G. David Johnson

Deep-sea mystery solved: astonishing larval transformations and extreme sexual dimorphism unite three fish families

The oceanic bathypelagic realm (1000–4000u200am) is a nutrient-poor habitat. Most fishes living there have pelagic larvae using the rich waters of the upper 200u200am. Morphological and behavioural specializations necessary to occupy such contrasting environments have resulted in remarkable developmental changes and life-history strategies. We resolve a long-standing biological and taxonomic conundrum by documenting the most extreme example of ontogenetic metamorphoses and sexual dimorphism in vertebrates. Based on morphology and mitogenomic sequence data, we show that fishes currently assigned to three families with greatly differing morphologies, Mirapinnidae (tapetails), Megalomycteridae (bignose fishes) and Cetomimidae (whalefishes), are larvae, males and females, respectively, of a single family Cetomimidae. Morphological transformations involve dramatic changes in the skeleton, most spectacularly in the head, and are correlated with distinctly different feeding mechanisms. Larvae have small, upturned mouths and gorge on copepods. Females have huge gapes with long, horizontal jaws and specialized gill arches allowing them to capture larger prey. Males cease feeding, lose their stomach and oesophagus, and apparently convert the energy from the bolus of copepods found in all transforming males to a massive liver that supports them throughout adult life.

The caudal skeleton of a 20 mm Triodon and homology of its components

Abstract We provide a detailed description of the caudal skeleton of the smallest specimen of a three-tooth puffer on record, a 20 mm standard length Triodon macropterus. The compound centrum supports the parhypural and five hypurals. Hypural five, which has a cartilaginous core, was interpreted erroneously by Tyler (1970, 1980) as uroneural 2, a structure that is not preformed in cartilage in acanthomorphs. We also found a second epural in Triodon, which was not reported by Tyler (1970, 1980). Both hypural 5 and epural 2 are also present in the two larger specimens of Triodon we studied. We discuss previous descriptions of the caudal-fin skeleton of Triodon and conclude by re-emphasizing the unexpectedly large number of putatively plesiomorphic characters of Triodon compared to all other plectognaths.

A developmentally “tail-less” adult cowfish, Lactoria cornuta, from Oman (Ostraciidae, Tetraodontiformes)

Abstract A 145 mm SL specimen of the ostraciid Longhorn Cowfish, Lactoria cornuta (Linnaeus, 1758), collected along the coast of Oman, has only small rudiments of the caudal fin and a much shortened caudal peduncle in which the posteriormost vertebrae are either abnormally developed or fused. The otoliths are too deteriorated to allow aging, but the gonads are mature, and we presume that an adult specimen of this size is several years old. Remarkably, this “tail-less” specimen survived without a functional caudal peduncle and caudal fin, even though the long caudal fin in ostraciid fishes is the main source of the rapid propulsion required for predator avoidance. The anatomical peculiarities of the rudimentary termination of the vertebral column and caudal fin are described and illustrated. We also comment on the potential evolutionary implications of such abnormalities.

A new genus and species of the family Symphysanodontidae, Cymatognathus aureolateralis (Actinopterygii: Perciformes) from Indonesia

A new genus and species of the percoid family Symphysanodontidae, Cymatognathus aureolateralis are described based on three specimens collected from North Sulawesi, Indonesia. The new species shares with the confamilial genus Sym-physanodon the unique supraneural and spinous dorsal-fin pterygiophore insertion pattern usually of 0/0/0+2+1/1/, T-shaped first supraneural, foreshortened base of the penultimate ventral procurrent caudal-fin ray, well-developed outer tooth patches at anterior tips of both jaws as well as along the medial surface of most of the length of the coronoid process of the dentary. The new species, however, is distinguishable from members of Symphysanodon by the following diagnostic characters: posterior tip of coronoid process of dentary abruptly depressed, so that teeth on anterior portion appear as an elevated patch, anterior tip of upper jaw not notched, and posterior nostril horizontally slit-like. Although the new species superficially resembles the members of the genus Giganthias (Giganthiidae) and some members of the subfamily Anthiadinae (Serranidae) in the unique characters it shares with Symphysanodon, it differs from Giganthias in having the above-mentioned unique pterygiophore insertion pattern and tips of all dorsal- and pelvic-fin spines smooth (vs. pterygiophore insertion pattern 0/0/2/1+1/1/, and tips of second, third and/or fourth dorsal- and pelvic-fin spines serrated), and from the members of Anthiadinae in having two flat opercular spines (vs. three) and 10xa0+xa015 = 25 vertebrae (vs. 10 + 16-18 = 26-28). A revised diagnosis of the Symphysanodontidae is presented.

Reconsidering pectoral girdle and fin morphology in Anguillidae (Elopomorpha: Anguilliformes)

The morphology of the pectoral girdle and fin of Anguillidae is reconsidered via the inclusion of skeletal components that have previously been unassessed. For example, the pectoral girdle and fin in Anguilla were erroneously reported to lack a scapular bone, a cartilaginous scapulocoracoid plate and a cartilaginous propterygium. The pectoral morphology of Anguilla is also compared with the closely related genus Nemichthys, including additional data on the anatomy of this eel family.