Siriella occulta, Daneliya & Price & Heard, 2018

Daneliya, Mikhail, Price, W. Wayne & Heard, Richard W., 2018, Revision of the Siriella brevicaudata species group (Crustacea: Mysida: Mysidae) from the West Indo-Pacific, European Journal of Taxonomy 426, pp. 1-80 : 43-49

Siriella occulta sp. nov.

urn:lsid:zoobank.org:act:B96BA8A6-EE2D-4660-8680-08B32FEC18BF

Figs 18–21

Siriella sp. A – Grabe et al. 2004: 2321, fig. 3c.

Diagnosis

Carapace with anterodorsal margin angular, well-produced, nearly covering subrostral process; apically rather narrow, but not acute; sides straight. Carapace with postcervical elevation more strongly developed in female. Telson slightly shorter than last abdominal somite, 1.6–1.7 times as long as wide anteriorly and 1.5 times as wide anteriorly as posteriorly. Telson apically with slight emargination, almost bilobate, with small ventral spinules, not visible dorsally, about 0.1 times as long as posterolateral terminal pair of spiniform setae. Lateral margins of telson with three or four anterior and 9 to 13 posterior spiniform setae after gap, gradually increasing in length towards apex. Telson terminal posterolateral pair of spiniform setae 0.20–0.23 times as long as telson and 1.1–1.3 times as long as subterminal spiniform setae. Subterminal pair of spiniform setae 1.1–1.2 times as long as preceding posterolateral. Labrum with very small, barely visible anterior spine, <0.1 times as long as rest of labrum. Maxilla 1 with distal robust smooth setae. Maxilla 2 endopod segment 2 with five or six lateral setae along entire margin. Pereopod 1–3 merus 3.1–3.3 times as long as wide. Uropodal exopod 3.6 times as long as wide; exopod segment 1 is 2.5–3.0 times as long as segment 2, with four to six distolateral spiniform setae. Uropodal endopod with 15 to 20 medial spiniform setae, not extending to ramus apex.

Etymology

From the Latin word occulta (feminine), meaning ‘hidden, secret’, referring to the hidden, barely visible subrostral process and telson emargination spinules of the species.

Material examined

Holotype

SAUDI ARABIA: ♂ (+ slide), 6.5 mm long, Arabian (Persian) Gulf, 82-005 A, site 8, 61.5° F (16.4° C), 40‰, larval + trawl, 2 Apr. 1982, H. McElroy leg. ( USNM 1459145 ).

Paratypes

SAUDI ARABIA: 4 ♂♂, 5.5–6.5 mm long, 4 ♀♀, 6.0– 6.5 mm long, same label data as for the holotype ( USNM 1459146); 6 ♂♂, 4.5–5 mm long, 5 ♀♀, 4.5–5 mm long, 1 immature ♀, Arabian Gulf, 720611 B / 11m, site 2, date unavailable, Skimmer, Zaal leg. ( USNM 1459147).

BAHRAIN: 1 immature ♀, E coast, Arabian Gulf, st. 40, 1991, J. A. Mansoor and H. Sulman leg. ( USNM 1459148); 3 ♀♀ (1 broken), 4–4.5 mm long, 3 juveniles, all damaged, E coast, Arabian Gulf, st. 103, 1991, J. A. Mansoor and H. Sulman leg. ( USNM 1459149); 1 juvenile (broken), E coast, Arabian Gulf, st. 105, 1991, J. A. Mansoor and H. Sulman leg. ( USNM 1459150); 1 ♀ (+ slide), 5 mm long, 1 immature ♂, E coast, Arabian Gulf, st. 110, 1991, J. A. Mansoor and H. Sulman leg. ( USNM 1459151); 1 immature ♂, 1 immature ♀, E coast, Arabian Gulf, st. 117, 1991, J. A. Mansoor and H. Sulman leg. ( USNM 1459152); 5 ♂♂ (2 broken), 4–4.5 mm long, 3 ♀♀ (2 broken), 5.5 mm long, 1 immature ♂, 3 immature ♀♀, 4 juveniles (2 broken), E coast, Arabian Gulf, st. 125, 1991, J. A. Mansoor and H. Sulman leg. ( USNM 1459153).

Description

Body length of males 4.5–6.5 mm, of females 4.5–6.5 mm.

Male (holotype)

CARAPACE. With anterior part slightly wider than abdominal somite 1. Carapace with anterodorsal margin broadly angular, nearly covering spiniform subrostral process; apically rather narrow, but not acute; sides straight ( Fig. 18A, C ). Carapace posterior margin exposing three thoracic somites.

