Stereolepididae, Smith & Ghedotti & Domínguez-Domínguez & McMahan & Espinoza & Martin & Girard & Davis, 2022
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publication ID |
https://doi.org/ 10.1590/1982-0224-2021-0160 |
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publication LSID |
lsid:zoobank.org:pub:1F73D544-76AB-451F-BCAF-CDB5EB83DF56 |
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persistent identifier |
https://treatment.plazi.org/id/420088FA-8845-4090-8616-646A766F05CE |
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taxon LSID |
lsid:zoobank.org:act:420088FA-8845-4090-8616-646A766F05CE |
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treatment provided by |
Felipe |
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scientific name |
Stereolepididae |
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fam. nov. |
Stereolepididae new family Smith, Ghedotti & Davis urn:lsid:zoobank.org:act:420088FA-8845-4090-8616-646A766F05CE
Type genus. Stereolepis Ayres, 1859 View in CoL .
Species included. Stereolepis doederleini Lindberg & Krasyukova, 1969 View in CoL and S. gigas View in CoL
Ayres, 1859.
Diagnosis. Species in Stereolepididae can be distinguished from all other acropomatiforms by a unique combination of 26 vertebrae (12 precaudal and 14 caudal), 9–12 dorsal-fin spines, and the presence of a supramaxilla ( Tab. 2). Species in Acropomatidae , Banjosidae , Epigonidae , Glaucosomatidae , Malakichthyidae , Pempheridae , Synagropidae , and Schuettea have 24–25 vertebrae, and species in Champsodontidae , Creediidae , Dinolestidae , and Lateolabracidae have 27 or more vertebrae. The remaining acropomatiform families have overlapping total vertebral counts, but there is also diagnostic variation in the number of precaudal vertebrae. Among acropomatiforms with 26 vertebrae, Howellidae , Ostracoberycidae , Scombropidae , and Symphysanodontidae have 10–11 precaudal vertebrae and species in Polyprion have 13 precaudal vertebrae. These counts differ from the 12 precaudal vertebrae found in Stereolepis . Among acropomatiforms with 26 vertebrae (and 12 precaudal vertebrae), species in the Bathyclupeidae and Hemerocoetidae have eight or fewer dorsal-fin spines compared with the 9–12 dorsal-fin spines found in Stereolepis . Finally, the Pentacerotidae can be separated by its lack of a supramaxilla; whereas, this element is present in the jaws of stereolepidids. These features and a variety of other meristic counts and character states for acropomatiforms are summarized in Tab. 2.
Schuettea . The two species in Schuettea are Australian shallow water marine fishes that have been traditionally classified as monodactylids (e.g., Regan , 1913; Nelson et al., 2016). In contrast, Tominaga (1968) suggested that Schuettea belonged in its own family that is closely allied with the Pempheridae (a family Regan [1913] allied with Monodactylidae ). We included Monodactylus and the available sequences for Schuettea in our phylogenetic analysis of acropomatiforms following Tominaga’s (1968) suggestion.
