Acidostoma Lilljeborg, 1865

Stoddart, H. E. & Lowry, J. K., 2012, Revision of the lysianassoid genera Acidostoma and Shackletonia (Crustacea: Amphipoda: Acidostomatidae fam. nov.), Zootaxa 3307 (1), pp. 1-34 : 4

Acidostoma Lilljeborg, 1865

Acidostoma Lilljeborg, 1865a: 34 . ― Lilljeborg, 1865b: 24. ― Bate, 1866: 333. ― Boeck, 1871: 121. ― Boeck, 1876: 192. ― Sars, 1890: 37. ― Della Valle, 1893: 782. ― Stebbing, 1906: 14. ― Chevreux & Fage, 1925: 30. ― Stephensen, 1929: 52. ― Gurjanova, 1951: 157. ― Hurley, 1963: 36. ― Dahl, 1964: 49. ―J.L. Barnard, 1969: 317. ― Lincoln, 1979: 56. ― Lowry & Stoddart, 1983: 283. ― Diviacco & Ruffo, 1989: 470. ― Barnard & Karaman, 1991: 454.

Diagnosis. Maxilla 1 palp 1-articulate or absent. Pereopod 6 coxa posterior lobe much deeper than anterior lobe. Uropod 3 rami without plumose setae. Telson about as long as broad or broader than long.

Type species. Anonyx obesus Bate & Westwood, 1861 , by monotypy.

Species composition. Acidostoma contains 10 species: Acidostoma australis sp. nov.; A. hancocki Hurley, 1963 ; A. laticorne Sars, 1879 ; A. merimbula sp. nov.; A. molarifera Margulis, 1963 ; A. namibiensis sp. nov.; A. neglectum Dahl, 1964 ; A. obesum ( Bate & Westwood, 1861) ; A. ortum J.L. Barnard, 1967 ; A. pectinata Gurjanova, 1951 .

Remarks. The gnathopod 1 of Acidostoma species has been described in the literature as both subchelate ( Bate 1862, Lilljeborg 1865, Boeck 1871) and simple ( Chevreux & Fage 1925, J.L. Barnard 1969, Griffiths 1975, Lincoln 1979) and sometimes in-between ( Barnard & Karaman 1991: 454 "gnathopod 1 nearly simple"). It seems to us that the gnathopod 1 is functionally simple but technically subchelate with an extremely acute palm. There is also slight sexual dimorphism in the gnathopod 1. In females the palm is minutely pectinate and usually defined by a robust seta; in males the palm is often rugose rather than pectinate and, although distinguishable from the remainder of the posterior margin, is less clearly defined (see, for example, Figure 14 , male and female G1 of A. namibiensis ). The gnathopod 1 of Shackletonia robusta has been consistently described as simple.

Species of Acidostoma are widely regarded as associates, even ectoparasites, of anthozoans. As pointed out by Dahl (1964) the evidence for this is very slim but seems convincing, especially when taken in conjunction with the conical mouthpart bundle apparently adapted for sucking. Della Valle (1893) recorded A. neglectum (as A. laticorne ) from the column of the sea anemone Condylactis aurantiaca ( Delle Chiaje, 1825) ; Ansell (1969) found A. neglectum in the burrow of the sea anemone Peachia hastata Gosse, 1855 ; and Vader (1967) recorded A. obesum (as A. nodiferum ) associated with the sea anemone Actinostola callosa ( Verrill, 1882) . Vader found the faeces of two specimens contained a tangle of tubular objects, at least part of which were nematocysts, and Dahl found the same thing in the proctodaeum of A. negectum 1, indicating that the animals do actually feed on the anemones. For most species little or nothing is directly known of their associations, lifestyle or habitat. Dahl (1964) and Vader (1967, 1984) have shown that at least some species of Acidostoma live with and feed on anemones. Macquart- Moulin (1984) reported one species of Acidostoma with a nocturnal swimming phase. This is a reproductive swimming male stage which probably occurs in all species.

Figures

FIGURE 14. Acidostoma namibiensis sp. nov., holotype female, 5 mm, SAM A6050, off Saldanha Bay, South Africa; paratype male, 4.5 mm, AM P.46667, off Cape Cross, Namibia. Scales represent 0.2 mm.