[Ichthyology • 2026] Crossorhombus pescadores • A New lefteye Flounder of the Genus Crossorhombus (Teleostei: Bothidae) from Penghu Islands, western Taiwan

Crossorhombus pescadores 

 Amaoka, Su & Ho, 2026

DOI: doi.org/10.3897/zookeys.1273.167628

Abstract

A new lefteye flounder, Crossorhombus pescadores sp. nov., is described based on five specimens collected from Penghu Islands. This new species differs from the other four congeners by having a pair of small black spots on the caudal fin, a horizontal triangular bluish-black marking on the blind side of body in male, the front wings of the marking reaching the base of dorsal and anal fins, and a combination of morphometric characters, including a larger head, deeper body, smaller eyes, fewer dorsal- and anal-fin rays and lateral-line scales, and other characters. A key to all five nominal species of Crossorhombus is provided.

Key words: Biodiversity, ichthyology, identification key, sexual dimorphism, taxonomy, western Pacific

Crossorhombus pescadores sp. nov., NMMB-P 42260, holotype, male, 99.8 mm SL, preserved.
A. Ocular side; B. Blind side.

Paratypes of Crossorhombus pescadores sp. nov., showing ocular sides (odd numbers) and blind sides (even numbers).
A. HUMZ 237066, immature male, 74.8 mm SL; B. NMMB-P 42263, female, 92.4 mm SL; C. NMMB-P 42262, immature female, 58.0 mm SL.

 Crossorhombus pescadores sp. nov

Diagnosis. A species of Crossorhombus differing from its congeners in having: caudal fin with light-gray band along posterior sub-margin; a pair of small black spots on band at upper and lower fourth rays, respectively; a bluish-black, horizontal triangular marking on blind side of body in male; a series of dark blotches along dorsal and ventral margins of body; combination of some meristic and proportional characters: large head; small upper and lower eyes; slightly longer pectoral-fin on ocular side; fewer dorsal- and anal- fin rays and fewer scales in lateral line and others.

Etymology. The specific name “pescadores” is the old name of the type locality, meaning “fishermen” in Portuguese. It is treated as a noun in apposition.

 Kunio Amaoka, Yo Su and Hsuan-Ching Ho. 2026. A New lefteye Flounder of the Genus Crossorhombus (Teleostei, Bothidae) from Penghu Islands, western Taiwan. ZooKeys. 1273: 15-25. DOI: doi.org/10.3897/zookeys.1273.167628 [13 Mar. 2026]

[Ichthyology • 2025] Pseudorhombus bahudaensis • Resolving the Pseudorhombus arsius cryptic species complex (Teleostei: Paralichthyidae): Phylogenetic Evidence and Description of A New Species

 

Pseudorhombus bahudaensis 

Acharya, Behera, Mohanty, Ray, Patro, Mishra & Mohapatra, 2025 

DOI: doi.org/10.11646/zootaxa.5711.3.4

Abstract

The Gangetic Largetooth flounder, Pseudorhombus arsius (Hamilton, 1822), long treated as a single Indo-Pacific species, represents a cryptic species complex. Using a combination of morphological, morphometric, and molecular data, we discovered a distinct lineage that warrants recognition as Pseudorhombus bahudaensis sp. nov. Phylogenetic analyses of COI sequences revealed multiple polyphyletic clades, with two well-supported groups corresponding to P. arsius and the new species. Divergence dating indicates a separation of approximately 17 million years despite extensive morphological overlap. Diagnosis of the new species is supported by vertebral counts, subtle scale morphology, and differences in the position of the lateral line relative to the eye. These findings highlight the importance of integrating genetic and morphological evidence in resolving cryptic flounder complexes and provide a basis for re-evaluating distribution records attributed to P. arsius across the Indo-Pacific.

Pisces, Pseudorhombus bahudaensis, Pseudorhombus arsius, cryptic species complex

Pseudorhombus bahudaensis sp. nov. 

Smrutirekha ACHARYA, Rajesh Kumar BEHERA, Swarup Ranjan MOHANTY, Dipanjan RAY, Shesdev PATRO, Subhrendu Sekhar MISHRA and Anil MOHAPATRA. 2025. Resolving the Pseudorhombus arsius cryptic species complex (Teleostei, Paralichthyidae): phylogenetic evidence and description of Pseudorhombus bahudaensis sp. nov. Zootaxa. 5711(3); 381-397. DOI: doi.org/10.11646/zootaxa.5711.3.4 [2025-10-20]

[Ichthyology • 2025] Integrated Molecular and Morphological Analyses Resolve Long-Standing Classification Challenges in the Sinistral Flatfish Family Bothidae (Teleostei: Carangiformes)

  

Bothidae Smitt, 1892
Taeniopsettidae Amaoka, 1969

Monolenidae  n. fam. 
Grammatobothidae n. fam. 

in Tongboonkua, Chanet et Chen, 2025. 