In our analysis, Schuettea was recovered among the Acropomatiformes with strong support, and it was separated from its traditional ally, Monodactylus . The specific placement of Schuettea was not well supported in our analysis ( Fig. 5 View FIGURE 5 ); it was resolved sister to Champsodon in our most likely hypothesis ( Fig. 5 View FIGURE 5 ). Our analysis did not place Schuettea sister to Pempheridae , and there are multiple moderately or strongly supported nodes separating these two clades ( Fig. 5 View FIGURE 5 ). In support of his pempherid- Schuettea hypothesis, Tominaga highlighted that these clades share 10+15 vertebrae, a lateral line that reaches to the posterior margin of the caudal fin, and anteriorly extended epaxial muscles that reach the frontals. Additionally, Tominaga highlighted three features that were unique to Schuettea in his study: rib-like ossicles on the first and second hemal spines, a posterior extension of the gas bladder, and three anal-fin pterygiophores inserted anteriorly to the first hemal spine. Our preliminary osteological investigation focusing on acropomatiforms found that Schuettea (based on a dried skeleton) has cycloid scales (also shared with some or all acropomatids, bathyclupeids, creediids, dinolestids, hemerocoetids, pempherids, scombropids, synagropids, and Verilus ), has a reduced number of dorsal-fin spines (five) and a larger number of dorsal- and anal-fin rays (28–32), has a spineless first dorsal-fin pterygiophore, and lacks a procurrent spur and supramaxilla (Johnson, 1984; Rosa, 1995; Nelson, 2006; Yamanoue, 2016; current study; Tab. 2). While externally dissimilar, many of these features are shared with the Champsodontidae , Creediidae , and Hemerocoetidae that have been typically recovered as a clade (Near et al., 2013, 2015; Thacker et al., 2015; Sanciangco et al., 2016; Ghedotti et al., 2018; Satoh, 2018; Fig. 2 View FIGURE 2 ) and where we recovered Schuettea in our analysis ( Fig. 5 View FIGURE 5 ). Clearly, a more detailed examination using morphological and molecular data is needed to conclusively place Schuettea . Because of the nature of the preliminary morphological examination and the poor molecular support, we are not prepared to describe a new family for Schuettea . There remains a good chance that it is sister to or within a currently recognized acropomatiform family, and subsequent research will be needed to determine whether it should be classified within that family or in its own family. For now, we classify both species of Schuettea as incertae sedis in the Acropomatiformes , and this clade can be diagnosed from all other acropomatiforms by having 24 vertebrae (10 precaudal and 14 caudal), five dorsal-fin spines, and 28–32 anal-fin and 28–31 dorsal-fin rays ( Tab. 2).
Phylogeny of the Acropomatiformes . The Acropomatiformes is one of the major clades in the recently recognized Eupercaria, and several early large-scale molecular phylogenies circumscribed this clade without recognizing it or focusing on its intrarelationships ( Smith , Wheeler, 2006; Smith , Craig, 2007; Betancur-R et al., 2013a; Near et al., 2013, 2015; Thacker et al., 2015; Fig. 2 View FIGURE 2 ; Tab. 1). Davis et al. (2016), Mirande (2016), Sanciangco et al. (2016), and Rabosky et al. (2018) all provided phylogenies and family-level classifications for the acropomatiforms, but Ghedotti et al. (2018) and Satoh (2018) were the first studies to explicitly focus on the intrarelationships of the Acropomatiformes ( Fig. 2 View FIGURE 2 ). Across previous acropomatiform studies ( Fig. 2 View FIGURE 2 ), the lack of consistent clades, the few repeated results, and the limited number of strongly supported nodes is somewhat surprising. In an attempt to resolve relationships within the Acropomatiformes with strong support, we purposefully chose taxa to cover the diversity of acropomatiforms, and we greatly expanded the number of base pairs (Tab. 1). Increasing the number of base pairs in an analysis often results in phylogenies with more support and well-supported hypotheses (e.g., Harrington et al., 2016; Longo et al., 2017; Martin et al., 2018). This increase in data combined with being the first study to include all families of acropomatiforms resulted in phylogenies with considerably more support than previous studies ( Figs. 3–4 View FIGURE 3 View FIGURE 4 ). Despite many new hypothesized relationships in our study, there are several clades of acropomatiforms that we recovered that recent molecular studies have also recovered. There are four clades shared among our analyses and many previous studies that we will focus on beyond the placement of Hemilutjanus : 1) Acropomatidae , Epigonidae , Howellidae , Ostracoberycidae , Scombropidae , and Symphysanodontidae ; 2) Banjosidae and Pentacerotidae ; 3) Champsodontidae , Creediidae , Hemerocoetidae , and potentially Schuettea ; and 4) Glaucosomatidae and Pempheridae ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ).
