Psammogammarus wallacei Vonk, Hoeksema & Jaume 2011

Adult male. Eyeless. Body (Fig. 2A) elongate and slender, unpigmented, somites devoid of relevant armature or sculpturing except for robust seta present on posteroventral angle of urosomite III (Fig. 8B). Head lacking rostrum; lateral lobes evenly rounded; antennal sinus hardly indicated, unnotched. Pereiopodal coxae narrow, hardly overlapping. Epimeral plates (Fig. 8A) with acute posteroventral angles, that of epimeral plate III more produced than rest; armature of ventral margin of plates (flagellate robust setae) as 1-3-3 or 1-2-3; posterior margin of plates each with single simple seta implanted adjacent to posterodistal angle. Antennule short, about half as long as body length (Fig. 2A). Peduncle segments relative length as 100: 77: 43; proximal segment provided with stout flagellate robust seta subdistally on ventromedial margin (Fig. 2B, C). Main flagellum about as long as peduncle, with armature on medial and lateral margins exactly as depicted; armature of two most proximal articles and terminal article differing from rest as figured. Accessory flagellum 2-articulate, overreaching distal margin of proximal article of main flagellum. Antenna (Fig. 2A, D) shorter, about three-quarters length of antennule. Gland cone slender, straight, pointing anteriorly; relative length of three distal segments of peduncle as 48: 100: 88. Flagellum short, slightly longer than distal segment of peduncle. Labrum trapezoidal. Paragnaths (Fig. 8D) with distinct, well developed inner lobes; outer lobes each with 4 stout tricuspidate setae on tip. Left mandible (Fig. 3A) incisor with 5 rounded teeth, lacinia with 4 teeth; spine row composed of 7 elements; molar columnar, molar seta shorter than right mandible counterpart. Palp 3-segmented, distal segment shorter than middle segment, provided with 6 stiff simple setae along medial margin but not in a regular row; middle segment with three flagellate stiff setae on medial margin. Right mandible (Fig. 3B) differing from left counterpart in almost quadrate lacinia with distal margin finely denticulated except for two larger rounded denticles at one angle; spine row comprising 5+3 elements. Maxillules (Fig. 3C) symmetrical, coxal endite (= inner plate) with 4+2 marginal setae; basal endite (= outer plate) with 9 robust setae distally, 4 of which bicuspid and placed conforming an inner row, rest denticulated and conforming outer row. Endopod (= palp) faintly 2-segmented, distal segment slightly expanded distally, with 4 broad, short denticulated robust setae on distal margin, and 1–2 denticulated setae subdistally on outer surface of segment. Maxilla (Fig. 3D) inner plate with oblique row of 4 plumose setae; distal margin with 4 pinnate setae and 4 simple setae with blunt tip provided with pore; two pinnate setae subdistally on medial margin of plate as figured. Outer plate distal margin with 10 simple setae with blunt tip, two shorter, ordinary simple setae, plus seta with a few pinnules proximally as figured. Maxilliped (Fig. 3E) basal endite (= inner plate) subrectangular, straight distal margin provided with three short subtriangular robust setae, two of which smooth, third with two rounded denticles; other armature on endite comprising subterminal oblique row of 5 pinnate setae on anterior surface, and three simple setae subterminally on posterior surface. Ischial endite (= outer plate) with convex outer margin; straight inner margin with 6 simple setae with blunt tip; distal margin oblique, with 4 pectinate robust setae. Other relevant armature on endite comprising submarginal row of 4 simple setae with blunt tip running subparallel to inner margin on posterior surface. Merus-dactylus (= palp) as in Fig. 3E, F, with claw (= dactylus+unguis) as long as propodus. Coxal gills on gnathopod II and pereiopods III-VI (Fig. 2A); gills II (Fig. 4D) and III-IV (Fig. 5B) each longer than basis of corresponding pereiopod, gills V-VI (Fig. 6A, B) shorter than basis; gill VI reduced. Gill II narrow, sausage-shaped, rest ovoid; all provided with short stalk. Gnathopod I (Fig. 4A-C) propodus clearly longer than carpus, elongate (1.9 times as long as broad), with parallel anterior and posterior (= lateral and medial) margins. Palm margin oblique, convex, finely serrated, with submarginal row of about 10 short flagellate robust setae along medial side. Palm angle not produced, ordinarily with two unequal flagellate robust setae, but extraordinarily with 3–4 (Fig. 4C). Coxa (Fig. 4B) slightly broader than long, with evenly rounded anterior margin; posterior margin slightly excavated. Gnathopod II (Fig. 4D) propodus elongate (1.9 times as long as broad) with