Siriella tabaniocula, 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 : 51-57

Siriella tabaniocula sp. nov.

urn:lsid:zoobank.org:act:1952D554-4B1B-4557-8E60-0FC4F540D80A

Figs 22–25

Diagnosis

Carapace with anterodorsal margin almost evenly rounded, not covering subrostral process. Carapace dorsal surface with slight tubercle and clear postcervical elevation. Eye cornea white, with three goldenyellow horizontal stripes. Telson 0.9 times as long as last abdominal somite, not reaching distolateral spiniform setae of uropodal exopod, 1.5–1.7 times as long as wide anteriorly and 1.5 times as wide anteriorly as posteriorly; lateral margins with three or four anterior and 11 to 13 gradually increasing in length posterior spiniform setae. Telson with terminal posterolateral pair of spiniform setae 0.18– 0.19 times as long as telson and 1.3–1.4 times as long as subterminal pair; subterminal spiniform setae 1.4 times as long as preceding posterolateral. Telson with apical margin with three minute, but clearly visible central spinules, about 0.2 times as long as posterolateral terminal spiniform setae; without emargination. Labrum with anterior spine short, barely visible, <0.1 times as long as rest of labrum. Maxilla 1 with apical robust smooth setae. Maxilla 2 endopod segment 2 with three or four distolateral setae. Pereopod 1–3 merus 3.1–3.4 times as long as wide. Uropodal exopod 3.9–4.0 times as long as wide; segment 1 is 1.8–1.9 times as long as segment 2, with three to five distolateral spiniform setae. Uropodal endopod with 10 to 13 medial spiniform setae; terminal spiniform seta not reaching apical margin of ramus.

Etymology

The name tabaniocula is derived from Latin tabanus, meaning ‘horsefly’, and oculus, meaning ‘eye’, and denotes the unusual striped color of the eye cornea, reminiscent of the eye color in horseflies of the family Tabanidae (Diptera) .

Material examined

Holotype

AUSTRALIA: ♀, 6 mm long, Western Australia, Ningaloo Reef, 22.76912° S, 113.70458° E, off Ningaloo CReefs camp, 12 m, AUST-7299, ARMS 5, 20 May 2010, A. Fusaro leg., processed by A. Anker ( WAM C70257; slide C70257).

Paratype

AUSTRALIA: immature ♀, 5.5 mm long, same collection data as for holotype, parasitized by one large and several small specimens of dajid isopods ( WAM C70258).

Other material

AUSTRALIA: 1 immature ♀ (thoracopods missing), 4.5 mm long, Queensland, Lodestone Reef, 10 m, Pocillopera head, host for dajid, 1982, P. Dohorty leg., previously identified as Siriella hanseni by M. Băcescu ( NTM Cr000398).

Description

Female (holotype) Body length 6 mm.

CARAPACE. Head about as wide as abdominal segment 1. Anterior margin of carapace almost evenly rounded, not covering subrostral process ( Fig. 23B ); posterior margin exposing three thoracic segments. Dorsal surface of carapace with slight tubercle and clear postcervical elevation ( Fig. 23A ).

TELSON. Telson 0.88 times as long as last abdominal somite, 1.7 times as long as wide anteriorly and 1.5 times as wide anteriorly as posteriorly; lateral margins slightly tapering, with three anterior spiniform setae and 11 and 12 posterior spiniform setae after gap, gradually increasing in length towards apex; apically with three short dorsally visible spinules and two long plumose setae between them, longer than spiniform setae flanking them ( Fig. 23C ). Terminal posterolateral pair of spiniform setae of telson 1.4 times as long as subterminal and 0.18–0.19 times as long as telson; subterminal pair of spiniform setae 1.4 times as long as preceding posterolateral.

