Editorial Type:
Article Category: Research Article
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Online Publication Date: 09 Mar 2022

Osteology of the White Barracudina, Arctozenus risso (Bonaparte) (Aulopiformes: Paralepididae)

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Page Range: 115 – 130
DOI: 10.1643/i2020130
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Arctozenus risso, the White Barracudina, is a member of the Paralepididae, the largest family within the order Aulopiformes. In recent years the systematics of the family and the order has advanced significantly due to morphological, molecular, and holistic studies, which has led to a general agreement of their relationships. Some phylogenetic discrepancies remain in particular among the species-rich paralepidids, based on the difficulties in obtaining comprehensive taxon samples as well as the lack of morphological studies. We found an enlarged autopalatine following the enlarged ethmoid region of the skull. We identified a large ossification that covers the dorsal surface of the basibranchial copula as a basibranchial tooth plate and identified a second smaller tooth plate associated with basibranchial 4. However, the most peculiar structures are dorsal ligament ossifications that are associated with the anterior and posterior dorsal-fin pterygiophores, and supraneural 2. We hope the description of the skeletal anatomy of A. risso will help to solve some of the open questions of the phylogenetic relationships of the paralepidids and aulopiforms.

Copyright: © 2022 by the American Society of Ichthyologists and Herpetologists
Fig. 1.
Fig. 1.

Lateral view of Arctozenus risso (OS 22845, 91 mm SL), scale = 10 mm.

Fig. 2.
Fig. 2.

The cranium of Arctozenus risso (DMM IE11138, 142 mm SL): (A) overview of the skull and pectoral girdle, lateral view, cartilage is shown in blue, scale = 5 mm. (B) Photograph of the ethmoid region, dorsal view, scale = 2 mm. apal, autopalatine; dpal, dermopalatine; es, extrascapular; fr, frontal; mx, maxilla; pmx, premaxilla; rc, rostral cartilage.

Fig. 3.
Fig. 3.

The skull of Arctozenus risso (OS 22817, 73 mm SL). Cartilage is shown in blue, the extrascapulars and the right dermosphenotic are removed, scale = 2 mm: (A) lateral view, (B) dorsal view, (C) ventral view. asp, autosphenotic; boc, basioccipital; dsp, dermosphenotic; ec, ethmoidal cartilage; epo, epioccipital; exo, exoccipital; fr, frontal; hf, anterior hyomandibular facet; ic, intercalar; ioc, intraorbital cartilage; le, lateral ethmoid; met, mesethmoid; pa, parietal; pas, parasphenoid; pro, prootic; pto, pterotic; pts, pterosphenoid; soc, supraoccipital; v, vomer.

Fig. 4.
Fig. 4.

Lateral views of the infraorbital series with supraorbitals and the opercular series of Arctozenus risso (OS 22823, 156 mm SL). (A) Infraorbital series and supraorbitals, position of the eye is shown with a dashed line, scale = 5 mm. (B) Opercular series with the ligament shown in gray, scale = 2 mm. dsp, dermosphenotic; io, infraorbital; iop, interopercle; lio, interopercular ligament; op, opercle; pop, preopercle; so, supraorbital; sop, subopercle.

Fig. 5.
Fig. 5.

Lateral views of the suspensorium and jaw elements of Arctozenus risso (OS 22817, 73 mm SL), cartilage is shown in blue, scale = 2 mm. (A) Suspensorium, (B) upper jaw, (C) lower jaw. ang-ar, anguloarticular; apal, autopalatine; d, dentary; dpal, dermopalatine; ecp, ectopterygoid; enp, entopterygoid; h, hyomandibular; ih, interhyal; mc, Meckel's cartilage; mpt, metapterygoid; mx, maxilla; pmx, premaxilla; pop, preopercle; q, quadrate; rar, retroarticular; s, symplectic; smx, supramaxilla.

Fig. 6.
Fig. 6.

Medial view of the right ventral hyoid arch of Arctozenus risso (OS 22823, 156 mm SL), cartilage is shown in blue and ligament in gray, scale = 2 mm. br, branchiostegal; cha, anterior ceratohyal; chp, posterior ceratohyal; hhd, dorsal hypohyal; hhv, ventral hypohyal; ih, interhyal; lish, ligament of the Musculus sternohyoideus; uh, urohyal.

Fig. 7.
Fig. 7.

