Cymbasoma fergusoni Suárez-Morales & Mckinnon, 2016, sp. nov.

Cymbasoma fergusoni sp. nov.

(Figs 52, 53)

Material examined. Holotype: adult female from North West Cape, Western Australia (21°47.180’ S, 114°7.300’ E), partially dissected, ethanol-preserved; dissected parts mounted on slide in glycerine, sealed with Entellan®.

Date of collection: 20th October 1997. Slides deposited in the collection of the Museum of Western Australia (cat. WAM C61742).

Description of adult female. Body elongate, slender (Fig. 52 A); body length of holotype female 1.58 mm. Cephalothorax approximately 0.98 mm long, representing 63% of total body length. Midventral oral papilla moderately protuberant, located at 19% of cephalothorax length. Pair of medium-sized ocelli present, pigment cups moderately developed, medially separated, weakly pigmented; ventral cup larger than lateral cups. Cephalic area with straight lateral margins and produced "forehead”. Frontal area with medial protuberance flanked by lower rounded processes ornamented with transverse wrinkles (Fig. 53 B). Dorsal surface with small wart-like processes at level of antennulary bases (arrowed in Fig. 53 A). Ventral surface with additional cuticular elements: 1) pair of symmetrical, small crescent-shaped cuticular processes on anterior ventral surface located posterior to bases of antennules, with no adjacent striae; 2) nipple-like processes with adjacent transverse wrinkles; 3) pair of minute nipple-like processes in medial position (Fig. 53 B) above oral papilla; 4) perioral transverse wrinkles.

Urosome consisting of fifth pedigerous somite, genital double-somite and anal somite, together representing 15% of total body length. Relative lengths of urosomites (fifth pedigerous, genital double- and free anal somite) 25.1:49.3: 25.6 = 100, respectively (Fig. 53 F, G). Fifth pedigerous somite with slightly expanded lateral margins; dorsal surface with deep transverse striae (Fig. 53 E). Genital double-somite longest of urosome; ventral surface with field of transverse wrinkles adjacent to bases of ovigerous spines; dorsal surface with wrinkles in posterior half only (Fig. 53 D); anterior half swollen in dorsal view; with antero-lateral rounded processes visible in dorsal view (arrowed in Figs 52 F, 53D); antero-ventral process strong, forming thumb-like protuberance (Fig. 53 C); ventral surface of posterior half with notch visible in lateral view (arrowed in Fig. 53 C). Ovigerous spines paired, basally separated; slender, straight at their base, distally acute; spines short, about 23% of total body length (0.22 mm) (Fig. 52 A). Anal somite with medial constriction represented by incomplete suture in dorsal view, otherwise, dorsal and ventral surfaces smooth (Fig. 53 F). Caudal ramus subquadrate, about 1.2 times as long as wide, armed with three caudal setae.

Antennule length 0.34 mm, relatively short, representing about 22% of total body length and 33% of cephalothorax length; 4-segmented, segments 3 and 4 fused. Relative length of distal antennulary segment 46%. Short spiniform element 1 present on first segment; elements on second segment 2d1-2, 2v 1-3, and IId. Elements 2d1-2 modified, curved, with rugose surface (Fig. 52 B). Third segment with short, spiniform element 3, elements IIId and IIIv setiform, of normal aspect. Segment 4 bearing elements 4v 1-2; elements 4d1,2 and 4 v3 not observed. Setae IVd, IVv, Vd, Vv, Vm, and 4aes present. Element 5 absent. Subterminal elements b1-2 present; short, unbranched, apical elements 6aes; 61-2 present in specimen.

Incorporated first pedigerous somite and succeeding three free pedigerous somites each bearing a pair of biramous legs. Pedigerous somites 2–4, together accounting for 21% of total body length. Intercoxal sclerites of legs 1–4 subrectangular, posterior margin smooth. Bases of legs 1–4 with hair-like lateral seta (Fig. 52 C, D); on leg 3, this seta about 3.4 times longer, sparsely setulated and thicker than those on other legs (Fig. 52 E). Endopods and exopods of legs 1–4 triarticulated. Ramal setae all biserially plumose except spiniform outer seta on exopodal segments 1 and 3, and inner seta of first exopodal segment, these latter being slender, sparsely setulated. Outermost distal spines on third exopodal segment of legs 1–4 being half as long as segment. Outermost apical exopodal setae of legs 1–4 with inner margin naked, outer margin spinulose; outer spine of leg 1 first exopodal segment with short peduncle (Fig. 52 C). Outer margins of first and second endopodal segments of legs 1–4 protuberant (Fig. 52 C, D).

Armature formula of legs 1–4:

Fifth legs medially separate, bilobate; outer (exopodal) lobe short, cylindrical, distally truncate. Outer lobe armed with three distal setae, innermost slightly shorter than other two (Fig. 53 G). Inner lobe digitiform, arising from base of exopodal lobe, unarmed, shorter, reaching to about half the length of outer lobe; right inner lobe distally bifurcate, left lobe with medial twist (arrows in Fig. 53 H).

Male: unknown.

Type locality. North West Cape, Western Australia (21°47.180’ S, 114°7.300’ E).

Etymology. This species is named for the RV Cape Ferguson, which has conducted marine research on behalf of the Australian Institute of Marine Science throughout northern Australia since 2000.

Diagnosis. Cymbasoma with frontal area bearing medial protuberance flanked by lower rounded processes ornamented with transverse wrinkles. Antennules representing about 22% of total body length and 33% of cephalothorax length; third and fourth antennulary segments fused, second segment with modified elements 2d1-2. Genital double-somite with anterior half swollen in dorsal view and with antero-lateral wart-like processes visible in dorsal view; antero-ventral process strong, forming thumb-like protuberance; ventral surface of posterior half with notch. Fifth leg with short outer lobe armed with three distal setae, innermost being shorter; inner lobe arising proximally, unarmed. Right inner lobe distally bifurcate. Ovigerous spines short, representing 23% of total body length.

Remarks. Cymbasoma fergusoni sp. nov. belongs to the group of Australian Cymbasoma displaying a narrow, elongate fifth leg inner lobe and three exopodal setae. The main characters that are distinctive of this species include the unique tumor-like processes on the anterolateral margins of the cephalothorax and the prominent, thumb-like anteroventral process of the genital double-somite. This kind of processes has not been observed in other congeners so far. Also, it has a medial protuberance in the frontal area; a similar process has been described in the Costarrican species C. alvaroi (Suárez-Morales et al. 2013); however, in C. fergusoni this process is flanked by two other smaller protuberances, thus differing from C. alvaroi in which these secondary processes are absent (Suárez-Morales et al. 2013a: fig. 6A). Also, the Costarrican species lacks processes on the genital double-somite and striae on the fifth pedigerous somite, both characters are present in C. fergusoni. In addition, the fifth leg inner lobe is short, barely reaching to halfway down the outer lobe length. Both lobes are slightly bent inwards and slightly asymmetrical, with one of them being distally bifurcate, a character not previously observed in any other species of the genus.