relatively elongate in Porichthyinae , with the length of the centra ranging from 1.3 to 1.5 times their depth, whereas the length of the second ural centrum is approximately two-thirds that of the first ural centrum. There is a dorsal prezygaphophysis on the neural spine of the second preural centrum that is prominent and contacts the neural spine of the preceding vertebra in all Porichthyinae ; the size of the ventral prezygapophysis on the haemal spine of the second preural centrum is variable in the subfamily [absent in Porichthys greenei (UF 226105, 60.7 mm SL), Porichthys porosissimus (Cuvier, 1829) (MZUSP 45398, 40.0 mm SL) and Porichthys margaritatus (Richardson, 1844) (USNM 101730, 19.3 mm SL)]. Although absent in most Porichthyinae , a ventral postzygapophysis on the second preural centrum was found in two specimens of Porichthys notatus (VIMS 38017, 84.0 mm SL and VIMS 38018, 84.8 mm SL), one specimen of Porichthys plectrodon Jordan & Gilbert, 1882 (USNM 302134, 75.5 mm SL), one specimen of Porichthys margaritatus (UF 226009, 70.2 mm SL) and most specimens of Aphos porosus (Valenciennes, 1837) ; in all of these individuals, the postzygapophysis is substantially smaller than the prezygapophysis. Although the occurrence of a ventral postzygapophysis on the second preural centrum varies individually, members of Porichthyinae were the only taxa of Batrachoidiformes to have this process ( Fig. 11A, C View Figure 11 ).

A dorsal prezygapophysis on the first ural centrum is present in most representatives of Porichthyinae , although its prominence varies both intraspecifically and ontogenetically [absent only in two specimens of Porichthys porosissimus (MZUSP 45398, 40.0 and 34.5 mm SL); and a single specimen of Porichthys pauciradiatus (UF 226549, 44.6 mm SL); for an example of ontogenetic variation, see Fig. 13 View Figure 13 ]. A ventral prezygapophysis on the first ural centrum is present in most examined specimens of Aphos porosus , Porichthys notatus , Porichthys margaritatus and the Porichthys porosissimus / plectrodon species complex. Neural and haemal spines of the second preural centrum are elongate and are 1.1–2 times longer than the spines of more anterior preural vertebrae. Two specimens of Porichthys notatus (VIMS 38017, 84.0 mm SL and FMNH 122401, 120.2 mm SL) have a small, circular posthaemal cartilage of the second preural vertebra ( Fig. 11A View Figure 11 ).

Each hypural supports five or six principal caudal-fin rays, with the ventral hypural usually supporting one ventral procurrent caudal-fin ray (although the support for the ventral procurrent ray varies intraspecifically; see Table 2). One or two dorsal procurrent rays are present. Two dorsal procurrent rays, both supported by the posterior epural, is the most common condition. One specimen of Porichthys greenei ( UF 220105 , 60.71 mm SL) does not have any procurrent rays. The single ventral procurrent caudal-fin ray is supported by either the ventral hypural or the distal caudal radial cartilage of parhypural .

The margin of the parhypural flange varies from deeply to slightly concave, although it is almost straight in some specimens ( Porichthys bathoiketes Gilbert, 1968 UF 228539, 73.5 mm SL). The articular edge of the parhypural flange projects anteroventrally, forming an acute stay that articulates with the haemal spine of the second preural centrum. A distinct triangular spine projects from the tip of the acute stay of the parhypural flage in most examined specimens ( Figs 11–14 View Figure 11 View Figure 12 View Figure 13 View Figure 14 ). In Porichthys , the entire margin of the parhypural has spine-like projections.

The epurals of Porichthyinae lie at a narrow angle (<40°) relative to the longitudinal axis. The outline of the epurals varies from slightly convex ( Porichthys porosissimus VIMS 1132 , 55.7 mm SL) to curved ( Porichthys porosissimus / plectrodon USNM 302134, 56.1 mm SL), although there is substantial individual variation in some species (see accounts for species of Porichthys below).

