Cymbasoma galerus, Suárez-Morales, Eduardo & Mckinnon, David, 2016

Suárez-Morales, Eduardo & Mckinnon, David, 2016, The Australian Monstrilloida (Crustacea: Copepoda) II. Cymbasoma Thompson, 1888, Zootaxa 4102 (1), pp. 1-129 : 18-21

Cymbasoma galerus sp. nov.

( Figs 9 , 10 )

Material examined. Holotype: adult male from Werribee, Port Phillip Bay, Victoria, Australia (37°57.085’ S, 144°47.128’ E), undissected, mounted on slide in glycerine, sealed with Entellan®. Date of collection: 21st May 1985. Slide deposited in the collection of MTQ, Australia (cat. MTQ W34375).

Description of adult male. Total body length 0.75 mm. Cephalothorax 0.38 mm long, representing 50% of total body length ( Figs 9 A, 10A). Midventral oral papilla weakly developed, located at 26% of cephalothorax length ( Figs 9 A, 10C). Cephalic region slightly protuberant bilaterally in dorsal view. Pair of dorsal ocelli present, weakly developed; pigment cups medium-sized. Ocelli separated by the length of less than one eye diameter, faintly pigmented. Ventral ocellus about same size and diameter as eyes. No sensilla observed between antennulary bases. Forehead area with cap-like rounded protuberance ornamented with deep transverse cuticular ridges ( Fig. 10 B). Other cuticular processes weak, represented by faint striae on perioral area ( Fig. 10 C).

Urosome consisting of fifth pedigerous, genital (carrying genital complex), preanal, and anal somites ( Fig. 9 C, D). Fifth pedigerous somite with smooth ventral surface. Genital somite slightly shorter than fifth pedigerous somite. Genital somite with cuticular striation on dorsal surface. Genital complex of type II ( Suárez-Morales & McKinnon 2014), represented by pair of moderately divergent, digitiform genital lappets ( Figs 9 C, 10F), these being slightly asymmetrical, reaching to midlength of long anal somite. Rounded, protuberant medial process present at common basal joint of lappets ( Fig. 10 F), lappets ornamented with scattered cuticular papillae only on distal half and along inner margins of lappets. Anal somite about twice as long as preanal somite in dorsal and lateral views, comprising 30% of urosome length; no suture visible on ventral or dorsal surfaces ( Figs 9 C, D, 10A, F). Caudal rami subrectangular, approximately 1.5 times as long as wide, about as long as anal somite. Each ramus with three caudal setae.

Antennulary length 0.27 mm. Antennules relatively long, representing 40% of total body length, and 75% of cephalothorax length; 5-segmented, all segments separated, with segment 5 located distal to geniculation ( Fig. 9 B). Length ratio of antennulary segments, from first to fifth 10.4: 26.1: 11.3: 34.2: 18 (= 100). Setal element 1 on first segment slender, setiform, moderately long, reaching halfway along second segment. Antennulary elements 2v 1-3, 2d1,2, and IId present on second segment, with element IId reaching distal margin of fifth segment. Setal elements IIId, IIIv, and 3 present on third segment; element 3 slender, curved. Fourth segment with elements 4d 1-2, 4v 1– 3, IVd and IVv. Fifth segment with 5 “b”-group setae, elements b1-3 short, unbranched. According to Huys et al. (2007) setal nomenclature of the distal segment, elements A and B and 2–7 present.

Incorporated first pedigerous somite and succeeding three pedigerous somites each bearing well-developed biramous legs. Pedigerous somites 2–4, together accounting for 31% of total body length in dorsal view. Coxae of each pair unarmed, joined by intercoxal sclerite which is slightly longer than wide. Bases of legs 1–4 separated from coxae posteriorly by oblique articulation; with hair-like lateral seta ( Fig 10 D, E); on leg 3, this seta about 3.2 times longer, sparsely setulated in distal half and slightly thicker than those on the other legs. Endopods and exopods of legs 1–4 triarticulated. Exopods of legs 1–4 longer than endopods. Flexible, slender, inner seta present on first exopodal segment of legs 1–4.

Outer spine on distal exopodal segment of legs 1–4 about 0.3 times as long as segment. Also, outermost apical exopodal setae of legs 1–4 with inner margin smooth, outer margin sparsely spinulose.

Armature formula of legs as follows:

Female: unknown.

