Monstrillopsis boonwurrungorum, 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 : 308-311

Monstrillopsis boonwurrungorum sp. nov.

( Figs 4–5 )

Material examined: Holotype: adult male from Port Phillip Bay , (Station C of Kimmerer & McKinnon 1985), Victoria, Australia (38°2.583’S; 144°57.08’E), partially dissected, slide-mounted in glycerine, sealed with Entellan®. Date of collection: 5 January 1984. Slide deposited in MTQ, Australia (cat. MTQW24269 ).

Description. Male: Total body length of adult holotype: 0.91 mm. Cephalothorax 0.45 mm long, representing almost 50% of total body length. Antennule 0.42 mm long, about as long as cephalothorax ( Fig. 4A, B ) and representing almost 50% total body length. Oral papilla small, located anteriorly, about 26% of way back along ventral surface of cephalothorax ( Fig. 4C, D ). Pair of relatively large ocelli present, pigment cups moderately developed, separated by less than half eye diameter, weakly pigmented; ventral cup slightly larger than lateral cups. Forehead rounded, moderately protuberant, with no observable cuticular ornamentation. Ventral surface of cephalic area bearing low, rounded process between bases of antennules (arrowed in Fig. 4C ). One pair of weakly developed nipple-like cuticular processes on anterior ventral surface between antennule bases and oral papilla (arrowed in Fig. 4D ). Otherwise, cephalic ventral surface smooth except for faint preoral horizontal striations ( Fig. 4C, D ).

As usual in male monstrilloids, antennules five-segmented, geniculate ( Fig. 4A , 5E ). In terms of pattern described by Grygier and Ohtsuka (1995), element 1 present on first segment, 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. Segment four bearing elements 4d 1,2 and 4v 1-3 as well as IVd ( Fig. 5E ). Following Huys et al.’s (2007) nomenclature, armature of terminal segment including elements 1 and 4–7 as well as unbranched elements A–D (latter on posterior margin). As usual in male Monstrillopsis , terminal antennular segment modified: inner expansion on proximal half bearing rounded process (arrowed in Fig. 5E ), with no special ornamentation; distal half forming remarkably long, distally curved, sabrelike structure representing 64% of length of segment ( Fig. 5E ).

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 29% of total body length in dorsal view. Intercoxal sclerites of legs 1–4 sub-rectangular, 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 and 2.5 times longer than in other legs, reaching beyond distal margin of first exopodal segment, and lightly setulate from distal 2/3 (arrow in Fig. 5A ). Endopodites and exopodites of swimming legs 1–4 triarticulate ( Fig. 5A ). 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 spinulose, inner margin lightly setulate ( Fig. 5B ).

Armature formula of swimming legs as in Monstrillopsis hastata .

Fifth legs absent. Urosome consisting of five somites: fifth pedigerous somite, genital somite with genital apparatus, two free postgenital somites (second of which referred to as preanal somite), and anal somite. Preanal and anal somites partially fused, with suture visible in ventral view (arrow in Fig. 4E ) and bilateral intersomite constriction. Ventral surface of genital somite forming enlarged base of cylindrical shaft with elongate distal genital lappets. Genital complex of type II. Lappets represented by pair of posteriorly directed, divergent, arm-like processes with rounded tips. Lappets reaching to midlength of anal somite ( Fig. 5C, D ). Caudal rami subrectangular, weakly divergent, approximately 1.5 times longer than wide, each ramus bearing four setae.

Female: unknown.

Type locality. Port Phillip Bay , Victoria, Australia (38°2.583’S; 144°57.08’E) .

Etymology. The specific epithet, a genitive noun, makes reference to the Boonwurrung people, a Kulin nation of aboriginal Australians who are the traditional owners of the coast and land along the northern, eastern, and southern shorelines of Port Phillip Bay. The name was Latinized using the masculine plural form.

