Sternaspis sherlockae, Salazar-Vallejo, 2017

Salazar-Vallejo, Sergio I., 2017, Cymonomus curvirostris Sakai 1965, Zoological Studies (Zool. Stud.) 56 (32), pp. 16-16 : 12-13

Sternaspis sherlockae sp. nov.

( Fig. 6 )

urn:lsid:zoobank.org:act:70BF765A-F219-4A81-8EA5-D3FD3DF860EC

Sternaspis scutata : Day 1967: 648, Fig. 31.I.a-d (non Ranzani, 1817).

Type material: Red Sea. Holotype ( BMNH 2013.410 ) and paratype ( BMNH 2013.411 ), Crossland Red Sea Expedition, 19 Jan. 1904 (paratype 19 mm long, 7 mm wide, abdomen 12 mm long, left shield plate 3 mm long, 3 mm wide).

Additional material: Red Sea. Two specimens ( BMNH 1869.6.30.3), Gulf of Suez, R. McAndrew, coll. (smaller specimen with introvert invaginated, 8 mm long, 4.7 mm wide, left shield plate 1.1 mm long, 1.5 mm wide; larger specimen with introvert exposed 17 mm long, 6 mm wide, abdomen 10.7 mm long, left shield plate 2.5 mm long, 2 mm wide; both specimens with genital papillae whitish, thick, tapered).

Description: Holotype ( BMNH 2013.410) complete, whitish, introvert grayish, swollen, shield reddish, banded, integument rugose, papillae mostly eroded ( Fig. 6A ). Body 16 mm long, 4 mm wide, abdomen 11 mm long, left shield plate 2.5 mm long, 2.4 mm wide.

Prostomium small, opaque, without eyespots ( Figs. 6B, D ). Peristomium rounded, slightly depressed below mouth, with small papillae extended ventrally, not extetended laterally or over the prostomial lobe. Mouth circular, completely covered with minute papillae.

First three chaetigers with 10-12 hooks, broken, slightly falcate. Genital papillae not visible in type specimens (whitish, short, tapered lobes in additional materials). Pre-shield region with 7 segments, without fascicles of capillary chaetae.

Shield with ribs and concentric lines, reddish, banded, suture extended through ⅔ of shield length, posteriorly indistinct ( Fig. 6C ). Anterior margins angular; anterior depression deep; anterior keels visible, but not exposed (exposed in paratype). Lateral margins medially expanded, reduced posteriorly. Fan truncate, not extended beyond posterior corners; barely crenulate; without median or lateral notches.

Marginal chaetal fascicles include 10 lateral ones, chaetae ovally arranged, and seven posterior fascicles, chaetae in a slightly curved arrangement. Peg chaetae not seen, probably broken.

Branchiae abundant, helicoidal, yellowish. Interbranchial filaments shorter, thinner, grayish. Branchial plates (observed in non-type specimen) oval, slightly divergent, truncate, rounded anteriorly ( Fig. 6G ).

Variation: The paratype is larger than the holotype; its introvert has 12-14 hooks, its shield has two small, lateral notches and its anterior keels are visible ( Fig. 6E ). Smaller specimens have shields with suture visible throughout shield, but soon the lateral plates fuse posteriorly and the suture is not visible ( Figs. 6F, H ).

Etymology: This species name is a modest homage to Emma Sherlock ( BMNH) in recognition of her kind support to all of my research activities. The epithet is a noun in the genitive case.

Remarks: Sternaspis sherlockae sp. nov. resembles S. thorsoni Sendall & Salazar-Vallejo, 2013 , another species from the Indian Ocean, because both have reddish, banded shields with deep anterior depressions and truncate posterior margins. However, they differ because in S. sherlockae the posterior corners are rounded, not projected, whereas in S. thorsoni they are projected posteriorly as rounded lobes. Another perhaps more relevant difference is the number of introvert hooks; in S. sherlockae there are 12- 14 hooks in 16 mm long specimens (holotype), whereas in S. thorsoni there are 16-20 hooks in 14 mm long specimens (holotype).

On the other hand, as indicated in the key below, S. sherlockae resembles S. spinosa from Indonesia, because both have shields with anterior margins acute and the posterior corners are not projected. These two species differ because the shield in S. sherlockae shield plates are longer than wide, and its anterior keels are divergent, and the branchial plates are parallel, whereas in S. spinosa the shield plates are wider than long, its anterior keels are parallel, and the branchial plates are divergent.

The record by Day (1967) of S. scutata resembles the holotype of S. sherlockae by having shield with alternating pale and brown bands, a wide deep anterior furrow, a fan with posterior margin crenulate, with a shallow median notch, and without projecting posterior corners. If they are conspecific, the species would extend along the Western Indian Ocean margin, from the Red Sea to South Africa, but this distribution needs confirmation based upon additional specimens.

Distribution: Red Sea, presumably in shallow water.

Figures

Fig. 6. Sternaspis sherlockae sp. nov. Holotype (BMNH 2013.410). (A) Ventral view. (B) Same, anterior end, frontal view. (C) Same, shield, frontal view; paratype (BMNH 2013.411). (D) Anterior end, frontal view. (E) Same, shield, frontal view, non-type specimens (BMNH 1869.6.30.3). (F) Smaller specimen, shield, frontal view. (G) Same, branchial plates, frontal view. (H) Larger specimen, shield, frontal view. Scale bars: A = 1.9 mm, B, E = 0.9 mm, C, G, H = 0.8 mm, D = 1.3 mm, F = 0.6 mm.