subparallel anterior and posterior margins; palm angle hardly produced, with two unequal flagellate robust setae; palm margin (Fig. 4E) finely serrated, half adjacent to palm angle hardly excavated, with submarginal row of ca. 9 short flagellate robust setae along medial side. Merus posterodistal angle slightly produced, but lacking pointed tip. Carpus triangular, short, less than half length of propodus. Pereiopods III-IV (Fig. 5A, B) subsimilar, with coxae much broader than long, subrectangular, expanded anteriorly into evenly rounded lobe and posterior margin not excavated, straight. Pereiopods V-VII unequal in length, P5 (Fig. 6A) shortest, P6 (Fig. 6B) longer than P7 (Fig. 6C). Basis of each pereiopod only moderately expanded, with subparallel margins and with posterodistal angle distinct but not overhanging. Nail (dactylus + unguis) of P6 more slender and clearly longer than those of P5 and P7. Unguis reduced in all limbs. Coxa V with expanded, evenly rounded anterior lobe. Pleopods progressively shorter towards posterior, biramous, rami multi-articulate, apparently similar at first sight, but differing remarkably in minute details as follows. Protopods each with two retinacles, and with flagellate robust seta placed proximo-laterally on anterior surface of segment (pleopods I-II; Fig. 7A, B), or on lateral margin (pleopod III; Fig. 7D). Protopod of pleopod I devoid of any other armature; protopod of pleopod II with seta on anterodistal margin (Fig. 7B, C); protopod of pleopod III with seta on distolateral angle (Fig. 7D, E). Short, subtriangular process protruding posterodistally on each protopod, those on pleopods I-II with smooth surface (Fig. 7A, C), that on pleopod III microspinulate (Fig. 7E). Proximal article of endopod of pleopod I with one reduced smooth seta proximally on anterior surface (Fig. 7A); seta absent from rest of pleopods (Fig. 7B, D); proximal seta on medial margin of article apparently unicuspid (Fig. 7A), vs. seta bifid on pleopods II-III (Fig. 7C, E). Proximal article of exopod of pleopod II sexually-dimorphic: proximal two-thirds of medial margin with row of short, curved denticles with rounded tip, and row of ordinary setules along distal third of margin (Fig. 7B, C). Uropods I-II strongly dissimilar in length (Fig. 8B), biramous, exopod shorter than endopod, and with margins of both protopod and rami provided with flagellate robust setae. Uropod I (Fig. 8C) protopod much longer than exopod, provided with stout basofacial robust seta and with pair of robust setae on each posterodistal angle, medial pair appreciably longer than lateral counterpart. Posterolateral margin of segment provided with 4 short robust setae, posteromedial margin with three. Exopod with 5 distal robust setae and with robust seta on posterolateral margin; endopod with 4 distal setae and with robust seta about midway on both margins, aside of reduced simple seta on anteroproximal surface of segment. Uropod II (Fig. 6D) protopod about as long as exopod, with one robust seta on distolateral angle and with transverse row of 4 robust setae on distomedial angle (see Fig. 8B). Margins of segment each with single robust seta about midway. Exopod with 4 distal robust setae and robust seta about midway of posterolateral margin; endopod with 5 distal robust setae and two robust setae along posteromedial margin. Lateral margin of exopod and medial margin of endopod each minutely serrated (Fig. 6D). Uropod III (Figs 2A; 5C) strongly elongated, all segments somewhat flattened, foliaceous, provided with numerous flagellate robust setae as figured. Protopod short; proximal segment of exopod about 2.2 times as long as protopod, distal segment exceedingly longer (1.5?) than proximal segment. Endopod elongate, pointed, much longer than protopod and attaining about 57% length of proximal exopodal segment; one robust seta on tip. Telson (Fig. 6E) cleft almost until base, slightly longer than broad, tip of each lobe shallowly excavated, provided with simple seta. Three flagellate robust setae on each lobe, one placed subdistally while other two proximally on lateral margin as figured. One penicillate seta disposed adjacent to one of lateral robust setae as in Figs 8B and 6E. Pair of long setae on dorsal surface of each lobe as figured. Adult female. As male except for gnathopod II, which displays more elongated carpus and evenly convex palm margin of protopod (compare Figs 4D, E and 5D). In addition, proximal article of exopod of pleopod II unmodified. Oostegites present on gnatopod II and pereiopods III-V, linear, provided with few sparsely set marginal setae (Fig. 5D). Condition of uropod III unresolved since none of two females collected retained it.