DOI: doi.org/10.1111/zsc.70020  

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ABSTRACT

The flatfish family Bothidae comprise 170 currently recognised species in 20 genera, classified under two subfamilies. Although previous morphological and molecular studies have supported the monophyly of the family, its intrafamilial relationships remain largely unexplored, and the monophyly of the 20 existing genera has yet to be thoroughly evaluated. This study aims to address these long-standing systematic issues, particularly at the generic level, and to elucidate the sister-group relationships within Bothidae using a comprehensive set of samples of 87 morphospecies across 19 genera, and DNA sequence data from two mitochondrial and three nuclear gene markers. Our results reveal that the subfamily Bothinae is paraphyletic with respect to monophyletic Taeniopsettinae. Additionally, ‘Bothinae’ can be subdivided into three main clades (Bothinae 1–3). At the generic level, while Grammatobothus is resolved as monophyletic (=Bothinae 1) and as the sister group to the remaining bothids, four other specious genera—Arnoglossus, Laeops, Parabothus, and Psettina—are not. To resolve these taxonomic inconsistencies, we integrate evidence from phylogeny, morphology, and biogeography. Consequently, we propose elevating Taeniopsettinae to family status, establishing two new families—Monolenidae (=Bothinae 2) and Grammatobothidae—each comprising a single genus, and restricting the family Bothidae to Bothinae 3. We also refine the usage of the valid generic names Arnoglossus (=Arnoglossus V), Laeops (=Laeops II), Parabothus (=Parabothus III), and Psettina (=Psettina III), and recommend the resurrection of previously synonymised bothid genera as well as the establishment of new genera. These taxonomic revisions are ongoing and will be elaborated upon in a forthcoming study.

Keywords: left-eyed flounder, morphology, multigene phylogeny, new family, Pleuronectoidei, systematics

Bothidae Smitt, 1892 

Taeniopsettidae Amaoka, 1969

Monolenidae  n. fam. Tongboonkua, Chanet & Chen, 2025

Type genus: Monolene Goode, 1880

Grammatobothidae n. fam. Tongboonkua, Chanet & Chen, 2025

Type genus: Grammatobothus Norman, 1926

 

Pakorn Tongboonkua, Bruno Chanet and Wei-Jen Chen. 2025. Integrated Molecular and Morphological Analyses Resolve Long-Standing Classification Challenges in the Sinistral Flatfish Family Bothidae (Teleostei: Carangiformes). Zoologica Scripta. DOI: doi.org/10.1111/zsc.70020 [25 September 2025]

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[Ichthyology • 2025] Filistriatus gen. nov. • Unlocking the Genomic Potential of Historical and Formalin-fixed Specimens: Phylogenetic insights from Museum-preserved Threadfin Fishes (Teleostei: Polynemidae)

Filistriatus gen. nov. Girard  
(A) Filistriatus plebeius (Broussonet 1782), Fresh specimen (USNM 471329) in lateral view.

Neurocranium in dorsolateral view of: 

(B) F. bifurcus (Motomura, Kimura & Iwatsuki 2001); (C) F. sexfilis (Valenciennes 1831);
 (D) Polydactylus virginicus (Linnaeus, 1758); (E) Leptomelanosoma indicum (Shaw, 1804) 

 in Girard​ et Chovanec, 2025.  

 DOI: doi.org/10.7717/peerj.20029

Abstract 

DNA sequencing continues to revolutionize our understanding of biodiversity, ecology, and evolution. While analyzing sequence data allows us to address countless questions, most of the world’s vertebrate museum specimens have been historically inaccessible for genetic sampling. This is partially due to the absence of modern genetic samples and/or the impact formalin has on DNA during the preservation of specimen vouchers. Recent studies have shown successful extraction of DNA from historic museum specimens using additional chemicals and/or exposing the sample(s) to heat, with these advances enhancing the possibility of capturing genomic information from type specimens, characterizing genetic diversity within species complexes, and incorporating rare samples into phylogenetic analyses. However, questions remain about the reliability of these data and utility of historic DNA in modern phylogenetic analyses. In this study, we use a commercial extraction kit that targets formalin-fixed, paraffin-embedded samples to successfully extract DNA from historic museum specimens of threadfin fishes (Teleostei: Polynemidae). These specimens represent rare, genetically uncharacterized taxa that have yet to be included in a phylogenetic analysis. Low-depth shotgun sequencing is then used to sequence mitochondrial loci from the historic samples. The resulting sequence data are assembled, validated, and incorporated into a newly generated mitochondrial dataset that is simultaneously analyzed with a previously published ultraconserved-element dataset to construct a phylogenetic framework. We then explore new and previously described morphological variation within this new evolutionary framework for threadfins, identifying several shared characters that warrant revision of the generic-level classification. These findings add to the growing body of literature that demonstrates sequencing historical DNA from museum specimens and analyzing these data with complementary datasets of molecular markers from modern genetic samples can provide reliable and comprehensive assessments of biodiversity, ecology, and evolution across fishes and other vertebrates.

