The Petalophthalmidae (Crustacea: Mysida) of the ANDEEP I–III expeditions to the Antarctic deep sea, with description of a new species and first record of photophores in mysids

Abstract

̶ Three ANDEEP expeditions yielded five Petalophthalmidae species of the genus Hansenomysis in 1030-3683 m depth on the floor of the Southern Ocean. Hansenomysis pseudophthalma sp. nov. is distinguished by features of the carapace, antenna, and telson. A fully adult specimen is first described for H. chini. A world key to the species of Hansenomysis is given. Unlike certain previous interpretations, the dactylus of thoracic endopods 3-5 has a single claw opposing a pair of modified paradactylary setae. Propodus and dactylus 6-8 are separate, not fused, and bear a smooth nail in all Hansenomysis species examined. Juveniles were available in three species and start with two bulb-shaped eye rudiments inside a common cuticular sheath forming a transverse bar. The bulbs then flatten, although a bulb-like formation persists until the adult stage; no eyeplate is formed. The carapace bears hepatic bulges resembling eyes in adult H. pseudophthalma and H. chini. The distal hyaline coat of bulges possibly represents lenses in H. pseudophthalma and H. sorbei. The modification of bulges is indicative of photophores, described for the first time here in the family Petalophthalmidae. The exclusive occurrence of mature photophores in adults points to possible role in reproductive behavior. http://zoobank.org/urn:lsid:zoobank.org:pub:8530B295-CF00-413D-830C-C41 C685FA467