Haustorius allardi, Hancock & Wicksten, 2018

Hancock, Zachary B. & Wicksten, Mary K., 2018, Two new species of sand-burrowing amphipods of the genus Haustorius Müller, 1775 (Amphipoda: Haustoriidae) from the northwestern Gulf of Mexico, Zootaxa 4459 (1), pp. 101-127 : 113-121

Haustorius allardi sp. nov.

Plates 6–10

Haustorius sp., Thomas 1976: 94. Genus two species b, Sweet 1996: 354 –360, figs. 137–139.

Type material: Holotype: Ovigerous female 2.8 mm; Grand Isle, LA, 29.2366° N, -89.9873° W; 28 July 2017 (Z.B. Hancock). Paratypes: Female 2.5 mm, Grand Isle, LA, 28 July 2017 (Z.B. Hancock). Male 2.0 mm, Holly Beach, LA, 29.7670° N, -93.4591° W, 27 July 2017 (Z.B. Hancock). Holotype has been deposited at NMNH, cataloged as USNM #1492391.

Additional material: 25 individuals, Holly Beach, LA, 27 July 2017 (Z.B. Hancock).

Etymology. Named in honor of Dr. David Allard, Professor of Biology at Texas A&M University-Texarkana, who first introduced Z.B. Hancock to invertebrate zoology.

Diagnosis. Antenna 1 flagellum 5-articulate, accessory flagellum 2–3 articulate; antenna 2 with 4–5 articles; mandible incisor bifid, with 4–5 accessory blades; mandibular palp 3 with 8 spines in comb row; maxilla 2 outer plate broad, gently curved medially and rounded distally; maxilliped outer plate broad, anterior angle obtuse with tooth-like spines along ¼ length of oral margin; pereopod 3 article 5 posterior lobe equal or slightly exceeding length of anterior margin; pereopod 5 article 6 with 2 spine groups; pereopod 6 article 5 posterior margin gently curved distally with 2–3 spine groups; pereopod 7 article 5 subtriangular with proximal and distal margins not parallel, proximal margin continuous with posterior margin, 1 spine group at posterior angle; uropod 1 peduncle bare or with 1 short setae, 2 interramal spines; telson cleft almost to base, lobes widely separated.

Description. Based on a 2.0 mm female collected at Holly Beach, LA, on 27 July 2017.

Head. Broad basally, rostrum subacute and extending 1/3 length of antenna 1 peduncular article 1; antennal sinuses weakly concave, not greatly produced anterolaterally. Eyes large, oval and lacking pigment.

Antenna 1. Peduncle article 1 with 6 plumos setae arranged radially along proximal margin, 2 stout penicillate setae at ventrodistal angle, 1 short spine along medially produced process, 2 thin setae on lateral surface; peduncle article 2 broadest distally with 10 plumose setae dorsally, 3 small spines, 4 long plumose setae and 2 penicillate spines concentrated at ventrodistally produced sinus; peduncle article 3 roughly ½ the width of peduncle article 2, 3 plumose setae and 2 short glassy spines inserted ventrodistally; flagellum 5-articulate each with small setae concentrated at junctions, 5 thin setae at terminal apex; accessory flagellum 2-articulate, thin setae at junctions and 4 setae at terminal apex.

Antenna 2. Peduncle article 3 stubby, slightly arched with 2 short setae distally; peduncle article 4 with large ventrodistally produced lobe, dorsally with 4 irregular spines, ventral lobe with 22 long plumose setae, 6 penicillate setae projecting anteriorly, 1 penicillate setae within ventrodistal sinus; peduncle article 5 weakly produced ventrodistally with 10 long plumose setae and 5 curved spines ventrally, dorsally with 3 irregular spines and 4 short setae; flagellum 5-articulate, article 1 slightly produced ventrodistally with 2 long plumose setae, 3 long setae dorsodistally; article 2 with 1 plumose setae; remaining articles with clusters of thin setae at each articulation; 6 setae inserted at terminal apex.

Upper and Lower Lip. Labrum broad, apical margin medially produced forming a V; lower lip inner lobes broadest at apex, roughly 2/3 length of outer lobe, oral margins lined with fine setae; outer lobes broad, slightly produced medially, densely lined with setae.

