Siriella inornata Hansen 1910
Creators: name: Talbot, Suzette
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Mysida
Mysidae
Siriella
Siriella inornata

description: Siriella inornata Hansen, 1910
(Figures 12, 13, 14, 15)
Siriella inornata Hansen, 1910:36, pl. IV, fig. 2a–k. — W.M. Tattersall, 1928: 106, fig. 28. — Illig, 1930: 563. — W.M. Tattersall, 1936a: 146. — W.M. Tattersall, 1936b: 279. — W.M. Tattersall, 1951: 65. — Gordan, 1957: 379. — O.S. Tattersall, 1960: 168, figs 1A–E. — Ii, 1964: 123. — Mauchline & Murano, 1977: 76. — Fenton, 1985: 37, 47 (key). — Carleton & Hamner, 1989: 464, table 1. — Muller, 1993: 38. — Panampunnayil, 1995: 1945 (table). — Lowry & Stoddart, 2003: 467. — Yerman & Lowry, 2007: interactive key.
Type material. SYNTYPES: 3 specimens, Zoological Museum, University of Copenhagen, Denmark; numerous specimens, Zoological Museum, University of Amsterdam, Netherlands.
Type locality. Siboga Station 37, Sailus ketjil, Pulau Satengar (as Paternoster Islands), Flores Sea; Siboga Station 40, anchorage off Pulau Kawassang, Pulau Satengar (as Paternoster Islands) Flores Sea; Siboga Station 41, 7°25’S 117°50.5’E, Flores Sea, Indonesia; Siboga Station 99, anchorage off North Ubian (6°7.5’N 120°26’E), Sulu Archipelago, Sulu Sea, Philippines.
Material examined. Seven specimens, plankton tow, surface, Lizard Is. lagoon centre, 1958 hrs May 29 1975 (STL-75-N5) (AM P73804). 2 females, plankton tow, surface, Lizard Is. lagoon centre, 2022 hrs May 16 1976 (STL-76-N9) (AM P73805). 1 juvenile, plankton tow, 5 m depth, Lizard Is. lagoon centre, 1935 hrs Jan. 7 1977 (STL-77-N9). 7 juveniles, plankton tow, 5 m depth, Lizard Is. lagoon centre, 1959 hrs Jan. 7 1977 (STL-77-N10). 2 specimens, plankton tow, surface, Lizard Is. lagoon centre, 2014 hrs Jan. 7 1977 (STL-77- N11) (AM P73806). 6 specimens, plankton tow, surface, Lizard Is. lagoon centre, 2027 hrs Jan. 7 1977, (STL- 77-N12) (AM P73807). 94 specimens, fixed trap, above Porites andrewsii, Long Reef, N. W. edge of Lizard Is. lagoon, overnight, Jan. 13–14 1978 (STL-78-F5) (AM P73808). 99 specimens, fixed trap, above Echinopora lamellosa, N.W. edge of Lizard Is. lagoon, overnight, Jan. 13–14 1978 (STL-78-F5) (AM P73809). 23 specimens, plankton tow, surface, Lizard Is. lagoon centre, 0 0 15 hrs Jan. 14 1978 (STL-78-N9) (AM P73810). 6 specimens, plankton tow, surface, Lizard Is. lagoon centre, 0 0 33 hrs Jan. 14 1978 (STL-78- N10) (AM P73811). 45 specimens, plankton tow, 5 m depth, Lizard Is. lagoon centre, 0 0 57 hrs Jan. 14 1978 (STL-78-N11) (AM P73812). 3 juveniles, fixed trap, above polythene sheet on sand, Lizard Is. lagoon floor, overnight, Jan. 16–17 1978 (STL-78-F7) (AM P73813). 2 juveniles, fixed trap, above sand, no polythene sheet, Lizard Is. lagoon floor, overnight, Jan. 16–17 1978 (STL-78-F8) (AM P73814). 51 specimens, fixed trap, above polythene sheet on P. andrewsii & E. lamellosa, Lizard Is. lagoon floor, overnight, Jan. 16–17 1978 (STL-87-F9) (AM P73815). 