Aphos : The epurals of Aphos porosus are markedly curved posteriorly, with a similar outline to that of most species of Porichthys (e.g. Porichthys notatus ; see specific accounts for further details); the posterior epural supports both the first and second procurrent fin rays. One specimen (USNM 309739, 152.3 mm SL) has a long anterior epural that supports the first procurrent caudal-fin ray ( Fig. 11F View Figure 11 ); the anterior epural supporting a procurrent fin rays was not observed in other members of Porichthyinae .

A ventral prezygapophysis on the first ural centrum of Aphos porosus is present in some specimens (e.g. USNM 309738, 77.5, 89.4 and 98.6 mm SL), but absent in others (USNM 309738, 152.3 mm SL and USNM 305505, 151.4 mm SL). Most specimens have a small ventral postzygapophysis on the haemal arch of the second preural centrum.

Porichthys : All species of Porichthys bear spine-like projections on the margin of the parhypural flange. Although the number, orientation and prominence of the spines are both inter- and intraspecifically variable, all examined specimens of Porichthys have one or more spines projecting from the margin of the parhypural flange, in addition to the spine in the articular edge ( Figs 11–14 View Figure 11 View Figure 12 View Figure 13 View Figure 14 ).

Porichthys bathoiketes : The epurals vary intraspecifically in Porichthys bathoiketes . In the paratype (UF 12965, 93.8 mm SL), the posterior epural has its anterior tip contacting the midpoint of the anterior epural. This displacement of the posterior epural shifts the first procurrent fin ray away from the anterior epural. In UF 228539 (73.5 mm SL), the epural bones are similar to those observed in most species of Porichthys , i.e. the epurals are parallel to each other and the anterior epural contacts the first procurrent ray ( Fig. 11B View Figure 11 ). The epurals of this specimen have sharply tapered anterior tips that curve slightly to become parallel to the body axis, which is reminiscent of the condition found in Porichthys cf. plectrodon (see below); posteriorly, the epurals are convex. In the paratype (UF 12965), anterior tips of the epurals are blunt.

Porichthys greenei : In Porichthys greenei , the distal tip of the anterior epural contacts the anterior margin of the posterior epural instead of extending posteriorly to contact the bases of the procurrent caudal-fin rays, as observed in all other species of Porichthys ( Fig. 12 View Figure 12 ). Porichthys greenei has extensions on the proximal region of the epurals that vary from a digitiform projection from the anterior tip (UF 226105, 60.7 mm SL) to a wide trapezoidal flange that extends most of the length of the epural (UF 226105, 44.0 mm SL). The triangular flanges on the posterior epural are typically smaller than those on the anterior epural and are restricted to its proximal edge. A flange is absent on the posterior epural in UF 226105 (60.7 and 50.7 mm SL).

Porichthysgreenei isuniqueamongBatrachoidiformes in having reduced counts of caudal-fin rays, with ten principal caudal-fin rays (I, 4, 4, I) and a single ventral and dorsal procurrent caudal-fin ray.The only exception is UF 2260105 (60.7 mm SL), which has no dorsal procurrent rays but does have six dorsal principal caudal-rays; this might have been the result of damage and regeneration of the first dorsal principal ray.

The parhypural flange is concave in Porichthys greenei but presents remarkable variation in the number, shape and prominence of spines ( Fig. 12 View Figure 12 ). As in all species of Porichthyinae , there is a distinct spine in the articular edge of parhypural (albeit weakly developed in UF 226105, 60.7 mm SL). Two specimens (UF 226105, 56.2 and 44.0 mm SL) have two additional prominent spines in the centre of the margin of the parhypural flange that are two times longer than the spine at the articular edge of the parhypural flange. In contrast, specimen UF 226105 (37.1 mm SL) has a single medial spine and UF 220105 (60.7 and 50.7 mm SL) has no other spines in the parhypural flange, although they have weak indentations in the posterior region of the flange.

