Seborgia relicta Holsinger 1980

Seborgia relicta Holsinger

MATERIAL EXAMINED.—TEXAS. HAYS COUNTY: Artesian well in San Marcos, holotype (USNM 171146), 23 Sept 1975. Paratypes from the same locality as follows: 45 and 10 from continuous sampling between 14 May 1974 and 16 Dec 1975.

DIAGNOSIS.—A very small subterranean species distinguished from Seborgia minima Bousfield (the only other species in the genus) by a distinct rostrum, lacking inferior antennal sinus, gnathopods of unequal size (in both sexes), proportionately longer ramus of uropod 3, produced and acuminate posterior corners of pleonal plates, and lacking spines on the telson. Largest male, 1.5 mm; largest female, 1.9 mm.

DESCRIPTION.—Sexes generally similar. Without eyes and pigment, of subterranean facies. Head with distinct rostrum; interantennal (lateral) lobe not produced, broadly rounded; inferior antennal sinus lacking. Antenna 1: approximately 33 percent length of body, about 25 percent longer than antenna 2; peduncular segment 1 shorter than combined lengths of segments 2 and 3; primary flagellum with 4 segments, with few esthetascs; accessory flagellum 2-segmented, very short, only ¼ to ⅓ length of 1st flagellar segment, terminal segment rudimentary. Antenna 2: peduncular segments 4 and 5 subequal in length, both lacking spines; flagellum with 3 or 4 segments, most bearing tiny esthetascs. Upper lip broadly rounded, apical margin incised. Mandible: molar weak, conical, with apical setule; incisor and lacinia mobilis well developed; spine row with 3–4 spines; palp segment 2 with 2–4 setae on inner margin distally, segment 3 with 3 apical setae and pilose inner margin. Maxilla 1: inner plate small, tapering distally, lacking apical seta(e); outer plate with 7 very weakly serrate, apical spines; palp with 3 stiff setae on apex and row of very fine setae on outer margin. Maxilla 2 having single plate with broad base and 3 or 4 stiff setae apically. Maxilliped: inner plate weak, sublinear, armed with 2 stiff setae apically; outer plate much broader but not extending to base of palp segment 3, apex rounded with mostly fine setae, inner margin with few stiff setae (or slender spines ?); palp weakly armed with few setae, segment 2 the longest. Lower lip: inner lobes a little lower than, but as broad as, outer lobes; lateral (mandibular) processes tapering distally.

Gnathopods subchelate, not sexually dimorphic. Propod of gnathopod 1 large, strong, widest distally, nearly 2 times size of 2nd propod; palm transverse, a little shorter than posterior margin, bearing few setules; defining angle produced into narrow boss with short, stout terminal spine; posterior margin elongate, uneven, medially piliferous; media setae lacking. Dactyl of gnathopod 1 long and slender, nail short. Segment 5 of gnathopod 1 very short, segment 2 long and slender. Coxal plate of gnathopod 1 deeper than corresponding body segment, longer than broad, margin with 4–5 setae. Propod of gnathopod 2 widest distally, palm transverse, 60–75 percent length of posterior margin, bearing few setules; defining angle distinct but not produced into boss, bearing short, stout spine; posterior margin elongate, uneven, medially piliferous; inferior medial setae of about 2. Dactyl of gnathopod 2 similar to that of 1st gnathopod. Segment 5 of gnathopod 2 not elongate but about 50 percent length of propod, segment 2 long and slender. Coxal plate of gnathopod 2 deeper than corresponding body segment, subrectangular, margin with variable number of setae, apparently depending on age of specimen. Coxal plate of pereopod 3 very deep, subrectangular, extending approximately 70 percent length of basis (segment 2), margin with about 3 setae. Coxal plate of pereopod 4 deeper and proportionately broader than that of pereopod 3, extending about 90 percent length of basis, margin with 3–6 setae. Pereopod 7 subequal in length to, or slightly longer than, pereopod 6, 45–50 percent length of body, longer than pereopod 5. Pereopods 5–7 very weakly armed; posterior margins of bases unevenly serrate and broadly expanded distally; dactyls of 6 and 7 about 45 percent length of corresponding propods, that of 5 about 55–60 percent length of corresponding propod. Coxal gills pedunculate, suboval, on pereopods 2–6. Sternal gills lacking. Brood plates of sexually mature female short, sublinear, with 2 or 3 long, apical setae.

Pleonal plates: posterior corners weakly produced, acuminate; posterior and ventral margins without setae or spines. Pleopods short, decreasing slightly in overall length posteriorly; peduncles with 2 coupling spines each on inner margin distally; rami with few segments, outer slightly longer than inner. Uronites free (not coalesced), without spines. Uropod 1: inner ramus a little longer than outer ramus and peduncle, armed with 2 short spines near distal end; outer ramus with 1 or 2 short spines near distal end; rami lanceolate, usually with narrow marginal incisions near distal spines; peduncle with 2 spines posterodistally. Uropod 2: inner ramus about 50 percent longer than outer ramus and peduncle, armed with 2 short spines near distal end; outer ramus with 1 short spine near distal end; rami lanceolate, with or without marginal incisions; peduncle with 2 spines posterodistally. Uropod 3 uniramous; peduncle about 2/3 length of ramus; ramus lanceolate, without spines but sometimes with apical seta. Telson a little longer than broad, gently tapering distally, without setae or spines; apical margin entire, subrounded.

VARIATION.—Larger, and presumably older, specimens have a few more setae on the coxal plates and bases of the gnathopods and pereopods 3 and 4, and on the bases of pereopods 5–7. In larger specimens there is also a trend toward elongation of the gnathopod propods and narrowing of the gnathopod dactyls.

TYPE-LOCALITY.—The artesian well in San Marcos, Hays County, Texas.

DISTRIBUTION AND ECOLOGY.—This species is known only from its type-locality where, based on continuous sampling between 14 May 1974 and 16 December 1975, it represented 1.11 percent of the total amphipod fauna collected (Table 2). Of the 56 specimens obtained, 46 were females and 10 were males, giving a sex ratio of 4.6 to 1 in favor of females. Out of the 46 females, 23 were ovigerous and 11 had setose brood plates but were not ovigerous. Ovigerous females were collected during all seasons of the year, and this fact, combined with the high percentage of sexually mature females, probably indicates continuous breeding throughout the year.

The clutch size of the 23 ovigerous females, ranging in size from 1.2 to 1.9 mm (X=1.50, SD=0.20, C.V.=0.13) is summarized as follows: N=23, range=1–3 eggs or embryos, X=1.43, SD=0.66, C.V.=0.46. Larger females (i.e., over 1.5 mm) were observed to generally brood more eggs than smaller females. The embryos measured approximately 0.35 mm in diameter. Males were also collected during all seasons of the year but were far less abundant and smaller than females. The size range for males was 1.0 to 1.5 mm. Juveniles, which by inference would be in the size range of 0.35 to 1.0 mm, were not found in the samples, but this might be explained by a loss through the sampling net of such tiny specimens or by a single molt upon emerging from the brood pouch that allows for a spurt of growth to 1.0 mm.

ETYMOLOGY.—The epithet relicta is from Latin, meaning “relict.”

TAXONOMIC