CYMOTHOOIDEA Leach, 1814

Superfamily CYMOTHOOIDEA Leach, 1814 Family CYMOTHOIDAE Leach, 1814

Remarks. Cymothoidae has been subject to numerous analyses confirming its monophyletic status (Trilles, 1999; Brandt and Poore, 2003; Smit et al., 2014). Brandt and Poore (2003) recognized the family and referred to Trilles (1999) for a diagnosis. Cymothoidae includes a speciose assemblage of primarily marine taxa characterized by an outline becoming widest at about pereon 5; coxal plates 5-7 visible; pleonite one similar to others and large, ovoid pleopods ( Brandt and Poore, 2003). Members of the family are characterized by often having a large size (1-6 cm), and all are parasitic on fish. Cymothoidae is one of the largest families of isopods, and they have been described as parasites on nearly every marine fish family as well as some freshwater groups (Smit et al., 2014).

Isopods have a modest fossil record (Schram and Koenemann, 2021). Because their classification at the family and genus level is so dependent on morphology that does not frequently fossilize, comparison of fossil and extant isopods is precarious (Poore and Bruce, 2012). The fossil remains described here as they are preserved do not provide sufficient morphological detail to assign the fossil to a genus within the Cymothoidae with certainty. Generic characters used to classify isopods include details of the head, mouthparts, and pereopods, none of which is preserved in the specimen ( Brandt and Poore, 2003; Poore and Bruce, 2012). Furthermore, assigning fossil forms to extant genera is severely limited because in many cases preservable hard parts are also not present (Poore and Bruce, 2012).

The new fossil is similar to species of Livoneca Leach, 1818 ; Nerocila Leach, 1818 ; and Aegathoa Dana, 1853 , all of which are known from coastal Maryland today (marylandbiodiversity.com; OBIS). Each of these taxa are characterized by an overall ovate pereion and pleonites much narrower than pereionites. The fossil differs somewhat in narrowing strongly anteriorly beginning at pereonite five, unlike in these extant genera wherein the pereon maintains a broadly convex margin along its entire length. Thus, because assignment of fossil isopods to extant taxa is limited by preservation, and because the specimen differs from the extant, geographically proximal forms, we elect to name a new genus to accommodate the new material.