Iiella malayensis, Fukuoka, Kouki, 2011

Fukuoka, Kouki, 2011, A new species of the genus Iiella Băcescu, 1968 (Crustacea: Mysida: Mysidae) from Malaysia, with notes on I. elegans (Tattersall, 1960), Zootaxa 3091, pp. 60-68 : 61-66

publication ID	https://doi.org/ 10.5281/zenodo.204655
DOI	https://doi.org/10.5281/zenodo.5676820
persistent identifier	https://treatment.plazi.org/id/081587D1-FFF3-A555-FF5B-FC9BFAB1FBA5
treatment provided by	Plazi
scientific name	Iiella malayensis
status	sp. nov.

Treatment

Iiella malayensis sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined. Holotype: adult male (6.4 mm, dissected), 02°13.667’N 104°04.068’E, off Sibu Island, Southeast off Malay Peninsula, Malaysia, surface, hand-net, 20: 21, 17 Oct. 2008, coll. S. Sawamoto, NSMT-Cr 21626. Paratypes: 4 adult males (6.2–6.8 mm) and 2 adult females (6.8, 6.8 mm), 02°13.667’N 104°04.068’E, off Sibu Island, Southeast off Malay Peninsula, Malaysia, surface, hand-net, 20: 28, 16 Oct. 2008, coll. S. Sawamoto, NSMT-Cr 21627; 2 adult males (6.3, 6.7 mm) and 2 adult females (6.2, 7.0 mm), same data as NSMT-Cr 21627, ZRC 2011.0100; 1 adult female (7.0 mm, dissected), same data as holotype, NSMT-Cr 21628; 38 adult males (5.4– 6.6 mm) and 6 adult females (5.9–7.4 mm), same data as holotype, NSMT-Cr 21629; 40 adult males (5.3–6.8 mm) and 5 adult females (7.2–7.8 mm), same data as holotype, ZRC 2011.0101.

Description. Integument smooth. Thoracic somites without sternal processes. First abdominal somite slightly longer than second somite; second somite almost as long as third somite; last four somites gradually increasing in length from third to sixth somites; in female, pleural plate of first somite expanded posteriorly, extending to posterior margin of second somite.

Carapace produced anteriorly into low triangular rostral plate with slightly concave lateral margins, not extending to base of antennular peduncle ( Fig. 1 View FIGURE 1 A, B). Anterolateral corner of carapace rounded. Posterior margin of carapace ( Fig. 1 View FIGURE 1 C) emarginate, exposing last thoracic somite dorsally; posterodorsal margin split at each side; posterolateral margin slightly serrulate.

Eyes ( Fig. 1 View FIGURE 1 A, B) developed, 1.4–1.6 times as long as broad in dorsal view; cornea occupying 0.4–0.45 of eye; eyestalk without papillae.

Antennular peduncle of male ( Fig. 1 View FIGURE 1 A) robust; first segment 1.7 times as long as broad; second segment 0.3 of first segment in length, armed with 3 robust spiniform setae on lateral margin; third segment twice as long as second segment along mesial margin, 1.4 times as long as broad. Antennular peduncle of female ( Fig. 1 View FIGURE 1 B) slightly slenderer than that of male; first segment twice as long as broad; second segment 0.4 of first segment in length, armed with 3 robust spiniform setae on lateral margin; third segment 1.5 times as long as second segment along mesial margin, 1.7 times as long as broad.

Antennal scale of male ( Fig. 1 View FIGURE 1 A, D) extending to anterior margin of second segment of antennular peduncle, 3.3 times as long as broad, with transverse suture near apex; lateral margin of scale straight, smooth, terminating in spiniform process extending to proximal 0.3 of apical lobe of scale; antennal peduncle ( Fig. 1 View FIGURE 1 D) 1.3 times longer than scale. Antennal scale of female ( Fig. 1 View FIGURE 1 B, E) not reaching anterior margin of second segment of antennular peduncle, 3.0 times as long as broad; antennal peduncle ( Fig. 1 View FIGURE 1 E) 1.4 times longer than scale.

