Ekman (1905) established the genus Metaboeckella after examining the specimens from which Sars (1904) described the species Boeckella dilatata from Lake Wakatipu. His grounds for creating a new genus were two (1) the finding of but two articulations in the endopodites of the first and also fifth legs of the female, and (2) the lack of spines on the endopodite of the female fifth pair. It is felt that this genus was established on a few atypical specimens since Sars remarked (1904) in describing the species that he had only a limited number of specimens, most of which were young. The author has had the advantage of taking specimens from Lake Wakatipu at varying seasons of the year and from a number of different localities. It would appear that the Copepods in this lake and other similar large oligotrophic lakes are monocylic, for at most seasons hauls contain little but immature animals. Females carrying fully-developed eggs appear in numbers only during the late spring and early summer. Many specimens have been dissected, and it has been found that the endopodites of the female fifth legs show a variation from 1–3 segments, bearing from 0–4 spines (Text-fig. 2, figs. 3, 3A, 3B). Regarding the segmentation of the endopodite of the first leg the articulations are indistinct, but in many the three segments can be discerned (Text-fig. 1, fig. 5). It is therefore felt that there is no justification for retaining the genus Metaboeckella.
Boeckella triarticulata Thomson. Text-fig. 1, figs. 1 and 7; Text-fig. 2, fig. 4; Text-fig. 3, fig. 1.
1882. Boeckia triarticulata Thomson.
1889. Boeckella triarticulata de Guerne & Richard.
1894. Boeckella triarticulata Sars.
1939. Boeckella triarticulata var. quarta Brehm.
Specific Characters (in part after Sars, 1894)
Female: Length 2.1–2.5 mm (Text-fig. 1, fig. 1).
Antennule extends to approximately the end of caudal furca. Body spindle-shaped, width greatest in region of first thoracic segment. Lappets consist of two lobes, the outer sharply tapered reach approximately the end of the genital segment, the inner lobes are asymmetrical, somewhat hamate and less than half the length of outer lobes Genital segment asymmetrically bulged, exceeds the combined length of the following two segments. The caudal furca are short, expanded distally, and bear a median fringe of fine setae. Furcal setae very plumose. Fifth legs, exopodite spine number 1:2:7; endopodite 1:1:6; (characteristic of genus). The strong spine on inner margin of segment 2 serrate with approximately 7 teeth on each side. Last segment somewhat longer than segment 2 but much more narrow, with median terminal spine equal in length to whole segment; flanking spines sub-equal and less than half length of median spine. Spines bear fine setae. Endopodite is in length equal to first two segments of exopodite (Text-fig. 2, fig. 4). Egg number large, usually exceeds 32, eggs relatively small.
Male: Length, 2.0–2.1 mm.
Right antennule geniculate, 7 segments anterior to hinge very tumified, segments posterior to hinge number 5, but articulation may be indistinct. (Text-fig. 1, fig. 7.)
Right Fifth Leg: First segment somewhat triangular and produced into an outer spine, which does not exceed second segment in length, second segment of greater length than first segment also ends in a spine, third segment forms a strong sickle-shaped claw thickened proximally. Endopodite consists of one segment, somewhat expanded at base, sides more or.
Text-fig. 1—Fig. 1—Boeckella triarticulata (Christchurch pond). Fig. 2—B. dilatata (Lake Wakatipu). Fig. 3—B. hamata (Lake Lyndon). Fig. 4—B. propinqua (Pond, Canaan Track, Nelson). Fig. 5—First leg, male, B. dilatata (Lake Wakatipu). Fig. 6—Terminal segs. right antennule of male B. propinqua. Fig. 7—Terminal segs, right male antennule B. triarticulata.
less parallel but terminate in a small point. In length the endopodite equals approximately the first two segments of the exopodite.
Left Fifth Leg: The basipodite is expanded into a serrated lamella. The exopodite is composed of three segments, the first two of which each bear a spine. The claw which is longer, more slender and less curved than that of the right leg is composed of segments 2 and 3, the articulation between the last two segments may be indistinct. The endopodite is one-segmented, slight, and about half the length of that on the right side (Text-fig. 3, fig. 1).
Variations. (1) Colour: Specimens showing red and blue patches, as well as colourless individuals have been taken. Miss Thomson (unpublished work) after a season's observation of this species in one pond reached the conclusion that colour was not characteristic of any one population, but variable within a population due to some unknown factor.
(2) Antennule: The length varies from population to population extending from the last abdominal segment to the end of the caudal furca, but never to end of caudal setae.
(3) Thoracic Lappets: The outer lobes may equal the genital segment or extend to almost the end of the last abdominal segment.
(4) Right Fifth Leg of Male: The length of the spine on first segment of exopodite may vary from half to nearly the whole length of the second segment. The claw is stouter in some populations.
(5) Left Fifth Leg: The form of the basipodite lamella may be triangular or pear-shaped. The serrations appear more marked on the pear-shaped form.