Cymbasoma colefaxi, 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 : 9-12

Cymbasoma colefaxi sp. nov.

( Figs 3 , 4 )

Material examined. Holotype: adult male from Warneet, Western Port Bay, Victoria, Australia (38°13.200’ S, 154°189.758’ E), partially dissected, ethanol-preserved; dissected parts mounted on 3 slides in glycerine, sealed with Entellan®. Date of collection: 15th May 1983. Slides deposited in the collection of MTQ, Australia (cat. MTQ W34371).

Description of adult male. Total body length 0.78 mm. Cephalothorax 0.38 mm long, representing about 50% of total body length ( Fig. 3 B). Midventral oral papilla weakly developed, positioned at 25% of cephalothorax length ( Fig. 4 A). Cephalic region slightly protuberant bilaterally in dorsal view. Pair of dorsal ocelli present, weakly developed; pigment cups relatively small. Ocelli separated by the length of one eye diameter, faintly pigmented. Ventral ocellus relatively large, about twice the diameter of eyes. Pair of sensilla between antennulary bases. Antero-ventral surface of cephalothorax between antennulary bases and oral papilla bearing conspicuous cuticular medial rounded protuberance ornamented with minute papillae ( Fig. 4 A). Dorsal and ventral surfaces of cephalic area smooth except for faint striae at either side of oral papilla.

Urosome consisting of fifth pedigerous somite, genital somite (carrying genital complex), preanal somite, and anal somite. Genital somite as long as fifth pedigerous somite. Genital complex of type II ( Suárez-Morales & McKinnon 2014), represented by pair of moderately divergent, slightly asymmetrical genital lappets, right lappet slightly longer, narrower than left lappet ( Fig. 3 D, E). Lappets posteriorly directed in lateral view ( Fig. 4 A), reaching to midlength of anal somite. Pair of spiniform medial processes present at common basal joint of lappets ( Fig. 3 E). Lappets ornamented with few scattered cuticular papillae. Anal somite about twice as long as preanal somite in dorsal view, comprising 30% of urosome length; no suture visible on ventral or dorsal surfaces, cuticular hyaline frill absent. Caudal rami subrectangular, approximately 1.3 times as long as wide, as long as anal somite ( Fig. 3 D). Each ramus with three setae.

Antennulary length 0.31 mm. Antennules relatively long, but shorter than in C. bitumidum , representing 35% of total body length, and 66% of cephalothorax length; 5-segmented, all segments separated, with segment 5 located distal to geniculation ( Fig. 3 A). Length ratio of antennulary segments, from first to fifth 14.5: 19.7: 11.3: 29: 25.5 (= 100). Setal element 1 on first segment relatively short, spiniform, reaching proximal 1/3 of second segment. Antennulary elements 2v 1-3, 2d1,2, and IId present on second segment, with element 2v 2 relatively longer than other elements of this group on segment, reaching well beyond proximal margin of fourth segment ( Fig. 3 A). Element IId flexible, long, reaching distal end of fifth segment. Elements IIId, IIIv, and 3 present on third segment, the latter being slender, setiform, remarkably long, reaching beyond distal margin of fourth segment. Fourth segment with elements 4d1,2, 4v 1– 3 and IVd present; setal element IVv absent in specimen. Fifth segment with 5 “b”-group setae, elements b1-3 dichotomously branched distally; element 61 present in distal position. According to Huys et al. (2007) setal nomenclature of the distal segment, elements A, B, E and 1–7 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 ( Fig. 3 B). 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 basipodal seta ( Fig. 4 B–D); on leg 3, this seta about 2.5 times longer, sparsely setulated in distal half and slightly thicker than those on the other legs ( Fig. 4 D). Endopods and exopods of legs 1–4 triarticulated, third exopodal segment of leg 1 with row of spinules on medial anterior surface ( Fig. 4 C). Exopods of legs 1–4 longer than endopods. Ramal setae all biserially plumose except spiniform outer seta on exopodal segments 1 and 3. Flexible, slender, sparsely setulated inner seta present on first exopodal segment of legs 1–4. Outer spine on distal exopodal segment of legs 1–4 shorter than segment. Also, outermost apical exopodal setae of legs 1–4 with inner margin sparsely spinulose. Armature formula of legs as follows:

Female: unknown.

