Lagusia Vari 1978

Lagusia Vari, 1978

Lagusia Vari, 1978: 523.

Type species. — Datnia micracanthus Bleeker, 1860; by original designation.

Diagnosis. — The presence of stripes on the body in small to midsized specimens and the lack of a direct attachment of the extrinsic swimbladder muscle to the rear of the neurocranium serve in combination to delimit Lagusia from all other genera of the Terapontidae. Lagusia is furthermore delimited externally from other members of the family by the distinctive pattern of dark pigmentation on the caudal fin in mid- and large-sized specimens consisting of a dark basal bar continuous ventrally with a band of dark pigmentation extending along the ventral rays of the lower lobe of the caudal fin (Fig. 1).

Phylogenetic placement. — Vari (1978: Fig. 9) proposed that Lagusia was a relatively basal member of the Terapontidae (the Teraponidae of that study), but that hypothesis was complicated by the lack of cleared and stained preparations of the species. Dissections and examination of two cleared and stained specimens in this analysis have confirmed the presence in the genus of the characters supporting that placement of the genus within that phylogeny (see character summaries in Vari, 1978). Of particular note is the presence in the genus of the well developed extrinsic swimbladder muscle running anteriorly to the posttemporal, a feature synapomorphic for the family. The muscle in Lagusia is a simple mass with an attachment anteriorly to the posterior of the posttemporal common across the Terapontidae, but lacking the medial connective tissue attachment of the anterior part of the muscle and the posterior of the neurocranium present in the majority of genera of the Terapontidae. The absence of this medial connective tissue band is limited to five basal genera in the family, all of which interestingly are restricted to brackish and freshwaters of Australia, New Guinea and Sulawesi, contrary to the broader distribution of the rest of the Terapontidae, many species of which are broadly distributed in marine waters from East Africa to Fiji.