Tuatara: Volume 3, Issue 3, November 1950
New Zealand Terrestrial Isopods
New Zealand Terrestrial Isopods
“But so crafty have crustaceans been in keeping dark and not courting unnecessary observation, that very few persons know how numerous are the species or how astonishingly multitudinous are the individuals of some of those species. Still less known is the great variety of situations in which they may be successfully sought for. It is not only the shores of the sea and its various depths, down to about three thousand fathoms, that yield them. Out of the many miscellaneous dwellings which they favour, a few may be mentioned as samples, some of them being themselves crustaceans since the list includes the gills of a lobster, the cheek of a prawn, the abdomen of a hermit-crab, the viscera of a shore-crab, as well as the eye of a sprat, the mouth of a cod, the back of a turtle, the floating gulf weed, the slates of a roof, the fruit in a garden, the leaves of a tree, a deep well, a horse-pond, a cart rut after a shower of rain, or a packet of dried mud. In all these stations different kinds may at times be found. Some are parasites pure and simple, degraded in shape or almost without any definiteness of form; some are semi-parasitic and proportionately lethargic; others are free-living and extremely vivacious; nor are there wanting some so framed as to extort admiration even from the ignorant, a success of which nature has every reason to be proud, since even the best work of art or the most finished essay cannot always command it.”
—T. R. R. Stebbing (1894).
To the average person the term “Crustacea” has the somewhat limited application of the familiar reddish-hued animal frequently encountered in trams. In reality, it covers a multitudinous range of species, rivalling, and only excelled in numbers and variety by, the orders of insects. Yet these species are to be found almost everywhere, including the back garden, for two of the orders of the group have invaded the land so successfully as in some cases to become garden pests. These two are the Orders Isopoda, or, more colloquially, the “slaters, sow-bugs, pill-bugs, woodlice,” and the Order Amphipoda, or “hoppers.” Both are found in garden litter, in rotting grass, under rotting wood, and in particular under the ground covering of leaves and decaying undergrowth in the bush. Both groups require a fairly high degree of moisture, and both groups form a comparatively large proportion of the leaf-mould fauna of New Zealand.
There is one very easy method of telling an amphipod from an isopod—the amphipod bounds away in leaps out of all proportion to page 116 its size, whilst the isopod scuttles to the nearest cover with ferocious intent and all seven pairs of legs moving like overworked pistons. Or, and for the terrestrial species this is as reliable, the amphipod is flattened or compressed as though its sides had been pressed together; the isopod is likewise compressed but in the other plane, as though it had been lightly trampled on.
Most people know what an isopod looks like, under one name or another. “Woodlice” or “slaters” are the most common New Zealand terms for them. There is only one other kind of animal which may be mistaken for an isopod—a millipede found in New Zealand, mainly in high country. To tell them apart, turn the specimen on its back, and if the number of legs is obviously more than seven pairs, the animal is a millipede.
History: The first scientist to describe any of the native isopod species from this country was J. D. Dana, who led the United States Exploring Expedition of 1851-52. Most of his specimens were collected from the Bay of Islands, from such exotic—sounding places as Wykare and Taiammai. The only copy of the Crustacean section of his report which I know to be in New Zealand is in the Turnbull Library. Since Dana's expedition, isopod collections have been made by one French and at least three German expeditions. In New Zealand, Charles Chilton and G. M. Thomson have described new species. The greater proportion of new species recorded other than by these latter, are in somewhat sketchily described and sparsely illustrated papers by Budde-Lund—these are also very hard to procure.
Of the forty-eight species known from New Zealand, four (Porcellio scaber, Armadillidium vulgare, Porcellionides pruinosus and Ligia exotica), are cosmopolitan. The last-named is mentioned as being found in this country by Jackson (1941) in his “Checklist of the Terrestrial and Fresh-water Isopoda of Oceania,” but I have seen no verification of this record. Amongst those of Pacific distribution are Actaecia euchroa, found in Tasmania, and Trichoniscus thomsoni which is recorded from Austral Island in the Polynesian Group.