Mandibles. Incisor bifid; left mandible with short, conical lacinia mobilis, 4 blunt accessory blades, molar weakly triturative with a dorsal bifid tooth; mandibular palp article 2 with 1 thin setae orally, 2 short setae aborally; palp article 3 with 8 spines in median comb row, 10 glassy spines inserted terminally; right mandible like left except without lacinia mobilis, 5 accessory blades.

Maxilla 1. Inner plate narrow, orally with 6 thin spines; outer plate broad basally and narrowing terminally, 11 stout apical teeth; palp article 2 with 1 plumose seta aborally, 1 long plumose setae inserted along apex surrounded by dense cluster of thin setae; bailer lobe very small, weakly produced, lined with setae.

Maxilla 2. Outer plate broad, minutely curved medially, oral margin densely lined with long plumose setae, aboral margin with thin setae, distal margin broadly rounded; inner plate thick, curled orally and lined with finely pectinate setae, roughly ½ length of outer plate.

Maxilliped. Inner plate broadest medially, oral margin lined with glassy spines, 5 apical spine teeth, aboral surface bare; outer plate very broad, aboral surface rounded, smooth, 7 stout teeth along ¼ length of oral surface interspersed with smaller teeth, medially with thin pectinate setae; palp article 1 smooth, short; palp article 2 narrow, distal margin produced orally and densely lined with fine setae; palp article 3 geniculate, anterior curvature lined with finely pectinate setae, terminal margin with cluster of glassy setae.

Gnathopod 1. Simple, fossorial. Coxa rounded dorsally, ventral margin minutely curved anteriorly, 3 long plumose setae on anterior angle; article 2 long, narrow proximally and broadening distally, 3 pectinate setae on posterior margin, posterodistal angle with cluster of fine setae; article 3 short, stubby with 2 curved setae posteriorly; article 4 strongly curved, forming elbow, bare; article 5 broad, club-like and produced posteriorly, anterior surface with 1 short spine proximally, posterior margin densely lined with long finely pectinate hooked setae, medially with 4 short spines; article 6 slightly oval and curved posteriorly, lined with fine pectinate hooked setae; article 7 minute, nail-like.

Gnathopod 2. Minutely chelate. Coxa rounded dorsally, anteriorly produced with 7 plumose setae along blunt angle, bare elsewhere; article 2 long, narrow with 4 glassy setae on posterior margin, posterodistal angle with cluster of fine setae, bare elsewhere; article 3 minute, forming elbow; article 4 slightly produced posterodistally; article 5 broadest medially, slightly narrowing proximally, posterior margin lined with fine setae, distally with cluster of short hooked spines, anterior margin with 2 thin spines proximally, anterodistal margin with cluster of thin spines; article 6 tear-drop shaped with dense distal cluster of finely pectinate setae, posterodistal margin strongly hooked; article 7 minute, flexor surface relatively flat. Female: oostegite minute, vestigial, with 4 glassy spines on terminal margin.

Pereopod 3. Coxa semi-lunate, extending to a sharp point anteriorly, 4 long plumose setae on posterodistal angle, bare elsewhere; article 2 club-like, broadening distally, 2 plumose setae distally on posterior margin; article 3 stubby, inconspicuous, 1 plumose seta on posteroproximal margin; article 4 broadest medially, roughly the length of article 2, anterior margin with 7 plumose setae, cluster of 3 long plumose setae on posterodistal margin followed by 5 glassy setae; article 5 with posteroventrally produced lobe roughly the length of anterior margin, stout spines line the margin of the cup, 3 long plumose setae concentrated at proximal border; article 6 curved to form spoonlike structure, margins lined with 8 stout spines. Female: oostegite narrow, moderately lunate and lined with glassy spines.