35 specimens, fixed trap, above P. andrewsii, no polythene sheet, Lizard Is. lagoon floor, overnight, Jan. 16–17 1978 (STL-78-F10) (AM P73816). 2 specimens, fixed trap, above sand, deep lagoon floor, Lizard Is. lagoon, overnight, Jan. 17–18 1978 (STL-78-F11) (AM P73817). 3 juveniles, fixed trap, above sand, deep lagoon floor, Lizard Is. lagoon, overnight, Jan. 17–18 1978 (STL-78-F12) (AM P73818). 3 juveniles, fixed trap, above sand & algal mat, deep lagoon floor, Lizard Is. lagoon, overnight, Jan. 17 –181978 (STL-78-F13) (AM P73819). 116 specimens, plankton tow, surface, Lizard Is. lagoon, 2004 hrs Feb. 2 1980 (J.M.L. 2.2.1) (AM P73820). 5 specimens, plankton tow, 6 m depth, Lizard Is. lagoon, 2107 hrs Feb. 2 1980 (J.M.L. 2.2.3) (AM P73821). 54 specimens, plankton tow, surface, Lizard Is. lagoon, 1930 hrs Dec. 1 1980 (Grindley #7) (AM P74038). 361 specimens, plankton tow, surface, Lizard Is. lagoon, 2130 hrs Dec. 1 1980 (Grindley #8). 69 specimens, plankton tow, surface, Lizard Is. lagoon, 2330 hrs Dec. 1 1980 (Grindley #9). 217 specimens, plankton tow, surface, Lizard Is. lagoon, 0 130 hrs Dec. 2 1980 (Grindley #10). 103 specimens, plankton tow, surface, Lizard Is. lagoon, 0 330 hrs Dec. 2 1980 (Grindley #11). 5 specimens, plankton tow, surface, Lizard Is. lagoon, 0 530 hrs Dec. 2 1980 (Grindley #12) (AM P74039). 3 specimens, light trap, Lizard Is. lagoon, 2000–0400 hrs Dec. 20–21 1993 (Alexander) (AM P74040). 6 specimens, light trap, Lizard Is. lagoon, 2000–0400 hrs Dec. 21–22 1993 (Alexander) (AM P74041). Total: 1330 specimens.
Size range: 345 males, 7.5–12.5 mm. 92 immature males, 5.5–9.0 mm. 256 females, maximum of 20 young in marsupium, 9.5–13.2 mm. 73 females, marsupium empty, 9.6–14.5 mm. 209 immature females, 4.0– 10.1 mm. 346 juveniles, 1.5–6.5 mm.
Description. Head: eyes, stalked, large, black, globose, (diameter of adult male cornea, 0.9 mm), (Figs 12 A, B). Rostrum shallow, obtusely triangular with small sharp point, slight pseudo-rostral process protruding beneath (Fig. 12 A). Antennal scale as long as antennular peduncle, narrow (length almost 4x maximum width), lateral spine towards distal end of outer margin, small terminal lobe present (Fig. 12 C). Labrum rounded, anteriorly directed medial spiniform process almost 0.5x length of labrum proper (Fig.12 D). Mandibular palp with moderately broad basal article (maximum width almost 0.5x total length) (Figs 12 E, F). Maxillule and maxilla typical of the genus, maxilla markedly setose (Figs 12 G, H). First thoracic somite fused with head, endopod of 1st thoracic limb modified as a gnathopod, stout, basis enlarged, exopod natatory, epipodite delicate, leaf-like (Fig. 13A).
Pereon: endopod of 2nd thoracic limb modified as fairly robust gnathopod, (Fig. 13B), endopods of thoracic limbs 3–8 slender, elongate, dactylus terminating in a long narrow nail, all exopods natatory, with setose flagella and broad, flat proximal articles having a spine on the outer distal margin, except thoracic limb 8 in which margin is rounded, males with genital organ projecting from coxal area of 8th thoracic limb (Fig. 13C).