Habitat: Although the term “terrestrial isopoda” has been used in this article to cover all forms of the Sub-order Oniscoidea, a number of the members of the sub-order are not truly terrestrial but littoral. These include Ligia novaezealandiae, Tylos neozelanicus, Scyphoniscus waitatensis, Actaecia euchroa and A. opihensis, and Scyphax ornatus. Nearly all of the truly terrestrial species are to be found under stones or wood, where the requisite degree of moisture is present.
This habitat has had some influence on their distribution as is shown by specimens which Chilton reported to have been carried far down country on logs during a flood. The occurrence of Trichoniscus magellanicus and of species of Deto in South America has also been attributed page 117 to carriage by prevailing oceanic currents, although there is still some doubt as to the specific identities of the two forms.
Perhaps the most interesting of the New Zealand species is Trichoniscus commensalis, which is found in ants' nests. This curious cohabitation is not uncommon in other parts of the world; in England and Europe Platyarthrus sp, and in South Africa Phylloniscus sp., Schoblia, Titana, and Kogmania sp. are commonly discovered commensal with ants or termites.
Prevention: It has already been mentioned that one of the best places to find isopods is in the back garden. In some cases they may become so numerous as to attack vegetables, plants and cultivated mushroms, their chief food being vegetable matter. They also show a liking for decaying wood or leaf mould. For those gardeners troubled by them, one recommended procedure is as follows: Trap a dozen or so, bottle them in alcohol of strength 75-95 per cent., and post with all details to a zoologist for identification. (N.B.—Do not expect an immediate answer—some of the material of the 1872-6 “Challenger” expedition is still being examined.) Then commence an all-out attack with paris green. One method is “to mix 4 ozs. paris green with 6d. bran and a little sugar. Moisten with treacle mixed with hot water and form into little balls. Place balls all round plants or under light boards where slaters gather. This is poison.”
A recent gardening column recommended D.D.T. In spite of the proven affinity of D.D.T. for chitin, it does not seem to be very effective on isopods. Paris green is the time-tried prescription, and can be bought in numerous proprietary mixtures.
Identification: To a certain extent, identification is made easy by the varied sculpturing on the back of animals. However, as in most crustacean groups, many of the species differ in points which are comparatively insignificant, and resort must be had to the examination of mouth-parts and appendages for specific identification. Again, some species differ in a number of very small points, each in itself not particularly obvious, but forming a complex of a quite distinctive nature. As a result, it is hard, and in fact impossible, to construct a key which will include all recorded species, and satisfactorily separate them without using these characters as distinguishing ones. For that reason it is necessary to explain some of the terms used.
Porcellio scaber, for instance, is an isopod which is unable to roll up into a ball (i.e., to “conglobate”). The head, or cephalon, carries two pairs of antennae. The first antennae are extremely small and lie between the second antennae of seven segments. The first five segments of the second antennae comprise the “penduncle,” the remaining two the flagellum. (In Ligia novaezealandiae there are 20 flagellar segments). The eyes are compound. On the under-surface of the page 118 head are the mouth and mouth-parts. The body is of thirteen segments, the first seven forming the thorax or pereion, and the remaining six, the abdomen (fig. 1). The outer lateral portions of the thoracic segments are known as “epimera” or “epimeral plates.” The sixth abdominal segment is a triangular piece, the “telson,” carrying a pair of short, stout appendages (uropoda) each of which has two terminal branches (rami). Each of the seven thoracic segments bears one pair of legs on the ventral surface, whilst the under-surface of the first five abdominal segments is furnished with a pair of over-lapping platelike appendages (pleopoda) (fig. 15). The first two, or in some species the second pair only, are narrowed and modified in the male. The females lack this modification. Instead the thoracic segments are modified ventrally to form a broodpouch or “marsupium” in which the eggs and young are carried. The external plates of the pleopoda overlap other soft, vascular, leaf-like plates which are part of the pleopoda and are used for respiration.
The paired mouth-parts, as found in the Oniscoidea, named from the lowest and outermost pair first are:
Maxillipeds: A pair of somewhat oblong, flattened appendages, the median borders straight and fitting close together, and serving as a covering for the other mouth-parts. They have near the end a short, flattened, segmented palp (e.g., figs. 26, 27).
