Urohaustorius yurrus Barnard & Drummond 1982

Urohaustorius yurrus

DIAGNOSIS.—Dorsolateral armament rows on articles 1 and 2 of antenna 1 and article 4 of antenna 2 mixing spines and setae. Armament row on article 4 of antenna 2 even. Accessory flagellum not reduced. Main flagellar articles of male antenna 1 thickened, aesthetascs 2–5 per article and present on basal articles, article 5 of male not bulbous. Coxa 1 not larger than coxa 2, both bearing only tiny setules. Spines on dactyl of pereopod 5 set singly in tandem. Dactyls of pereopods 6–7 well developed. Article 2 of pereopod 7 with 2 (rarely 3) posteroproximal setae. Male sternite 6 with short, broad, blunt ventral protuberance. Epimeron 2 bearing blunt, small to obsolescent tooth, with 2–3 facial setae in horizontal row. Tooth of epimeron 3 small to obsolescent. Inner rami of uropods 1–2 much shorter than outer rami. Dorsolateral margin of peduncle on uropod 2 with stout spine(s). Apicolateral corner of peduncle on uropod 3 with stout spines, outer ramus with setae and spines laterally on article 1. Telson entire, bearing short apical setules.

GENERAL DESCRIPTION.—In contrast to U. urungari, more and stouter spines on article 1 of antenna 1, especially in female (generally E, 3S, 2P); more spines on article 4 of antenna 2, especially in female; much narrower article 5 of antenna 2 in males, both adult and subadult; narrower article 6, and longer and thinner dactyl, of pereopod 5; different form of male process on sternite 6; article 2 of pereopod 7 with most commonly 2 (exceptionally 3) proximoposterior marginal setae, in contrast to the usual 3 (occasionally 2) in U. urungari; greater number of spines (usually 4, even in subadults) on the posterodorsal corner of uropod 3 peduncle (U. urungari = 2, exceptionally, 3); presence of spines as well as setae on outer ramus of uropod 3 in females as well as males; more sharply angled bulge medially at base of outer ramus; less massively glandular, shorter, and apically much more broadly rounded telson, reaching less than half way along the outer ramus of uropod 3.

DESCRIPTION OF MALE.—Holotype male “r,” 3.00 mm: Probably subterminal; head about 70% as long as wide, rostrum about 23% as long as remainder of head. Primary flagellum of antenna 1 with 10 articles, aesthetasc formula = 0–0–1–2–2–2–2–2–1–0; accessory flagellum 7-articulate, not shortened; all short elements on article 2 of antenna 1 very thin. Facial formula of mixed spines and setae on article 1 of antenna 1 = E, 3S, 2P; on article 4 of antenna 2 = P, PSE–PSESESESE–SEESEESESESESESESESS; on article 5 = SESESEESESESS; article 5 of antenna 2 about 72% as long as article 4, 40% as wide as long; article 3 with 3 facial setae; flagellum 9-articulate.

Right incisor simple, left with 2 weak teeth, choppers on molars with 4 cusps; formula on right and left third palpar articles = 1–3–6–1. Inner plate of maxilla 1 with 1 short apical seta, 1 large apicomedial seta; outer plate with 11 spines. Inner plate of maxilla 2 with 3 medial setae. Inner plate of maxilliped with 4 medial setae, outer plate with 1 apicolateral seta; palp article 2 with 5 setae in facial row, article 3 with 2 setae in facial row.

Coxa 1 broadly subtriangular; coxa 2 similar, but apex blunter; coxa 3 with long ventral setae all in posterior half, posterior margin naked; coxa 4 with 2 long ventral setae, 3 setules and 4 long or medium posterior setae and 5 setules.

Setal and spine formulas for pereopod 3 = 3, 5, 2–1–1–1, 5 + 4 + 1; on pereopod 4 = 3, 4, 2–1–1–1–1–1, 4 + 4 + 1; posterior margin of articles 5–6 with single row of mostly even large serrations. Article 2 of pereopods 5–7 with progressively medium to sparse setal densities posteriorly, long setae = 8–4–2 respectively; article 2 of pereopod 5 lacking mediofacial brush, dactyl with 5 spines in tandem.

Peduncular spine formulas on pleopods 1–3 = 2 and 1, 2 and 0, 2 and 1; segmental formulas = 17–11, 14–10, 14–12 (not proliferate); basal setal formulas = 8–1–2–3, 2–1–1–1, 5–1–1–2.

Epimeron 2 with 3 setae in left horizontal row, 2 in right.