Pleon: females with small uniramous pleopods (Fig. 12 B), male pleopods 2–5 biramous, with spirally coiled pseudobranchiae, setae of 3rd pleopods unmodified (Fig. 13D), 4th pleopods longer than 3rd, exopod and endopod terminate in elongate modified setae, exopod with 2 robust setae projecting from terminal article, outer seta, naked, elongate, rod-like, almost straight, slightly swollen apically, ending in crenulate border surrounding tip, inner robust seta shorter (slightly less than 0.5 length of outer), curved, naked, except for row of short setules distally on lateral edge, penultimate and pre-penultimate articles flattened and distally enlarged, both with paired unmodified setae, penultimate with additional curved naked robust seta on inner distal margin, endopod with 2 strong, curved, acutely pointed robust setae on terminal article, both with a fringe of small setules on either margin, outer seta elongate, inner seta thick, short, length about 0.3x length of outer seta (Figs 13 E, F). Uropodal exopod moderately broad, longer than endopod, 13–16 graduated robust setae along outer border of proximal article, endopod tapered, row of 66–67 robust setae on inner margin (Fig. 14 A). Telson linguiform, with broad base, pronounced ‘waist’, strongly tapered distally, terminating beyond diaresis of uropodal exopod, 3 pairs stout robust setae on basal lateral margins, more distally, a short diastema, followed by 38–40 robust setae on each margin, terminating in a long stout seta, with 3 small apical setae and 2 long delicate plumose setae (Figs 14 A, B).
FIGURE 13. Siriella inornata Hansen, 1910. A, right 1st thoracic limb. B. right 2nd thoracic limb. C, left 8th thoracic limb (male). D, right 3rd pleopod (male). E, right 4th pleopod (male). F, right 4th pleopod, terminal articles of endopod and exopod. Scalebars = A, B, C, F: 0.2 mm; D, E: 0.5 mm.
Remarks. Like S. anomala and S. distinguenda, S. inornata is a large species, with prominent dark eyes. Males can be identified by the characteristic armature of both rami of the 4th pleopods, while the structure of the tail fan may be used to distinguish females and young stages from those of similar species, such as S. anomala and S. distinguenda. As the differences are slight, positive identification is often difficult. In S. inornata the uropodal exopod is distinctly longer than the endopod and its distal article is fairly short and broad, less than 0.5x the length of the proximal article, while in the other 2 species, it is narrower and at least 0.5–0.6x the length of the proximal article. The telson is longer than that of the other species, reaching clearly beyond the diaresis in the uropodal exopod.
Behaviour. Evidence of the strong tendency of S. inornata to migrate up into the surface layers at night is provided by Professor Grindley's series of surface plankton samples, taken every 2 hours over a 24 hour period, in the Lizard Island lagoon. The numbers of S. inornata caught were as follows: 0 at 1730 hrs, 54 at 1930 hrs, 361 at 2130 hrs, 69 at 2330 hrs, 217 at 0 130 hrs, 103 at 0 330 hrs, 5 at 0 530 hrs and 0 at 0 730 hrs (Fig. 15).
This indicates that they moved into the surface layers after dark, with numbers peaking in the middle of the night and that by dawn most of them had descended to lower levels. S. inornata was also well represented in samples taken in those of the fixed traps that were set above living corals during the day and left overnight. It is probable, therefore, that this mysid shelters in or around corals during daylight hours. It appears to be markedly photophobic. It was never found in samples taken over pale backgrounds, such as sand or rubble, nor was it taken in the light trap used to sample near-reef zooplankton, even when it was placed directly over living corals. Professor Alexander’s 2 light trap samples from the lagoon contained 9 specimens of S. inornata, but since this mysid migrates into the upper water layers in large numbers at night, the presence of only a few in a trap deployed for a period of 8 hours on each of 2 successive nights suggests that it was not strongly attracted to the light source.
Associated mysid species. The following 4 species were taken in more than half of the 28 samples in which S. inornata occurred; Anisomysis laticauda, A. incisa, Pseudanchialina inermis and Haplostylus pacificus. A. laticauda was present, usually in large numbers, in 25 of them.
Habitat. Coral reefs in lagoons and nearshore waters.
Distribution. This tropical inshore species is known from southern Indonesian waters, the Sulu Sea, (Hansen 1910), the northern and southern Philippines (W.M. Tattersall 1951) and the Ryukyu Islands between Japan and Taiwan (Fukuoka & Murano 1997). It may also occur in the Singapore Strait (O.S. Tattersall 1960). In Australia it has been found in northern Queensland, in Princess Charlotte Bay (W.M. Tattersall 1928) and the Great Barrier Reef at Low Isles (W.M. Tattersall 1936a), Heron Island (Fenton 1982) and Davies Reef (Carleton & Hamner 1989).