HEAD APPENDAGES. Eyes large, cylindrical, 1.2 times as long as wide and 0.7 times as long as head width. Antennae 0.3 times as long as body. Peduncle of antenna 1 thin, much longer than peduncle of antenna 2; segment 1 slightly longer than segments 2 and 3 together, with two distolateral bunches of one and two plumose setae; segment 2 with two distolateral and one distomedial plumose setae; segment 3 with bunch of two short lateral setae and two distomedial bunches of one and three long plumose setae ( Figs 23B , 24B ). Segment 2 of antenna 2 peduncle 1.3 times as long as segment 3 ( Fig. 24A ). Antennule inner flagellum normal, not dilated or meandering in proximal part. Antennal scale about as long as peduncle of antenna 1, 1.6 times as long as peduncle of antenna 2 and 3.1 times as long as wide; lateral spine in distal part; distal segment with five setae. Total antennal scale length 1.2 of length from scale base to lateral spine base; maximal width 1.3 of distal width ( Fig. 24A ). Labrum with small, barely visible, anterior spine, <0.1 times as long as rest of labrum ( Fig. 24C ). Mandibular palp segment 2 with few short and long setae; segment 3 is 0.5 times as long as segment 2, with three proximal medial setae, two–three lateral and one distal setae; palm with four setae ( Fig. 24D ). Maxilla 1: inner lobe with about 10 smooth apical robust setae ( Fig. 24E ). Maxilla 2 ( Fig. 24F ): exopod oval, with 14 plumose setae; endopod segment 1 with three medial setae; endopod segment 2 oval, slightly larger than exopod, 1.7 times as long as wide, with three lateral setae and 13 long medial spiniform setae and simple setae, longer than spiniform setae; endites with strong spiniform setae.

MAXILLIPEDS. Exopod of thoracopods 8–9-segmented ( Fig. 24I ). Maxilliped 1 without endites; basis, preischium, ischium and merus with medial setae; merus also with 1 long distolateral seta, about as wide as long; carpopropodus and dactylus with medial and lateral setae ( Fig. 24G ). Maxilliped 2 ( Fig. 24H ): basis medial margin with one proximal seta and distal bunch of setae; preischium with one medial seta; ischium about as long as wide, with one lateral and numerous medial setae; merus about twice as long as wide and 1.5 times as long as ischium, with distolateral bunch of two long setae and three groups of long and short medial setae; carpopropodus about as long and as wide as merus, with thin lateral, two medial bunches and paradactylary bunch of stronger setae; dactylus 0.25 times as long as carpopropodus, with several simple and strong serrated setae; dactylary unguis long, about 2.5 times as long as dactylus.

PEREOPODS. Pereopodal endopods ( Fig. 25 A–F): preischium with one seta; ischium about half as long as merus; segment 1 of carpopropodus 0.4 times as long as segment 2, with one–two distal lateral setae and distal medial bunch of long setae; carpopropodus segment 2 four times as long as wide, with two lateral short setae, a bunch of two short distolateral setae and proximal medial bunch of long setae; dactylus twice as long as wide and 0.3 times as long as carpopropodus segment 2, surrounded by blunt setae, serrated in distal half, about twice as long as dactylus (excluding unguis); dactylus with terminal medial seta and strong unguis, 1.5 times as long as dactylus; dactylus together with dactylary unguis about half as long as carpopropodus. Pereopods 1–3 wider than pereopods 4–6; carpopropodus 0.9 times as long as merus ( Fig. 25 A–C). Pereopod 1 ( Fig. 25A ): basis with distomedial bunch of long thick setae; merus 3.4 times as long as wide, with six medial groups of setae. Pereopod 2 ( Fig. 25B ): basis with three thin distomedial setae; merus 3.1 times as long as wide, with rather irregular groups of medial setae. Ischium of pereopods 1–4 laterally strongly convex, with one lateral seta and many short and long medial setae. Merus of pereopods 1–2 with five thin lateral setae and irregularly set short and long medial setae. Pereopod 3 ( Fig. 25C ): basis with one distal medial seta; merus 3.2 times as long as wide, with two lateral setae and about four irregular groups of medial setae. Pereopods 4–6 ( Fig. 25 D–F): basis with one proximal and one distal medial setae; merus four times as long as wide. Pereopod 4 ( Fig. 25D ): ischium lateral margin with one proximal seta, medial margin with three short median setae and two distal groups of bunches with long and short setae; merus lateral margin with 3 median setae and distal bunch of two setae, medial margin with five groups of long setae. Pereopod 5 ( Fig. 25E ): ischium lateral margin with one proximal and one distal setae, medial margin with two median setae and distal bunch of long setae; merus with three lateral setae and three groups of three–four medial setae. Pereopod 6: ischium with one proximal lateral and one distal medial setae; merus with four lateral setae and two medial bunches of two setae ( Fig. 25F ).

UROPODS. Uropodal exopod 3.9–4.0 times as long as wide, 2-segmented; border between segments barely visible; two flexor muscles of segment 2 present; segment 1 with three to five distolateral spiniform setae, 1.8–1.9 times as long as segment 2 ( Fig. 23E ). Uropodal endopod shorter than exopod, with 13 broadly set medial spiniform setae, extending almost to apex, distally becoming shorter ( Fig. 23D ).

Male

Unknown.