Lateral margin of peduncle on uropod 1 with 7 setae, apicolateral corner with 1 setule; of uropod 2 with 1 disjunct lateral spine and 2 apicolateral spines; dorsal setae = 1 and 2; setae of rami = 7–5 and 8–3; inner rami extending 58% and 50% along outer. Apicolateral corner of peduncle on uropod 3 with 3 spines (1 fewer than normal for this species), medial margin with 1 weak seta; ventromedial apical row with about 8 mixed setae; spine formula on lateral margin of article 1 of outer ramus = e, SE, SE, Ee; article 2 about 23% as long as article 1.

Telson about 1.1 times as wide as long, entire, broadly rounded apically; telsonic formula = 1, 2P, 1, P, 1, 1.

Lateral gland clusters well developed in pleonites 3–6, uropod 3 and telson.

Male “p,” 2.38 mm: Presumably terminal adult. Modified first antenna of 10 articles, basal 4 or 5 thickened, aesthetascs long, formula = 5, 4, 4, 5, 5, 5, 4, 2, 2, 0; reduced accessory flagellum of 6 thin articles. Article 1 of antenna 1 with 1 thin spine (spine-seta?) and 2 short, thicker spines + 2P; fine dorsal spines on article 2 = 6 short to medium + 2 long apical. Article 5 of antenna 2 half as wide as long, 70% as long as article 4; facial spine-seta formula for article 4 = P, P, E, P–SESESSS–PSESESSESESESS/P, SESESSS–PSSESESSESESS; for article 5 = SSE, SSE, SE, SE, SS/SESESESESESS. Most proximal seta of maxillary palp distinctly disjunct from 2 apical. Setal and spine formula for pereopod 3 = 3, 5, 2–1–1–1, 4 + 4 + 1; for pereopod 4 = 3, 5, 2–1–1–2, 4 + 4 + 1.

Dactyl of pereopod 5 with 4/5 spines in tandem, most proximal disjunct. Sternal projection well developed, short, broad-based, blunt. Pereopod 7 with 2 proximal setae on posterior margin. Peduncular spine formulas of pleopods 1–3 = 2 and 1, 2 and 0, 1 (!) and 0; segmental formulas = 14–10 (proliferating), 11(+)–9, 12–10; basal setal formulas = 3(+)–2–1–3, 4–1–0–1, 5–1–1–3. Epimeron 2 with blunted cusp, 3 large facial setae in horizontal row plus 2 much shorter setae, 1 dorsal, 1 ventral, to the third seta. Epimeron 3 with well-developed small cusp, 3 ventral marginal setae, posteriorly excavate, posterior margin with 3 setules.

Peduncle of uropod 1 with 6 lateral, 6 medial, and 3 large dorsal setae; outer ramus with 2 clear apical and 1 subapical setae, in addition to marginals. Peduncle of uropod 2 with 2 midlateral spines closely juxtaposed and 2 apical spines in close tandem; outer ramus, in addition to marginals, with 1 clear central apical and 2 subapical setae, 1 on each side. Peduncle of uropod 3 with 4 apicolateral spines; lateral spine-seta formula on article 1 of outer ramus = ES, ES, Ee/ES, ES, Ee; article 2 about 20% as long as article 1 and 80% as wide as long. Telson about as wide as long, broadly rounded, glandular, extending about 20% along outer ramus of uropod 3; telsonic formula = 2P, 1, P, 1, 1/2P, 1, P, 1.

Male “o,” 2.28 mm (sternite illustrated): Antenna 1 flagellum of 10, accessory flagellum of 7, articles; aesthetasc formula = 0–0–2–2–2–2–2–1–1–0/0–0–1–2–2–2–2–1–1–0. Article 5 of antenna 2 about 40% as wide as long and 48% as long as article 4; flagellum of 8 articles. Epimeron 2 with blunt cusp and 2 horizontal setae. Epimeron 3 with strong cusp.

Subadult male “s,” 2.05 mm: With short penial processes and small sternite 6 projection. Antenna 1 flagellum of 8 articles; accessory of 5; aesthetasc formula = 0–2–2–2–2–1–1–0. Article 5 of antenna 2 about 45% as wide as long and 74% as long as article 4. Article 2 on outer ramus of uropod 3 about 34% as long as article 1. Telson 84% as tall as wide; formula = 2P, 1, P, 1.

