Prohyperia, Zeidler, Wolfgang, 2015

Zeidler, Wolfgang, 2015, A review of the hyperiidean amphipod genus Hyperoche Bovallius, 1887 (Crustacea: Amphipoda: Hyperiidea: Hyperiidae), with the description of a new genus to accommodate H. shihi Gasca, 2005, Zootaxa 3905 (2), pp. 151-192 : 182

Genus Prohyperia gen. nov.

Type species: Hyperoche shihi Gasca, 2005 , by monotypy.

Diagnosis. Sexually mature specimens with body length 10–12 mm. Ovigerous females with relatively few eggs or larvae (type with 26 eggs). Habitus similar to Hyperia . Pereonites all free. Coxae free from pereonites. Epimeral plates rounded or sub-rectangular. Head large, semi-circular, slightly deeper than first pereonite and about as long as the first two pereonites. Eyes occupy entire lateral surface of head in females, slightly less in males, separated dorsally. First antennae with three-articulate peduncle; callynophore much longer than peduncle. Second antennae of females four-articulate, usually much shorter than the first. Maxilliped with poorly developed inner lobe, barely produced beyond base of outer lobes. Mandibles with three-articulate palp in both sexes; molar with prominent oval-shaped dentate process; left mandible with well-developed lacina mobilis, slightly narrower than incisor. Maxillae 1 with broad, leaf-like palp; outer lobe with four large denticles terminally and bunches of very strong setae. Gnathopoda similar in structure, strongly chelate, especially in males and mature specimens, with elongated carpus overlapping propodus; carpal process of G1 armed with several strong setae on anterior margin; carpal process of G2 with few short setae or bare. Pereopoda all simple. Pereopods 3 & 4 distinctly longer than P5–7. Telson triangular, length about half of peduncle of U3.

Sexual dimorphism. Apart from the long filamentous antennae, males differ from females in the following characters: the habitus is slightly more slender; the gnathopoda and pereopoda are also more slender but the gnathopoda are stronger, with a more developed carpal process; the head is relatively smaller and the eyes occupy slightly less surface area; the rami of U3 have a proximal excavation on the inner margin, a male character found in other allied genera.

Remarks. The type species was originally described from a single female captured at 1136 m in the Gulf of California ( Gasca 2005). It was originally placed in the genus Hyperoche , not without some hesitation (Gasca pers. com.), based on the structure of the gnathopoda which are more like Hyperoche than Hyperia , and this seemed a logical decision at the time. However, this placement is not supported by the current review of the genus because several characters that distinguish Hyperoche are not present in H. shihi . Namely, pereonites 1 & 2 are not fused dorsally; the coxae of pereopod 7 are not fused with the pereonite; the carpal process of the gnathopoda is not knife-shaped and the anterior margin is not denticulate but bare or armed with a few strong setae; similarly the posterior margin of the propodus of the gnathopoda is not denticulate; the inner lobe of the maxilliped is not well developed and the outer lobes are relatively small; the mandibular molar is not laminate but has a well-developed dentate cusp; the incisor and lacinia mobilis of the left mandible have fewer teeth (about half of Hyperoche species) and the terminal article of the mandibular palp is relatively longer (about 1.8 x second article), whereas in Hyperoche it is marginally shorter, or only a little longer (up to 1.5 x second article).

It resembles Hyperia in that pereopods 3 & 4 are longer than pereopods 5–7 with the latter being similar in length and structure, and in having a mandibular molar with a well-developed dentate cusp. It differs from Hyperia mainly in the structure of the gnathopoda, especially in lacking the characteristic spoon-shaped carpal process. Also, the carpal process is usually drawn out, especially in males, overlapping the propodus and dactylus, as in some species of Phronima , and is usually bare or only armed with a few setae, especially in gnathopod 2. In addition, the outer lobes of the maxilliped are relatively smaller and the inner lobe is much reduced, and the incisor and lacinia mobilis of the left mandible have fewer teeth. Although only a few specimens are known, the body of females also seems to be more elongate and the pereon less globular than found in Hyperia . Other than Hyperia it does not resemble any other genus of Hyperiidae and thus a new genus is proposed here to accommodate it.