Maemonstrilla crenulata, 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 : 333-337

Maemonstrilla crenulata sp. nov.

( Figs 21–23 )

Material examined. Adult female holotype from Scott Reef , Western Australia (14°2.3’S; 121°53.3’E; Station CH of McKinnon et al. 2013), partially dissected, slide-mounted in glycerine, sealed with Entellan ®. Date of collection: 30 November 2009. Slide deposited in collection of WAMC, Australia (cat. WAMC55072 ).

Description. Female: Total body length of holotype 1.75 mm. Cephalothorax elongate, robust, 1.03 mm long, representing up to 60% of total body length ( Fig. 21A ), with faint reticulate pattern limited to small areas of ventral and dorsal surfaces of cephalic area ( Figs. 21A , 22A ). Pair of spine-like scales present on dorsal posterior margin of third pedigerous somite. Antennule relatively short, 0.34 mm, representing 18% of total body length and 31% of cephalothorax length ( Fig. 21A ). Oral papilla well developed, thick, with wide base, located anteriorly, about 19% of way back along ventral surface of cephalothorax ( Fig. 22A ). Pair of relatively large ocelli present, pigment cups separated by more than eye diameter, weakly pigmented; ventral cup slightly smaller than lateral cups. Forehead with moderate-sized medial rounded protrusion and two sensilla. Two pairs of nipple-like cuticular processes on anterior ventral surface between antennule bases and oral papilla, this area showing transverse striation pattern ( Fig. 22A ).

Antennule four-segmented, with weak division between segments 3 and 4 ( Fig. 22B ). 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, element 2d 2 being the longest. Third segment with elements 3, IIId, and IIIv. Segment four bearing elements 4d and 4v 1-3 as well as IVd, IVv, Vd, Vm, and 5. Element 4v 1 longest among those of groups 4v and 4d. Elements of group 2v moderately longer than those of groups 4v and 4d. Outer distal setae b 1-3 dichotomously branched, b 4,5 unbranched. Apically, elements 6 1,2 present together with aesthetasc 6aes.

1,2

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 26% of total body length in dorsal view. Second pedigerous somite largest of somites 2–4, representing almost 43% of this somite group. Third pedigerous somite with dorsal pair of spine-like scales in middle of posterior margin. Dorsal surface of fourth pedigerous somite with row of three pit setae near posterior margin ( Figs. 21A , 22C ). Intercoxal sclerites of legs 1–4 wide, slender, without ornamentation on surface or along distal margin. Basis of legs articulating with rectangular coxa along diagonal line. Coxa of legs 1–4 with patches of minute spinules plus crenulation-like transverse indentations along outer margin. Basis with thin lateral seta on legs 1, 2, and 4; on leg 3, this seta thicker, biserially setulate and 3–5 times longer than in other legs, reaching distal margin of exopodal ramus ( Fig. 23C ). Endopodites and exopodites of swimming legs 1–4 triarticulate ( Fig. 23A–C ); outer margin of first endopodal segment of legs 2 and 3 with notch (arrowed in Fig. 23B, C ). Outer margin of first exopodal segment of legs 2–4 with spiniform processes; similar processes also present on outer margin of third exopodal segment of leg 1 (arrowed in Fig. 23A ). Ramus setae all lightly and biserially plumose except for spiniform outer setae on exopodal segments 1 and 3. Outer apical exopodal seta of swimming legs 1–4 with outer margin spinulose, inner margin naked ( Fig. 23A–C ).

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

Fifth legs paired, rod-like, distally bilobed, inner lobe with one seta, outer lobe with one distal and two subdistal setae ( Fig. 21C ). These legs relatively short, reaching to midlength of compound genital somite. Urosome consisting of four somites: fifth pedigerous somite, compound genital somite with incomplete transverse suture on dorsal surface, and two free postgenital somites, i.e. the preanal and anal somites ( Fig. 21B ). Ventral surface of genital somite bearing ovigerous spines arising from low conical projection of anterior half; this area also with anteroventral rounded protuberance (arrowed in Fig. 22D ). Posterior half of genital compound somite with ventral margin straight, unmodified ( Fig. 21B ). Copulatory opening located on ventral surface at posterior base of ovigerous spine cone (arrowed in Fig. 21C ). Tips of ovigerous spines reaching to between legs 2 and posterior margin of cephalothorax. Spines cylindrical, straight, rugose in distal one-third and tapering distally ( Fig. 21 D ). Caudal rami short, quadrate, each bearing five setae.

Male: unknown.

Etymology. The specific epithet, an adjective, makes reference to the unique crenulated margin of the coxa of legs 1–4.