The gill arches and the basihyal of Arctozenus risso (OS 22823, 156 mm SL), cartilage is shown in blue. Dorsal gill arch elements in ventral (A) and dorsal view (B), scale = 2 mm. (C) Ventral gill arch elements, dorsal view, gill rakers are only shown for the right side, the ventral basibranchial copula cartilage is shown through the basibranchial dorsal ossification, scale = 5 mm. bb, basibranchial; bbdo, basibranchial dorsal ossification; bbtp, basibranchial tooth plate; bh, basihyal; bhtp, basihyal tooth plate; cb, ceratobranchial; eb, epibranchial; hb, hypobranchial; lgr, lateral gill rakers; mgr, median gill rakers; pb, pharyngobranchial; pbtp, pharyngobranchial tooth plate.

Fig. 8.
Fig. 8.

Lateral view of the vertebrae and intermuscular bones of Arctozenus risso. (A) Abdominal and caudal vertebrae (OS 22822, 103 mm SL), scale = 2 mm. (B) Photograph of the anterior epineurals (OS 22823, 156 mm SL), pectoral girdle and extrascapular removed, scale = 1 mm. (C) Photograph of the posterior intermuscular bones (OS 22823, 156 mm SL), scale = 2 mm. (D) Photograph of the intermuscular bones of the mid-trunk region (OS 22823, 156 mm SL), scale = 2 mm. c, centrum; epn, epineural; epp, epipleural; ha, haemal arch; hs, haemal spine; ls, lateral-line scale; my, myorhabdoi; na, neural arch; ns, neural spine; pto, pterotic; rb, rib.

Fig. 9.
Fig. 9.

Lateral view of the dorsal-fin skeleton, supraneurals, and dorsal ligament ossifications of Arctozenus risso (OS 22823, 156 mm SL). (A) Dorsal fin, cartilage is shown in blue, scale = 2 mm. (B) Photograph of the supraneurals and anterior dorsal ligament ossifications, supraneurals are marked with dashed lines, the mirrored right side is shown, scale = 5 mm. (C) Photograph of the posterior dorsal ligament ossifications, the mirrored right side is shown, scale = 2 mm. c, centrum; do, dorsal ligament ossification; dr, distal radial; epn, epineural; epp, epipleural; es, extrascapular; f, fin ray; mr, middle radial; pmr, proximal-middle-radial; ptph, pterygiophore; sn, supraneural.

Fig. 10.
Fig. 10.

Lateral view of the anal-fin and caudal-fin skeleton of Arctozenus risso, cartilage is shown in blue. (A) Overview of the anal fin with the associated haemal spines (OS 22823, 156 mm SL), scale = 2 mm. Detail of the anterior (B) and posterior (C) anal pterygiophores (OS 22823, 156 mm SL), scale = 2 mm. (D) Caudal-fin skeleton (OS 22817, 73 mm SL), the fin rays are not shown, scale = 5 mm. dr, distal radial; ep, epural; f, fin ray; ha, haemal arch; hs, haemal spine; hy, hypural; mr, middle radial; na, neural arch; ns, neural spine; phy, parhypural; pmr, proximal-middle-radial; pr, proximal radial; ptph, pterygiophore; pu, preural centrum; u, ural centrum; un, uroneural.

Fig. 11.
Fig. 11.

The appendicular skeleton of Arctozenus risso, cartilage is shown in blue. (A) Lateral view of the pectoral girdle and the first lateral-line scale (OS 22817, 73 mm SL), fin rays are not shown, scale = 2 mm. (B) Lateral view on the scapulocoracoid (OS 22823, 156 mm SL), scale = 1 mm. (C) Ventral view of the pelvic girdle (OS 22817, 73 mm SL), right fin rays are not shown, scale in D. (D) Detail of the dorsal side of the pelvic girdle (OS 22817, 73 mm SL), only the left autonomous lateral cartilage and distal radials are shown and fin rays were removed, scale = 0.5 mm. bpt, basipterygium; cl, cleithrum; co, coracoid; dr, distal radial; f, fin ray; lpc, lateral pelvic cartilage; ls, lateral-line scale; pcl, postcleithrum; plb, pelvic bone; pt, posttemporal; ra, radial; sc, scapula; scl, supracleithrum.

Contributor Notes

1 Research-Institute for Farm Animal Biology (FBN), Institute of Muscle Biology and Growth, Dummersdorf, Germany.
2 Department of Cytology and Evolutionary Biology, University of Greifswald, Zoological Institute and Museum, Greifswald, Germany.
3 Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, 70191 Stuttgart, Germany.
4 Department of Fisheries, Wildlife, and Conservation Sciences, Oregon State University, 104 Nash Hall, Corvallis, Oregon 97331; Email: peter.konstantinidis@oregonstate.edu. Send reprint requests to this address.

Associate Editor: M. P. Davis.

Received: 16 Sept 2020
Accepted: 30 Aug 2021
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