Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 70, 1940-41
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Genus Isotoma Bourlet, 1839.

Abd. III and Abd. IV approximately equal. Bothriotrichia absent. Ant. IV without sense rods. Ocelli eight to each side. Post-antennal organ present. Empodial appendage present. Furcula well developed, dentes much longer than manubrium. Furcula generally with many ventral setae. Three species of Isotoma occur in this country, two being endemic and the other almost cosmopolitan.

Key to the New Zealand Species of Isotoma.
1. All ocelli large and approximately equal. 2
Some ocelli distinctly smaller than the others. 3
2. Bluish-grey species. Mucro with three teeth in line. Claw without any teeth. I. maritima Tullberg
3. Violet species with ochreous intersegmental bands. Mucro with three equal teeth, not in line. Claw with two inner and two outer lateral teeth. I. pallidafasciata sp. nov.
Two ocelli on each side smaller than rest. Pale greyish-violet species. Mucro with three unequal teeth not in line. Claw with two small outer lateral teeth and one very small inner tooth. I. exiguadentata sp. nov.

Isotoma maritima Tullberg, 1871. Plate 53, fig. 225.

This littoral species, which is widely distributed throughout the Northern Hemisphere, was found among mussels on rocks at Muriwai, Auckland, and in shore debris, Waiheke Island, Auckland, by Mr. E. D. Pritchard, and was reported by Womersley in 1936. It has not been found elsewhere.

It is a small insect up to 1·3 mm. long, recognized by its bluish-grey colour and small head, which is not as long as Th. II and III together. There are eight ocelli to each side, postantennal organ broad elliptical, larger than an ocellus. Mucrodens twice as long as manubrium. Mucro tridentate, the three teeth almost in line and diminishing in size from apical tooth back. Claw without any teeth.

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Isotoma pallidafasciata sp. nov. Plate 53, figs. 226–228.

Colour: Ochreous brown with an overlay of pale greyish-violet. Narrow pale ochreous bands on the anterior margins of the metathorax and Abds. I, II, III and IV. A very dark violet narrow band around posterior margin of Abd. III and partly around Abd. IV. Strong violet coloured pigment along mid-dorsal line and on sides of Abd. VI. Legs bluish-violet, furcula pale yellow. Antennae violet on first segment and very dark bluish-black on other three segments.

Clothing: Thickly clothed with moderately long plain setae.

Body: Length 1·75 mm. Antennae twice as long as head, the four segments related as 7: 10: 10: 14. Ocelli eight to each side, all large, but the anterior two largest, and situated on dark fields. Post-antennal organ narrow, elliptical and longer than an ocellus. Ventral tube short. Abd. III very slightly longer than Abd. IV.

Legs: Claw with two external lateral teeth and two inner teeth, one just past one-third down from claw base and the other, a very small tooth, at about two-thirds down. Empodial appendage reaching half-way down claw, sharply pointed, with narrow outer lamella reaching to tip and broader inner lamella reaching to about half-way. Inner lamella supplied with small blunt tooth on its forward edge. A single non-clavate tenent hair to each foot. Claw lightly striated.

Furcula: Well clothed with setae. Manubrium to mucrodens as 12: 33. Mucro with three teeth, apical, sub-apical and external lateral all of equal height.

Locality: Aratiatia Rapids, in soil.

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Type: Slide 3/587, Dominion Museum Collection.

Isotoma exiguadentata sp. nov. Plate 53, figs. 231–234.

Colour: Pale greyish-violet, with narrow, colourless intersegmental bands on anterior margins of all segments. Legs, antennae, and furcula paler, but third and fourth antennal segments very dark violet.

Clothing: Well clothed with short, plain setae.

Body: Length 1 mm. Antennae only slightly longer than head, relative lengths of the four segments being as 10: 16: 20: 36. Ocelli eight to each side, the inner posterior two small, remainder all large. Postantennal organ very large, being long and elliptical and equivalent to about four ocelli. Abd. III and Abd. IV equal. Ventral tube short and cylindrical.

Legs: Claw with two outer very small lateral teeth at about one-third down and a single extremely small inner tooth at about one-third. (Both visible only with an oil immersion objective.) No tenent hair. Empodial appendage about one-third as long as claw, sharply-pointed with complete broad outer lamella and semi-circular inner lamella reaching to about half-way.

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Furcula: Manubrium to mucrodens as 5: 7. Dens annulated and corrugated, mucro with apical tooth, larger central tooth, and small exterior lateral tooth.

Locality: Akatarawa, in bush soil.

Remarks: This species is rather similar to I. pallidafasciata sp. nov., from which it is distinguished by the different dentition of the claws and the excessively large post-antennal organ.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Type: Slide 3/588, Dominion Museum Collection.