Spectacular morphological novelty in a miniature cyprinid fish, Danionella dracula n. sp.

The four described species of Danionella are tiny, transparent fishes that mature at sizes between 10-15 mm.

“The four described species of Danionella are tiny, transparent fishes that mature at sizes between 10–15 mm”

Species of the genus Danionella possess unique morphological novelties in males.

“Species of the genus Danionella are further remarkable in possessing a number of unique morphological novelties in males.”

In male Danionella, the gut and genital ducts are redirected so that both open between the pelvic fins.

“These include a redirection of their gut and genital ducts so that both open in between the pelvic fins”

Four species of the genus Danionella, maturing at sizes of 10-15 mm in length and including some of the smallest fishes and vertebrates, have been described from Myanmar and northeastern India.

“So far, four species of the genus Danionella, maturing at sizes of 10–15 mm in length and including some of the smallest fishes and vertebrates, have been described from Myanmar and northeastern India3–6.”

The four recognized species of Danionella have been distinguished by fin-ray counts and internal anatomy.

“The four recognized species have thus been distinguished by fin-ray counts and internal anatomy4–6”

Progenetic miniatures undergo profound developmental truncation, giving rise to striking morphological novelties not shown in their larger relatives, while proportioned dwarfs retain a normal developmental trajectory despite their reduced body size.

“Progenetic miniatures undergo profound developmental truncation, giving rise to striking morphological novelties not shown in their larger relatives, while proportioned dwarfs retain a normal developmental trajectory despite their reduced body size (e.g., refs. 5, 12, 14, 41, and 42).”

Danionella translucida is a transparent cyprinid fish with the smallest known vertebrate brain.

“Danionella translucida (DT), a transparent cyprinid fish1,2 with the smallest known vertebrate brain, was recently developed as a novel model organism for the optical investigation of neuronal circuit activity in vertebrates3,4.”

In D. dracula, mature males have huge odontoid fangs that resemble teeth in their arrangement and appearance.

“in which mature males have huge odontoid fangs that resemble teeth in their arrangement and appearance6”

In Danionella dracula, the apparatus of males is similar to that of females, as the anterior flange on the outer arm, its connection to the lateral process of the second vertebra, and the flange connecting outer and inner arms are all missing.

“However, in Danionella dracula, the sister taxon to all other Danionella6 (Fig. 4), the apparatus of males is similar to that of females, as the anterior flange on the outer arm, its connection to the lateral process of the second vertebra, and the flange connecting outer and inner arms are all missing (Fig. 4).”

Britz et al.6 obtained an age of the most recent common ancestor (MRCA) of Danionella of 29.5 (95% confidence interval 27.4-31.9).

“Based on the results of Britz et al.6, who obtained an age of the most recent common ancestor (MRCA) of Danionella of 29.5 (95% confidence interval 27.4–31.9)”

Within Cypriniformes, the morphological and developmental correlates of miniaturization have been especially well characterized.

“Within Cypriniformes, the morphological and developmental correlates of miniaturization have been especially well characterized.”

The genome assembly is from an individual Danionella dracula.

“We present a genome assembly from an individual Danionella dracula (the Dracula fish; Chordata; Actinopterygii; Cypriniformes; Danionidae; Danioninae).”

Male Danionella have a large drumming muscle that originates from expanded bony flanges on the os suspensorium of their Weberian apparatus and inserts on a hypertrophied fifth rib.

“a large drumming muscle that originates from expanded bony flanges on the os suspensorium of their Weberian apparatus and inserts on a hypertrophied fifth rib”

Male Danionella have a conical drumming cartilage that probably works like a drumstick on the anterior swimbladder chamber.

“and a conical drumming cartilage that probably works like a drumstick on the anterior swimbladder chamber4–6,9.”