The structure of the neural spine of the second preural centrum is intraspecifically variable in Porichthys greenei . A full neural spine of the second preural centrum, including an elongate rod-like distal portion with a cartilaginous core, is present in some specimens ( UF 226105 , 50.7 and 37.1 mm SL; Fig. 12A, B View Figure 12 ), whereas the distal portion is lacking in others ( UF 226105 , 60.7 and 56.2 mm SL; Fig. 12C, D View Figure 12 ). One specimen ( UF 226105 , 44.0 mm SL) has a distinct distal component, although it is reduced and does not extend beyond the distal tip of the proximal component of the neural spine of the second preural centrum. Some specimens ( UF 2206105 , 50.7 and 37.1 mm SL) have two neural spines on the second preural centrum; the larger specimen also has two haemal spines on the second preural centrum. As in other taxa, this individual plasticity is likely to be a response to malformation of vertebral bodies during development ( Witten & Hall, 2015) .

Porichthys margaritatus : The parhypural flange is straight to slightly concave in this species. The only exceptions observed were in one specimen ( UF 226009 , 70.3 mm SL) that has a sharp indentation at approximately the midpoint of the flange, and in another ( USNM 101730 About USNM , 33.40 mm SL) that bears two anterior bulges, both of which are slightly smaller than the spine on the articular edge .

Spines on the parhypural flange, as observed in all other species of Porichthys , were found only in the largest specimen examined (UF 226009, 99.2 mm SL; Fig. 11C View Figure 11 ), which has a small triangular anterior spine in the anterior region of the flange. All other specimens have only a distinct spine on the articular edge of the parhypural flange ( Fig. 13 View Figure 13 ). Larger specimens could not be examined to determine whether this variation is attributable to ontogenetic or individual variation.

The epurals in most specimens of Porichthys margaritatus are simple rod-shaped elements that lack flanges or other outgrowths. However, in three specimens a short trapezoidal flange projects from the anterior extremity of the anterior epural ( UF 226009 , 89.4 , 78.8 and 70.3 mm SL) .

The prominence of the dorsal prezygapophysis on the first ural centrum is highly variable, ranging from highly developed and contacting the base of the neural arches of the second preural centrum (UF 226009, 99.2 mm SL) to weakly developed (USNM 101730, 19.3 mm SL). This is likely reflective of ontogenetic variation, because smaller specimens typically have

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).

reduced or even absent dorsal prezygapophyses (UNSM 101730, 19.3 and 27.9 mm SL), whereas in the two largest specimens examined (UF 226009, 99.2 and 89.4 mm SL) these processes are well developed ( Fig. 13 View Figure 13 ). The smallest specimen to have a prominent dorsal prezygapophysis is 33.4 mm SL (USNM 101730). The specimen UF 226009 (70.2 mm SL) has a relatively small ventral postzygapophysis on the haemal arch of the second preural centrum (about half the depth of dorsal prezygapophysis on the first ural centrum). Another variation observed in this species concerns the presence of two neural spines on the second preural centrum (USNM 101730, 39.2 mm SL and UF 226009, 89.4 and 70.2 mm SL), with the last of these specimens also having two haemal spines.

Porichthys notatus : In this species, the dorsal prezygapophysis of the first ural centrum is prominent and contacts the base of the neural spine of the second preural centrum in all examined specimens. The margin of the parhypural flange varies from straight to concave (USNM 104503, 98.3 mm SL and FMNH 122401, 120.2 mm SL, respectively). The spines on the parhypural flange are less prominent in Porichthys notatus than in other members of the genus. Although all specimens have a distinct spine on the articular edge of the parhypural flange, only USNM 104530 (98.2 mm SL) has a distinct spine in the anterior quarter of the parhypural flange. Specimens USNM 104530 (98.3 mm SL) and VIMS 38017 (84.0 mm SL) were found with a short indentation on the anterior part of the flange ( Fig. 11A View Figure 11 ). FMNH 122401 has a continuous margin of the parhypural flange, without any spine or indentation, except for the one on the articular edge.

Other intraspecific variations include the presence of a postzygapophysis on the second preural centrum and the occurrence of distal caudal cartilages. Two specimens ( VIMS 38017 View Materials , 84.0 mm SL and USNM 104503 About USNM , 98.2 mm SL) have weakly developed ventral postzygapophyses on the haemal arch of the second preural centrum, which are approximately half of the depth of the ventral prezygapophysis on the first ural centrum. Thus, specimen VIMS 38107 View Materials was the only specimen of Batrachoidiformes to have a dorsal postzygapophysis on the second preural centrum ( Fig. 11A View Figure 11 ); this process is small, with its length only about one-third that of the dorsal prezygapophysis on the first ural centrum. Specimens FMNH 122401 About FMNH (120.2 mm SL) and VIMS 38017 View Materials (84.0 mm SL) have a small, circular posthaemal distal cartilage of the second preural centrum; no other specimen of this species examined has this element .

