The razorfish, Aeoliscus, enters the LRT as an upside-down sea horse

Figure 1. Aeoliscus in vivo at full scale on a 72 dpi monitor.

Aeoliscus strigatus (Günther 1861, aka Centriscus strigatus, Amphisle strigata; 15cm) is the extant razorfish or shrimpfish. In the large reptile tree (LRT, 1834+ taxa) the shrimpfish nests with the sea horse, Hippocampus (Fig. 2). Thus Aeoliscus can be thought of as an upside-down sea horse despite many morphological difference (= no other tested vertebrate is closer). The dorsal fins have migrated to the caudal area. The caudal fin migrates to the anal area, bending the vertebral column to do so (Fig. 2). The tiny mouth, perhaps the smallest among vertebrates, is used like an eye-dropper to suck up minute brine shrimp. The preoperculum and operculum are large to produce suction for the tube mouth.

The preoperculum extends anteriorly beyond the orbit, merging with the quadrate (Fig. 2, at least in Gregory’s 1933 drawing). The lacrimal is absent (at least in Gregory’s 1933 drawing). As in the sea horse the naris is close to the orbit. The orbit is confluent with the antorbital fenestra. The supratemporal is absent or fused.

The shape of Aeoliscus was for hiding among sea grasses and other vertical sea floor environmental elements. The counter-shading of the body increases the illusion of slender background elements.

Figure 2. Aeoliscus anatomy from Gregory 1933 compared to related taxa in the sea horse / pipefish clade. Tetrapod analog colors applied here.

Aeoliscus lives in shallow sunlit waters
protected from predators by the poisonous spines of nearby brainless sea urchins. Fertilized eggs and hatchlings drift without parental care. Males and females are nearly identical.

References
Gregory WK 1933. Fish skulls. A study of the evolution of natural mechanisms. American Philosophical Society 23(2) 1–481.
Günther A 1861
. Catalog of Fishes in the British Museum 3: 586pp. British Museum, London.

wiki/Hippocampus
wiki/Aeoliscus

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