DESCRIPTION OF FEMALE.—Ovigerous female “n,” 2.40 mm: Formulas on article 1 of antenna 1 = E, 3S, 2P/E, 2S, 2P; all elements on article 2 very thin, 3 of them short; flagellum of 7 articles; accessory of 5; aesthetascs very long but no more than 2 per article. Article 3 of antenna 2 with 2 facial spines; formula for article 4 (even) = P, P, E–PSSESESS–PSESESSESEESESS; on article 5 = SSESESESESESS.

Coxa 3 with 6 long ventral setae, 1 posterior. Coxa 4 with 4 long ventral setae, 4 posterior. Formula for pereopod 3 = 3, 3, 2–1–1, 4 + 4 + 1; for pereopod 4 = 3, 4, 2–1–1–1, 4 + 4 + 1. Dactyl of pereopod 5 with 4 spines in tandem, article 2 with 7 long posterior setae; of pereopod 6 with 4; of pereopod 7 with 2 posterodorsal marginal setae, slightly thickened.

Epimeron 2 with 2 setae.

Uropod 1, lateral setae of peduncle = 6 + 2 setules, dorsal = 2; rami = 6 and 4, left side damaged. Uropod 2 peduncle with 1 small midlateral spine plus 2 others of normal size, including apical, all 3 in tandem; dorsal setae = 2(1); ramal setae = 6 and 3. Peduncle of uropod 3 with 4 apicolateral spines: inner ramus like male; lateral spine-seta formula = ES, EE, Ee/S, ES, Ee, spines very fine, not short and thick. Telson almost as long as broad, formula = 2P, 1, P, 1.

Ovigerous female “g,” 2.20 mm: Closely resembling the above, but with 1 short plumose seta fewer on article 2 of antenna 1 (illus.); 7 marginal setae on outer ramus of uropod 1; 1 lateral and 1 apical spine and 2 apical setae on right peduncle of uropod 2; 3 apical spines on left peduncle of uropod 3, 4 on right; spine-seta formula of outer ramus of uropod 3 = ?–ES–EE/S–Ee–Ee.

Female “m,” 2.90 mm. With brood young. This specimen is much larger than other ovigerous females in the collection but conforms to the specific requirements. Armament row on article 1 of antenna 1 consisting of 2 fine spines (?spine-setae) and 2 thick short spines + 2P; 5 very fine spines on article 2 confined to distal 1/3 of article, 2 apical spines very long; main flagellum of 8 articles; unreduced accessory flagellum of 7; aesthetasc formula = 0–0–2–1–2–2–2–0. Formula of even armament row on article 4 of antenna 2 = P, P, EE–SEESESES–PSEESE–3SESESESS; article 5 formula = 3SESES–ESESES3ES. Dactyl of pereopod 5 with 5 spines in tandem. Epimeron 2 with 2 setae. Peduncle of uropod 1 with 7 lateral and 2 dorsal setae. Left peduncle of uropod 2 with 1 stout lateral spine and 2 apical spines, and in addition, more proximally, 2 short, middorsal spines, 1 of moderate thickness, 1 very fine; right peduncle with 2 midlateral marginal spines in tandem, and in addition 2 short, proximodorsal spine-setae. Ramal setae on uropods 1–2 = 9–6 and 8–4. Peduncle of uropod 3 with 3 apicolateral spines on left side; right side damaged, with 2; article 1 of outer ramus with sharply angled, basal, medial bulge, lateral setal formula = EE, ES, Ee/EE, E, (E)e, spines very fine; article 2 about 17 percent as long as article 1. Telson sparsely glandular, broadly and evenly rounded apically, reaching about 20% along outer ramus; telsonic formula = 1, 2P, 1, P, 1/1, 2P, 1, P, 1.

BROOD JUVENILES (about 0.75 mm).—Notes based on both juveniles in brood pouch of female “m”: Primary flagellum of antenna 1 with 4 articles, aesthetascs elongate; accessory flagellum 3-articulate; peduncular setae sparse. Article 3 of antenna 2 with 1 long seta and 1 setule; article 4 with 2 long spines and 1 penicillate setule on apical corner, ventral apex with 1 long plume, no facial armaments; article 5 with 1 long and 1 penicillate setule at ventral apex, dorsal apex with 1 long spine and 1 thin seta, no facials. Articles 4 and 5 of pereopods 3 and 4 lacking facial setae, article 4 with 1–2 apicoposterior setae, article 5 with 1 pair of apicoposterior spines only; formula on article 6 = 1 + 1 + 0; dactyl much more elongate than in adult, spines highly serrate. Dactyls of pereopods 3–7 very elongate and with large sharp subapical thorn; no spines on dactyl of pereopod 5. Articles 4–6 of pereopod 5 with apical sets of spines, but none set facially. Inner rami of uropods 1–2 shorter than in adult, each with only 1 apical seta, peduncle of each with only 1 apicomedial seta total.

