Table 1.
Specimens examined.
Fig 1.
Left lateral windowing in preserved adult males.
(A) Equulites elongatus (AMNH PVD 82-06/19a), 80.1 mm SL, top in lateral view, bottom in ventrolateral view. (B) Photolateralis stercorarius (AMNH PVD 99-11/30a), 97.2 mm SL, top in lateral view, bottom in ventrolateral view. Dashed line indicates anterior-most extent of visible translucent window. Photographs taken by J.S.S. and are original to this work.
Fig 2.
Left lateral views of fresh adult male Equulites leuciscus.
THAI 24−56. Specimens on day of acquisition from fish market, before preservation. (A) Top in dorsolateral view and bottom in ventrolateral view under ambient light. Dashed line indicates anterior-most extent of visible window. (B) Lateral view of fish dissected on right side on right side and illumined with light at wavelength of most common bacterially produced light in ponyfishes (482 + /- 18 nm) through light-organ window into gas bladder (to approximate how light would travel, be reflected, and emitted in this species). (C) Lateral view of dissection under ambient light. Abbreviations: silvery reflective gas bladder (gb), transparent gas bladder window (w). Photographs taken by J.S.S. and are original to this work.
Fig 3.
Left lateral view of esophageal light organs in situ.
Light organ outlined in dotted line. (A) Equulites rivulatus male AMNH uncat. PVD 82-06/19a, 61.7 mm SL (B) Photolateralis stercorarius male AMNH uncat. PVD 03-04/07a, 62.0 mm SL. (C) Photolateralis stercorarius female AMNH uncat. PVD 03-04/07a, 62.5 mm SL. White and black arrows indicate position of anterior and posterior windowing respectively. Abbreviations: connective tissue with dark chromatophores and iridophores (ct), esophagus (es), gas bladder with reflective silvering (gb), longitudinal striated muscle (lm). Photographs taken by M.J.G. and are original to this work.
Fig 4.
Male Equulites elongatus (AMNH uncat. PVD 82-06/19a) light organ.
(A) Dissected specimen showing relative positions of light organ, gas bladder, and external windowing. Photograph taken by J.S.S. and is original to this work. (B) μCT reconstruction of light organ and esophagus in left anterodorsal view. Inset shows a section of the esophagus (MT stain). Scale bar, 0.5 mm. Arrows indicate approximate locations of cross sections. (C) Anterior cross section of light organ and esophagus showing connecting ducts (MT stain). (D) μCT cross section at approximate location of C. (E) Posterior cross section of light organ (TB stain). (F) μCT cross section at approximate location of E. (G) Cross section of central chamber from posterior region of light organ at a location similar to medial asterisks in E and F (MT stain). (H) Cross section of tubules from posterior light organ containing bacteria (MT stain). Abbreviations: bacteria (b), tubular bacterial chambers (bc), circular striated muscle (cm), connective tissue (ct), simple cuboidal epithelium (cu), ducts and chambers connecting to esophageal lumen (*), esophagus (es), guanine in connective tissue (g), kidney (kd), longitudinal striated muscle (lm), liver (lv).
Fig 5.
Male Equulites elongatus light organ in posterior view.
(A) Light organ in posterior view from anterior gas bladder in situ (SIO 96−98, 83.1 mm SL) with screening tissues retracted. (B) Dorsoposterior view of excised light organ, esophagus, and anterior stomach (AMNH PVD 82-0/19a, 76.3 mm SL) with ventral screening band of tissue partially extended. (C) Diagrammatic light organs in left posterolateral view. Left image shows an unobscured translucent window into the gas bladder similar to photo in (A). Middle image shows a translucent window with shutter partially covering window with tissue containing separated chromatocytes and iridocytes similar to photo in (B). Right image shows a translucent window with shutter covering window obscuring light into the gas bladder. Orange oval indicates window into gas bladder. Blue arrows indicate direction and degree of longitudinal muscle contraction. Abbreviations: connective tissue (ct), esophagus (es), longitudinal muscle (lm), stomach (st). Photographs taken by M.J.G. and are original to this work.
Fig 6.
Histological sections of Equulites leuciscus and Photolateralis stercorarius light organs.
(A) Equulites leuciscus male light organ longitudinal section showing the muscular, dorsal light occluding shutter (AMNH PVD 02-01/30r, 63.3 mm SL) (MT stain). (B) Close up view of longitudinal section of shutter from same section shown in A (MT stain). (C) Cross section of central chamber from posterior light organ connecting to tubular bacterial chambers at left in Photolateralis stercorarius (AMNH PVBD 03-04/07a, 57.7 mm SL) (TB stain). (D) Close up view of ciliated columnar epithelium lining central chamber in P. stercorarius (TB stain). Abbreviations: bacteria (b), bacterial chambers (bc), chromatocyte (cc), circular striated muscle (cm), columnar epithelium (co), connective tissue (ct), ducts and chambers connecting to the esophageal lumen (*), guanine (g), longitudinal striated muscle (lm), shutter (sh).
Fig 7.
Dice μCT scanned three-dimensional and sectional reconstructions of light organs in five equulitine species shown in phylogenetic context.
Phylogeny at left from the scientific literature [12,15,30]. Longitudinal CT sections are on or very near the median line. The chevrons indicate approximate locations of light windows in light organs along the median line. Abbreviations: esophagus (es), gas bladder (gb), light organ (lo), stomach (st).