Maxillae: Two pairs, the second maxillae outermost. These latter are broadly plate-like, without teeth, and only partly divided into inner (median) and outer lobes. The first maxillae (e.g., figs. 21, 22, 23) have two (outer and inner) branches or lobes arising from a slender transverse basal segment. The outer lobe may have setae or it may have eight or more curved teeth terminally; and the inner, which is more slender and weaker, has two or more brush-like tufts of setae.
Mandibles: Pear-shaped appendages (e.g., figs. 13, 14) ending in a curved process bearing a few strong teeth. The inner margin may carry a ridged upraised area (“molar process”).
Above these paired appendages is the unpaired upper lip.
The first thoracic segment is often provided with an outwardly bent or rolled up border along its lateral margin. In forms which conglobate, this border has a cleft at the rear corner. When the animal rolls up, the leading edge of the epimera of the second segment fits into the cleft which may be continued forward as a furrow along the lower aspect of the border of the first segment. The furrow is known as the “coxopodite sulcus” or “sulcus,” and the segment is spoken of as being “sulcate.” This character is a very important aid in distinguishing species.
Identification in most cases requires dissection of mouth-parts. This can best be done with finely sharpened mounting needles under a dissecting microscope. The parts may be removed together, stained page 119 lightly in eosin and dissected apart in a drop of clove oil on a slide, or dissected separately from the animal and then placed in clove oil. They should be mounted in Canada Balsam when they have been com-completely cleared of the clove oil. The eosin makes it easier to keep track of parts when they have been cleared, but if staining is intense it tends to mask diagnostic features.
References: The latest and most complete check-list is Jackson's “Check-list of the Terrestrial and Freshwater Isopoda of Oceania,” in the Smithsonian Miscellaneous Collections, Vol. 99, No. 8, 1941. Bowley (1935) has further separated the species of Phalloniscus, in the Journal of the Royal Society of Western Australia, Vol. 21, a paper which Jackson apparently overlooked. There is one other checklist, that of Chilton in the Transactions of the New Zealand Institute, Vol. 42, 1910. Jackson's is the better from the point of nomenclature, and gives references to all original descriptions. I have used his systematic nomenclature throughout. The most useful general work is Chilton's “The Terrestrial Isopoda of New Zealand” in the Transactions of the Linnean Society of London, Vol. 8, 1901. Note: A key to the sub-orders of the Isopoda is also given. It will serve as an introduction to any further keys to the order which may appear.
Two species are insufficiently described to be keyed out: Spherillo brevis and Oniscus cookii. Oniscus cookii is probably identical with P. kenepurensis.
The group, Spherillo setaceus, S. bipunctatus and S. squamatus, has not been figured or described in sufficient detail to determine whether or not the pleon is sculptured. Accordingly, the key has been arranged to separate them in either dichotomy.
Acknowledgment: I wish to thank Miss Eileen A. Bowley for her kind permission to reproduce figures 14, 16, 17, 18 from her paper on Phalloniscus; and Dr. Willard G. van Name for permission to adapt the portion dealing with the nomenclature of the appendages from the introduction to his work “The American Land and Freshwater Isopod Crustacea” (Bulletin American Museum Natural History. vol. 76).