Diagnosis. Maemonstrilla with cephalothorax mostly non-reticulated, reticulation limited, faint. Cephalothorax representing 60% of total body length. Antennule relatively short, representing 31% of cephalothorax length. Oral papilla thick, with wide base. Inner seta present on first exopodal segment of legs 1–4. Outer margin of coxa of these legs crenulate. First endopodal segment of legs 2 and 3 with outer notch. Third pedigerous somite with two dorsal spine-like scales on posterior margin. Anteroventral process of compound genital somite rounded, with secondary apical protrusion. Fifth leg biramous, exopodal lobe with three setae, endopodal lobe with one distal seta.

Remarks. Among the Australian species, only Mae. crenulata sp. nov. is assignable to the Maemonstrilla turgida species group as defined by Grygier and Ohtsuka (2008) mainly by the lack of reticulation on most of the cephalothorax, as well as the antennules and pedigerous somites, the presence of a pair of spiniform processes on the dorsal posterior margin of the third pedigerous somite, the presence of an inner seta on the first exopodal segment of legs 1–4, the bilobed fifth leg with one endopodal and three exopodal setae, and the unmodified posteroventral margin of the genital compound somite. Additional characters shared with Mae. turgida include the body length (within the range of Mae. turgida as described by Grygier and Ohtsuka 2008), widely separated eye cups, the relatively large, ventrally projecting oral papilla, the short, subquadrate caudal rami, and the fifth legs reaching only to about midlength of the compound genital somite.

This is the largest species of Australian Maemonstrilla recorded. The new species has several important differences from the closely related Mae. turgida : 1) the cephalothorax is relatively shorter in Mae. turgida (49.4– 54.8% of total body length) ( Grygier & Ohtsuka 2008) than in Mae. crenulata sp. nov. (60%); 2) the antennule length is 41.6–51.3% that of the cephalothorax in Mae. turgida ( Grygier & Ohtsuka 2008) vs. 31% in Mae. crenulata ; 3) the anteroventral process of the compound genital somite is merely rounded in Mae. turgida ( Grygier & Ohtsuka 2008, fig. 27H) but has a secondary apical protrusion in Mae. crenulata ; 4) in the new species, the coxae of legs 1–4 have a series of deep indentations and patches of minute spinules along the outer margin, but in Mae. turgida , the indentations are absent and the coxal margins of legs 1–4 have only patches of very small spinules ( Grygier & Ohtsuka 2008, fig. 25F); 5) in the new species, the third exopodal segment of leg 1 and the first exopodal segment of legs 2–4 bear an outer row of spiniform processes that are absent in Mae. turgida ( Grygier & Ohtsuka 2008, fig. 27); 6) in Mae. crenulata , the first endopodal segment of legs 2 and 3 has an outer notch that is absent in Mae. turgida ( Grygier & Ohtsuka 2008, fig. 27); 7) in the antennule armature of Mae. turgida , the elements of groups 2v and 2d are equally long ( Grygier & Ohtsuka 2008, fig. 24B), but in Mae. crenulata , element 2d 2 is clearly longer and element 2d 1 is shorter than the other elements in these groups. It is notable that in these species, both belonging to the Mae. turgida group, elements 4v 1,2 are longer than those in group 4d, thus diverging with the pattern observed in the known species of the hyottoko group, in which both groups of elements are equally long; 8) leg 5 is longer and more slender (length/width ratio = 6.0) in the new species than in Mae. turgida (3.0). Also, in the new species the inner lobe does not reach the distal margin of the outer lobe ( Fig. 21C ), whereas in Mae. turgida the inner lobe is longer than the outer one ( Grygier & Ohtsuka 2008, fig. 27G).

Figures

FIGURE 21. Maemonstrilla crenulata, adult female. A) habitus showing partial faint reticulation of anterior part of cephalothorax, dorsal view; B) urosome showing fifth legs and proximal section of ovigerous spines, lateral view; C) same, ventral view; D) detail of terminal part of ovigerous spines. Scale bars: A =500 µm, B–D= 100 µm.

FIGURE 22. Maemonstrilla crenulata, adult female. A) cephalic area showing oral papilla, faint reticulation and cuticular striation, lateral view; B) left antennule, dorsal view; C) urosome, dorsal view; D) urosome showing anteroventral rounded process of genital compound somite (arrow), fifth legs omitted. Scale bars: A–D = 100 µm.

FIGURE 23. Maemonstrilla crenulata, adult female. A) first swimming leg showing ridges on outer margin of third exopodal segment (arrow); B) second swimming leg showing notch on outer margin of first endopodal segment (arrow); C) third swimming leg showing notch on outer margin of first endopodal segment (arrow). Scale bars: A–C = 100 µm.