Diagnosis. Terminal antennular segment strongly modified, with smooth inner rounded expansion and elongate distal half, latter sabre-like and representing more than 60% of length of segment. Cephalothorax with anterior ventral protuberance on cephalic part, widely separated from oral papilla. Two free postgenital somites present before anal somite, with preanal and anal somites partially fused but well distinguishable. Genital complex of type I, its lappets with rounded tips. Caudal rami with four setae.

Remarks. This new species shares several important characters with its Australian congener Mon. hastata sp. nov., including the position of the oral papilla, the body proportions, the presence of four caudal setae, the remarkably elongate sabre-like antennular process, and the general structure of the genital complex (type II). Monstrillopsis boonwurrungorum differs from Mon. hastata in several ways, including 1) the presence of an antero-ventral cephalic protuberance, which is absent in Mon. hastata ; 2) the presence of a ventral suture and lateral constriction dividing the preanal and anal somites, vs. fused somites in Mon. hastata ; 3) a relatively longer distal sabre-like process of the fifth antennular segment (58% of that segment’s length in Mon. hastata vs. 64% in the present species); 4) the lack of ornamentation on the same segment’s proximal rounded process, which has a row of four spiniform elements in Mon. hastata ; 5) the subquadrate intercoxal plates, vs. rectangular plates in Mon. hastata ; and 6) the distally rounded lappets of the genital complex vs. distally attenuated lappets with nipple-like tips in Mon. hastata . In addition, the perioral cuticular ornamentation and the development of the post-antennular nipple-like processes are clearly weaker in Mon. boonwurrungorum (see Fig. 4D ) than in Mon. hastata ( Fig. 2A ).

This male specimen differs from all its known congeners in having a very long sabre-like distal part of the fifth antennular segment, comprising more than 60% the length of the segment, and a smooth proximal inner rounded protuberance on that segment. An anteroventral cephalic protuberance between the antennular bases has been observed previously only in two other species of the genus, Mon. cahuitae ( Suárez-Morales et al. 2013) from Costa Rica and Mon. fosshageni Suárez-Morales & Dias, 2001 from off Brazil. In these two species the process arises very close to the oral papilla ( Suárez-Morales et al. 2013 fig. 4D; Suárez-Morales & Dias 2001 fig. 36), not widely separated from it as in Mon. boonwurrungorum (see Fig. 4C ). Also, the genital complex is of type I in both of these species but type II in Mon. boonwurrungorum , and the distal sabre-like antennular process of the fifth antennular segment is clearly shorter in Mon. cahuitae (32% of segment length) and Mon. fosshageni (43%) than in Mon. boonwurrungorum (64%). In addition, Mon. boonwurrungi has only four caudal setae vs. six in Mon. cahuitae ( Suárez-Morales et al. 2013); the number of setal elements is unknown in Mon. fosshageni .

Figures

FIGURE 2. Monstrillopsis hastata sp. nov., adult male. A) cephalic area, ventral view; B) same, dorsal view; C) urosome and caudal rami, dorsal view; D) urosome showing genital complex, ventral view; E) urosome, lateral view, showing fifth legs and features of genital complex. Scale bars: A–-E = 100 µm.

FIGURE 4. Monstrillopsis boonwurrungorum sp. nov., adult male from Australia. A) habitus, dorsal view; B) habitus, lateral view; C) cephalic area showing medioventral protuberance (arrow), lateral view; D) cephalic area showing faint nipple-like ventral processes (arrow), ventral view; E) urosome showing genital complex, ventral view. Scale bars: A, B= 200 µm, C–E= 100 µm.

FIGURE 5. Monstrillopsis boonwurrungorum sp. nov., adult male. A) second swimming leg with outer basipodal seta of third swimming leg (arrow); B) detail of ornamentation of outer apical spiniform seta of third exopodal segment of second swimming leg; C) urosome showing genital complex, dorsal view; D) same, lateral view; E) right antennule, dorsal view. Scale bars: A, C–E = 100 µm, B = 25 µm.