Porichthys pauciradiatus View in CoL : This species is unique among Batrachoidiformes View in CoL in having a single epural bone ( Fig. 11E View Figure 11 ). This condition was observed in both examined specimens, and is found otherwise only in other groups of fishes, such as in Gobiidae View in CoL ( Fig. 31A View Figure 31 ), Callionymidae View in CoL ( Fig. 31D View Figure 31 ), Achiridae View in CoL ( Fig. 32C View Figure 32 ), Lophiiformes ( Monod, 1968) View in CoL and Gobiesocidae ( Konstantinidis & Conway, 2010) View in CoL , among others. The epural is elongate and has an enlarged anterior base (approximately four times wider than its posterior tip), which bears anterior and posterior flanges. The anterior flange is trapezoidal and has an irregular margin and an anterior digitiform projection. The posterior flange is thinner than the anterior one and has a semi-elliptical outline. An elliptical foramen is present on the base of the epural.

The cleared and stained specimen examined (UF 226549, 44.6 mm SL) has no dorsal prezygapophysis on the first ural centrum, but the specimen examined with CT (UF 226549, 50.24 mm SL) has a dorsal prezygapophysis. We could not determine whether this is an ontogenetic (as observed in Porichthys margaritatus View in CoL ) or individual variation. However, we note here that, although the female specimen that lacks the process is relatively small (44.6 mm SL), it has reached or is close to maturity, because it has developed ovaries with large oocytes. In all other species of Porichthys View in CoL , specimens at this length have a distinct dorsal prezygapophysis.

Porichthys porosissimus View in CoL / plectrodon View in CoL species complex: In this study we did not distinguish species of Porichthys plectrodon View in CoL and Porichthys porosissimus View in CoL . Gilbert & Kelso (1971) proposed that Porichthys porosissimus View in CoL has a restricted distribution in southern Brazil and Uruguay, whereas Porichthys plectrodon View in CoL is distributed from coastal areas of central Brazil to the Mid-Atlantic Bight of the east coast of North America. The material examined to date includes specimens from both geographical regions, but the morphological characters proposed by Gilbert & Kelso (1971) to differentiate these species (gill raker counts and otolith shape) were not observed in specimens from both geographical regions. To avoid misleading inferences regarding the variation observed, we describe the caudal skeleton of these species as a single species complex.

The specimens of the Porichthys porosissimus View in CoL / plectrodon View in CoL species complex examined have a pair of spines on the articular edge of the parhypural flange, which is in contrast to the single spine observed in all other representatives of Porichthyinae . However, this condition might reflect a plesiomorphic character, because two small spines in the articular edge of the parhypural flange were observed among the species of Batrachoidinae and Thalassophryinae.

Dorsal prezygapophyses on the first ural centrum were found in all specimens> 48 mm SL. A single specimen of the Porichthys porississimus / plectrodon complex was found to have a small ventral prezygapophysis on the first ural centrum (MZUSP 45398, 35.0 mm SL); however, the occurrence of this ventral process is considered to be an intraspecific variation, because all other examined specimens lack ventral prezygapophyses.

The epural bones are simple, varying from slightly convex to concave. The anterior tip of the anterior epural in MCZ 170729 About MCZ (150.8 mm SL) is curved and contacts the neural spine of the second preural centrum. The anterior epural has a flange in the proximal edge, of variable prominence; it is distinct and trapezoidal in one specimen ( VIMS 1132 View Materials , 55.7 mm SL; Fig. 11D View Figure 11 ) but slender in another ( VIMS 1132 View Materials , 81.6 mm SL). The epurals of MZUSP 45398 View Materials (40.0 mm SL) have angular extensions projecting from the anterior tip of both bones .

