Siriella thompsonii ( H. Milne-Edwards, 1837 )

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 : 35-38

publication ID	https://doi.org/ 10.5281/zenodo.198856
DOI	https://doi.org/10.5281/zenodo.6202170
persistent identifier	https://treatment.plazi.org/id/D5636D42-9442-FF98-FF3C-FF49FB63607F
treatment provided by	Plazi
scientific name	Siriella thompsonii ( H. Milne-Edwards, 1837 )
status

Treatment

Siriella thompsonii ( H. Milne-Edwards, 1837) View in CoL

( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 )

Cynthia thompsonii H. Milne-Edwards 1837: 462 .

Cynthia View in CoL inermis— Kroyer 1861: 44, figs. 6a–g.

Siriella indica — Czerniavsky 1882: 103. — Taf. 31, figs. 1–16.

Siriella thompsonii View in CoL — Sars 1883: 40 –41. — Thiele 1905: 447 –449, figs. 7–9. — Hansen 1910: 31. — Colosi 1922: 1 –22. — W. Tattersall 1913: 870 –871; 1923: 280; 1926: 9; 1939: 234; 1943: 63–64; 1951: 60–61. — Coifmann 1937: 21 –23, pl. 8, figs. 12a–e, pl. 9, figs. 12f–g. — Holmquist 1957: 44 –45. — O. Tattersall 1962: 223 –225, pl. 2. — Pillai 1973: 47, figs. 15–16. — Stuck et al. 1979: 234, figs. 2f, 3f, 4f, 5f. — Price et al. 1987: 47. — Escobar-Briones & Soto 1991: 80 – 89. — Wang & Liu 1994: 84 –86, fig. 11; 1997: 203. — Panampunnayil 2002: 371 –372, figs. 1A–C. — Murano & Fukuoka 2008: 41 –45.

Material examined. 1 female with eggs, Sta. 3 (35° 04'S, 44° 59'E), southern Indian Ocean, 0 3.02.2004, 22:33 hr., BN, sampling depth: surface waters. — 4 adult males, 2 immature males, 2 spent females, 1 female with eggs, 5 immature females, and 7 juveniles, Sta. 4 (36° 59'S, 45°E), southern Indian Ocean, 0 3.02.2004, 23:32 hr., BN, sampling depth: surface waters.

Diagnosis. Acute rostral projection. Large eyes. Antennal scale 4–5.6 times as long as broad. Uropodal exopod bears 2–8 spines, Lateral margin of telson bears 14–31 spines. Apex of telson subtruncate or slightly arched.

Description. Carapace anteriorly produced into triangular narrow rostrum with pointed apex extending near middle of first antennular segment ( Figs. 2 View FIGURE 2 A, B); antero-lateral corners rounded. Eyes large with expanding cornea, nearly extending too distal end of first segment of antennular peduncle.

Antennular peduncle of male much broader than female, second segment short, with 2 long setae on inner dorsal margin. First segment narrow, as long as third; outer margin concave, with 2–3 long and 2 small setae on distal corner ( Fig. 2 View FIGURE 2 C). Antennular peduncle of female slender, first segment narrow, as long as succeeding 2 segments combined, outer margin concave, with 2 long and 1 short setae on dorsal corner; second segment short, with 1 long setae on inner distal corner and 2 short setae on outer distal corner; third segment with 1 long seta at distal 1/3 of inner margin and 3 long setae at inner distal corner ( Fig. 2 View FIGURE 2 D).

In male, antennal scale more slender than in female, 5.6 times as long as broad, extending to distal end of third segment of antennular peduncle, terminal lobe as long as broad; outer margin naked, terminating in spine; distal suture present ( Fig. 2 View FIGURE 2 E). Antennal scale of female extending near distal end of third segment of antennular peduncle, 5 times as long as broad; terminal lobe slightly shorter than broad; distal suture present ( Fig. 2 View FIGURE 2 F). Antennal peduncle in female more slender than in male ( Figs. 2 View FIGURE 2 E, F), extending little more than half of the antennal scale and in male extending to distal 1/3 of antennal scale; second segment longest, 3.6 times as long as third in male and four times as long as third in female.