Key to the Suborders of Isopoda
|Uropoda terminal or subterminal||3|
|2.||Uropoda forming, together with the terminal pleon segment (telson), a caudal fan. Pleopoda for the most part natatory.||Cymathoidea (Flabellifera)|
|Uropoda valve-like, inflexed ventrally and arching over the pleopoda||Idoteoidea (Valvifera)page 120|
|3.||Pleopoda not modified for air-breathing. Marine and fresh-water forms||4|
|Pleopoda modified for air-breathing. Terrestrial, inland and littoral forms||Oniscoidea|
|4.||Pleopoda generally covered by a thin opercular plate (the modified first pair of pleopods)||Aselloidea (Asellota)|
|Pleopoda never covered by an operculum||5|
|5.||Pleon laterally compressed. Free-living, freshwater forms||Phreatoicidea|
|Pleon depressed. Parasitic forms with free-swimming larval stages. Marine||Bopyridea (Epicaridea)|
Key to New Zealand Species of Oniscoidea
|1.||Mandibles with well-developed molar (fig. 13). Inner lobe of 1st maxilla with three plumose setae||2|
|Mandibles without molar, its place taken by a brush-like seta or tuft of setae (fig. 14). Flagellum of 2nd antenna with six segments at most||12|
|2.||Uropoda elongate, exposed (fig. 1). First antenna 3-segmented, mobile||3|
|Uropoda opercular, concealed under telson. First antennae single-segmented, immobile (fig. 9)||Tylos neozelanicus|
|3.||Flagellum of second antenna many-segmented||4|
|Flagellum of second antenna usually not more than six-segmented||5|
|4.||Eyes large, angle of eye near median line rounded; pleon segments narrowing successively towards telson—pleon thus not distinctly marked off from rest of body; telson with posterior margin apical and serrate||Ligia exotica|
|Eyes acutely angled near median line; pleon segments of similar width, considerably narrower than abdomen and marked off from it distinctly; telson posterior margin rounded||Ligia novaezealandiae|
|5.||Head with cephalon front triangularly produced (fig. 24)||6|
|Head with cephalon rounded in front (fig. 7)||7|
|6.||Body oblong-oval, with well marked ridges or tubercles dorsally, (fig. 25)||Notoniscus helmsii|
|Body oval, with indistinct tubercles (fig. 24)||Notoniscus australis|
|7.||Dorsal surface and antennae with distinct tubercles (fig. 8)||8|
|Dorsal surface smooth, or nearly so (fig. 7)||10|
|8.||Tubercles on body arranged irregularly||Trichoniscus otakensis|
|Tubercles on body arranged more or less regularly in transverse rows||9page 121|
|9.||Outer ramus of uropod about twice as long as inner (fig. 8)||Trichoniscus kermadecensis|
|Outer and inner rami of uropods almost equal in length||Trichoniscus commensalis|
|10.||Dorsal surface with scattered longish setae. Flagellum of second antenna with not more than 4 segments. Animal small, about 4 mm.||Trichoniscus phormianus|
|Dorsal surface without scattered setae. Animal large, about 7-8 mm.||11|
|11.||Flagellum of second antenna with no more than five segments (fig. 7)||Trichoniscus thomsoni|
|Flagellum of 7-10 segments||Trichoniscus magellanicus|
|12.||Inner lobe of maxilla 1 with 5-15 plumose setae||Family Eubalidae (not known from N.Z.)|
|Inner lobe of maxilla 1 with 2 plumose setae, e.g., fig. 21||13|
|13.||Maxilliped with terminal segments of moderate size, palp large and well-developed, longer than acute inner plate (fig. 26)||14|
|Maxilliped with terminal segments small, palp feeble, hardly longer than truncate inner plate (fig. 27)||20|
|14.||Peduncle of uropod dilated, simulating pleura of pleon||15|
|Peduncle of uropod not dilated||16|
|Family Scyphacidae (Detonidae)|
|15.||Eyes large, crescentic, outer branch of uropoda large, dilated distally (e.g., figs. 4, 29)||Actaecia euchroa|
|Eyes moderate, outer branch of uropoda minute, not dilated distally (fig. 19)||Actaecia opihensis|
|16.||Outer lobe of maxilla 1 with strong fringe of setae on outer distal lobe (fig. 21)||17|
|Outer distal lobe of maxilla 1 without such fringe (Fig. 22)||18|
|17.||Large, up to 10 mm. in length; body with small, irregular, roughened tubercles; peduncle of antenna with margins of segments fairly smooth||Scyphoniscus magnus|
|Small, up to 3.5 mm. in length; body with small rounded tubercles arranged more or less regularly; antenna covered with short, stout setae||Scyphoniscus waitatensis|
|18.||Eyes very large, crescentic; occupying whole lateral margins of cephalon and nearly meeting in front; ocelli very numerous, about 150-200 arranged in four longitudinal rows. Eyes of moderate size, with many ocelli||Scyphax ornatus 19|
|19.||Male with lateral portions of first segment of pereion not expanded; surface of pereion with prominent, blunt spines||Deto aucklandiae|
|Male with lateral portions of first segment of pereion forming balloon-like expansions; surface of pereion with irregular pointed tubercles (Fig. 2)||Deto bucculenta page 122|
|20.||Uropoda produced, reaching beyond telson which is usually narrow and conically produced (fig. 5). Usually unable to roll up into a complete ball, i.e., to “conglobate”||21|