The 1330 specimens from the Lizard Island survey were all caught in the lagoon, mostly in surface plankton hauls made at night, or in fixed traps set overnight above living coral heads. The 23 specimens captured by the Great Barrier Reef Expedition were recorded from comparable areas. They were taken in night tow-nettings at the Low Isles anchorage and over the Low Isles flat. Adults were caught in May and June, but only immature specimens in October and November (W.M. Tattersall 1936a). At Lizard Island, samples were not taken in all months of the year, but mature adults, including females carrying young, were found in January, February, May and December.
Siriella lacertilis, sp. nov. (Figures 16, 17, 18)
Type material. Type specimens deposited in the Australian Museum, Sydney: Holotype: adult male, AM P74061, fixed trap above sand, near Research Point, N. W. edge of Lizard Is. lagoon, overnight, Jan. 13–14 1978 (STL-78-F4). Paratype: adult female, AM P74062, plankton tow, surface, Lizard Is. lagoon centre, 2342 hrs Jan. 8 1978 (STL-78-N7).
Type locality. Lizard Island lagoon.
Additional material examined One female, light trap, on sand between corals (light on), reef E. of Palfrey Is., Lizard Is lagoon, 2146 hrs Jan. 4 1975 (STL-75-T8) AM P74042. 1 male, light trap, on living Porites, (light on), reef E. of Palfrey Is., Lizard Is. lagoon, 2228 hrs Jan. 4 1975 (STL-75-T11) AM P74043. 1 female, vertical plankton haul, Lizard Is. lagoon centre, 2300 hrs Jan. 8 1975 (STL- 75-V1) AM P74044. 1 female, push net, over sandy floor, 10 m depth, Lizard Is. lagoon centre, 1515 hrs May 17 1976 (STL-76-P6) AM P74045. 1 male, light trap, reef flat off research station, Sept. 1976 (Smith & Marshall) AM P74046. 1 juvenile, push net, over coral rubble, 2 m depth, passage between Palfrey & South Is., Lizard Is. lagoon, 1550 hrs Jan. 9 1977 (STL-77-P5) AM P 74047. 4 specimens, plankton tow, 5–6 m depth, Lizard Is. lagoon centre, 2325 hrs Jan. 8 1978 (STL-78-N6) AM P74048. 5 specimens, plankton tow, surface, Lizard Is. lagoon centre, 2342 hrs Jan. 8 1978 (STL-78-N7) AM P74049. 4 specimens, plankton tow, surface, Lizard Is. lagoon centre, 2357 hrs Jan. 8 1978 (STL-78-N8) AM P74050. 1 female, hand net, over sand near Research Point, N. W. edge of Lizard Is. lagoon, 0 0 20 hrs Jan. 9 1978 (STL-78-H3) AM P74051. 7 specimens, fixed trap, above sand near Research Point, N. W. edge of Lizard Is. lagoon, overnight, Jan. 10–11 1978 (STL-78-F1) AM P74052. 3 specimens, fixed trap, above sand near Research Point, N. W. edge of Lizard Is. lagoon, overnight, Jan. 13–14 1978 (STL-78-F3) AM P74053. 1 male, fixed trap, above sand near Research Point, N. W. edge of Lizard Is. lagoon, overnight, Jan. 13–14 1978 (STL-78-F4) AM P74054. 1 juvenile, fixed trap, above horizontal plate of favid coral, Echinopora lamellosa, reef S. of Research Point, overnight, Jan. 13–14 1978 (STL-78-F6) AM P74055. 3 specimens, plankton tow, surface, Lizard Is. lagoon centre, 0 0 15 hrs Jan. 14 1978 (STL-78-N9) AM P74056. 6 specimens, plankton tow, surface, Lizard Is. lagoon centre, 0 0 33 hrs Jan. 14 1978 (STL-78-N10) AM P74057. 3 specimens, plankton tow, 5–6 m depth, Lizard Is. lagoon centre, 0 0 57 hrs Jan. 14 1978 (STL-78-N11) AM P74058. 1 female, fixed trap, above deep lagoon floor, disturbed sand, Lizard Is. lagoon, overnight, Jan. 17–18 1978 (STL-78-F13) AM P74059. 1 juvenile, plankton tow, 6 m depth, Lizard Is. lagoon, night, Feb. 2 1980 (J.M.L. 2.2.3. 2107) AM P74060. Total: 48 specimens.
