Tiny, toothless Stylephorus now nests with another blenny: toothy Gigantura

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Untested traits include
those cylindrical eyeballs and that elongate lower caudal fin.

Figure 1. Gigantura compared to Stylephorus to a reduced scale.
Figure 1. Gigantura compared to Stylephorus to a reduced scale.

Gigantura indica
(Brauer A 1901, Konstantinidis and Johnson 2016; 20 cm standard length, not counting the caudal fin, Figs 1–3) is the extant telescope fish. Comparisons with sister taxa indicate the indicated ‘palatine’ with teeth is actually the premaxilla in figure 2 from Gregory 1933. The toothless maxilla (green) is located at the posterior mandible. The postorbital (=circumorbital ring) is reduced to two vestiges. This small fish can swallow prey larger than itself.

Figure 2. Skull of Gigantura from Gregory 1933. Colors added here.
Figure 2. Skull of Gigantura from Gregory 1933. Colors and new labels added here.
Figure 3. Gigantura magnified.
Figure 3. Gigantura magnified to show facial details including the cylindrical eyeballs.

Stylephorus chordatus
(Shaw, 1791, Regan 1924, Figs 4, 5) is the extant tube-eye or thread-tail. It was considered an oarfish relative (Fig 6), but here nests with Gigantura (Figs 1–3). Note the large eyes and flexible neck. Convergent with seahorses and oarfish, the tube-eye also feeds on tiny plankton sucked in as its tubular mouth enlarges the oral cavity by 40x (Figs 4, 5).

Figure 4. Stylephorus skull animated. Colors added here.
Figure 4. Stylephorus skull animated. Colors added here. Compare to Gigantura in figure 1. The maxilla (mx) labeled here is actually the anterior portion of the postorbital. And now you know why ray-fin fish can be difficult to score.
Figure 1. Stylephorus ontogeny and feeding
Figure 5. Stylephorus ontogeny. Feeding animated. Much enlarged. Note the eye-cylinders.

Both of these odd deep-sea fish
find a last common ancestor in the large reptile tree (LRT, 2223 taxa) close to Acanthemblemaria, the tube blenny (Fig 7). So all three are blennies.

Figure 7. Traditional fish cladogram nesting Stylephorus with opahs and oarfish.
Figure 7. Traditional fish cladogram nesting Stylephorus with opahs and oarfish.

Acanthemblemaria aceroi
(genus: Metzelaar 1919; species: Hastings, Eytan and Summers 2020) is a newly described tube blenny described with a µCT scan skeleton. Note the vestige maxilla (green) detached from the lacrimal (tan). Here it nests with Neoclinus, the sarcastic fringhead blenny.

Figure 7. Acanthemblemaria, the tube blenny is presently the last common ancestor of Gigantura and Stylephorus in the LRT. Note the emphasis on the eye sockets and the diminution of the maxilla (green) with a large vestige posteriorly, as in Gigantura (Fig 1).
Figure 7. Acanthemblemaria, the tube blenny is presently the last common ancestor of Gigantura and Stylephorus in the LRT. Note the emphasis on the eye sockets and the diminution of the maxilla (green) with a large vestige posteriorly, as in Gigantura (Fig 1).

Housekeeping the ray-fin fish clade continues unabated,
testing taxa together that rarely get tested together in trait analysis.

References
Brauer A 1901. Über einige von der Valdivia-Expedition gesammelte Tiefseefische und ihre Augen. Sitzungsberichte der Gesellschaft zur Beförderung der Gesamten Naturwissenschaften zu Marburg 8: 115–130.
Konstantinidis P and Johnson GD 2016. Osteology of the telescope fishes of the genus Gigantura (Brauer, 1901), Teleostei: Aulopiformes. Zoological Journal of the Linnean Society 179(2):338–353.
Regan CT 1924. The morphology of the rare oceanic fish, Stylophorus chordatus, Shaw; based on specimens collected in the Atlantic by the “Dana” expeditions, 1920–1922. Proceedings of the Royal Society B 96(674): PDF
Shaw G 1791. Description of the Stylephorus chordatus, a new fish. Transactions of the Linnean Society of London, 2d Ser: Zoology 1:90–92.

wiki/Stylephorus
wiki/Sarcastic Fringehead
wiki/Acanthemblemaria
wiki/Gigantura

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