Siriella affinis 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 : 7-9

Siriella affinis Hansen, 1910

(Figures 3, 4)

Siriella affinis Hansen, 1910: 35 –36, pl. III, fig. 3a–i. — W.M. Tattersall, 1922: 445. — Illig, 1930: 562. — W.M. Tattersall, 1951: 64. — Gordan, 1957: 378. — Ii, 1964: 89. — Pillai, 1965: 1692, fig. 16. — Mauchline & Murano, 1977: 76. — Murano, 1983: 82. — Fenton, 1985: 37, 45 (key). — Carleton & Hamner, 1989: 464, table 1. — Muller, 1993:32. — Lowry & Stoddart, 2003: 465. — Yerman & Lowry, 2007: interactive key.

Type material. SYNTYPES: 5 specimens, Zoological Museum, University of Copenhagen, Denmark; 20 specimens, Zoological Museum, University of Amsterdam, Netherlands.

Type locality.. Siboga Station 66, bank between the Islands of Bahuluwang and Tambalongang, south of Salayar, 8–10 m depth, Indonesia; Siboga Station 106, anchorage off Pulu Tongkil, Sulu Archipelago, 13 m depth, Sulu Sea, Philippines.

Material examined. One immature male, 5.3 mm, plankton tow, surface, Lizard Is. lagoon, 2130 hrs, Dec. 1 1980 (Grindley #8) (AM P73783).

Description. Head: eyes stalked, cornea hemispherical, stalk without antero-distal spine. Rostrum triangular, apex acute. Antennal scale moderately broad, three times longer than wide, shorter than antennular peduncle, lateral margin without setae, spine on outer distal corner, apical suture present, distal margin rounded, distal and medial margins setose. Labrum with anteriorly directed medial spiniform process less than half length of labrum proper (Fig. 3C). Basal article of mandibular palp expanded, length two times maximum width (Fig. 3D).

First thoracic somite fused with head, limbs with short robust endopod, modified as a gnathopod, exopod natatory, epipodite leaf-like (Fig. 3F).

Pereon: integument smooth; endopod of second thoracic limb stout, modified as a gnathopod (Fig. 3G), thoracic limbs 3–8 with endopod fairly robust, dactylus terminating in a strong nail (Fig. 3H), exopods of all thoracic limbs natatory, developing genital organ at base of 8th limb (Fig. 4A).

Pleon: pleopods 2–5 biramous, pseudobranchial rami spirally coiled, pleopods 3 and 4, endopod and exopod subequal, terminal setae unmodified (Figs 4B, C); uropodal endopod slightly shorter than exopod, endopod without diaresis, a row of 35 robust setae on medial margin distal to statocyst, slender plumose setae on both margins, exopod with diaresis, 3 distal robust setae on lateral margin of proximal article, slender plumose setae on distal article and medial margin of proximal article (Fig. 4D); telson linguiform, narrow, shorter than uropod, lateral margins each with 2 stout basal robust setae and 15–16 more distal robust setae, increasing in size towards the apex and ending in 3 short apical robust setae and 2 slender plumose setae (Fig. 4E).

Remarks. Hansen (1910) described this species as being closely allied to Siriella vulgaris . The eyes of S. affinis are darker and slightly larger than those of S. vulgaris (Figs 3B, 23A) and the antero-lateral spine on its antennal scale is much closer to the apex than is that of S. vulgaris (Figs 3A, 23C). In S. affinis the thoracic endopods are relatively robust and end in a broad dactylus and nail with a spine at the suture between them (Fig. 4A), while in S. vulgaris , the dactylus and nail are long and slender with a fine bristle at the suture (Fig. 24C). In both species the males have unspecialised natatory pleopods with coiled pseudobranchiae. In both, the uropodal exopod is slightly longer than the endopod (Figs 4E, 25B), but in the exopod of S. affinis , the outer distal corner of the proximal article is sharply angled and usually carries only 3–5 marginal robust setae (Fig. 4D), while in S. vulgaris it has a more gradual curve, with about 5–7 robust setae extending further up the margin ( Fig. 25 B). In S. affinis the uropodal endopod has 35 robust setae in its marginal row. They consist of about 11 large setae separated from each other by groups of 3 or 4 small setae. (In S. vulgaris there are 46–50 robust setae in the marginal row.) Both species have a slender linguiform telson reaching beyond the diaresis in the exopod and in both, the telson carries 2 stout basal setae on each side and more posteriorly, a row of lateral setae that gradually increase in size towards the apex. The Lizard Island specimen of S. affinis has 15 or 16 robust setae in each lateral row, while S. vulgaris has 17–21.

FIGURE 3. Siriella affinis Hansen, 1910 (immature male, 5.3 mm). A, left antenna. B, anterior cephalothorax. C, labrum. D, right mandible. E, left maxilla. F, right 1st thoracic limb. G, left 2nd thoracic limb. H, left 4th thoracic limb. Scalebars = B: 0.5 mm; E: 0.1mm; A, C, D, F, G, H: 0.2 mm.

Associated mysid species. The single specimen from the Lizard Island lagoon was captured with seven other mysid species, including 10 specimens of S. vulgaris .

Habitat. Pelagic in coral reef areas.

Distribution. Described from Indonesia and the Sulu Archipelago ( Hansen 1910) and taken from northern and southern Philippine localities and Micronesia ( W.M. Tattersall 1951), the Gulf of Mannar, between India and Sri Lanka ( W.M. Tattersall 1922) and the northern Arabian Sea ( Nayeem et al. 1992), S. affinis has a distribution very similar to that of S. vulgaris , according to Tattersall and it is often taken with it.

In Australia, as well as the single specimen from the Lizard Island lagoon, S. affinis has been collected in Great Barrier Reef waters off Heron Island ( Fenton 1985) and from Davies Reef ( Carleton & Hamner 1989).

FIGURE 4. Siriella affinis Hansen, 1910 (immature male). A, left 8th thoracic limb. B, left 3rd pleopod. C, left 4th pleopod. D, left uropod, ventral view. E, right uropod and telson. Scalebars = A, B, C, D, E: 0.2mm.

Figures

FIGURE 25. Siriella vulgaris Hansen, 1910. A, endopod of left uropod, ventral view. B, telson and right uropod, dorsal view. C, telson. Scalebars = A – C: 0.2 mm.