Siriella brevispina, Biju, Abraham, Jasmine, Purushothaman & Panampunnayil, Saramma U., 2010

Biju, Abraham, Jasmine, Purushothaman & Panampunnayil, Saramma U., 2010, Mysids (Crustacea: Peracarida) from the southern Indian Ocean with descriptions of two new species, Zootaxa 2652, pp. 33-46 : 38-40

Siriella brevispina sp. nov.

( Fig. 4 )

Material examined. Holotype. Spent female (IOBC-0511H-10-50-2010), 8.3 mm, dissected. Paratypes. 1 female with eggs (IOBC-0511P-10-50-2010), 6.5 mm. –1 immature female (partially damaged), (IOBC-0511-10-50-2010).

Type locality. Sta. 4 (36° 59'S, 45°E), southern Indian Ocean, 0 3.02.2004, 23:32 hr., BN, sampling depth: surface waters.

Diagnosis. Triangular rostrum. Labrum with long anterior process. Inner margin of uropodal endopod armed with 67 spines, arranged alternately with long and short spines; uropodal exopod armed with 4 spines. Telson short, lateral margin with 3 short spines, apical margin with 2 pairs of short spines and 1 pair of long plumose setae.

Description. Rostrum produced anteriorly into triangular plate with concave lateral margin, extending to basal 1/4 of first segment of antennular peduncle ( Fig. 4 A). Anterolateral corners of carapace rounded, posterior margin emarginated, leaving last 2 thoracic somites dorsally exposed.

Eye of moderate size, extending to middle of first segment of antennular peduncle.

Antennular peduncle slender, first segment narrow, as long as succeeding 2 segments combined, outer margin concave, with 2 long setae on dorsal corner (in figure, one masks the other). Second segment short, with 1 long seta on inner distal corner and 2 short and one long setae on outer distal corner; third segment with 1 long seta at distal 2/3 of inner margin and 3 long setae at inner distal corner ( Fig. 4 B).

Antennal scale extending near distal end of third segment of antennular peduncle, slightly more than 5 times as long as broad; outer margin naked, terminating in a spine, terminal lobe slightly shorter than broad; distal suture present ( Fig. 4 C). Antennal peduncle slender, extending distal 1/3 of antennal scale, second segment longest, 4 times as long as third ( Fig. 4 C).

Labrum with long anterior process ( Fig. 4 E).

Endopod of first thoracic limb short, robust and terminating in strong claw ( Fig. 4 D). Endopod of second thoracic limb, short, robust, merus longer than carpopropodus, terminal claw long and stout. Endopod of third to seventh thoracic limbs rather stout, carpopropodus not divided into subsegments, merus longer than carpopropodus, terminal claw moderately slender ( Fig. 4 F–H). Endopod of eighth thoracic limbs missing from specimens.

Uropodal exopod and endopod overreaching posterior end of telson ( Fig. 4 J). Proximal end of exopod armed with 4 spines. Uropodal endopod slightly longer than exopod, armed on inner ventral margin with 67 spines showing alternate arrangement of 1 longer and 1 to 5 shorter ones ( Fig. 4 J).

Telson short, triangular, 1.2 times longer than width of base ( Figs. 4 I, J). Lateral margin armed with 3 stout spines, first 2 closely set and last one set at relatively longer interval, posterior margin of telson slightly arched, with 2 pairs of stout spines; outer slightly longer than inner, and pair of plumose setae; small median spines absent ( Figs. 4 I, J).

Body length: mature female 8.3 mm.

Etymology. The specific name refers to the short spines on the telson.

Remarks. Murano and Fukuoka (2008) divided the genus Siriella into 9 groups and 5 subgroups of species from Pacific and Indian waters. Details of this classification have been described by Murano and Fukuoka (2008) and hence are not dealt with here. Siriella brevispina is allied to species of the Brevicaudatagroup and the Thompsonii-subgroup (Thompsonii-group). The new species is aligned with the Brevicaudatagroup in not only having a short telson, but also shares the following characters associated with the Thompsonii-subgroup: (1) anterior margin of carapace with triangular rostral plate, (2) labrum with long process on anterior margin, and (3) inner margin of the uropodal endopod showing alternate arrangement of longer and shorter spines. Examination of male specimens could bring more clarity to the affinity of this species to either the Brevicaudata or Thompsonii-group.

The new species is easily distinguished from other species of this genus by the shape and spinulation of the telson, the labrum with a long anterior process and spinulation on the uropodal endopod.

Figures

FIGURE 4. Siriella brevispina sp. nov., holotype, (spent female, 8.3 mm). A, anterior part of the body; B, antennule; C, antenna; D, first thoracic endopod; E, labrum; F, third thoracopod; G, fifth thoracic endopod; H, seventh thoracopod; I, telson (paratype, female, 6.5 mm); J, telson and uropods.