The larval attachment organ of the bowfin Amia ocellicauda Richardson, 1836 (Amiiformes: Amiidae) and its phylogenetic significance.

Larval attachment organs (LAOs) are unicellular or multicellular organs that enable the larvae of many actinopterygian fishes to adhere to a substrate before yolk-sac absorption and the free-swimming stage. Bowfins (Amiiformes) exhibit a sizable LAO on the snout, which was first described in the late 19th and early 20th centuries. In this study, we document the LAO of Amia ocellicauda (Richardson, 1836) using a combination of scanning electron microscopy (SEM) and light microscopy, and histochemistry. We examined material representing three stages with SEM ranging in size from 5.8 to 11.2 mm in notochord length and one stage histochemically. We compare the LAO of A. ocellicauda to that of the lepisosteid Atractosteus tropicus Gill, 1863 and show that although the LAOs of A. ocellicauda and A. tropicus are both super-organs, the two differ in the ultrastructure of the entire organ. A. ocellicauda possesses two distinct lobes, with the organs arranged on the periphery with none in the middle, whereas A. tropicus also possesses two lobes, but with the organs scattered evenly across the super-organ. The individual organs of A. ocellicauda possess adhesive cells set deep to support cells with the adhesive substance released through a pore, whereas A. tropicus possesses both support cells and adhesive cells sitting at a similar level, with the adhesive substance released directly onto the surface of the organ. We additionally provide a table summarizing vertebrate genera in which attachment organs have been documented and discuss the implications of our study for hypotheses of the homology of attachment organs in the Holostei.

Three scleral ossicles in the West African Denticle herring Denticeps clupeoides (Clupeiformes: Denticipitidae).

The eyes of teleostean fishes typically exhibit two ossifications, the anterior and posterior sclerotics, both associated with the scleral cartilage. The West African Denticle herring Denticeps clupeoides has three scleral ossifications, including the typical two associated with the scleral cartilage (anterior and posterior sclerotic) and a third ossification (Di Dario's ossicle), spatially separated from the scleral cartilage and located within the anteromedial wall of the sclera. The medial rectus muscle inserts on the medial surface of Di Dario's ossicle, suggesting that this third sclerotic may play a role in forward rotation of the eye in this surface feeding fish.

The larval attachment organ of the tropical gar Atractosteus tropicus Gill, 1863 (Lepisosteiformes: Lepisosteidae).

Larval attachment organs (LAOs) are unicellular or multicellular organs that allow larvae to adhere to a substrate before yolk-sac absorption and the free-swimming stage. This study documents the LAO of tropical gar, Atractosteus tropicus, using a combination of scanning electron microscopy and light microscopy. It is shown that the LAO of A. tropicus is a super-organ surrounded by a wall and containing at its centre many smaller multicellular organ units, each comprised of attachment and support cells. Attachment cells are secretory and house large vacuoles filled with a glycoprotein. At hatching, the super-organ is well developed and occupies almost the entire anteroventral surface of the head. During subsequent development, the smaller individual units begin to regress, until at 6 days post-hatching the super-organ and its individual units are no longer visible.

Psilorhynchus tysoni, a new species of torrent minnow from the Salween River drainage, western Thailand (Teleostei: Psilorhynchidae).

Psilorhynchus tysoni, new species, is described on the basis of 10 specimens, 23.3-53.8 mm SL from the Mae Nam Moei and Hue Mae Song Rivers, in the Salween River drainage in western Thailand. It belongs to the P. nudithoracicus species group and can be distinguished from other members of this group by a combination of characters, including features of body and fin coloration, head shape, and caudal fin-ray, vertebrae, and cephalic lateral-line canal pore counts. Phylogenetic analyses of a mitochondrial DNA data set (comprising 642 bp of cytochrome c oxidase subunit 1 and 1140 bp of cytochrome b) for 12 species of Psilorhynchus and one outgroup taxon resulted in phylogenetic hypotheses in which P. tysoni is a member of a clade equivalent to the P. nudithoracicus species group. Within this group P. tysoni is placed as the sister taxon of a putatively undescribed species of Psilorhynchus from Myanmar.