|Uropoda short and broad. Usually able to conglobate||30|
|21.||Flagellum of second antenna 2-segmented||22|
|Flagellum of second antenna 3-6 segmented||23|
|22.||Head prominently trilobed. Second antenna with both flagellar segments subequal||Porcellio scaber|
|Head not prominently tri-lobed. Second antenna with first flagellar segment longer than second and longer than ultimate segment of peduncle.||Porcellionides pruinosus|
|23.||Pleon with lateral expansions||24|
|Pleon with lateral parts of segments very little expanded (e.g., fig. 5)||27|
|24.||First pleopod of male having endopodite beset apically with denticles (fig. 17)||Phalloniscus armatus|
|First pleopod of male not having endopodite denticulate as in fig. 17||25|
|25.||Lateral lobes of cephalon produced in front of eyes into upwardly-projecting, moderately large, sub-acute lobes. First pleopod of male with apex produced to roughened, knob-like projection (fig. 16)||Phalloniscus kenepurensis|
|Lobes of cephalon not produced as above. Endopodite of first pleopod in male not as above||26|
|26.||Mandible with 2 “free” pencils between setose lappet and molar penicil (fig. 14); Tip of endopodite of first pleopod in male spined (fig. 18)||Phalloniscus chiltoni|
|Mandible with one “free” penicil between setose lappet and molar penicil||Phalloniscus punctatus|
1. Ligia novaezealandiae, dorsal view. 2. Deto bucculenta, adult male 3. Cubaris suteri. 4. Actaecia euchroa. 5. Philoscia oliveri. 6. Cubaris milleri. 7. Trichoniscus thomsoni. 8. Trichoniscus kermadecensis. 9. Tylos neozelanicus. 10. Telson and uropods of Armadillidium vulgare. 11. Terminal pleon segments, telson and uropods of Spherillo ambitiosus.
A2—Second antenna; C—cephalon; EN1, EN2—Endopodites of 1st and 2nd pleopods; EX 1-5—exopodites of 1st to 5th pleopods; FL—flagellum of second antenna; FP—free penicil of mandible; IL—inner lobe of maxilla; IP—inner plate of maxilliped; IR—inner ramus (endopodite) of uropod; MO—molar; MP—molar penicil; OL—outer lobe; OR—outer ramus (exopodite) of uropod; PA—maxilliped palp; PE—peduncle of second antenna; PL—pleon segments; PS—plumose setae; PU—peduncle of uropod; TE—telson.
|27.||Body with granulations arranged in three longitudinal rows||Philoscia novae-zealandiae|
|Body without these granulations so arranged||28|
|28.||Flagellum of second antenna with three segments||29|
|Flagellum of second antenna with five or more segments||Philoscia brevicornis|
|29.||Base of uropods subtriangular, narrowing proximally, inner margin of base with dense fringe of very short setae (fig. 5)||Philoscia oliveri|
|Base of uropods subrectangular, inner surface scabrous and with a few setae||Philoscia pubescens|
|Base of uropods subtriangular; inner surface without dense fringe of setae||Philoscia fragilis|
|30.||Outer branch of uropoda large and broader than long, filling space between telson and pleura of 5th pleon segment; attached terminally to peduncle which is not (or scarcely) visible from above (fig. 10)||Armadillidium vulgare|
|Outer branch of uropoda small, inserted on inner side of the enlarged base; space between telson and pleura of 5th segment filled by peduncle of uropod (e.g., fig. 11)||31|
|31.||Surface of body with crests or tubercles||32|
|Surface of body nearly smooth||43|
|33.||Body with longitudinal flanges, many tubercles between the flanges; posterior margin of 7th segment in particular bearing large, prominent conical teeth||Spherillo hamiltoni|
13. Left mandible of Tylos neozelanicus, showing well-developed molar. 14. Left mandible of Phalloniscus chiltoni showing “molar penicil,” or tuft of setae taking place of molar. 15. Ventral view of pleon segments of Porcellio scaber, showing expodites and endopodites of pleopods. 16. Endopodite of first pleopod in male of Phalloniscus kenepurensis. Enlarged portion showing denticulate apex. 17. Endopodite of first pleopod, male, of Phalloniscus armatus. Enlarged portion shows denticles at apex. 18. Tip of endopodite of Phalloniscus chiltoni, showing spines. 19. Uropod of Actaecia opihensis, showing minute exopodite. 20. Uropod of Merulana chathamensis, showing minute exopodite. 21. First maxilla of Scyphoniscus waitatensis. Outer lobe with strong fringe of setae, and inner with two plumose setae. 22. First maxilla of Ligia novaezealandiae. Outer lobe without strong fringe of setae, and inner with three plumose setae. 23. First maxilla of Scyphax ornatus, outer lobe, showing lack of setae. 24. Notoniscus australis, dorsal view. 25. Notoniscus helmsii, dorsal view. 26. Right half of maxilliped of Deto aucklandiae, with large, well-developed palp. 27. Terminal segments of maxilliped of Armadillidium vulgare, palp and inner plate subequal. 28. Ventral view of first and second pereion segments of Spherillo rugulosus, showing notch on inferior lateral margin. 29. Telson and uropods of Actaecia euchroa. Outer branch of uropod dilated terminally.