The parhypural flange has two conspicuous spines at the midpoint region, which are highly protruded in VIMS 1132 (55.71 mm SL; Fig. 11D View Figure 11 ). Specimens from the North Atlantic (e.g. VIMS 1132) bear an additional spine on the anterior portion of the paryhypural flange ( Fig. 11D View Figure 11 ). MZUSP 45398 (40.0 mm SL) has only a pair of spines at the articular edge of the parhypural flange, but lacks spines on the posterior region of its margin. The dorsal prezygapophysis of the first ural centrum is small and does not reach the origin of the neural arches of the second preural centrum. As in Porichthys margaritatus , the prominence of dorsal prezygapophyses likely reflects ontogenetic variation; the largest dorsal prezygapophysis was observed in the largest specimen (VIMS 1132, 81.6 mm SL), whereas the dorsal prezygapophysis is absent in the smallest specimen examined (MZUSP 45398, 34.5 mm SL).

Other intraspecific variations observed include two neural spines on the second preural centrum (MZUSP 45398, 34.5 mm SL) and a marked hook-like process projecting from the posterior margin of haemal spine of the second preural centrum (VIMS 1132, 81.6 mm SL).

Porichthys cf. plectrodon : The six specimens examined in the lot USNM 302134, which were collected from the northeastern coast of Brazil, have similar gill raker counts and otolith shape to specimens from the northern Atlantic; therefore, they do not allow confident identification between Porichthys porosissimus and Porichthys plectrodon , following the criteria proposed by Gilbert & Kelso (1971). However, all examined specimens of USNM 302134 were consistently found to have a distinctive hockey-stick-shaped posterior epural; this shape was not found in any other species of Batrachoidiformes ( Fig. 11 View Figure 11 ). Given the consistent dissimilarity between the shape of the epurals of the specimens of this lot and of the other specimens of the Porichthys porosissimus / plectrodon complex, we describe the morphology of these specimens separately. Based on locality, we suggest that these might represent Porichthys plectrodon , although a full taxonomic revision of this species complex is warranted.

The posterior epural is convex posteriorly (most prominent in two specimens: 48.7 and 56.1 mm SL), but the proximal region curves anteriorly, resulting in a posterior epural with a hockey-stick shape. The base of the posterior epural is more gently curved in a 53.5 mm SL ( Fig. 14B View Figure 14 ) specimen than in other specimens, but the curvature is greater than that observed in Porichthys bathoiketes (UF 228539; Fig. 11B View Figure 11 ); all other species of Porichthys have straight posterior epurals. The shape of the anterior epural varies from convex to concave, with an anterior flange extending through the proximal region and a digitiform outgrowth at the proximal tip (this latter projection is absent in the 53.5 mm SL specimen).

The parhypural flange of specimens from this lot has a regular sinuous outline, with a proximal angular projection that bears a spine, followed posteriorly by a shallow concavity ( Fig. 14 View Figure 14 ). The 56.1 mm SL specimen has a sharp indentation on the posterior third of the flange. Specimens of the Porichthys porosissimus / plectrodon complex typically have a pair of spines in the articular edge of the parhypural flange, but a 48.7 mm SL specimen from this lot has an additional spine projecting proximally from the pair of spines on the anterior edge. Two larger specimens (77.1 and 56.1 mm SL) have another spine between the anterior edge and the proximal projection.

Dorsal prezygapophyses on the first ural centrum were observed in all examined specimens of USNM 302134 About USNM (N = 6). As in Porichthys margaritatus , the prominence of this process increases during ontogeny. The smallest examined specimen (48.7 mm SL) bears weakly developed dorsal prezygapophyses, whereas these processes are greatly developed and contact the base of the neural spine in larger specimens (56.1 and 77.7 mm SL). Two specimens (53.5 and 75.5 mm SL) were found to have a small ventral prezygapophysis on the first ural centrum, the length of which is approximately half that of the dorsal prezygapophysis. The 75.5 mm SL specimen has a small ventral postzygapophysis on the second preural centrum, similar to the size of the ventral prezygapophysis of the first ural centrum. The posterior margin of the haemal spine of the 56.1 and 53.5 mm SL specimens has hook-like projections, which in the smaller specimen contact the articular edge of the parhypural flange. Other variation includes two neural spines on the second preural centrum on the 77.7 mm SL specimen .