976


Journal of Paleontology 91(5):968–980


(male) of the antennular peduncle; anterior end rounded with apparent segmentation (Figs. 3.1, 6,1, 7.4). Labrum pyriform, more or less symmetrical, half as wide as


long (Fig. 3.1, 6.1, 7.4). Mandibles well developed (Figs. 3.1, 6.1, 7.4). Three-segmented palp, first article shortest; second article slightly longer than wide; third article about twice as long as broad. Third article of the right mandible with serrate outer margin. Gnathobasic processes of the left and right mandibles are not discernable; only the molar process is tenuously observed as a flat platelike structure provided with spines. Maxillule difficult to define, without any trace of separation


between the sympod and the lobes (Fig. 5.5). Maxilla exopod is seen as a plate attached to the outer side of the basis, with the outer margin markedly convex; two basal endites and endopod probably two-segmented (Figs. 3.2, 6,1, 7.5). The first thoracopod differs considerably from the remain-


ing thoracic appendages: modified as short maxilliped without exopod (Figs. 3.2, 6.1, 7.6). Endopod short and robust; apparently with four segments not clearly delineated, dactylus fused with nail to form a claw. Female second to eighth thoracopods with oostegites


without any trace of structures (Figs. 5.3, 5.4, 6, 7.15, 7.16). Uropod exopod 3-articulate, longer and broader than endopod, extending slightly beyond telson apex; distal two articles about one third length of the basal article. Telson short, about sub-equal in length to the last


abdominal somite, twice as long as broad (Figs. 3–6, 7.15, 7.16); lateral margins converging distally; apex of telson bidentate; telson cleft to about one-third of its length.


Etymology.—This species is named after “El Pinetell,” the bed of Alcover limestones unit (Catalonian) in which the species was found.


(Fig. 3.2). Second thoracopod longer than first one, without epipodite and with exopod and oostegite (Figs. 3.2, 6.1). Endopod with preischium, ischium and merus fused, twice as long as broad; unsegmented carpopropodus three times as long as greatest width, tapering somewhat distally; dactylus short with pointed nail. Exopod shorter than endopod with basal plate and 6-segmented flagellum (Fig. 7.6). Third to fourth thoracopods with endopod elongated and


robust, much longer than the other thoracopods (Figs. 3.1, 6.1, 7.9, 7.10). Endopod preischium difficult to define, ischium and merus subequal in length; carpopropodus 4-segmented, longer than merus; dactylus with pointed distal nail. Exopod apparently much shorter than endopod. Fifth thoracopod with endopod about one half longer than


the fourth (Figs. 3.1, 6.1, 7.11). Endopod preischium difficult to define, ischium and merus subequal in length; carpopropodus 4-segmented, longer than merus; dactylus with pointed distal nail. Exopod apparently much shorter than endopod. Sixth to eighth thoracopods quite different from the rest,


with preischium and ischium more or less fused, merus short, undivided carpopropodus more or less swollen anteriorly; dactylus with pointed distal nail (Figs. 3.1, 6.1, 7.12, 7.13, 7.14). Exopods apparently much shorter than endopods. Eighth thoracopod exopod with basal plate and 5-segmented flagellum (Fig. 7.14). Female pleopods uniramous, reduced to unsegmented


Remarks.—The placement of Aviamysis n. gen. in the order Mysida family Mysidae, as defined by Wittmann et al. (2014) seems beyond doubt. This assignment is supported by the presence of eight thoracopods without branchiae and with endopods divided in a number of segments, female with seven pair of oostegites, female with five rudimentary pleopods, and the presence of statocysts on the endopod of uropods. Its taxonomic situation among the diverse subfamilies included in the Family, however, is relatively ambiguous. The family Mysidae is divided at present into ten


subfamilies (Meland et al., 2015), of which, Aviamysis has a clear affinity to the subfamily Boreomysinae. Boreomysinae are characterized by the following: a smooth outer margin on the antennal scale ending in non-articulate spine; seven pairs of oostegites; endopods of the third to the eighth thoracopods with carpus distinct and propodus usually divided into two or three subsegments; pleomeres without projecting pleural plates; females with pleopods reduced to unsegmented rods; exopod of uropods divided by a rudimentary, transverse articulation; statocyst containing a small, non-mineralized statolith; and telson with apical cleft (Tattersall and Tattersall, 1951;Wittman et al., 2014). Two extant genera are included in this sub- family: Boreomysis Sars, 1869, and Birsteiniamysis Tchindo- nova, 1981. In accordance with this definition of the subfamily, the


lobes (Figs. 5.1, 5.2, 6.1), increasing in length from first to fourth and fifth pairs; fifth pleopod extending to posterior end of posterior abdominal somite. Uropod endopod slender, with statocyst, not extending to


telson apex, outer margin sinuous (Figs. 3–6, 8.2). Statocyst trace apparently circular with a maximum diameter of ~1mm,


placement of Aviamysis in the Boreomysinae seems reasonable. In particular, different morphological characters traditionally regarded as plesiomorphic features between the order Mysida, as discussed by Schlacher et al. (1992), are present on the subfamily Boreomysinae (e.g., subdivided exopod of uro- pods and seven pairs of oostegites). The remaining Mysidae taxa usually have two or three pairs of oostegites (Wittmann et al., 2014). An additional shared character state in the basal taxa


Petalophthalmidae, Boreomysinae, and Rhopalophthalminae (and also in the more derived Siriellinae) is the presence of a suture in the exopod of uropod. With reference to molecular phylogeny (Meland and Willassen, 2007), the divided exopod gains support as an ancestral state in Mysida evolution (Meland et al., 2015).


Figure 7. Detailed reconstructions of the main appendages of Aviamysis pinetellensis n. gen. n. sp.: (1, 3–15) PI1, holotype female, (2, 16) PI47, male paratype. (1) Female antennule; (2) male antennule; (3) antenna; (4) labrum, mandibles and the lanceolate-shaped median ventral projection arising from front of the labrum; (5) maxillule; (6) maxilla; (7) 1st thoracopod; (8) 2nd thoracopod; (9) 3rd thoracopod; (10) 4th thoracopod; (11) 5th thoracopod; (12) 6th thoracopod; (13) 7th thoracopod; (14) 8th thoracopod; (15) female telson and uropods in ventral view; (16) male telson and uropods in dorsal view. Scale bar 1–14=0.5mm; scale bar 15, 16=0.2mm.


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