Labrum with long frontal process; tip slightly curved ( Fig. 2 View FIGURE 2 G). Second segment of mandibular palp expanded, 1.6 times as long as third segment in male ( Fig. 2 View FIGURE 2 H) and 1.8 times as long ( Fig. 2 View FIGURE 2 I), inner margin with 3 short setae in male and one short seta in female; outer margin with 16 long setae in male ( Fig. 2 View FIGURE 2 H) and 13 setae on corresponding part in female; third segment with 7 long setae in male and 3 long setae in female ( Fig. 2 View FIGURE 2 I) on proximal 2/3 part of outer margin.

Mandible, maxillule, and maxilla are of type common for the genus ( Figs. 2 View FIGURE 2 J–L).

Endopod of first thoracic limb short, robust, merus longer than carpopropodus terminating in strong claw ( Fig. 3 View FIGURE 3 A). Endopod of second thoracic limb, short, robust, merus longer than carpopropodus, terminal claw long and stout. Endopod of fourth to seventh thoracic limbs subequal, slightly longer than third ( Fig. 3 View FIGURE 3 B), becoming more slender towards posterior limbs, carpopropodus not divided into subsegments; terminal claw moderately slender ( Figs. 3 View FIGURE 3 B, C). Endopod of eighth thoracic limb more narrow than preceding limbs, carpoprodus slightly shorter than merus; not divided into subsegments ( Fig. 3 View FIGURE 3 D).

First male pleopod; exopod 10-segmented, endopod absent ( Fig. 3 View FIGURE 3 E). Second pleopod; endopod 11 and exopod 12 segmented ( Fig. 3 View FIGURE 3 F). In third to fifth pleopods, both rami with 12, 13 and 11 segments, respectively, and without any modified setae ( Figs. 3 View FIGURE 3 G–I). Pseudobrachial rami nearly straight in first and fifth pleopods and spirally coiled in second to fourth pleopods.

Uropodal exopod and endopod overreaching telson ( Fig. 3 View FIGURE 3 J). Proximal segment of exopod armed with 7– 8 spines in adult male ( Fig. 3 View FIGURE 3 J) and 4–5 in adult female ( Fig. 3 View FIGURE 3 M). Uropodal endopod slightly longer than exopod, armed on inner ventral margin with 64–68 spines showing alternate arrangement of 1 longer and 1 to 5 shorter ones ( Figs. 3 View FIGURE 3 J, L).

Telson 1.5 times longer than last abdominal segment, 2.7 times as long as broad in male ( Fig. 3 View FIGURE 3 J) and 2.8 times longer than broad in female ( Fig. 3 View FIGURE 3 N), extending beyond articulation of uropodal exopod. Lateral margin of telson armed with 2 stout spines on basal widened part, followed by comparatively narrow naked part, then posterior series of 27–29 spines in male ( Fig. 3 View FIGURE 3 J) and 20–22 spines in female, the spines gradually increasing length posteriorly ( Fig. 3 View FIGURE 3 N). Distal margin of telson slightly arched, with 2 pairs of long spines, outer slightly longer than inner, 3 median small spines and pair of plumose setae ( Figs. 3 View FIGURE 3 K, O).

Body length: adult male 10.2–10.4 mm, adult female 8.7–9.7 mm.

Remarks. The present specimens agree with previous descriptions, except for minor variations as follows: In the present specimens lateral margins of the telson bears 22-31 spines, while in earlier descriptions only 14-20 spines are reported ( Sars 1885; Ii 1964; Pillai 1973). The present specimens measure up to 10.4 mm, which is the maximum size observed.

Population differences of S. thompsonii have been observed in morphological characters ( Ii 1964; Pillai 1973; Panampunnyil 2002). Tattersall (1962) reported that in many species of the genus Siriella , changes in form take place with growth even after the animal has attained sexual maturity. This fact is particularly noticeable in S. thompsonii .

Distribution. Widely distributed in the tropical Atlantic, Pacific and Indian Oceans.

Kingdom	Animalia
Phylum	Arthropoda
Class	Malacostraca
Order	Mysida
Family	Mysidae
Genus	Siriella