Australomonstrillopsis crassicaudata, Suárez-Morales & Mckinnon, 2014

Suárez-Morales, Eduardo & Mckinnon, A. David, 2014, The Australian Monstrilloida (Crustacea: Copepoda) I. Monstrillopsis Sars, Maemonstrilla Grygier & Ohtsuka, and Australomonstrillopsis gen. nov., Zootaxa 3779 (3), pp. 301-340 : 315-318

Australomonstrillopsis crassicaudata sp. nov.

( Figs 9–10 )

Material examined. Adult male from Davies Reef , Queensland, Australia (19°7.34’S; 146°53.024’E), undissected, ethanol-preserved, slide-mounted in glycerine, sealed with Entellan ®. Date of collection: 5 October, 1985. Slide deposited in MTQ, Australia (cat. MTQW34270 ) .

Description. Male: Total body length of adult holotype 0.54 mm. Cephalothorax 0.25 mm long, representing 47% of total body length. Antennule 0.22 mm long, representing 81% of cephalothorax length ( Fig. 9B , 10F ). Oral papilla small, located anteriorly, about 25% of way back along ventral surface of cephalothorax (arrowed in Fig. 9B ). Pair of ocelli present, pigment cups moderately developed, separated by half eye diameter, weakly pigmented; ventral cup about as large as lateral cups. Forehead rounded. Ventral surface of perioral area with three sac-like protrusions ( Fig. 9B, D ), one between usual nipple-like processes and surrounded by field of transverse cuticular striae, additional pair of larger processes flanking oral papilla (arrowed in Figs 9B , 10F ). Cephalothorax with irregular pattern of coarse cuticular folds and protuberances visible in lateral and ventral views ( Figs 9B , 10F ).

Antennules five-segmented, geniculate ( Fig. 9A ). In terms of pattern described by Grygier and Ohtsuka (1995), element 1 present on first segment, biserially setulate; elements 2d 1, 2d 2, 2v 1, 2v 2, 2v 3, and IId present on second segment. Third segment with elements 3, IIId, and IIIv; element 3 remarkably long, reaching to midlength of fourth segment. Segment four bearing elements 4d 1 and 4v 1-3 as well as IVv and IVd. In terms of Huys et al. ’s (2007) nomenclature, terminal segment with reduced armature, only elements 1, 2, and 5 and unbranched elements A–D being present on both antennules. Terminal antennular segment with low inner rounded expansion and secondary rounded protuberance on proximal half, and distal half modified as short, distally curved, sabre-like structure ( Fig. 10A ).

First pedigerous somite incorporated into cephalothorax; this and succeeding three free pedigerous somites each bearing pair of biramous swimming legs. Pedigerous somites 2–4 together accounting for 27% of total body length in dorsal view. Intercoxal sclerites of legs 1–4 sub-quadrate (legs 1 and 2) to sub-rectangular (legs 3 and 4), without ornamentation on surface or along distal margin. Basis of legs articulating with rectangular coxa along diagonal line. Basis with thin, naked lateral seta on legs 1, 2, and 4; on leg 3, this seta thicker, lightly setulate from base, and 3.5–4 times longer than in other legs, reaching well beyond distal margin of exopodal ramus ( Fig. 10C ). Endopodites and exopodites of swimming legs 1–4 triarticulate ( Fig. 10A, B ). Ramus setae all lightly and biserially plumose except for spiniform outer seta on exopodal segments 1 and 3 and inner seta of first exopodal segment, these all being short and slender. Outer apical exopodal seta of swimming legs 1–4 with outer margin smooth, inner margin lightly spinulose. There is no inner seta on first exopodal segment of legs 1–4 ( Fig. 10A, B ).

Armature formula of swimming legs:
	basis	endopodite	exopodite
leg 1	1-0	0-1;0-1;1,2,2	I-0;0-1;I,2,2
legs 2–4	1-0	0-1;0-1;1,2,2	I-0;0-1;I,1,2,2

Fifth legs absent. Urosome consisting of five somites: fifth pedigerous somite, genital somite with genital apparatus, two free postgenital somites, and anal somite, longer than second free postgenital somite. Ventral surface of genital somite forming protuberant base of very short shaft with distal genital lappets. Lappets represented by pair of rounded, poorly developed, posteriorly directed processes separated by shallow medial notch ( Fig. 9C ). Postgenital somite bearing ventral rounded process (arrowed in Fig. 10E ). Caudal rami each with five setae, but rami of remarkably unusual form: massively developed, almost as long as anal and preanal somites combined, with transverse suture resembling intersegmental division ( Fig. 10D ). Each ramus with several processes, each being armed distally with one seta. Innermost process longest, cylindrical, with outer basal secondary process, each process armed with single terminal seta. Other processes including medial one armed with single seta and outer one, with two setae ( Fig. 9C ).

Female: unknown.

Type locality. Davies Reef, Queensland, Australia (19°7.34’S; 146°53.024’E).

Etymology. The specific epithet, an adjective, is a combination of two Latin terms, crassus meaning bulky, and cauda meaning tail or posterior appendage. It refers to the unusual development and size of the caudal rami.

Remarks. This male specimen is similar to those of the genus Monstrillopsis in the possession of a modified fifth antennular segment with inner rounded protuberances and an attenuated distal half resembling a short, curved, sabre. Also, the oral papilla is far anterior on the cephalothorax ( Sars 1921; Suárez-Morales et al. 2006). As described and discussed in the genus comparisons, this species has a combination of characters not found in any other known monstrilloid, such as the reduced genital complex, the sac-like protuberances in the perioral area of the cephalothorax, the absence of an inner seta on the first exopodal segment of legs 1–4, the presence of a process on the ventral surface of the postgenital somite, and the remarkable, highly modified structure of the caudal rami, with a development and size which are unique among all known monstrilloids. The female of this species is unknown but it is expected that it could be easily recognizable by the presence of these unique characters, particularly the modified caudal rami and the lack of an inner seta on the first exopodal segment of legs 1–4.

Figures

FIGURE 9. Australomonstrillopsis crassicaudata gen. et sp. nov., adult male A) left antennule, dorsal view; B) habitus showing bulging perioral processes (arrows), ventral view; C) urosome and caudal rami showing suture-like constrictions (arrows), ventral view; D) cephalic area showing oral papilla (arrow) and adjacent protuberances. Scale bars: A, C, D = 50 µm, B = 100 µm.

FIGURE 10. Australomonstrillopsis crassicaudata gen. et sp. nov., adult male. A) first swimming leg; B) fourth swimming leg; C) outer basipodal seta of third swimming leg; D) urosome and modified caudal rami, dorsal view; E) same with caudal setae cut short, lateral view; F) habitus, lateral view (swimming setae omitted). Scale bars: A–E= 50 µm, F= 100 µm.