The largest repeated clade found within the acropomatiforms is the Acropomatidae , Epigonidae , Howellidae , Ostracoberycidae , Scombropidae , and Symphysanodontidae or what we refer to as the Acropomatoidei. The acropomatoids were first grouped together by Near et al. (2013) who included the Acropomatidae , Howellidae , and Ostracoberycidae in their study. Subsequent studies by Near et al. (2015), Thacker et al. (2015), Davis et al. (2016), Sanciangco et al. (2016), Ghedotti et al. (2018), and Satoh (2018) continued to recover this clade as new families and more data were added to the analyses. Interestingly, the acropomatoids were not recovered in analyses based on fewer than 5.000 base pairs (i.e., Smith , Wheeler, 2006; Smith , Craig, 2007; Tab. 1) or in analyses with substantial (>50%) missing data (e.g., Betancur-R et al., 2013a; Mirande, 2016; Rabosky et al., 2018; Tab. 1). Given the recurrent discovery of this clade in studies that had sufficient DNA-sequence data (i.e., more than 5.000 bps) and studies that emphasized overlapping data relative to increased taxonomic sampling (i.e., studies with less than 30% missing data), it is possible that many of the conflicting results depicted in Fig. 2 View FIGURE 2 are due to data insufficiency rather than data conflict. The acropomatoids have substantial morphological variation, and our preliminary morphological investigation did not identify any synapomorphies for this group. Species in this clade are predominantly found in the deep sea (although many deep-sea families have species that reside in shallower waters; Fig. 6 View FIGURE 6 ), and the acropomatoids include many of the acropomatiforms that were formerly included in the “serranids” (sensu Katayama, 1959).
In addition to the acropomatoids, one of the most frequently recovered clades in studies that have included many acropomatiforms is the sister-group pairing of Banjosidae and Pentacerotidae . This sister-group pairing has been recovered in every molecular analysis that included both families ( Fig. 2 View FIGURE 2 ) except Satoh (2018). In a detailed morphological study of the Pentacerotidae, Kim (2012) included Banjosidae as one of his outgroup taxa. Although there was no formal outgroup analysis, Kim suggested that Chaetodontidae and Ostracoberycidae were the most likely sister groups to the Pentacerotidae . Subsequent molecular analyses consistently place the Chaetodontidae within the Acanthuriformes and Ostracoberycidae in the Acropomatiformes (Near et al., 2013; Davis et al., 2016; Sanciangco et al., 2016; Smith et al., 2016). Most molecular studies have recovered ostracoberycids among the acropomatoids ( Fig. 2 View FIGURE 2 ). Interestingly, Kim (2012) noted that he allied the chaetodontids with the pentacerotids because chaetodontids shared four of the pentacerotid synapomorphies (his SA3, SA4, SA5, and SA7) and because they have strongly compressed bodies. Banjosids share these four formal synapomorphies and this one informal synapomorphy (compressed bodies) with the pentacerotids (Kim, 2012). There is no explanation in Kim (2012) for why chaetodontids were preferred over banjosids, but given the molecular results presented by Near et al. (2013, 2015), Thacker et al. (2015), Davis et al. (2016), Mirande (2016), Sanciangco et al. (2016), Ghedotti et al. (2018), Rabosky et al. (2018), and the current study ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ), it is clear that this banjosid sister-group relationship is supported and should be explored more explicitly with morphological data.
Another clade of acropomatiforms that is consistently recovered is the group that includes Champsodontidae , Creediidae , Hemerocoetidae , and, potentially, Schuettea . We refer to this clade informally as the “champsodontoids”. While Creediidae and Hemerocoetidae have been consistently recovered together in previous studies ( Fig. 2 View FIGURE 2 ; Tab. 1), the placement of Champsodontidae among, or even in, the acropomatiforms has been the most problematic family-level placement in the order (Tab. 1). Despite some ambiguity, this clade has been consistently recovered in previous studies (Near et al., 2013, 2015; Thacker et al., 2015; Sanciangco et al., 2016; Ghedotti et al., 2018; Satoh, 2018; Tab. 2) with a few exceptions that potentially lacked sufficient data ( Smith , Craig, 2007) or had extensive missing data (Mirande, 2016; Rabosky et al., 2018). Relative to other acropomatiforms, the champsodontoids are characterized generally by larger vertebral counts, the loss of both the procurrent spur and supramaxilla, more median fin-ray elements, and few to no dorsal- and anal-fin spines ( Tab. 2). The monophyly and support of this clade will depend on the inclusion, or not, of Schuettea and the phylogenetic placement of the clade given its movement in our analyses ( Figs. 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 ).