Pereopod 4. Coxa large, completely covering article 2, roughly oval and rounded anteriorly, bare, ventrodistally flattened and recurved posteriorly with 3 glassy setae flanking each side of curvature, bare elsewhere; article 2 club-like, broad, 3 long plumose setae on posterior margin, 1 thin setae on anterior margin; article 3 stubby, inconspicuous, with 1 plumose setae on posterior margin; article 4 broadest distally, club-like, 3 plumose setae on anterior margin, posterior margin with 8 plumose setae, anterodistal margin forming slight shelf over article 5, 1 thin spine on anterodistal angle; article 5 with small posteriorly produced lobe bearing 3 long spines and 3 stout spines, 3 plumose setae along proximal border, anterior margin bare medially, 1 thin spine on anterodistal angle; article 6 somewhat tear-drop shaped with 5 long, thin spines inserted at terminal apex. Female: oostegite narrow, lunate, lined with 15 long spines.

Pereopod 5. Coxa with posterior lobe slightly larger than anterior with 8 glassy setae, anterior lobe bare; article 2 large, ovoid with 11 long plumose setae along anterior margin, posterior margin with 12 plumose setae, distal margin somewhat produced anteriorly; article 3 small, inconspicuous, overhung by article 2; article 4 with 5 rows of stout spines on exterior surface, 9 plumose setae on poserior margin, 8 plumose setae on anterior margin; article 5 with 4 rows of stout spines on exterior surface, posterodistally produced lobe extending roughly ¼ length of article 6 with 5 plumose setae and 2 strong spines, anterodistal margin with dense cluster of strong spines; article 6 stubby, broad with 2 spine groups on anterior margin, posterior margin bare, 5 glassy spines inserted terminally.

PLATE 6. Female, 2.0 mm. L) Lateral view of Haustorius allardi sp. nov.; R) dorsal view of rostrum; A1) antenna 1; A2) antenna 2 (inner surface); PL) pleon.

Pereopod 6. Coxa produced posterodistally with 6 plumose setae, bare elsewhere; article 2 greatly expanded, ovoid, anterior margin lined with plumose setae, 2 large spines inserted distally, posterior margin with 6 short plumose setae proximally, bare distally; article 3 small, inconspicuous, with 1 plumose setae on anterior margin; article 4 subtrapezoidal, widest distally, anterior margin lined with plumose setae, 2 short spine groups distally, posterior margin gently curved and lined with plumose setae, 3 large spines posterodistally, distal margin relatively flat with thin setae at anterior and posterior angles; article 5 subquadrate, posterior margin with 1 short spine, anterior margin with 2 large spine groups, anterodistal angle with 4 large spines, distal margin gently curved proximally but without distinct anterior angle, row of strong spines medially; article 6 long, narrow, anterior margin bare, posterior margin with 2 spine groups, terminal apex with 7 strong spines.

PLATE 7 . Female , 2.0 mm. MX 1) Maxilla 1 ; MX2) maxilla 2; MXP) maxilliped; LL) lower lip; MD) mandible, with arrow indicating a magnified view of the accessory blades.

PLATE 8. Female, 2.0 mm. G1) Gnathopod 1, with arrow indicating a magnified view of article 7; G2) gnathopod 2, with arrow indicating a magnified view of the chela; P3) pereopod 3.

Pereopod 7. Coxa small, subrectangular with 4 glassy setae on posterodistal margin, bare elsewhere; article 2 greatly enlarged, roughly circular, bare on posterior margin, anterior margin lined with 10 long plumose setae, 4 dagger-like spines beginning medially on anterior margin; article 3 small, inconspicuous, 1 short spine inserted at anteroproximal junction; article 4 subtriangular, proximal margin deeply sloped and continuous with posterior margin, not parallel to distal margin, with 5 plumose setae, proximal and distal margins forming blunt angle posteriorly with 2 strong spines, distal margin flat with 3 small teeth-like spines and 3 finely pectinate setae along posterior ¼ of margin, bare elsewhere, anterodistal angle with 4 large spines, anterior margin flat with 1 spine group; article 5 subquadrate, anterior and posterior margins roughly parallel, anterior studded with 4 spine groups increasing in size and number distally, posterior margin bare except at distally produced shelf bearing cluster of small spines and setae, exterior surface with 2 clusters of fine setae; article 6 narrow, 3 spine groups on posterior margin, 2 spine groups on anterior margin, 6 strong spines inserted at terminal apex.

