Maemonstrilla hoi, 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 : 323-328

Maemonstrilla hoi sp. nov.

( Figs 14–17 )

Material examined. Adult female holotype from Port Phillip Bay, Victoria, Australia (38°16.085’S; 144°40.0815’E; Kimmerer & McKinnon 1985), partially dissected, ethanol-preserved, three slides mounted in glycerine, sealed with Entellan ®, cephalothorax damaged in mounting medium. Date of collection: 15 October 1984. Slides deposited in collection of MTQ, Australia (cat. MTQW34272 ) .

Description. Female: Total body length of holotype 1.3 mm. Body robust. Cephalothorax short, robust, representing up to 56% of total body length ( Figs. 14A , 17A, B ), reticulate on dorsal and ventral surfaces. Reticulation not reaching pedigerous somites 2–4 but present on antennular segments ( Fig. 15B ). High reticular ridges only on second and proximal part of third antennular segments, appearing as marginal keel-like structures (arrowed in Fig. 15B ). Antennule short, robust, 0.19 mm long, representing 18% of cephalothorax length ( Fig. 14A ). Oral papilla conical, nearly straight, protruding ventrally, located anteriorly, about 19% of way back along ventral surface of cephalothorax ( Fig. 14B ). Pair of relatively large ocelli present, pigment cups separated by less than half eye diameter, unpigmented; ventral cup slightly smaller than lateral cups. Forehead with wide medial rounded protrusion. Three pairs of nipple-like cuticular processes on anterior ventral surface posterior to antennule bases, with adjacent pattern of transverse cuticular striae on preoral surface ( Fig. 14B ).

Antennule four-segmented, with weak division between segments 3 and 4, third segment represented by inner lobe partially fused with succeeding fourth segment ( Fig. 15B ). Antennules unusually inserted 15% of way back along cephalothorax, at same level as ocelli. In terms of pattern described by Grygier and Ohtsuka (1995), element 1 present on first segment, relatively long and slender, reaching to beyond midlength of second antennular segment. Elements 2d 1-2, 2v 1-3, and IId present on second segment; among 2v and 2d groups, elements 2v1 and 2v3 longest, elements 2d 1-2 and 2v 2-3 clustered at distal margin of segment. Third segment with elements 3, IIId, and IIIv; element 3 long and slender, reaching to midlength of fourth segment. Segment four bearing elements 4d 1,2 and 4v 1-3 as well as IVd, IVv, Vd, Vv, Vm, and 5. Elements of groups 2v and 3 longer than those of groups 4v and 4d. Outer distal b 1-3 branched, but seta b 4 unbranched. Apically, only element 6 2 present on antennules, element 6 1 possibly broken off, sockets observed on both antennules.

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 30% of total body length in dorsal view, third somite being the largest, alone representing 38% of their combined length. Intercoxal sclerites of legs 1–4 low and wide with dorsally produced corners, surface of sclerites naked. Coxae with smooth outer margins. 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, biserially setulate, about 6 times longer than that on leg 1 and 3 times longer than those on legs 2 and 4, reaching well beyond distal margin of exopodal ramus ( Fig. 16C ). Endopodites and exopodites of swimming legs 1–4 triarticulate ( Fig. 16A–D ). Ramus setae all lightly and biserially plumose except for spiniform outer setae on exopodal segments 1 and 3, latter seta with outer margin smooth, inner margin spinulose ( Fig. 16E ). Outer apical exopodal seta of swimming legs 1–4 with outer margin spinulose, inner margin naked ( Fig. 13E ). No inner seta on first exopodal segment of legs 1–4; seta represented by cuticular notch or socket-like structure.

Armature formula of swimming legs as in Maemonstrilla ohtsukai sp. nov.

Fifth legs paired, rod-like, with two lightly setulate setae, one distal, one subdistal ( Figs. 14D , 15A ). Fifth legs longer than in Mae. ohtsukai , reaching posterior margin of anal somite ( Figs. 14C , 15A ). Urosome consisting of four somites: fifth pedigerous somite, compound genital somite with incomplete transverse suture, and two free postgenital somites, i.e. the preanal and anal somites ( Fig. 15A ). Ventral surface of genital somite bearing ovigerous spines arising from low, conical projection of anterior half. Posterior half of genital compound somite with tongue-like ventral protuberance (arrowed in Fig. 14C ). Copulatory opening on ventral surface at posterior base of ovigerous spine cone (arrowed in Fig. 15A ). Tips of ovigerous spines reaching to between legs 2 and posterior margin of cephalothorax. Spines cylindrical, smooth, and straight in proximal three-fourths; distal one- fourth moderately swollen and tapering distally ( Fig. 15A ). Specimen with large mass of eggs on ventral surface ( Fig. 17A, B ). Caudal rami subrectangular, weakly divergent, approximately 1.6 times longer than wide, each ramus bearing six setae. Inner dorsal seta thinnest (seta VII of Huys and Boxshall 1991; arrowed in Fig. 15A ).