Type locality. Warneet, Western Port Bay, Victoria, Australia (38°13.200’S, 145°18.758’E).

Etymology. The species is named after Alan N. Colefax in honour of his contribution to the seminal volume on Australian marine plankton ( Dakin & Colefax 1940).

Diagnosis. Cymbasoma with conspicuous medial protuberance on cephalic area covered with distal minute papillae. Second antennulary segment bearing moderately developed seta 2v 3 and remarkably long element 3. Antennule representing 35% of total body length and 66% of cephalothorax length. Fifth pedigerous somite with smooth ventral surface. Genital complex of type II, slightly asymmetrical, with rounded distal tips, basal joint between lappets with pair of spiniform processes, ornamented with few scattered papillae. Three caudal setae.

Remarks. This species of Cymbasoma can be distinguished from its congeners by its possession of a unique combination of four features: 1) the presence of a ventral cephalic protuberance; 2) a type II genital complex ( Suárez-Morales & McKinnon 2014) with a pair of spiniform processes at the medial insertion of the genital lappets; 3) three caudal setae; 4) anal somite without constriction. The only other known species with similar genital lappets, with a basal pair of spines are C. tenue Isaac, 1974 (cf. Suárez-Morales & Riccardi 1997) and C. rochai (cf. Suárez-Morales & Dias 2001). The new species differs from C. tenue in several important characters; the high rounded cephalic ventral protuberance of the new species is absent in C. tenue , with a weakly produced ventral surface between the antennule bases ( Suárez-Morales & Riccardi 1997: fig. 2B). The antennulary armature shows some additional differences. Element 1 (sensu Grygier & Ohtsuka 1995) on the first segment is remarkably short in C. tenue (cf. Suárez-Morales & Riccardi 1997: fig. 2D) whereas it is clearly longer in the new species. Element 4v 1 is long, setiform in C. tenue and short, spiniform in the new species. Element 3 is extremely long in the new species, reaching beyond the distal margin of the fourth segment, whereas it barely reaches midlength of the fourth segment in C. tenue (cf. Suárez-Morales & Riccardi 1997: fig. 2D). In addition, the third endopodal segment of leg 1 has a row of spinules ( Fig. 4 C) which are absent in C. tenue (cf. Suárez-Morales & Riccardi 1997: fig. 3A). The new species shares with C. rochai the presence of a ventral cephalic protuberance but differs in the number of caudal setae (three in the new species, four in C. rochai ) (cf. Suárez-Morales & Dias 2001: fig. 28) and also in the length of the genital lappets; these are very short in C. rochai , barely reaching the posterior margin of the genital somite whereas they reach the middle of the anal somite in the new species. The remarkably long antennulary element 3 is also a distinctive character of the new species. As in C. tenue , in C. rochai this element reaches only about halfway of the fourth segment and element 4v 1 is long, setiform, thus diverging from the pattern observed in the new species.

Figures

FIGURE 3. Cymbasoma colefaxi sp. nov., adult male. A) right antennule, dorsal view; B) habitus, dorsal view, antennules omitted; C) anterior cephalic region, ventral view; D) urosome, dorsal view; E) genital complex and lappets, ventral view. Scale bars: A = 200 µm, B = 100 µm, C – E = 50 µm.

FIGURE 4. Cymbasoma colefaxi sp. nov., adult male. A) habitus, lateral view, arrow indicates ventral cephalic protuberance; B) second leg; C) first leg; D) third leg. Scale bars: A = 200 µm, B – D = 100 µm.