The final acropomatiform clade that is consistently recovered is the grouping of Glaucosomatidae and Pempheridae (Betancur-R et al., 2013a; Near et al., 2013, 2015; Thacker et al., 2015; Davis et al., 2016; Mirande, 2016; Sanciangco et al., 2016, Ghedotti et al., 2018; Rabosky et al., 2018 [albeit outside of the Acropomatiformes ]; Satoh, 2018; current study; Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). This sister-group pairing is the most consistent result across all acropomatiform studies, and it has been found in all analyses with more than six loci ( Fig. 2 View FIGURE 2 ; Tab. 1). While there are no known morphological synapomorphies to unite this group, the ubiquity of their relationship across molecular studies ( Fig. 2 View FIGURE 2 ) provides striking support for the placement of these two families together. This clade, while frequently recovered with DNA-sequence data, has not been recovered in morphological analyses and would benefit from morphological investigations, particularly considering Tominaga’s (1968) hypothesis that pempherids and Schuettea are closely related.
While we are beginning to recognize well-supported clades across a diversity of studies examining the Acropomatiformes , the monophyly of the traditional “ Acropomatidae ” is continually being rejected, and it should not be recognized further. The family Acropomatidae was described (as Acropomidae) by Gill (1893) as one of the families of his Percoidea. Most studies in the late 19th century and early 20th century allied members of the modern Acropomatidae , Malakichthyidae , and Synagropidae with the Apogonidae or “ Serranidae ” (sensu Katayama, 1959) and did not treat them as a single natural group (e.g., Jordan, Richardson, 1910; Regan , 1913; Schultz, 1940). Katayama (1959), in the most extensive comparative morphological investigation of the “ Acropomatidae ”, split these taxa across three subfamilies (his Acropominae, Döderleininae, and Malakichthyinae), none of which has the same composition as any modern “acropomatid” family. Despite Katayama (1959: fig. 39) classifying these species in three subfamilies, he did illustrate the included genera as what we would refer to as a monophyletic group in his pre-cladistic phylogeny. Further, he placed this assemblage in a trichotomy with ( Stereolepis + ( Coreoperca +Siniperca )) and Lateolabrax . This clade was sister to a clade composed of Niphon and Ostracoberyx , and these taxa were referred to as the “ Acropoma- stem group”. Gosline (1966) treated the “acropomatids” as part of his “oceanic percichthyids”. Johnson (1984: 464) recognized the modern “ Acropomatidae ”, but he noted that he knew “of no synapomorphy that unites the acropomatids, and further work will be necessary to test their monophyly”. Following Johnson’s (1984) study, many studies treated the “ Acropomatidae ” as a family that included the modern Acropomatidae , Malakichthyidae , and Synagropidae (Nelson et al., 2016) , but other authors variously included members of the Howellidae , Scombropidae , Symphysanodontidae , and Polyprionidae within the Acropomatidae (e.g., Heemstra, 1986; Nelson, 1994, 2006; Heemstra, Yamanoue, 2003). More recent authors conducting morphological analyses (e.g., Prokofiev, 2007; Schwarzhans, Prokofiev, 2017) have provided evidence to refute the monophyly of the “ Acropomatidae ”. Across all these morphological studies, it is clear that a close relationship among a number of acropomatiform clades were being recognized, but the limits and relationships of the families and the order as a whole remained unclear.