Labrum ( Fig. 1 View FIGURE 1 F) with long, median, frontal, acute process and 2 or 3 short, acute processes on each side of it.

Mandibular palp ( Fig. 1 View FIGURE 1 G) slender; second segment 3.4 times as long as broad; third segment 0.8–0.9 of second segment in length.

Maxillule ( Fig. 1 View FIGURE 1 H): lateral lobe with 15 cuspidate setae on distal margin and 6 setae on posterior surface; mesial lobe with 3 long and several short setae on distal margin.

Maxilla ( Fig. 1 View FIGURE 1 I): second segment of endopod 2.3 times as long as broad, armed with short, fine setae on distal 0.5–0.6 of lateral margin and long setae on mesial and apical margins; exopod not extending to distal margin of first segment of endopod, armed with long, plumose setae on lateral and apical margins.

Endopod of first and second thoracopods ( Fig. 2 View FIGURE 2 A, B) short, robust. Endopod of third to eighth thoracopods ( Fig. 2 View FIGURE 2 C–H): ischium equal in length in third to fifth thoracopods, gradually decreasing in length from fifth to eighth thoracopods, armed on mesial margin with many setae which are gradually decreasing in number from sixth to seventh thoracopods, and single seta in eighth thoracopod; merus shorter than ischium, same in length from third to fifth thoracopods, gradually decreasing in length from fifth to eighth thoracopods; carpopropodus gradually increasing in length from third to eighth thoracopods, 1.2–3.5 times as long as merus, divided into 6 subsegments in third and fourth thoracopods, 7 in fifth, 8 in sixth, 9 in seventh and 11 in eighth; dactylus with slender claw. Exopod of thoracopods ( Fig. 2 View FIGURE 2 A, B, G, H) with 10- or 11-segmented flagellum in male and 9- or 10-segmented flagellum in female; distolateral corner of basal plate rounded in first and eighth thoracopods and pointed in second to seventh one.

Genital appendage of male on eighth thoracopod ( Fig. 2 View FIGURE 2 I) armed with 3 plumose setae on anterior margin and 3 short setae on distal margin of anterior lobe.

Female with reduced oostegite on seventh thoracopod and developed oostegite on eighth one.

All pleopods of male biramous. First, fourth and fifth pleopods ( Fig. 3 View FIGURE 3 A, D, E) with endopod reduced to unsegmented lobe, exopod 8-segmented in first and fourth pleopods, 7-segmented in fifth pleopod. Second pleopod ( Fig. 3 View FIGURE 3 B) with 7-segmented endopod and 8-segmented exopod. Third pleopod ( Fig. 3 View FIGURE 3 C) with endopod 7-segmented; exopod elongate, extending to posterior 0.25 of sixth abdominal somite, 3.3 times longer than endopod, 4-segmented; first segment subequal to endopod in length, divided into 4 subsegments, first 3 short subsegments occupying 0.4 of first segment; second segment 1.1 times as long as first segment; third segment 0.6 of second segment in length; fourth segment 0.8 times as long as third segment, armed with 2 short, setulose setae on distal end and 1 small spiniform seta on distal 0.17 of lateral margin.

All pleopods of female rudimentary, uniramous. First pleopod ( Fig. 3 View FIGURE 3 F) 2-segmented with short second segment. Second to fifth pleopods ( Fig. 3 View FIGURE 3 G–J) unsegmented; second pleopod slightly longer than third; third to fifth pleopods subequal in length.

Uropodal endopod ( Fig. 3 View FIGURE 3 K–N) tapering distally, extending to tip of apical setae of telson in male and overreaching tip of apical setae in female, armed with 1 long robust spiniform seta on ventral surface of statocyst region and 12–17 short spiniform setae on proximal 0.2 to distal 0.1 of mesial margin, last 3 short setae increasing in interval length. Uropodal exopod ( Fig. 3 View FIGURE 3 K, M, N) slightly shorter than endopod, armed with 13–15 long, setulose, spiniform setae on lateral margin.

