A new temporary fish parasitic gnathiid isopod, Elaphognathia alcalai (Crustacea: Isopoda: Gnathiidae), from Philippine coral reefs.

Gnathiid isopods are the most prevalent and ecologically important temporary ectoparasites of coral reef fishes and are important for supporting the functional integrity of coral reefs. Through their role as parasites, gnathiids can influence community dynamics in their ecosystem. The family Gnathiidae constitutes 12 genera, including the genus Elaphognathia that can be distinguished from other genera by the deeply excavated frontal border, dramatic lengthening of the mandibles, and addition of apical cusps in adult males. There are currently 25 known species of Elaphognathia described over a period of 130 years, with only five species molecularly characterized. The present study contributes to the knowledge of this genus by providing a comprehensive integrative description of the 26th species of Elaphognathia, the first novel gnathiid species described from the Philippines. Larval gnathiids were collected in the Central Indo-Pacific (Philippines), using light traps, separated, kept alive to molt into adults, and preserved in 95% ethanol for morphological and molecular characterization. Species description was based on light and scanning electron microscopy of the adult male, prepared in the program DEscriptive Language for Taxonomy (DELTA), using a modified Gnathiidae character set. Key distinguishing features of the new species are the presence of a pseudoblade, with the anterior tip dorsally visible, a large, rounded inner lobe with semi-smooth ridges, and conical protrusions on the inferior (dorsal) and superior (ventral) margin of the mandible, as well as the excavated frontal margin with two equal superior frontolateral processes with sinuate superolateral margins. The novel species can be distinguished from other molecularly characterized Elaphognathia (E. sugashimaensis and E. rangifer) by ~27% variation in COI sequences. More molecular data are required in order to elucidate a more accurate phylogenetic analysis of this genus.