Beginning with Smith , Craig (2007), molecular studies began to include multiple genera of “acropomatids” and were consistently finding the family polyphyletic (Betancur-R et al., 2013a; Near et al., 2013, 2015; Thacker et al., 2015; Davis et al., 2016; Mirande, 2016; Sanciangco et al., 2016; Ghedotti et al., 2018; Rabosky et al., 2018; Fig. 2 View FIGURE 2 ; Tab. 1). Across the previous and current molecular studies, the Acropomatidae , Malakichthyidae , and Synagropidae were always found independent of each other ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). The sister groups of each family varied among studies. Seven of the previous studies and the current study recovered a clade composed of the acropomatoids (Near et al., 2013, 2015; Thacker et al., 2015; Sanciangco et al., 2016; Ghedotti et al., 2018; Satoh, 2018; Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). Among these studies and the current study, the most common sister group for the Acropomatidae was the Ostracoberycidae , which was not one of the families that traditional studies had classified within the Acropomatidae . The sister group to Malakichthyidae was less consistent across studies or across methods in our study ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). Our core ML analysis recovered Malakichthyidae sister to a clade composed of Bathyclupeidae , Champsodontidae , Creediidae , Stereolepididae , and Synagropidae ( Fig. 3 View FIGURE 3 ). In contrast, our results from the ST analysis place a clade composed of Banjosidae , Dinolestidae , Pentacerotidae , and Stereolepididae sister to Malakichthyidae ( Fig. 4 View FIGURE 4 ). The only shared member from the malakichthyid sister-group clades between our two analyses was Stereolepididae , which is, overall, the most consistent sister group in previous studies (Near et al., 2013, 2015; Thacker et al., 2015; Davis et al., 2016; Rabosky et al., 2018). The specific sister group to Malakichthyidae remains contentious ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). The third “acropomatid” family is Synagropidae , which we consistently recovered sister to Bathyclupeidae across methods and datasets with strong support ( Figs. 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). In contrast, no previous studies recovered a bathyclupeid sister group for Synagropidae , and the only repeated sister group in previous analyses was Howellidae (Mirande, 2016; Rabosky et al., 2018; Fig. 2 View FIGURE 2 ). While these two studies recovered a howellid sister group, most studies (noted above) place Howellidae in a distantly related and well-supported clade with Acropomatidae , Epigonidae , Ostracoberycidae , Scombropidae , and Symphysanodontidae . Therefore, every previous molecular study with multiple “acropomatid” families and the current study show that the “ Acropomatidae ” is polyphyletic ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). Most studies have found the Acropomatidae sister to Ostracoberycidae (Near et al., 2013, 2015; Thacker et al., 2015; Davis et al., 2016; current study; Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ). The current study shows that Synagropidae is sister to Bathyclupeidae ( Figs. 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 ) and the placement of Malakichthyidae among the acropomatiforms has conflicting results ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ).
Our study included considerably more data than all previous studies that included substantive acropomatiform taxa (Tab. 1), and it was the first study to include every acropomatiform family and every genus classified as incertae sedis. Our results were recovered with considerable support (>80% of nodes were well or moderately well supported across all three analyses; Figs. 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 ), and outside of the placement of the champsodontoids, most relationships were shared among the acropomatiforms across methods ( Figs. 3–4 View FIGURE 3 View FIGURE 4 ). Relative to studies with limited sequence data (e.g., Smith , Craig, 2007) and studies with extensive missing data or goals well outside of the Acropomatiformes (e.g., Betancur-R et al., 2013a; Sanciangco et al., 2016; Rabosky et al., 2018), there is more consistency of relationships than not (e.g., Near et al., 2013, 2015; Thacker et al., 2015; Davis et al., 2016; Ghedotti et al., 2018; Satoh, 2018; current study). Perhaps much of the conflict that researchers are finding among studies of percomorph groups is due more to insufficient data rather than conflicting data. Certainly, including as many species as possible has benefits (Wiens, Tiu, 2012; Borden et al., 2013; Tang et al., 2021), but the inclusion of taxa with insufficient comparable data has resulted in contradictory phylogenies for the Acropomatiformes ( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ; Tab. 1).
Evolution of the Acropomatiformes. Through our work to resolve the placement of Hemilutjanus, we have taken this opportunity to examine the limits and relationships of the Acropomatiformes. One of the striking changes in our understanding of percomorph relationships that came following our improved understanding of fish relationships or Smith’s (2010: 523) impending “renaissance” brought on by molecular systematics is that we have approximately 20 repeatedly recovered clades (orders in Davis et al., 2016) of percomorphs of which three-quarters of these clades are completely new to science. These are newly recognized clades, so we have studied little more than their phylogeny since their identification over the last decade (Betancur-R et al., 2013a; Near et al., 2013; Davis et al., 2016; Sanciangco et al., 2016; Smith et al., 2016; Rabosky et al., 2018). This is a dynamic time in fish phylogenetics because the classification of fishes is fluid and changing, and we are now able to explore the morphology, biology, and evolution of these percomorph orders (e.g., Thacker, 2014; Davis et al., 2016; Harrington et al., 2016; Ghedotti et al., 2018; Rabosky et al., 2018; Girard et al., 2020). The dominant biological phenomena that have been recognized among acropomatiforms are that this relatively small order of ~300 species includes a surprisingly large number of bioluminescent and deep-water species (for percomorphs) that previous studies have suggested evolved independently multiple times (Davis et al., 2016; Ghedotti et al., 2018) and that they are poorly represented in the Eastern Pacific (Schwarzhans, Prokofiev, 2017).
