Dactylopleustes yoshimurai, Tomikawa, Ko, Hendrycks, Ed A. & Mawatari, Shunsuke F., 2004

Tomikawa, Ko, Hendrycks, Ed A. & Mawatari, Shunsuke F., 2004, A new species of the genus Dactylopleustes (Crustacea: Amphipoda: Pleustidae) from Japan, with a partial redescription of D. echinoides Bousfield and Hendrycks, 1995, Zootaxa 674, pp. 1-14 : 3-10

Dactylopleustes yoshimurai sp. nov.

[Japanese name: Ezo­tengunouniyadori, new] ( Figures 1 –5)

Type material

Holotype: ovigerous female, 4.3 mm (12 slides), NSMT­Cr 15894, Itanki, Muroran City, Hokkaido, 42°20'N, 141°1'E, 17 October 2003, collector K. Yoshimura. Paratypes: one ovigerous female, 5.4 mm (undissected), NSMT­Cr 15895; two juveniles, 3.3 mm and 3.4 mm (24 slides); three juveniles, 2.9, 2.9, 3.2 mm (undissected), CMNC 2004­1306, same data as holotype. All specimens were found in association with the urchin, S. intermedius .

Other material

Two juveniles (3.3 mm, 3.4 mm, slide mounts), taken from S. intermedius , Fukushima Town, Hokkaido, 17 December 2003, collector K. Yoshimura: 17 juveniles (2.7–3.9 mm), taken from S. intermedius, Tomiura, Noboribetsu City , Hokkaido, 19 November 2003, collector K. Yoshimura.

Diagnosis

Antenna 1 subequal to antenna 2, accessory flagellum minute, one­articulate; pereopods 5–7, posterodistal lobes of basis angular, anterior margins of propodus with 15–21, 13–19, and 13–16 short spines respectively; upper lip, medial notch shallow; lower lip, outer lobes horizontal; mandible, palp article 2 with setae, accessory spine row with 13–14 slender blades; maxilla 1, outer plate with 17–18 spines; maxilla 2, outer plate with 9–12 stout, spine­like setae; maxilliped, inner plate with 6 small apical spines; uropods slender; telson length 1.4–1.5 times width.

Description

Holotype, ovigerous female, NSMT­Cr 15894.

Head: length (excluding rostrum) exceeding pereonite 1; eye large, reniform; rostrum, blunt, deep, reaching about 0.5 times antenna 1 peduncular article 1; lateral head lobe narrowly rounded. Antenna 1: short, length about 0.3 times body length, length ratio of peduncular articles 1–3 = 1: 0.54: 0.28; accessory flagellum small, scale­like, one­articulate; primary flagellum eight­articulate, articles with distal setae. Antenna 2: length subequal to antenna 1, peduncular article 4, length subequal to article 5, both with clusters of setae; flagellum short, about 0.7 times as long as peduncle length, nine­articulate, article 1 long, 1.7 times as long as article 2, articles with distal setae.

Pereonites, Pleonites, and Urosomites: smooth. Coxae: coxa 1 shorter than 2, length 0.78 times coxa 2, ventrally rounded, with four cusps on hind corner; coxa 2–3 with four, and three cusps on hind corner; coxa 4, posteroventral lobe subacute, posterior margin strongly excavated; coxa 5, aequilobate, anterior lobe bare, posterior lobe with fine setae; coxa 6 with fine setae on posterior margin; coxa 7 bare.

Upper lip (paratype, CMNC 2004­1306): ventral margin shallowly incised, lobes slightly asymmetric apically. Lower lip: outer lobes broad, horizontal; inner lobes deep. Mandible: left and right incisors eight and seven dentate respectively; left lacinia mobilis broad, eight­dentate, right lacinia mobilis absent; left and right accessory spine rows with 13 and 14 slender blades respectively; palp three­articulate, ratio of articles 1–3 = 1: 2.5: 4.5, article 1 unarmed, article 2 with four inner marginal setae, article 3 with five marginal, four apical setae, and outer facial fine setae. Maxilla 1: inner plate (paratype, CMNC 2004­1306) small, with apical seta; outer plate broad, rounded apically, with 17 slender spine­teeth; palp two­articulate, longer than outer plate, article 2 with six apical spines. Maxilla 2: inner plate with 15 setae apically; outer plate distinctly bent distomedially, rounded apically, with 12 spine­like setae and three setae apically. Maxilliped: inner plate short, not reaching base of palp, apical margin sloping medially, with six evenly spaced apical button­like spines, two setae apically, and three setae medially; outer plate narrow, bent medially, with a strong apical spine and setae; palp four­articulate, article 2 1.1 times as long as article 1, articles 3 and 4 with micropectination on medial margin.

Gnathopod 1: basis, anterior margin setose, posterior margin weakly expanded, with medial setae; ischium short, with posterodistal seta; merus, ventral margin setose; carpus, length 2.1 times width, ventral margin with two clusters of setae and distal setae, with medial setae; propodus narrowly subrectangular, slightly curved, shorter than carpus, length 2.4 times width, ventral margin with 2 spines and setae, with medial setae, palm transverse; dactylus stout, overhanging palm, length 0.4 times article 6, with setae. Gnathopod 2: as for gnathopod 1 except basis narrower and longer; carpus, length 2.8 times width, ventral margin with three clusters of setae and distal setae, with medial setae; propodus, slightly narrow distally, length 2.8 times width, ventral margin with one spine and setae, palm slightly shorter than that of gnathopod 1, slightly parachelate.

