Pseudorhabdosynochus justinella is a diplectanid monogenean parasitic on the gills of the red grouper, Epinephelus morio.

[1] The specific name justinella is in honor of parasitologist Jean-Lou Justine from National Museum of Natural History in France.

The description by Kritsky, Bakenhaster & Adams in 2015[1] includes the following: Body fusiform, dorsoventrally flattened, with a slight constriction at level of male copulatory organ (MCO); peduncle with small tegumental scales having rounded anterior margins.

Four eyespots lacking lenses immediately anterior to pharynx; members of posterior pair larger, slightly closer together than those of anterior pair; accessory chromatic granules small, irregular in outline, uncommon in cephalic region.

Pharynx ovate to subspherical, muscular; esophagus short to nonexistent; intestinal ceca blind, extending posteriorly to level of peduncle, with ends slightly diverging.

Ventral bar robust, with medial constriction, tapered ends, longitudinal medioventral groove.

Germarium pyriform, lying at midlength of trunk, with dorsoventral distal loop around right intestinal cecum; ootype lying slightly to left of body midline and surrounded by well-developed Mehlis' gland; uterus banana-shaped when empty, delicate.

Egg 118–119 μm (n = 1) long, 54–55 μm (n = 1) wide.Kritsky, Bakenhaster & Adams (2015) wrote that "examination of the holotype, three paratypes, and voucher specimens from red grouper off Florida and Mississippi indicated that the original description of P. yucatanensis Vidal-Martínez, Aguirre-Macedo & Mendoza-Franco, 1997[3] was based on specimens representing two distinct species of Pseudorhabdosynochus", namely P. yucatanensis sensu stricto and a new species, P. justinella Kritsky, Bakenhaster & Adams, 2015.

In both species, the vaginal sclerite possesses an elongate sigmoid distal tube attached to the distal end of the chamber, the ventral bar is short and robust, the deep root of the ventral anchor is shorter than the superficial root, and the dorsal anchors of the two species are morphologically indistinguishable.