Cinusa Schioedte and Meinert, 1884

Hadfield, Kerry A., Bruce, Niel L. & Smit, Nico J., 2010, Redescription of the monotypic genus Cinusa Schioedte and Meinert, 1884 (Isopoda, Cymothoidae), a buccal-cavity isopod from South Africa, Zootaxa 2437, pp. 51-68 : 52-65

Genus Cinusa Schioedte and Meinert, 1884

Cinusa Schioedte and Meinert, 1884: 312 .– Stebbing, 1910: 425.– Nierstrasz, 1931: 138.– Barnard, 1940: 491.– Kensley, 1978: 78.

Diagnosis. Body oval, asymmetrical. Cephalon small deeply immersed into pereonite 1, posterior margin not trilobed. Eyes present, distinct. Pereonite 1 short, lateral margins convex, wider than two thirds the length of pereonite 2; pereonites 4–7 decreasing in width and length posteriorly, widest at pereonites 3 and 4; pereonite 7 posterior margin deeply concave. Pleonite 1 distinctly narrower that pleonite 2 (0.7 as wide as 2; 0.6 as wide as pleonite 5); pleonite lateral margins acute.

Antennae bases close-set, almost contiguous; antennule composed of 7 articles, antenna with 10 articles, antennule slightly stouter than antenna. Mandible palp articles not expanded, articles 2 and 3 with setae. Maxilliped palp article 3 with spines. Pereopod 1–7 basis with carina; pereopods 1–3 merus with ventral lobe. Pleopods rami all lamellar, not setose, simple, with slight protrusion on ventral surface of each ramus. Broodpouch without posterior pocket. Uropods more than half the length of pleotelson, rami of similar lengths, apices rounded.

Type species: Cinusa tetrodontis Schioedte and Meinert, 1884 , by monotypy. Types held in the Zoological Museum, University of Copenhagen.

Remarks. The original Latin diagnosis given by Schioedte and Meinert (1884), by today’s standards contains little more than family-level characters. A new diagnosis is given here, comparable to that now available for other related genera.

Cinusa is best identified by the rounded anterolateral margins of pereonite 1 that does not project anteriorly, maxilliped palp article 3 with spines and pleopod peduncles without retinaculae. The body is widest anteriorly, at pereonite 3.

Similar genera are Ceratothoa Dana, 1852 and Cymothoa Fabricius, 1793 which are also found inside the buccal cavity of their fish hosts but can be separated by Cymothoa and Ceratothoa having anterolateral margins of pereonite 1 which are produced around the cephalon while Cinusa has rounded margins and is less produced. Ceratothoa species also have contiguous antennal bases, Cymothoa species have well-separated bases and Cinusa has almost contiguous bases but still separated. Both Ceratothoa and Cymothoa are widest around pereonites 5–6 whereas Cinusa is widest around pereonites 3–4.

Distribution. The genus is known from the Indian Ocean coast of South Africa, from Cape of Good Hope to Port Elizabeth; Schioedte & Meinert (1884) cited the genus as occurring in the eastern Indian Ocean while Nierstrasz (1931) cited the Pacific Ocean; we regard these records as unconfirmed and doubtful.