TELSON. Barely shorter than last abdominal somite, 0.6 times as long as uropodal endopod, 1.6 times as long as wide anteriorly and 1.5 times as wide anteriorly as posteriorly ( Fig. 18D ). Telson apically with slight emargination, bilobate, with three rather small ventral spinules, not visible in dorsal view, 0.1 times as long as posterolateral terminal pair of spiniform setae; with two long plumose setae, longer than spinules flanking them ( Fig. 18E ). Telson lateral margins slightly tapering, with three anterior and 12 and 13 posterior spiniform setae after gap, increasing in length towards apex. Terminal pair of spiniform setae 0.23 times as long as telson and 1.3 times as long as subterminal pair of spiniform setae, which is 1.2 times as long as preceding posterolateral spiniform setae.

HEAD APPENDAGES. Eyes 1.4 times as long as wide and 0.6 times as long as width of anterior part of carapace. Peduncle of antennae 1 more robust than in female, about twice as long as peduncle of antenna 2; segment 1 is 2.2 times as long as wide; segment 3 is 1.7 times as long as wide and as long as segment 1; male process along posteromedial margin of segment 3, conical, its distal protruding part 0.3 times as long as segment 3 ( Fig. 18 A–B, F). Male antennule inner flagellum normal, not dilated or meandering in proximal part. Antennal scale with clear distal articulation, only slightly shorter than peduncle of antenna 1 and 1.6 times as long as peduncle of antenna 2; scale 3.0 times as long as wide, 1.3 times as long as length from scale base to base of outer spine; maximum width 1.4 times its distal width; distal segment with five setae ( Fig. 18A, G ). Labrum with very small, barely visible anterior spine, <0.1 times as long as rest of labrum ( Fig. 18H ). Mandible ( Fig. 18I ): palp segment 2 is 2.3 times as long as wide with short setae along margins; segment 3 half as long as segment 2, with 11 long proximomedial, 11 short distomedial and six long distolateral setae. Distal robust setae of maxilla 1 smooth ( Fig. 18J ). Maxilla 2 exopod oval, with 16 setae; endopod segment 1 with two medial setae; endopod segment 2 with six lateral setae along entire margin and multiple medial setae and stronger, finely serrated setae flanking them; endites with robust, finely serrated setae ( Fig. 18K ).

MAXILLIPEDS. Exopod of thoracopods 8–9-segmented ( Fig. 19E ). Maxilliped 1 without endites; segments short and strong; basis with group of distomedial setae; preischium with one seta; ischium with seven medial setae; merus, the largest segment, 1.2 times as long as wide, with 11 medial and one distolateral setae; carpopropodus with five lateral, eight anterodistal and two distomedial setae; dactylus with strong smooth unguis, five lateral, three medial and four anterior setae; dactylary setae about as long as unguis; unguis slightly longer than dactylus ( Figs 18L , 19A ). Maxilliped 2 ( Fig. 19 B–C): basis with proximal medial seta and distal medial group of setae; ischium, the widest segment, 1.1 times as long as wide, with numerous setae along medial margin and one lateral seta; merus 1.9 times as long as wide and 1.7 times as long as ischium, with three medial groups, each with two setae and two distolateral setae; carpopropodus 2.1 times as long as wide, with five distal anterolateral setae, three medial bunches of one or two long setae, short distal posteromedial seta and distal anteromedial bunch of four serrated setae; dactylus wider than longer, 0.15 times as long as carpopropodus, with strong smooth unguis, four medial, four anterior strong serrated setae and three thin lateral setae; unguis 4.0 times as long as dactylus.

PEREOPODS. Pereopodal endopods ( Fig. 19D, F ): ischium about half as long as merus; medial and paradactylary setae of carpopropodus distally serrated; carpopropodus with secondary joint, two medial bunches of three–four long setae and three short lateral setae; dactylus with strong unguis. Pereopods 1–3 ( Fig. 19D ): basis with distomedial bunch of setae; preischium without setae; ischium laterally convex, 1.7 times as long as wide, with one–two lateral setae and many short and long medial setae; merus 3.1–3.3 times as long as wide, with four–six medial groups of long and short setal bunches, two–three lateral setae and distolateral bunch of one–three setae; carpopropodus 4.4–4.7 times as long as wide and 0.7 times as long as merus; dactylus 0.15–0.17 times as long as carpopropodus and about as long as wide; dactylar unguis 1.5–1.8 times as long as dactylus; paradactylary setae not reaching ungual apex. Pereopod 6 ( Fig. 19F ): preischium with four setae; ischium 1.8 times as long as wide, with nearly parallel margins, two medial setae and distomedial bunch of four setae; merus 4.3 times as long as wide, with four medial groups of one or two setae and four lateral setae; carpopropodus 6.3 times as long as wide; dactylus 1.5 times as long as wide; dactylary unguis 2.3 times as long as dactylus. Penis cylindrical, with two long apical setae, directed posteriorly ( Fig. 19G ).

PLEOPODS. Pleopod 1 uniramous; ramus 10-segmented; pseudobranchiae bilobate; inner lobe nearly straight, with apical seta, outer lobe L-shaped, with 3 lateral setae ( Fig. 20A ). Pleopods 2–5 biramous; rami 11-segmented; pseudobranchiae bilobate, spirally coiled, with four lateral setae ( Fig. 20B ). Terminal setae of pleopod rami not modified. Proximal segments of pleopod rami 0.3–0.4 times as long as wide.