Size range: 8 males, 5.0– 6.7 mm. 6 immature males, 4.3–5.2 mm. females, maximum of 6 young in marsupium, 5.7, 6.3 mm. 1 female, marsupium empty, 5.0 mm. 11 immature females, 3.8–6.5 mm. 20 juveniles, 1.7–4.5 mm.
Diagnosis. Head: eyes red-brown, prominent, hemispherical, diameter greater than that of eyestalk. Carapace short, exposing last 3 thoracic segments dorsally, frontal plate rounded, rostrum forming a shallow obtuse curve, an acutely pointed pseudo-rostral spine projecting beneath it, cervical groove conspicuous (Figs 16 A, B). Male antennular peduncle stout, 3rd article broad, appendix masculina with dense brush of sensory setae (Fig. 16 A), female antennular peduncle slender (Fig. 16 B). Scale of antenna broad, length to width ratio about 3 to 1, spine and notch on outer margin at about three quarter length, distal lobe small, suture faintly visible. Antennal peduncle with strong spine on outer border of distal article at base of scale (Fig. 16 C).
Labrum rounded, cordiform, anteriorly directed spiniform process small, barely extending beyond edge of labrum proper (Fig. 16 D). Mandible with well-developed molar process, basal article of palp not markedly broader than distal article (Fig. 16 E). Maxillule and maxilla as in other members of the genus, with palp of maxillary endopod expanded to form an oval plate (Figs 16 F, G). First thoracic somite fused with head, endopod of 1st thoracic limb modified as a gnathopod, broad, stout, setose on inner border, dactylus terminating in a strong curved nail, exopod natatory, epipodite large, delicate, leaflike (Fig. 17A).
FIGURE 17. Siriella lacertilis sp. nov. A, 1st thoracic limb. B, 2nd thoracic limb. C, 4th thoracic limb. D, 8th thoracic limb (male). Scalebars = A, B, C, D: 0.2 mm.
Pereon: endopod of 2nd thoracic limb broad, stout, functioning as a gnathopod, dactylus terminating in a long nail, curved at tip (Fig. 17B), 3rd and 4th limbs robust (Fig. 17C), limbs 5–8 relatively slender, ovoid genital organ at base of 8th thoracic limb of males (Fig. 17D).
Pleon: pleopods 2–5 biramous, natatory, with spirally coiled pseudobranchial rami, 3rd and 4th pleopods without modified terminal setae (Figs 18A,B). Uropodal exopods longer than endopods, with proximal article having 3 graduated robust setae distally at angle of outer margin, inner margin of endopod with 14–15 evenly spaced, graduated robust setae, increasing in size from statocyst towards distal edge, a row of fine vertical setae projecting upward from outer margin, endopod and distal article of exopod fringed with plumose setae (Fig. 18C). Telson broadly linguiform, truncated, wide posterior border slightly emarginate, barely reaching level of robust setae on proximal article of uropodal exopod, base of telson with 3 stout robust setae on each lateral border, more distally, a diastema on each side, followed by 7 graduated robust setae, posterior border with 4 long, stout robust setae, outer 2 slightly shorter than inner 2, flanking 3 or 4 minute central setae and a pair of long, delicate plumose apical setae (Fig. 18D).
FIGURE 18. Siriella lacertilis sp. nov. A, 3rd pleopod (male). B, 4th pleopod (male). C, right uropod, ventral view. D, telson and left uropod, ventral view. Scalebars = A, B, C, D: 0.2 mm
Etymology. From the Greek ‘lacerta’; a lizard, ‘lacertilis’; of the lizard, referring to the type locality, Lizard Island.