Type locality. Werribee, Port Phillip Bay, Victoria, Australia (37°57.085’ S, 144°47.128’ E).

Etymology. The species name, a noun in apposition from the Latin, meaning a hat or cap refers to the frontal cap-shaped protuberance that is distinctive of this species.

Diagnosis. Cymbasoma with conspicuous cap-like medial protuberance on cephalic area ornamented with transverse ridges. Oral papilla weakly developed. Antennule representing 40% of total body length and 75% of cephalothorax length. Fifth pedigerous somite with smooth ventral surface. Genital complex of type II, with thumb-like, slightly asymmetrical lappets, inner margins and distal tips of lappets with cuticular papillae. Basal joint between lappets produced into rounded protuberance. Three caudal setae.

Remarks. This species has a unique combination of characters including a frontal striated protuberance, a genital somite with corrugate dorsal surface, a genital complex with thumb-like asymmetrical lappets ornamented with papillae and a strong medial rounded protuberance at the insertion of the lappets. There are other species with a relatively strong rounded medial protuberance on the male genital complex: C. tropicum (cf. Martin Thompson & Easterson 1983), C. quadridens Davis, 1947 (cf. Suárez-Morales & Pilz 2008), C. gracile Gurney, 1927 , C. bullatum (cf. Suárez-Morales 2007), and the Australian C. annulocolle sp. nov. ( Fig. 17 A, D, F). The new species differs from these other species in the asymmetry of the lappets, which are symmetrical in the other species. Also, most of them lack a strong frontal protuberance; a frontal process is present in C. annulocolle , but it is weaker and differently shaped ( Figs 15 C, 17C) than in the new species C. galerus ( Fig. 10 C). In addition, a cephalic protuberant process is present in C. rochai but it occupies a ventral position ( Suárez-Morales & Dias 2001) rather than a frontal one as in the new species. Also, in both C. rochai (cf. Suárez-Morales & Dias 2001) and C. tropicum (cf. Martin Thompson & Easterson 1983) four caudal setae are present vs. three such setae in the new species. Most importantly, in both C. quadridens (cf. Suárez-Morales & Pilz 2008) and in C. annulocolle the inner margins of lappets are ornamented with a row of spinules, whereas in the new species the inner margin is smooth except for a few scattered papillae. As for C. gracile , the available comparative data are limited ( Gurney 1927), but the lappets are symmetrical, smooth and the anal somite has a constriction and a suture ( Gurney 1927: fig. D), thus diverging from the asymmetrical lappets ornamented with papillae and the non-constricted anal somite of the new species. Following Suárez-Morales’ (2000a) key to the males of Cymbasoma the Australian new species keys down to C. thompsonii ( Giesbrecht, 1893) . These species differ in the structure of the genital complex, with weakly divergent, distally rounded lappets with a flat medial margin in C. thompsonii vs. a conspicuous medial process between strongly divergent, distally tapering lappets in the new species.

Figures

FIGURE 9. Cymbasoma galerus sp. nov., adult male. A) habitus, lateral view; B) right antennule, dorsal view; C) urosome and genital lappets, lateral view; D) same, dorsal view. Scale bars: A = 100 µm, B – D = 50 µm.

FIGURE 10. Cymbasoma galerus sp. nov., adult male. A) habitus, dorsal view, antennules omitted; B) cephalic region, dorsal view; C) same, lateral view; D) first leg; E) second leg; F) urosome and genital complex, ventral view. Scale bars: A = 100 µm, B – F = 50 µm.

FIGURE 15. Cymbasoma annulocolle sp. nov., adult male from Werribee, specimen A. A) habitus, dorsal view; B) right antennule, dorsal view; C) cephalic region, dorsal view, specimen A; D) urosome dorsal view. Scale bars: A = 200 µm, B – D = 100 µm.

FIGURE 17. Cymbasoma annulocolle sp. nov., adult males from Werribee. A) urosome and genital complex, ventral view; B) same, dorsal view; C) cephalic region, lateral view, specimen B; D) specimen A, detail of genital complex, ventral view; E) detail of ornamentation of genital lappets, specimen A; F) specimen B, detail of genital complex, ventral; G) detail of ornamentation of genital lappets, specimen B. Scale bars: A – C = 100 µm, D, F = 50 µm, E, G = 20 µm.