Pereopod 3: basis, anterior margin setose, with medial setae; ischium short, with posterodistal setae; ratio of merus–propodus = 1: 1: 1.3, posterior margin of propodus with 16 short spines; dactylus, posterior margin finely pectinate. Pereopod 4: as for pereopod 3 except basis setose on posterior margin; ratio of merus–propodus = 1: 0.7: 1, propodus relatively shorter and thicker than that of pereopod 3, posterior margin of propodus with 21 short spines. Pereopod 5: basis, posterior submargin with fine setae, posterodistal lobe angular; ischium short, anterior margin with spines; ratio of merus–propodus = 1: 0.66: 1, anterior margins spinose; propodus, anterior margin with 21 short spines, length 3.6 times width; dactylus, anterior margin weakly serrated. Pereopod 6: as for pereopod 5 except basis, inner surface with setae; ratio of merus–propodus = 1: 0.85: 1.3, propodus, anterior margin with 19 short spines, length 3.7 times width. Pereopod 7: as for pereopod 6 except; ratio of merus–propodus = 1: 0.77: 1, propodus, anterior margin with 16 short spines.

Coxal gills: present on pereopods 2–6, pear shaped, laminar, largest gill on pereopod 4. Brood plates: broad, with simple marginal setae of medium length. Pleopods: peduncles, outer margin setose, retinaculae paired; pleopod 1, inner and outer ramus 11 and 12­ articulate; pleopod 2, same as pleopod 1; pleopod 3, inner and outer ramus 10 and 11­articulate. Epimeron 1: narrow, posterior margin straight, with two anteroventral setae. Epimeron 2: posteroventral corner acuminate, ventral margin with 3 setae. Epimeron 3: wider than 1 and 2, posterior margin weakly convex, posteroventral corner produced into a broad tooth, ventral margin with seven setae.

Uropods 1–3 slender, rami narrowly lanceolate, lacking terminal spine, marginally serially spinose. Uropod 1: peduncle spinose, length subequal to inner ramus, with nine dorsolateral and 7 dorsomedial spines; outer ramus slightly shorter than inner, with eight dorsolateral and four dorsomedial marginal spines; inner ramus with five dorsolateral and six dorsomedial marginal spines. Uropod 2: peduncle with one apicodorsal and one apicomedial spine, length 0.7 times inner ramus; outer ramus length 0.6 times inner ramus, with six dorsolateral and two dorsomedial marginal spines; inner ramus with four dorsolateral and five dorsomedial marginal spines. Uropod 3: peduncle length length 0.6 times inner ramus, with one apicodorsal spine, with two inner marginal setae; outer ramus length 0.5 times inner ramus, with three dorsolateral and one dorsomedial marginal spine; inner ramus with five dorsolateral and five dorsomedial marginal spines. Telson: with ventral keel, length 1.5 times width, dorsal surface with two setae, four penicillate setae, and 15 microscopic setules, lateral margins parallel. Egg number: 10. Male unknown.

Dactylopleustes yoshimurai sp. nov., holotype female, 4.3 mm (NSMT­Cr 15894). Setae on pleopod rami are omitted. Pleopod retinacula (coupling spines) are shown enlarged. Scale bars = 0.1 mm unless indicated otherwise.

Condition

Without the upper lip and the inner lobe of the maxilla 1. The right uropod 3 is small, possibly due to an early stage of regeneration.

Va r i a t i o n

No males were collected, so sexual dimorphism could not be documented. The spine numbers of the propodus of pereopods 5–7 decrease in the smaller sized individuals.

Remarks

The new species is most similar to Dactylopleustes echinoides . The two differ from all other species of Dactylopleustes in having the following combination of characters: 1) the eye is large, reniform; 2) coxa 1 is distinctly shorter than coxa 2, with four cusps on the hind corner; 3) basis of gnathopods 1–2 are setose; 4) outer lobe of the lower lip is horizontal; 5) the medial notch of the upper lip is shallow; 6) palp article 2 of the mandible is much longer than article 1, with setae and 7) palp article 4 of the maxilliped is slender (see key below).

Dactylopleustes yoshimurai is easily distinguished from D. echinoides by the following character states (states of D. echinoides are in parentheses): 1) antenna 1 with 8­articulate flagellum (vs 4–6), antenna 2 with 9­articulate flagellum (vs 4–5); 2) coxa 2 with four cusps on the hind corner (vs 3); 3) length of the propodus of gnathopod 1 is 2.4–2.8 times width (vs 2); 4) gnathopod 1 palm of the propodus is transverse (vs oblique); 5) pereopods 5–7, propodus with 15–21, 13–19, and 13–16 spines respectively (vs 11, 7, and 8); 6) pereopods 5–7, posterodistal lobes of basis are angular (vs round); 7) pereopods 5–7, length of propodus is 3.6–3.7 times width (vs 2.7–2.9); 8) pereopods 5–7, anterior margins of dactyls with very weak teeth (vs strong teeth); 9) uropods 1–3 are slender and long (vs short, stout); 10) telson, length 1.5 times width (vs 2 times); 11) outer plate of maxilla 1 with 17– 18 slender, spine­teeth (vs 15); 12) outer plate of the maxilla 2 with 9–12 stout, spine­like setae apically (vs 6); 13) accessory spine row of the mandible with 13–14 slender blades (vs 7); 14) palp article 3 of the mandible is 1.7–1.8 times as long as article 2 (vs 1.4) and 15) palp article 2 of the maxilliped is longer than article 1 (vs shorter).

Distribution

Known from shallow water around Muroran, Noboribetsu, and Fukushima, Hokkaido.

Figures

FIGURE 1. Dactylopleustes yoshimurai sp. nov., holotype female, 4.3 mm (NSMT­Cr 15894); paratype juvenile, 3.4 mm (CMNC 2004 ­ 1306). Lacinia mobilis of left mandible is indicated by an arrowhead. Scale bars = 0.1 mm unless indicated otherwise.