UROPODS. Uropodal exopod 1.2 times as long as endopod and 3.6 times as long as wide; exopod segment 1 is 2.2 times as long as segment 2, with six distolateral spiniform setae ( Fig. 20D ). Uropodal endopod with 19–20 medial spiniform-setae, distally becoming longer, occupying almost entire ramus length, though not extending to apex ( Fig. 20C ).

Female

Carapace with dorsal median elevation behind pleurocervical fissure ( Fig. 21A–B ). Peduncle of antenna 1 slender and longer than in male; segment 1 about 3 times as long as wide and 1.2 times as long as segments 2 and 3 together, with five short distal dorsolateral setae; segment 2 with five short distal dorsolateral and one long plumose distomedial setae; segment 3 is 1.2 times as long as wide, with one medial and four distomedial setae ( Fig. 21 B–C). Segment 3 of mandibular palp with three–four proximomedial setae ( Fig. 21D ). Pereopods 5 and 6 each with oostegite. Pleopods lamelliform, setose.

Comparison

Compared to other species of the brevicaudata group, S. occulta sp. nov. has a telson with the most gradually increasing posterolateral spiniform setae. It most closely resembles S. brevicaudata , but differs by having (1) the head without a cephalic tubercle, (2) the carapace with an angular anterodorsal margin (rounded in S. brevicaudata ), (3) the telson with more numerous, gradually increasing in length posterior spiniform setae (three or four short and two or three distinctly long in S. brevicaudata ), (4) the telson with relatively shorter terminal posterolateral pair of spiniform setae (0.36–0.53 times telson length in S. brevicaudata ), (5) a narrower uropodal exopod (3.1–3.4 times as long as wide in S. brevicaudata ) and (6) the uropodal endopod with a greater number of medial spiniform setae (10 or 11 in S. brevicaudata ). A number of additional characters distinguish S. occulta sp. nov. from different species of the group ( Table 1 ).

Distribution

Arabian (Persian) Gulf: Saudi Arabia and Bahrain ( Fig. 1 ). Type locality: Saudi Arabia.

Habitat and life history

In one case found in April at a water temperature of 16.4°C and salinity 40‰. Other habitat data were not recorded for this species. Larvigerous females from July to February. Number of larvae 3 to 15 (see detailed account in Grabe et al. 2004).

Remarks

During the survey of penaeid shrimps in Tubli Bay of the Arabian Gulf, together with the previously mentioned S. brevicaudata and other mysids reported by Grabe et al. (2004), an unknown species of Siriella was collected, which we describe here as S. occulta sp. nov. and include in the brevicaudata group.

Figures

Fig. 18. Siriella occulta sp. nov., holotype, ♂, length 6.5 mm, Arabian Gulf, Saudi Arabia. A. Anterior part of body, dorsal view. B. Anterior part of body, lateral view. C. Anterodorsal margin of carapace. D. Telson. E. Posterior part of telson, ventral view. F. Peduncle of antenna 1, dorsal view. G. Antennal scale and peduncle of antenna 2, ventral view. H. Labrum. I. Mandibular palp, medial view. J. Maxilla 1, posterior view. K. Maxilla 2 (endites not shown), anterior view. L. Distal part of maxilliped 1, anterior view. Scale bars: A–B = 0.5 mm; C, E, H, J–L = 0.1 mm; D, F–G, I = 0.25 mm.

Fig. 19. Siriella occulta sp. nov., holotype, ♂, length 6.5 mm,Arabian Gulf, SaudiArabia.A. Maxilliped 1, anterior view. B. Maxilliped 2, anterior view. C. Dactylus of maxilliped 2, anterior view. D. Endopod of pereopod 1, anterior view. E. Exopod of pereopod 1. F. Endopod of pereopod 6, anterior view. G. Penis. Scale bars: A–B, D–G = 0.25 mm; C = 0.1 mm.

Fig. 20. Siriella occulta sp. nov., holotype, ♂, length 6.5 mm, Arabian Gulf, Saudi Arabia. A. Pleopod 1, posterior view. B. Pleopod 4, posterior view. C. Uropodal endopod, dorsal view. D. Uropodal exopod, dorsal view. Scale bars: 0.25 mm.

Fig. 21. Siriella occulta sp. nov., paratype, ♀, length 5 mm, Arabian Gulf, Saudi Arabia. A. Dorsal part of carapace, lateral view. B. Anterior part of body, dorsal view. C. Peduncle of antenna 1, dorsal view. D. Mandibles with mandibular palp, posterior view. Scale bars: A–B = 1 mm; C = 0.5 mm; D = 0.1 mm.

Fig. 1. Distribution of species in the Siriella brevicaudata species group. Question mark (?) indicates published record requires verification.