Morphology relating to the monophyly of Filistriatus gen. nov.
 (A) Fresh specimen of Filistriatus plebeius gen. nov. (USNM 471329) in lateral view.
(B) Neurocranium of F. bifurcus gen. nov. (USNM 76627) in dorsolateral view. (C) Neurocranium of F. sexfilis gen. nov. (CSIRO C261) in dorsolateral view.
(D) Neurocranium of P. virginicus (FMNH 104648) in dorsolateral view. (E) Neurocranium of L. indicum (USNM 357716) in dorsolateral view.

Left frontal and medial supraorbital canal commissure colored in (B–E), with isolated colored frontals below each whole neurocranium. Arrow I indicates dark stripes along the longitudinal scale rows above the lateral line. Faint stripes also present along the longitudinal scale rows below the lateral line. Arrow II indicates reduced lateral pore of the supraorbital canal. Arrow III indicates reduced medial commissure of sensory canal on the dorsal surface of the frontal. Arrow IV indicates pronounced lateral pore of the supraorbital canal that is visible when viewing the side of the neurocranium. Arrow V indicates elevated medial commissure of sensory canal. Scale bars = five mm.

Taxonomic modifications to the Polynemidae

Filistriatus gen. nov. Girard  

Diagnosis: a genus of small-to-moderately-sized threadfins differentiated from all other genera of the Polynemidae by the following combination of characters: 7–9 dark stripes along the longitudinal scale rows above the lateral line, 7–9 faint stripes along the longitudinal scale rows below the lateral line, reduced lateral pore of the supraorbital canal, reduced sensory canal commissure on the dorsal surface of the frontal, 5–6 free pectoral-fin rays, and 54–72 lateral-line scales.

Type species: Polynemus sexfilis Valenciennes 1831

Included species: Polydactylus bifurcus Motomura, Kimura & Iwatsuki 2001, 

Polydactylus plebeius (Broussonet 1782), 

Polydactylus sexfilis (Valenciennes 1831), 

Polydactylus siamensis Motomura, Iwatsuki & Yoshino 2001.

Etymology: the generic name refers to the thread-like fin rays of the pectoral fin and the diagnostic stripes along the lateral flanks [fili (Latin) = thread and striatus (Latin) = striped]. Gender masculine.

Remarks: “Polydactylus” siamensis was characterized by several longitudinal dark stripes along the flank, 5 pectoral filaments, and 54–58 lateral-line scales (Motomura, Iwatsuki & Yoshino, 2001). Although we could not sample this taxon in this study, the species has the diagnostic characters of Filistriatus. The species is also reassigned to the new genus.

Matthew G. Girard​ and Kevin R. Chovanec. 2025. Unlocking the Genomic Potential of Historical and Formalin-fixed Specimens: Phylogenetic insights from Museum-preserved Threadfin Fishes (Teleostei: Polynemidae). PeerJ. 13:e20029. DOI: doi.org/10.7717/peerj.20029 [September 30, 2025]

[Ichthyology • 2022] Molecular Phylogeny of the Threadfin Fishes (Polynemidae) using Ultraconserved Elements

in Girard, Davis, Baldwin, ... et Smith, 2022. 

DOI: 10.1111/jfb.14997

  twitter.com/FishPhylogeny 

Abstract

Threadfins (Teleostei: Polynemidae) are a group of fishes named for their elongated and threadlike pectoral-fin rays. These fishes are commonly found in the world's tropical and subtropical waters, and are an economically important group for people living in these regions, with more than 100,000 t harvested in recent years. However, we do not have a detailed understanding of polynemid evolutionary history such that these fishes can be monitored, managed and conserved as an important tropical food source. Recent studies hypothesize at least one genus of threadfins is polyphyletic, and no studies have focused on generating a hypothesis of relationship for the Polynemidae using DNA sequences. In this study, we analyse a genomic dataset of ultraconserved-element and mitochondrial loci to construct a phylogeny of the Polynemidae. We recover the threadfins as a clade sister to flatfishes, with the most taxonomically rich genus, Polydactylus, being resolved as polyphyletic. When comparing our dataset to data from previous studies, we find that a few recent broad-scale phylogenies of fishes have incorporated mislabelled, misidentified or chimeric terminals into their analyses, impacting the relationships of threadfins they recover. We highlight these problematic sequences, providing revised identifications based on the data sequenced in this study. We then discuss the intrarelationships of threadfins, highlighting morphological or ecological characters that support the clades we recover.

Keywords: BOLD, COI, Eleutheronema, GenBank, paradise threadfins, Polydactylus

Hypotheses of relationships from partitioned likelihood analysis of the Polynemidae and outgroup taxa.

Matthew G. Girard, Matthew P. Davis, Carole C. Baldwin, Agnès Dettaï, Rene P. Martin and W. Leo Smith. 2022. Molecular Phylogeny of the Threadfin Fishes (Polynemidae) using Ultraconserved Elements. Journal of Fish Biology. DOI: 10.1111/jfb.14997 

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