PLATE 9. Female, 2.0 mm. P4) Pereopod 4; P5) pereopod 5; U1) uropod 1; U2) uropod 2; U3) uropod 3. PLATE 10. Female, 2.0 mm. P6) Pereopod 6; P7) pereopod 7; T) telson, with arrow indicating club-like penicillate seta, compare with corresponding in LT; LT) telson of Lepidactylus triarticulatus ; LP) pleon of L. triarticulatus , arrow indicating the continuous pleon with the urosome, compare with the corresponding structure PL on Plate 6. Drawings of L. triarticulatus from Robertson & Shelton (1980).

Pleopods. Pleopod 1 peduncle subrectangular with 5 setae along outer margin, inner ramus with 8 segments, outer ramus with 12 segments; pleopod 2 peduncle with distinct sinus at the insertion of the inner ramus, 5 setae on outer margin, inner ramus with 6 segments, outer ramus with 10 segments; pleopod 3 peduncle bean-shaped, flat along margin of rami insertion, 3 setae on outer surface, inner ramus with 5 segments, outer ramus with 8 segments.

Uropod 1. Peduncle lateral margin with 1 thin setae, 2 stout interramal spines; outer ramus with 3 spine groups on exterior margin opposite 2 glassy setae, 9 thin spines inserted terminally; inner ramus with 3 glassy setae, 5 spines on apex.

Uropod 2. Exterior margin of peduncle lined with fine setae interspersed with short spines, 2 plumose setae distally; inner ramus short, stubby, lined with needle-like spines; outer ramus slightly longer than inner 3 spines medially, dense cluster of thin glassy spines at apex.

Uropod 3. Peduncle broad with 5 spines on distal margin; inner ramus narrow, cluster of short setae medially, dense cluster of thin spines terminally; outer ramus 2-articulate, article 1 distal margin lined with thin spines, article 2 with 5 spines inserted terminally.

Telson. Deeply cleft almost to base forming two widely separated lobes, posterior margins of lobes with 3 large spines, medially produced shelf with 2 large spines and 1 thick, club-like penicillate seta.

Intraspecific variation. As with other haustoriids, spination varies with size ( Thomas & Barnard 1976). Smaller specimens lacked spines entirely on the anterodistal margin of pereopod 6 article 5. Pereopod 3 article 5 posteriorly produced lobe varies in size with body length also, and may be equal in length to the anterior margin or slightly larger. In specimens greater than 2.5 mm, the posterior lobe is somewhat oval and equal to 1.2x the length of the anterior margin. Similarly, specimens of this size have a 3-articulate antenna 1 accessory flagellum and interramal spines of uropod 1 peduncle varied between 2–3.

Color in life. Like that of Haustorius galvezi sp. nov.

Ecology. This species was sampled in the high intertidal zone at Holly Beach, LA. In late July on Grand Isle, LA, the intertidal zone was dominated by Lepidactylus triarticulatus , and H. allardi sp. nov. was only found subtidally to a depth of 1.5 m. The species occurs in both fine sand and mud. The range of H. allardi sp. nov. appears to be restricted to an area east of Sabine Lake to Barataria Bay. Thomas (1976) reported an undescribed species of Haustorius known only from the Delta region, which is likely H. allardi sp. nov.

Range: Holly Beach, LA to Grand Isle, LA.

Remarks. H. allardi sp. nov. co-occurs alongside L. triarticulatus at Grand Isle, LA, which it resembles and is easily confused with. In H. allardi sp. nov. pleonite 3 is pointed and strongly overhangs the urosome, while pleonite 3 is rounded and continuous with the urosome in L. triarticulatus (see Plate 6 and 10 for pleonite 3 comparison between L. triarticulatus and H. allardi sp. nov.). Pereopod 3 article 5 posterior lobe is never greater than the length of the anterior margin in L. triarticulatus and is rounded; in H. allardi sp. nov., the lobe is oval and may reach 1.2x the length of the anterior margin. Additionally, H. allardi sp. nov. has a strong, club-like penicillate seta medially on each lobe of the telson, while the corresponding seta in L. triarticulatus is narrow and short (see Plate 10). See Table 2 for a side-by-side comparison of H. allardi sp. nov. and L. triarticulatus .