Telson ( Fig. 3 View FIGURE 3 M, N) 1.1–1.2 times longer than sixth abdominal somite, 2.9–3.1 times as long as broad, with apical cleft; lateral margin armed with 1 long spiniform seta near base and 14 or 15 spiniform setae from proximal 0.24–0.3 to near apex, setae on medial part arranged in 2 or 3 groups with large and small setae; each apex with 1 long spiniform seta, which is 2–3 times as long as distalmost lateral setae; apical cleft occupying 0.18 of telson length, extending anteriorly between third and fourth lateral spiniform setae from posterior end, serrated with 23– 25 spines on entire length of each side.

Etymology. The specific name is derived from the type locality.

Remarks. Iiella malayensis is similar to I. ohshimai ( Ii, 1964) in having a deep cleft in the telson. However, I. malayensis differs from the original description of I. ohshimai ( Ii 1964) by the following characteristics. (1) In I. malayensis , the rostral plate is broad with shallow concave lateral margins, whereas in I. ohshimai it is narrow with deep concave lateral margins. (2) In I. malayensis , the labrum bears two or three spines on each side of a long median spine, whereas I. ohshimai bears four or five spines on each side. (3) In I. malayensis , the first segment of the exopod of the third male pleopod is almost the same length as the endopod and is divided into four subsegments composed of three short basal subsegments and one long distal subsegment, the length of which is 0.9 times that of the second segment. However, that of I. ohshimai is approximately 1.5 times longer than the endopod and is divided into five subsegments composed of four short basal subsegments and one long distal subsegment, the length of which is nearly identical to that of the second segment. (4) The telson of I. malayensis is armed with 15 or 16 lateral spiniform setae arranged in groups with short and long setae in the middle part, whereas that of I. ohshimai is armed with 10 or 11 subequally sized lateral setae. (5) In I. malayensis , the anterior end of the apical cleft of the telson overreaches the antepenultimate lateral spiniform seta, whereas in I. ohshimai , it extends to the antepenultimate lateral spiniform seta.

Iiella ohshimai View in CoL was originally described from Japanese waters ( Ii, 1964), and it was subsequently recorded in the Chinese coastal waters of the South China Sea ( Wang & Liu, 1987). Wang & Liu (1987) recognized some differences in these specimens from the original description by Ii (1964) in terms of the number of spines on each side of the median spine of the labrum, and the number of spiniform setae on the lateral margin of the second segment of the antennular peduncle, the mesial margin of the endopod of the uropod, and the lateral margin of the telson. Furthermore, the specimens by Wang & Liu (1987) differ from the original description in the length of the segments and the number of subsegments in the first segment of the exopod of the third male pleopod. Pertaining to these morphological differences it seems that I. ohshimai View in CoL , specimens described from the South China Sea, could be classified as a separate undescribed species of Iiella View in CoL . A close relationship between I. malayensis and Chinese specimens of I. ohshimai ( Wang & Liu 1987) View in CoL is suggested, based on the third male pleopod and the number of spiniform setae on the mesial margin of the uropodal endopod and lateral margin of the telson. However, I. malayensis is distinguishable from the Chinese specimens by the characteristics of the labrum and the length of the lateral setae of the telson.

Iiella malayensis is related to I. elegans View in CoL in terms of the large number of spiniform setae on the lateral margin of the telson. However, it is distinguished from I. elegans View in CoL by the following characteristics: (1) the rostral plate of I. malayensis does not extend to the base of the antennular peduncles, whereas that of I. elegans View in CoL extends beyond the base of the antennular peduncles; (2) in I. malayensis , the labrum bears two or three spines on each side of the long median spine, as opposed to the four or five in I. elegans View in CoL ; (3) in I. malayensis , the lateral setae of the telson are arranged in two or three groups with large and small setae in the median part, whereas these are subequal in size in I. elegans View in CoL ; and (4) in I. malayensis , the anterior end of the apical cleft of the telson extends between the third and fourth setae from the posterior end of the lateral margin in I. malayensis , but it extends between the second and third setae in I. elegans View in CoL .