URSTYLIDAE, Riehl & Wilson & Malyutina, 2014

Riehl, Torben, Wilson, George D. F. & Malyutina, Marina V., 2014, Urstylidae - a new family of abyssal isopods (Crustacea: Asellota) and its phylogenetic implications, Zoological Journal of the Linnean Society 170 (2), pp. 245-296 : 254-255

URSTYLIDAE FAM. NOV.

Zoobank registration urn:lsid:zoobank.org:act:5FAFBD95-32CB-4C73-B904-3DA4C73447B5

Type genus

Urstylis gen. nov., designated here.

Composition

Urstylis gen. nov.

Family diagnosis

Cephalothorax spatulate, widening posteriorly, prognathous. Pleotelson anterior margin ‘stalked’, not directly adjacent to preceding pereonites. Antenna merus and carpus both subsimilar or shorter than podomeres 1–4 together; merus shorter than carpus. Antennal scale present as rudimentary, unarticulated spine. Maxilliped palp article 2 width subequal to article 1 width. Pereopodal coxae setose. Pereopod I carposubchelate, more robust and shorter than pereopod II; ischium with dorsal setose lobe, carpus trapezoidal, widening distally, with dorsal and ventral margin lengths subsimilar. Pereopods II−VII similar in size and shape. Posterior pereopods dactylus posterior (ventral) claw scale-like, flattened in crosssection; distal sensillae basally enclosed between dorsal and ventral claws. Male pleopod I medial lobes ventrally ‘overriding’ lateral lobes. Male pleopod II exopod thick and slightly longer than wide. Pleopod III exopod bisegmented with clear articulation; distal article much narrower than proximal article, inserting distomedially; projecting near distal tip of endopod. Uropod insertions at posterolateral pleotelson margin; uropods long, styliform, exopod rudimentary (assumed for Urstylis thiotyntlus gen. et sp. nov.).

Family description

Body elongate, more slender in male than in female (assumed for U. thiotyntlus ). Cephalothorax spatulate, with anterolateral insertions of antennulae and antennae; lateral margins setose. Pereonal tagmosis 4:3. Pereonites 1–4 lateral margins subparallel, anteriorly rounded, and posteriorly abruptly narrowing (fossosome absent); articulations fully expressed, movable; lateral margins setose, pereonal collum absent. Coxae inserting lateroventrally, visible in lateral view. Posterolateral margins of pereonites 5–7 rounded, lateral margins setose. Pleonite 1 tergal and sternal articulations with pleotelson present, dorsally with two setae at posterior tergite margin. Pleotelson subrectangular, elongate, lateral outline with weak waist separating longer anterior and shorter posterior convex margin, posterior margin concave at uropod insertions; apex convex, broadly rounded, ventrally with setal ridges absent; longitudinal trough absent. Anal opening parallel to frontal plane. Marsupium with four pairs of oostegites (pereopods I– IV), oopore lateroventrally ( Fig. 1 ). Antennula and antenna orientated anteriorly. Antennula of six articles, axis inflected at articulation of elongate articles 1 and 2, article 1 longest and widest; aesthetascs simple, tubular. Antenna with six podomeres, precoxa– ischium squat, ischium elbow joint, article insertions at right angles, basis with unarticulated small spine (probably homologous with scale), flagellar articles each with several thin, tubular aesthetascs, more in male than in female. Mandible without palp, incisor process multidentate, gracile, much thinner than basal region; lacinia mobilis grinding or crushing, multidentate, right lacinia clearly smaller than left lacinia, left mandible incisor with dorsal cusps forming right angle to distal and ventral cusps. Maxilliped basis medioventrally with seta absent; palp narrower than basis, wider than endite, first article distolateral lobe present, fourth article distomedial lobe present. Pereopodal coxae ringshaped, setose; dactyli with two claws inserted terminally; ventral claw much smaller than dorsal claw, scale-like, basally enclosing distal sensillae.

Pereopod I modified, shortest and broadest, ischium with dorsal setose lobe, carpus broader distally, laterally flattened; pereopods II–VII similar in size, shape, and setation, getting slightly more slender from II to VII, carpus-propodus elongate, cylindrical, lengthening from pereopods II to VI. Opercular pleopods distally setose; setae asetulate. Male pleopod I proximally with subparallel lateral margins, distally widening, with no distolateral horns, lateral lobes not extending distally beyond medial lobes. Male pleopod II protopod slender, tapering distally, narrower than pleopod I. Female operculum stout, ovoid, without keel, broadly rounded distally, ventrally overlapping the lateral margins of the pleopodal cavity, distally not reaching anus. Pleopod III protopod and endopod subequal in length and width, endopod with three plumose distal setae, setae longer than endopod; exopod biarticulate, with distinct articulation, lateral outline not continuous, with lateral fringe of fine setae mostly restricted to proximal article, distal article length approximately 0.33 times proximal article length, approximately 0.5 times proximal article width, with conspicuous subterminal seta shorter than distal article. Pleopod IV exopod subequal in length to endopod, elongate, flat, with lateral fringe of fine setae, setae longer than exopod width, distally with plumose seta, seta slightly smaller than exopod. Pleopod V uniramous. Uropod long, styliform, biramous, exopod squat, minute, wider than long, with one or few setae; protopod exceeding the length of the pleotelson (known only in Urstylis zapiola and Urstylis solicopia manca).

Distribution

Species of Urstylidae have been found exclusively on abyssal soft sediments. They are known to occur in the western South Atlantic, near manganese nodules in the tropical North Pacific, and in the vicinity of hydrothermal vents near the Galapagos.

Figures

Figure 1. Urstylis zapiola gen. et sp. nov., adult female paratype USNM 1208014, ventral view of pereonites (Per) 4, 5, showing arrangement of reproductive organs, internal oostegite and gut; legs omitted for clarity. Scale bar = 0.1 mm.