HOLOTYPE.—NMV, male “r,” 3.00 mm (illus.).

TYPE-LOCALITY.—QM W.6386, station 58, Middle Banks, Moreton Bay, Queensland, coll. S. Cook, Sep 1972, 15.5 m, mud.

VOUCHER MATERIAL.—Type-locality: male “p,” 2.38 mm; female “n,” 2.40 mm; subadult male “s,” 2.05 mm; QM W.6390: male “o,” 2.28 mm (illus.); QM W.6384: female “m,” 2.90 mm; brood juveniles, ~0.75 mm; female “g,” 2.20 mm (illus.).

RELATIONSHIP.—Distinctions between U. yurrus and U. urungari have already been enumerated in the “General Description.” These 2 species are very close. They occur sympatrically in some situations. Some of their distinctive characters must be regarded as somewhat subjective (e.g., shapes of articles), and there are overlapping characters such as setation of article 2 of pereopod 7, where U. yurrus has most commonly 2 (but exceptionally 3), and U. urungari 3 (exceptionally 2) proximoposterior setae. The most important distinguishing characters are: shape of the protuberance on sternite 6 of the male; shape of article 5 of male antenna 2; and shape of the telson.

In the collections there is no male of U. urungari in which the flagellum of antenna 1 is modified by thickening of basal articles and proliferation of aesthetascs and so we cannot compare the 2 species in that terminal stage of development. All males of the 2 species in hand show a difference in shape of article 5 on antenna 2.

In all males of U. yurrus, whether with antenna 2 modified or not, article 5 is cylindrical to ovoid in shape and about half as wide as long; in all 29 males of U. urungari this article is bulbous and more than half as wide as long. No juvenile or subadult male of U. yurrus examined shows a structure similar to that of U. urungari on the sixth sternite. Juvenile males of U. yurrus have a poorly developed, wide-based, bluntly conoid process with no indication of the low, bilobed protuberance characteristic of U. urungari. Segregation on the basis of telson shape alone shows that (1) those individuals with broad, evenly rounded telsons also have only 2 setae on article 2 of pereopod 7; (2) article 6 of pereopod 5 is narrower and the dactyl relatively longer than that of U. urungari; (3) the peduncle of uropod 3 has 4 apicolateral spines; and (4) the armament of antenna 2 is predominantly spinous (particularly noticeable in the female). The alignment of the armament row on article 4 of antenna 2 and the setation of article 2 of pereopod 7 differentiates both species from U. parnggius; and the entire telson separates them from the clefted telson species such as U. pulcus, U. wingaro, and U. perkeus. The sporadic occurrence in both species of doubling or pairing of dactylar spines on pereopod 5 is a further indication of a close relationship to U. merkanius already obvious.

U. yurrus so closely resembles U. merkanius that it might be regarded as a neotenic estuarine morph of that species. The usual simple tandem arrangement of the dactylar spines on pereopod 5 of U. yurrus is no bar to such a theory because in small subadults and juveniles of U. merkanius no doubling of these spines has been observed, and some doubling in adults of U. yurrus and U. urungari has been noted below (page 82). Apart from this character, consistent distinctions between U. yurrus and U. merkanius are to be found in

1. The shape and setation of the telson. In U. yurrus the telson is broadly arched, and reaches less than halfway along the outer ramus of uropod 3; in U. merkanius the apex is much narrower. Adults and subadults of U. yurrus have only simple seta between groups of penicillate setules. They lack the second apicolateral pair of long stout spine-setae, one on each side of the midpair. In contrast, U. merkanius has 2 simple setae there. In female “x,” the apicolateral seta on each side is already well developed, although the brood plates are only about 1/3 grown and the 2 apical setae are small.

2. The shape of article 5 on antenna 2 in the male. This is cylindrical to ovoid in both adults and subadults of U. yurrus, and less than half as wide as long, but bulbous in all males of U. merkanius examined except for the single adult with modified antenna 1, in which it is narrower.

3. Shape of the male process on sternite 6; short, broad, and bluntly conoid in both adults and subadults of U. yurrus; fairly long, narrow, hooked, and apically acute in U. merkanius.

MATERIAL.—Queensland, Moreton Bay, Middle Banks, 104 specimens from 5 stations.

DISTRIBUTION.—Queensland, Moreton Bay, Middle Banks, 6–15 m, sand, mud.