Color

Peduncles of antennae, eyestalks, ventral half of cephalothorax, basal part of pereopods, marsupium, posterior half of abdominal somites (entire somite 6), telson (except for apex) and basal part of uropods bloody-red ( Fig. 22 ). Eye cornea white with three golden-yellow horizontal stripes. Antennal flagellae, thoracopods (except for dactyli), dorsal side of cephalothorax, anterior part of abdominal somites (except for somite 6) and uropods (except for basal part) transparent. Thorcopod dactyli and telson apex white.

Comparison

Living specimens of S. tabaniocula sp. nov. have characteristic eye cornea coloration (hence the name of the species), that is unknown in other species of the brevicaudata group. Siriella tabaniocula sp. nov. most closely resembles S. muranoi sp. nov., from which it differs by (1) the telsonal terminal spiniform setal length (terminal pair about as long as subterminal and 0.14 times as long as telson in S. muranoi sp. nov.), (2) labrum with a very small, barely visible anterior spine (small, well-developed, 0.2 times as long as the rest of the labrum in S. muranoi sp. nov.) and (3) slightly broader pereopods (merus of pereopods 1–3 is 3.8–4.1 times as long as wide in S. muranoi sp. nov.).

The new species is also similar to S. hanseni , differing by (1) the presence of a slight cephalic tubercle and postcervical elevation, (2) a shorter telson (about as long as last abdominal somite in S. hanseni ), (3) the pattern of posterior setation on the telson (graded with terminal posterolateral pair of spiniform setae clearly longer than subterminal pair against graded with three to six apical pairs about equally or nearly equally long in S. hanseni ) and (4) the telson with longer terminal posterolateral pair of spiniform setae (0.08–0.15 times as long as telson in S. hanseni ).

In addition, S. tabaniocula sp. nov. is rather closely related to the Japanese species S. lingvura , but is distinguished from it by (1) the presence of a slight cephalic tubercle and postcervical elevation, (2) a telson with a longer terminal posterolateral pair of spiniform setae (0.13–0.14 times as long as the telson in S. lingvura ), (3) fewer anterolateral spiniform setae on the telson (five or six in S. lingvura ), (4) a labrum with a small, barely visible spine (well-developed, 0.15 times as long as the rest of the labrum in S. lingvura ) and (5) a narrower uropodal exopod (3.6–3.7 times as long as wide in S. lingvura ).

Distribution

Indian Ocean, Western Australia: Ningaloo Lagoon (type locality); Pacific Ocean, Coral Sea, Queensland: Lodestone Reef ( Fig. 1 ).

Habitat

Depth to 10–12 m, in seagrasses. From our material twice recorded as the host of as yet unidentified dajid isopods.

Remarks

Specimens related to S. hanseni found in association with artificial reefs within Ningaloo Lagoon on the coast of Western Australia were compared with the type material and found to represent another new species within the brevicaudata group. The new species, S. tabaniocula sp. nov., is described herein. An additional specimen of this new species, which was collected from Lodestone Reef in Queensland, Australia, was found in the NTM.

Figures

Fig. 22. Siriella tabaniocula sp. nov., holotype, ♀, length 6 mm, Ningaloo Reef, Western Australia. Color photograph of living specimen. Scale bar: 1 mm.

Fig. 23. Siriella tabaniocula sp. nov., holotype, ♀, length 6 mm, Ningaloo Reef, Western Australia. A. Habitus, lateral view. B. Habitus, dorsal view. C. Telson. D. Uropodal endopod, dorsal view. E. Uropodal exopod, dorsal view. Scale bars: A–B = 1 mm; C–E = 0.25 mm.

Fig. 24. Siriella tabaniocula sp. nov., holotype, ♀, length 6 mm, Ningaloo Reef, Western Australia. A. Antennal scale and peduncle of antenna 2, ventral view. B. Antenna 1, dorsal view. C. Labrum. D. Mandibular palp, lateral view. E. Maxilla 1 (endite not shown), anterior view. F. Maxilla 2, anterior view. G. Endopod of maxilliped 1, posterior view. H. Endopod of maxilliped 2, posterior view. I. Exopod of maxilliped 1. Scale bars: A–D, G–I = 0.25 mm; E–F = 0.1 mm.

Fig. 25. Siriella tabaniocula sp. nov., holotype, ♀, length 6 mm, pereopod endopods, anterior views, Ningaloo Reef, Western Australia. A. Pereopod 1. B. Pereopod 2. C. Pereopod 3. D. Pereopod 4. E. Pereopod 5. F. Pereopod 6. Scale bars: 0.25 mm.

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