(Figure 10 after Barnard; 14, 16, 17, 18 after Bowley, 15, 27 after Sars, remainder after Chilton.)
|Body without flanges as above||34|
|34.||Tubercles large, about four on each segment of the mesosome; body, and especially tubercles, setose||Spherillo macmahoni|
|Body without tubercles as above||35|
|35.||Exopodite normal size, at least three times longer than broad; inferior lateral margin of first segment of trunk not grooved throughout its length||Spherillo tarangensis|
|Exopodite small or minute, at most twice as long as broad; lateral margin of first segment of trunk grooved throughout its length (“sulcate”)||36|
|36.||Epimeral segments 3 to 7 greatly produced posteriorly. Eyes small. Exopodite minute||Sphaerillo setaceus|
|Epimeral segments 3 to 7 not greatly produced posteriorly. Eyes normal or large. Expodite of uropod small||37|
|37.||Body with sparse small tubercles. Eyes normal size||Spherillo bipunctatus|
|Body with tubercles dense. Eyes large||Spherillo squamatus|
|38.||Body with flanges extending nearly whole length of each segment, rest of body between ridges comparatively smooth (fig. 6)||Cubaris milleri|
|Body without flanges arranged as above||39|
|39.||Inferior lateral margin of first epimeral segment deeply cleft, or “sulcate”||40|
|Inferior lateral margin of first epimeral segment non-sulcate||41|
|40.||Central portion of body segments very convex, sculptured and produced into transverse crests; crests forming transverse ridges (fig. 3)||Cubaris suteri|
|Body without transverse crests or body sculpturing as above||36|
|41.||Peduncle of uropod triangular in shape||Spherillo monolinus|
|Peduncle of uropod oblong-rectangular in shape||42|
|42.||Telson with faint suture across it||Spherillo speciosus|
|Telson without faint suture||Spherillo tarangensis|
|43.||Body with inferior lateral margin of first epimeral segment notched behind (fig. 28)||Spherillo rugulosus|
|Body with inferior margin of first segment grooved throughout its length||Sphaerillo danae|
|Body without groove or notch on inferior margin of first epimeral segment||44|
|44.||Outer branch of uropoda rudimentary or extremely small (fig. 20)||45|
|Outer branch of uropoda normal||46|
|45.||Telson longer than broad, noticeably shortened in middle, apex a little narrower than the base, margin directed upwards posteriorly||Merulana canaliculatus|
|Telson not showing these features||Merulana chathamensis page 127|
|46.||Exopodite large, inserted near apex of peduncle and reaching to apex||Spherillo marginatus|
|Exopodite normal, not inserted near apex of peduncle, and not reaching to apex||47|
|47.||Endopodite of uropod slender, long, not quite reaching to posterior margin of telson. Peduncle of uropod much longer than broad. Apex of peduncle narrowing posteriorly||Spherillo ambitiosus|
|Endopodite of uropod stout, normal in size, not reaching posterior margin of telson. Peduncle of uropod little longer than broad. Apex scarcely narrowing posteriorly||Spherillo rufomarginatus|