Remarks. Siriella lacertilis belongs to Ii's ' thompsonii ' group of the Genus Siriella. It is a member of a subgroup of species in which the frontal plate of the carapace is rounded, with an obtuse, barely developed rostrum and in which the telson is short and does not extend as far as the proximal article of the uropodal exopod. The subgroup also includes S. brevicaudata (Paulson 1875), S. hanseni (W.M. Tattersall 1922), S. lingvura (Ii 1964) and S. vincenti (W.M. Tattersall 1927). Other characteristics they have in common are; a medial pseudo-rostral spine below the anterior margin of the carapace, a pronounced cervical groove, uropods in which the exopod is longer than the endopod, with the row of robust setae on the endopod consisting of relatively few, fairly widely spaced uniform setae, not separated by groups of smaller setae.
In the 3 species of the subgroup in which the structure of the labrum has been examined, i.e. S. lacertilis, S. lingvura and S. vincenti, it was found to differ from that regarded as typical of the genus. In all the other species in which its structure has been recorded, the labrum is produced anteriorly to form a large forwardly directed medial spiniform process, with a length about half to three quarters that of the basal part of the labrum. The above 3 species are exceptional in having a cordiform labrum, with a rounded anterior margin, bearing a small medial process, the length of which is about a sixth to an eighth that of the body of the labrum.
Of the 5 species in the subgroup, S. lacertilis most closely resembles S. brevicaudata, as redescribed by W.M. Tattersall (1922). They are both small inshore mysids, (adult length about 6 mm) and the dimensions of their eyes (adult male cornea, 0.4 mm in diameter) and antennal scales are similar, although the eyes of S. lacertilis are red-brown in colour, while S. brevicaudata has black eyes. In both, the carapace has a conspicuous cervical groove, but the slight mid-dorsal tubercle present in S. brevicaudata, was not found in S. lacertilis.
The tail fans of the 2 species differ in several respects. S. lacertilis has 3 robust setae at the distal angle on the outer margin of the uropodal exopod's proximal article, while in S. brevicaudata, the article has 5 distal robust setae. In S. lacertilis the length of the exopod's distal article is about three quarter that of the proximal article, but in S. brevicaudata it is considerably shorter, with a length only one third that of the proximal article. In S. lacertilis, the uropodal endopod has 14–15 robust setae in the row bordering its inner margin, while in S. brevicaudata, it has 10–12.
The 2 species bear a strong resemblance to each other in the overall structure of the telson; in both, it is unusually truncated, with a broad, slightly emarginate posterior border, from which there extends a set of long, stout robust setae. They differ, however, in the proportions of the telson and in the number and arrangement of the setae. In S. lacertilis the width of the posterior margin is between a quarter and a third of the total telson length, but in S. brevicaudata, the apex is even broader, being half the length of the telson. In S. lacertilis, the 4 long, sub-equal posterior robust setae and the adjacent 2 rows of 7 shorter lateral setae make up a total of 18 robust setae on the distal margin of the telson, while S. brevicaudata ’s telson has only 10 or 12 distal robust setae. These form a graded series, with the 2 longest on either side of the 3 minute central setules and 2 plumose setae of the posterior margin. Lateral to each long robust seta are 3 progressively shorter setae, followed by 1 or 2 small setae at the angle of the posterior and lateral margins. Proximally, S. lacertilis has 3 stout robust setae on either side of the base of its telson and S. brevicaudata has 2 or 3 similarly positioned robust setae.
Associated mysid species. Of the 23 species found in the 19 samples containing S. lacertilis, 3 occurred in at least half of them. Anisomysys laticauda was present in 15, Pseudanchialina inermis in 14 and Anisomysis incisa in 10 of the samples.
Habitat. Coral reef, sublittoral and lagoonal. S. lacertilis was taken in small numbers in the Lizard Island lagoon and on the adjacent reef flat, in both light traps and fixed traps set over sand, rubble and living coral, the largest number occurring in fixed traps over sand. It was also caught in plankton hauls made around midnight in the lagoon, just below the surface and at a depth of 5- 6 m.
description: Published as part of Talbot, Suzette, 2009, A survey of Mysida from the Lizard Island area, Great Barrier Reef, Australia, Subfamily Siriellinae (Crustacea, Mysida, Mysidae), pp. 1-49 in Zootaxa 2114 on pages 20-30, DOI: 10.5281/zenodo.187927