Male: unknown.

Etymology. The species is named after Dr. Ju-shey Ho, California State University, Long Beach, for his abundant and valuable contributions to the knowledge of the symbiotic Copepoda.

Diagnosis. Cuticular ridges limited to cephalothorax and antennules, with high ridges along outer margins of antennular segments 2 and 3. Antennule relatively short, representing about 18% of cephalothorax length. Oral papilla conical, straight, not particularly long. Pigmented spots absent from body. Inner seta absent from first exopodal segment of legs 1–4; outer margin of coxa smooth. Posteroventral protrusion of genital compound somite developed into short, tongue-like process. Fifth leg uniramous, rod-like, relatively long, reaching posterior margin of anal somite, armed with two distal setae.

Remarks. For the same reasons as Mae. ohtsukai sp. nov., this new species is assignable to the Maemonstrilla hyottoko species group ( Grygier & Ohtsuka 2008). It displays cuticular reticulation only on the cephalothorax and antennules, in contrast to the extensive reticulation on the cephalothorax, lateral sides of the trunk, dorsum of the urosomites, and caudal rami shown by most other members of this species group ( Grygier & Ohtsuka 2008). A similar, reduced reticulation is present in Mae. simplex , in which only the cephalothorax is reticulate. In addition, Mae. simplex shares some other features with Mae. hoi sp. nov., including a conical, ventrally projecting oral papilla, long fifth legs, and general body shape and proportions; nonetheless, there are important differences between these two species. In Mae. hoi , the ventral protuberance of the genital compound somite is moderately developed, forming a small, tongue-like process, whereas this structure is very large and conspicuous in Mae. simplex ( Grygier & Ohtsuka 2008, fig. 22E). In Mae. hoi , the antennule is very short, about 18% of the cephalothorax length, but it is clearly longer (47% of the cephalothorax length) in Mae. simplex . The high cuticular ridges present along the outer margins of antennular segments 2–3 in Mae. hoi are absent in Mae. simplex , in which these margins are smooth. Some additional details of the antennule structure and armature are useful to separate these two species. Element 1 is longer in Mae. hoi , reaching to about midlength of the second segment, whereas it is quite short in Mae. simplex , barely reaching beyond the distal margin of the first segment ( Grygier & Ohtsuka 2008, fig. 18C). The distal part consisting of segments 3 and 4 is noticeably elongated in Mae. simplex , representing 62% of the total length of the antennule, whereas the same two segments represent only 43% of the antennule length in Mae. hoi . The third segment is clearly aligned with the longitudinal axis of the antennule in Mae. simplex (see Grygier & Ohtsuka 2008, fig. 18C), but in Mae. hoi , this segment appears reduced, forming a well-defined lobe protruding along the inner margin of the antennule ( Fig. 15B ). Finally, in M. simplex , antennular elements 2d 1-2 are distinctively smaller than elements 2v ( Grygier & Ohtsuka 2008, fig. 18C) whereas in Mae. hoi , all elements of both groups are represented by subequally long, slender setae ( Fig. 15B ).

Figures

FIGURE 13. Maemonstrilla ohtsukai sp. nov., adult female. A) first swimming leg with coxal sclerite; B) second swimming leg with coxal sclerite; C) third swimming leg with coxal sclerite; D) fourth swimming leg; E) ornamentation of outer apical spiniform seta of third exopodal segment of second leg; F) right antennule, dorsal view. Scale bars: A, C–E = 100 µm, B = 25 µm.

FIGURE 14. Maemonstrilla hoi sp. nov., adult female. A) habitus, dorsal view; B) cephalic area of holotype showing cuticular reticulation and oral papilla, lateral view; C) urosome showing fifth leg and tongue-like posteroventral process of genital compound somite (arrow), lateral view; D) detail of insertion of distal setae of fifth leg. Scale bars: A= 500 µm, B, C= 100 µm, D= 50 µm.

FIGURE 15. Maemonstrilla hoi sp. nov., adult female. A) urosome showing fifth legs, ovigerous spines, posteroventral protuberance of genital compound somite, genital pore (arrow), and caudal seta VII (arrow), ventral view; B) left antennule, dorsal view. Scale bars: A, B = 100 µm.

FIGURE 16. Maemonstrilla hoi sp. nov., adult female. A) first swimming leg; B) second swimming leg; C) third swimming leg with coxal sclerite; D) fourth swimming leg; E) ornamentation of outermost spine of third exopodal segment of second leg. Scale bars: A–D = 100 µm, E = 25 µm.

FIGURE 17. Maemonstrilla hoi sp. nov., adult female. Microphotograph. A) lateral view of holotype specimen showing egg mass; B) dorsal view of same specimen. Scale bars: A, B = 500 µm.