The evolution of bioluminescence among acropomatiforms has been explicitly studied by Davis et al. (2016) and Ghedotti et al. (2018). Both studies highlighted that approximately 10% of acropomatiforms are bioluminescent, and both studies included representatives of all four acropomatiform families that have bioluminescent species (Acropomatidae, Epigonidae, Howellidae, and Pempheridae; Tab. 1). Davis et al. (2016) suggested that bioluminescence evolved in the Acropomatidae, Epigonidae+Howellidae, and Pempheridae. Ghedotti et al. (2018) hypothesized that representatives of each family with bioluminescent species evolved bioluminescence independently in their analysis. Their study included more acropomatiforms, but it included fewer acropomatiform families and less DNA-sequence data. Further, they noted that bioluminescence may have evolved multiple times independently among epigonids. Our results present a different phylogeny of acropomatiform fishes relative to these two prior studies, and our phylogeny suggests three independent evolutions of bioluminescence: Acropomatidae, Pempheridae, and the ancestor of Epigonidae and Howellidae ( Fig. 6 View FIGURE 6 ). However, and as noted by Ghedotti et al. (2018), none of these families is wholly bioluminescent with between 6% and 92% of the species in each family being bioluminescent (Acropomatidae: 12 of 13 species are bioluminescent; Epigonidae: 3 of 47 species; Howellidae: 1 of 9 species; Pempheridae: 5 of 85 species). Further, Ghedotti et al. (2018) noted that the epigonids in Epigonus and Rosenblattia have different anatomies for their bioluminescent organs (Ghedotti et al., 2018). Taken together, this not only suggests that each bioluminescent family of acropomatiforms evolved bioluminescence independently, but it also suggests that epigonids may have evolved bioluminescence twice. If our higher-level phylogeny is correct and the species-level phylogeny and anatomical descriptions for the Epigonidae in Ghedotti et al. (2018) are correct, bioluminescence would have likely evolved at least five times in the Acropomatiformes, once in shallow water (Pempheridae) and four times in the deep sea (Acropomatidae, Howellidae, and twice in the Epigonidae). To further resolve questions around the evolution of bioluminescence in the Acropomatiformes, we need denser taxon sampling in the Acropomatidae, Epigonidae, Howellidae, and Pempheridae, with a particular emphasis on the Epigonidae and Pempheridae. Given our phylogenetic hypothesis, it is noteworthy that the shallow water bioluminescent pempherids obtain all necessary bioluminescent molecules through their diets, whereas the deep-water bioluminescent acropomatiforms rely on symbiotic bacteria (Ghedotti et al., 2018; Bessho-Uehara et al., 2020) and are restricted to the acropomatoids that invaded the deep sea prior to the evolution of bioluminescence.
Although not explicitly discussed in previous acropomatiform studies, the acropomatiforms are unusual for percomorphs in that more than half of the species can be found in deep water ≥ 200 m (Froese, Pauly, 2021). Relative to other percomorph ordinal-level clades identified by Davis et al. (2016), no other order is dominated by deep-sea fishes (Davis et al., 2016; Nelson et al., 2016; Froese, Pauly, 2021). Optimizing the invasions of the deep sea among acropomatiforms using parsimony and maximum likelihood demonstrate that acropomatiforms invaded the deep sea and shallow water multiple times ( Fig. 6 View FIGURE 6 ). Using parsimony, there is much ambiguity in the specific acropomatiform clades that have invaded the deep sea. Using maximum likelihood, we found that there was one invasion in the ancestor of the Acropomatiformes and one invasion in the ancestor of the Champsodontidae. The number of returns to shallow water suggested by our parsimony optimization are hampered by many ambiguous or equally parsimonious reconstructions, but in maximum likelihood, we see independent invasions in the Glaucosomatidae+Lateolabracidae+Pempheridae, Champsodontidae+ Schuettea, Creediidae, Dinolestidae, Hemilutjanus, Scombropidae, and Stereolepididae ( Fig. 6 View FIGURE 6 ). Transitions between shallow water and the deep sea and the evolution of bioluminescence are not that common in the Eupercaria (Froese, Pauly, 2021). Repeated transitions between shallow and deep environments within the 300 acropomatiform species is noteworthy. Similarly, the multiple evolutions of bioluminescence among just 300 species of acropomatiforms is also startling. These habitat invasions and luminescent adaptations are uncommon (but not rare) among percomorphs, but the frequency of these specializations and transitions demands further research on this largely unexplored and newly discovered order of fishes.
