Siriella vincenti W.M. Tattersall, 1927

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 : 33-36

Siriella vincenti W.M. Tattersall, 1927

( Figures 21 , 22)

Siriella vincenti W.M. Tattersall, 1927: 239 , fig. 97. — Hale, 1929: 361. — Illig, 1930: 561. — Dakin & Colefax, 1940: 131, fig. 221, — Gordan, 1957: 381. — Mauchline & Murano, 1977: 77. — Bacescu & Udrescu, 1984: 93. — Fenton, 1985: 37, 48 (key). — Muller, 1993: 44. — Panampunnayil, 1995: 1949 (table). — Lowry & Stoddart, 2003: 469. — Yerman & Lowry, 2007: interactive key.

Type material. SYNTYPES: 3 males, 8 females, South Australian Museum, Adelaide, Australia C1615. Type locality. Ten km off Semaphore, Gulf St Vincent, South Australia, 11–13 m depth.

Material examined. Two specimens, light trap, on sand (light on), passage between Palfrey & South Islands, 2111 hrs May 18 1976 (STL-76-LI3) AM P74064. 3 specimens, light trap, on sand (light on), passage between Palfrey & South Islands, 2122 hrs May 18 1976 (STL-76-LI4) AM P74065. Total: 5 specimens. Size range: 2 males, 5.9 & 6.0 mm, 3 juveniles, 1.8-2.1 mm.

Description. Head: eyes stalked, hemispherical (diameter of adult male cornea, 0.45 mm), colour, browngold. Rostrum forming a shallow rounded plate with a prominent pseudo-rostral process projecting beneath, cervical groove conspicuous ( Fig. 21 A). Antennal scale slightly shorter than antennular peduncle, length about 3x width, antero-lateral spine at about three quarter length of lateral margin, apical suture present in 1 adult specimen ( Fig. 21 B). Labrum cordate with rounded anterior margin, anterior medial spiniform process small, length about 0.2 x length of labrum proper ( Fig. 21 D). Mandibular palp with basal article moderately expanded, maximum width about 0.5x length ( Fig. 21 C). Palp of maxillary endopod fairly large, ovate ( Fig. 21 E). First thoracic somite fused with head, endopod of 1st thoracic limb short, robust, markedly broad and setose, forming a gnathopod, dactylus terminating in a long, curved nail, exopod natatory, epipodite large, leaf-like (Fig. 22A).

FIGURE 22. Siriella vincenti W.M. Tattersall, 1927 . A, right 1st thoracic limb. B left 2nd thoracic limb. C, right 8th thoracic limb. D, 3rd pleopod. E, left uropod. F, telson and right uropod. Scalebars = A, E, F: 0.5 mm; B, C, D: 0.2 mm.

Pereon: endopod of second thoracic limb broad and setose, modified to form a gnathopod, dactylus terminating in a long slender nail, exopod natatory (Fig. 22B). Endopods of thoracic limbs 3–8 forming pereopods, fairly short and robust, exopods natatory, genital organ at base of 8th thoracic limb in males (Fig. 22C).

Pleon: male pleopods 2–5 biramous with spirally coiled pseudobranchiae, none of the terminal setae of pleopods 3 (Fig. 22D) and 4 modified. Tail fan with uropodal exopod broader and longer than endopod, 4–5 robust setae on outer distal margin of proximal article of exopod, a row of 17–18 robust setae on ventral surface of inner margin of endopod (Fig. 22E). Telson broadly linguiform, rounded, not extending as far as diaresis in uropodal exopod, 4 stout robust setae on either side of telson base, more distally a diastema in each lateral margin forming a slight ‘waist’, beyond which 15–16 graded robust setae extend onto the apical margin, with the largest setae on either side of 3 minute apical setae and 2 long slender plumose setae (Fig. 22F).

Remarks. The 2 adult males from Lizard Island accord in almost all respects with Tattersall's (1927) description of S. vincenti from South Australia. The dimensions of the eyes and antennal scales are similar, but the eye colour recorded by Tattersall is black, while the Lizard Island specimens’ eyes are brown-gold. The antennal scales of Tattersall's specimens lack a distal articulation marking off a terminal lobe, but in 1 of the 2 Lizard Island specimens a terminal lobe is visible ( Fig. 21 B). The prominent pseudo-rostral spine below the rounded rostral plate corresponds with Tattersall's description, but the carapace of the Lizard Island specimens has a conspicuous cervical groove, not noted by him ( Fig. 21 A).

Tattersall's account does not include a description of the labrum. In the Lizard Island specimens it resembles those of S. lingvura and S. lacertilis , in being rounded, with an obtusely curved anterior border and a short anteriorly directed medial spiniform process ( Fig. 21 D). As in Tattersall's specimens, there is no articulation between the carpus and propodus of the thoracic legs (Fig. 22C). In the tail fan the row of robust setae on the uropodal endopod contains 17–18 setae, all of about the same size, while in Tattersall’s Figure 97f there are 21 correspondingly uniform setae. The telsons of the Lizard Island specimens have 4 basal robust setae on each lateral margin, as opposed to the 3 found by Tattersall. In other respects the telson matches his description.

Associated mysid species. Both samples contained specimens of Anisomysis pelewensis Ii 1964 , a species usually found on the sandy part of the lagoon floor.

Habitat. Sublittoral.

Distribution. Siriella vincenti is known from Australian waters only. The type locality for the species is 6 miles off Semaphore, which is located on the eastern shore of Gulf St. Vincent, adjacent to Port Adelaide. It has also been recorded from the vicinity of the Bass Strait (Fenton 1982), from New South Wales ( Dakin & Colefax 1940) and the Lizard Island lagoon, where a single damaged juvenile has been taken (collections of the Australian Museum).

All 5 specimens of the current survey were caught on the same night in 2 consecutive light trap samples. The trap was set on sand near coral in the shallow passage between South Island and Palfrey Island, which forms the south-western rim of the Lizard Island Lagoon.

Figures

FIGURE 21. Siriella vincenti W. M. Tattersall, 1927. A, cephalothorax (male, 5.9 mm). B, left antenna. C, left mandible. D, labrum. E, left maxillule with paragnath and maxilla. Scalebars = A: 0.5 mm; B, C: 0.2 mm; D, E: 0.1 mm.