Siriella anomala Hansen, 1910

Talbot, Suzette, 2009, A survey of Mysida from the Lizard Island area, Great Barrier Reef, Australia, Subfamily Siriellinae (Crustacea, Mysida, Mysidae), Zootaxa 2114, pp. 1-49 : 10-12

Siriella anomala Hansen, 1910

( Figures 5 , 6)

Siriella anomala Hansen, 1910: 41 , pl. V, figs 1a–l. — W.M. Tattersall, 1936a: 146. — W.M. Tattersall, 1936b: 279. — W.M. Tattersall, 1951: 79. — Gordan, 1957: 378. — Ii, 1964: 143, figs 38–39. — Mauchline & Murano, 1977: 76. — Fenton, 1985: 37, 45 (key). — Muller, 1993: 33. — Panampunnayil, 1995: 1945 (table). — Fukuoka & Murano, 1997: 523, fig. 3A–D. — Lowry & Stoddart, 2003: 465. — Yerman & Lowry, 2007: interactive key.

Type material. SYNTYPES: 11 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 Pulu Kawassang, Pulau Satengar (as Paternoster Islands), Flores Sea; Siboga Station 41, 7°25’S 117°50.5’E, 10 m depth, Flores Sea, Indonesia.

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 P73784). 4 specimens, plankton tow, surface, Lizard Is. lagoon centre, 2034 hrs May 16 1976 (STL-76-N10) (AM P73785). 3 specimens, plankton tow, surface, Lizard Is. lagoon, 2004 hrs Feb. 2 1980 (J.M.L. 2.2.1) (AM P73786). 63 specimens, plankton tow, 6 m depth, Lizard Is. lagoon, 2107 hrs Feb. 2 1980 (J.M.L. 2.2.3) (AM P73787). 1 male, light trap, Lizard Is. lagoon, 2000–0400 hrs, Dec.21 1993 (Alexander) (AM P73788). Total: 72 specimens.

Size range: 12 males, 7.9–11.0 mm, 2 immature males, 6.9–7.3 mm, 4 females, maximum of 11 larvae in marsupium, 8.8–10.9 mm, 2 females, parasite in marsupium, 10.6 & 11.0 mm, 3 females, marsupium empty, 8.6–10.1 mm, 8 immature females, 5.5–8.4 mm, 5 juveniles, 2.8–4.1 mm, 36 newly emerged larvae, 2.2–2.5 mm.

Description. Head: eyes large, dark, globose ( Figs 5 A, B) (diameter of adult male cornea, 0.8 mm), no spine at antero-distal corner of eyestalk. Rostrum obtusely triangular, pseudo-rostral process present beneath apex. Antennal scale as long as antennular peduncle, scale with apical suture, sexually dimorphic ( Figs 5 C, D). Labrum with long anteriorly directed medial spiniform process, more than half length of labrum proper ( Fig. 5 E). Mandibular palp with moderately expanded proximal article, length 3x maximum width ( Fig. 5 F). First thoracic somite fused with head, endopod of limb modified as a gnathopod, epipodite leaf-like.

Pereon: endopods of pereopods slender, fairly elongate, dactylus terminating in a long slim nail, exopods natatory (Fig. 6A).

Pleon: male pleopods with straight pseudobranchiae, endopods of pleopods 3 and 4 longer than exopods and terminating in an armature of modified robust setae (Fig. 6B, C, D, E): telson and uropods slender, uropodal exopod with about 13 robust setae on lateral margin of proximal article, distal article unusually elongate, slightly less than half total length of exopod, uropodal endopod with about 60 robust setae on inner margin, endopod shorter than exopod, telson with 3 pairs of stout basal robust setae and a distinct ‘waist’, more distally, each lateral margin lined with about 40 robust setae terminating in 3 small distal setae and a pair of long slender plumose setae, telson reaches level of diaresis in uropodal exopod (Fig. 6F).

Remarks. Siriella anomala is a large mysid with prominent black eyes. Males have a distinctive antennal scale in which the antero-lateral spine is positioned almost halfway down the lateral margin. At the base of the spine is a smoothly rounded concavity from which projects a strongly curved plumose seta. Beyond this the proximal lobe forms a long, fairly narrow extension terminating in a small distal lobe. Among the apical setae projecting from the lobe, the inner 2 are modified with the innermost bearing a group of flattened setules ( Fig. 5 C). The antennal scale of the female is long and relatively broad (length 4x maximum width) with an anterolateral spine near the distal end of the margin and none of the apical setae modified ( Fig. 5 D).

Parasites. A parasitic female choniostomatid copepod occupied the marsupium of 2 of the 9 mature S. anomala females captured. In each case the heart-shaped parasite completely filled the marsupial pouch.

Associated mysid species. Among the 15 mysid species taken with S. anomala , only Anisomysis laticauda Hansen, 1910 occurred in all 5 samples, while Siriella distinguenda , Siriella inornata , Haplostylus pacificus Hansen, 1912 and Pseudanchialina inermis Illig, 1906 were found in 3 of them.

Habitat. Pelagic in coral reef areas.

Distribution. Described from the Flores Sea in southern Indonesian waters ( Hansen 1910), S. anomala is also known from the Marshall Islands and the Philippines ( W.M. Tattersall 1951), Palau ( Ii 1964) and the Ryukyu Islands ( Fukuoka & Murano 1997). A single male has previously been recorded from Australian waters. It was taken by the Great Barrier Reef Expedition at the Low Isles anchorage ( W.M. Tattersall 1936a).

The Lizard Island specimens were all caught in the Lizard lagoon at night, the largest number being 63, taken in a plankton tow at a depth of 6 m.

FIGURE 6. Siriella anomala Hansen, 1910 . A, left 3rd thoracic limb (male). B, 3rd pleopod (male). C, 3rd pleopod (male), terminal articles of endopod. D, 4th pleopod (male). E, 4th pleopod (male), terminal articles of endopod. F, telson and right uropod (male). Scalebars = A, B, D, F: 0.5 mm; C, E: 0.2 mm.

Figures

FIGURE 5. Siriella anomala Hansen, 1910. A, anterior cephalothorax (male, 10 mm). B, lateral view (female, 10 mm). C, right antenna (male). D, right antenna (female). E, labrum. F, right and left mandibles. Scalebars = A, B: 1.0 mm; C, D, E, F: 0.5 mm.