Finally, this study highlights our natural biases to compare fishes from similar habitats. One of the likely reasons that no one had found the closest relatives to Hemilutjanus is that, while a shallow water fish, its closest relatives are in the deep sea. Further, its deep-sea relatives are poorly represented in the Eastern Pacific Ocean. By searching broadly for its potential relatives and benefiting from the molecular phylogenies that have grouped many of the species excluded from the “serranids” (sensu Johnson, 1993) into the Acropomatiformes (e.g., Smith, Wheeler, 2006; Smith, Craig, 2007; Betancur-R et al., 2013a; Near et al., 2013, 2015; Thacker et al., 2015; Davis et al., 2016; Mirande, 2016; Sanciangco et al., 2016; Rabosky et al., 2018; Tab. 1), we have been able to place Hemilutjanus in the Malakichthyidae. This phylogenetic placement also adds to the diversity of acropomatiforms in the Eastern Pacific Ocean, particularly in shallow waters. The addition of another shallow water fish in the Acropomatiformes, particularly one sister to a deep-sea clade, serves as a good reminder that acropomatiforms have many transitions between deep-sea and shallow-water habitats ( Fig. 6 View FIGURE 6 ), particularly for a recent group in the Eupercaria. Most orders dominated by deep-sea fishes have few to no transitions between shallow and deep-water habitats (e.g., Alepocephaliformes, Myctophiformes, Stomiiformes; Davis et al., 2016; Nelson et al., 2016). These transitions and the biases scientists have for making comparisons of fishes from similar locations and habitats may best explain why the Acropomatiformes was not recognized earlier and why its relationships have been so poorly understood.
Material examined. Acropomatiform specimens and skeletal material examined for meristic and anatomical features – abbreviations: ALC (formalin-fixed and alcohol-stored material); C&S (cleared-and-stained material); DS (dried-skeletal material); X (radiographed material). Acropomatidae (Acropoma hanedai, KUI 41815, ALC 2, C&S 2; A. japonicum, KUI 41855, ALC 2, C&S 2; Doederleinia berycoides, KUI 41745, ALC 1, C&S 1); Banjosidae (Banjos banjos, KUI 41491, C&S 1); Bathyclupeidae (Bathyclupea, SIO uncat., C&S 1); Champsodontidae (Champsodon snyderi, FMNH 120679, C&S 1); Dinolestidae (Dinolestes lewini, SIO 75-502, C&S 1); Epigonidae (Epigonus pandionis, FMNH 67480, C&S 1); Malakichthyidae (Hemilutjanus macrophthalmos, LACM 44038, X 1; H. macrophthalmos, SIO 12-3086, C&S 1; H. macrophthalmos, USNM 77623, ALC 1; Malakichthys wakiyae, KUI 41723, ALC 2, C&S 2); Pempheridae (Pempheris schomburgkii, FMNH 93774, C&S 1); Polyprionidae (Polyprion oxygeneios, KUI 19354, DS 1); Stereolepididae (Stereolepis gigas, SIO 15-1314, ALC 1); Symphysanodontidae (Symphysanodon octoactinus, FMNH 70766, C&S 1); Synagropidae (Parascombrops philippinensis, KUI 41495, C&S 1); incertae sedis (Schuettea scalaripinnis, ANSP 78163, DS 1).
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