The larva of Eustra (Coleoptera, Paussinae, Ozaenini):a facultative associate of ants

Abstract Larvae of the ground beetle genus Eustra Schmidt-Goebel are described and illustrated for the first time and some biological notes are reported. One specimen of an unknown Eustra species was collected while excavating a nest of the ant Pachycondyla javana Mayr, in Taiwan, which is the first report of a paussine associated with a member of the ant subfamily Ponerinae. Several larvae and adults of a second species, Eustra chinensis Bänninger, were collected in Shanghai under bark with no association with ants. First instar larvae of the latter species were also reared in the lab. The occurrence of larvae of the genus Eustra both inside and outside ant nests, together with a report of adults collected inside a nest in Taiwan, suggests that members of this genus may be facultative predators or facultative symbionts of ants, an attribute that has never been reported for this genus. The larvae of Eustra show several unique features, including a peculiar bidentate mandibular apex, an extremely long galea, one of two tarsal claws greatly reduced, abdominal setae (including those of terminal disk) elongate and clavate at apex, urogomphi wide and flattened, and inflated sensilla S-I. Larvae were studied by both optical and scanning electron microscopy, their morphological features are compared with those of other described Paussinae larvae, and their potential phylogenetic and functional significance are discussed.


Introduction
Eustra Schmidt-Goebel is an ozaenine genus (Carabidae: Paussinae) containing twenty-two species (reviewed by Deuve 2001). Adults in this Southeast Asian genus have the smallest body size of all members of the subfamily Paussinae. Many Eustra species live in caves and exhibit typical structural adaptations to a troglobitic life, including loss of pigmentation, loss of eyes, and long, delicate appendages. Other species are not cave-dwelling, but rather they have been collected in microhabitats typical of other ozaenines including under rocks and under bark. Recently larvae of two species of Eustra were collected in the fi eld. Both adults and larvae of Eustra chinensis Bänninger were collected in Shanghai while they were hibernating in rotting wood and a single larva of an unidentifi ed species of Eustra was collected during the excavation of nests of the ant Pachycondyla javana Mayr in Taiwan, suggesting for the fi rst time that at least some species of Eustra are facultatively associated with ants (Moore 2006).
Many diff erent animals, especially arthropods, profi t from a facultative or obligate association with ants (myrmecophily), bypassing the behavioral and chemical defenses of the hosts and adapting to the peculiar environmental conditions of the nests. Since myrmecophiles are rare and live in concealed environments, our knowledge of their behavior is sparse, and most of the information we do have has been inferred from structural features of adults and larvae (Di Giulio and Moore 2004;Di Giulio et al. 2011). Th e Paussinae, commonly known as fl anged bombardier beetles, are a good model taxon to study the evolution of myrmecophily in beetles, since members of this ground beetle subfamily have diff erent degrees of associations with ants, ranging from apparently none to obligate myrmecophiles (see Geiselhardt et al. 2007 and references therein). As far as we know all members of the tribes Protopaussini and Paussini are myrmecophilous, at least during the larval stage, and their associations with ants have either been directly observed in the fi eld or deduced from their remarkable structural adaptations. Most of these species associate with members of the ant subfamilies Formicinae and Myrmicinae.
In general, very little is known about the behaviour of the ozaenines (Di Giulio and Vigna Taglianti 2001;Moore and Di Giulio 2006;Moore 2008). Like most ground beetles, they are usually found under stones, bark, and rotting wood and they are nightactive predators on other arthropods. Ozaenine larvae are known for only nine species in four genera (Itamus, Sphaerostylus, Pachyteles and Physea) (see Di Giulio and Moore 2004). Th ey all have a terminal disk composed of modifi ed abdominal tergites and urogomphi, which is a synapomorphy for the subfamily (Bousquet 1986). Unlike the physogastric myrmecophilous larvae of the tribe Paussini which use their round terminal disk as a glandular symphilous organ (Oberprieler 1985;Bousquet 1986;Luna de Carvalho 1989;Di Giulio and Moore 2004;Di Giulio et al. 2011), free-living larvae of Metriini, Mystropomini and Ozaenini use their terminal disk as a door to close the galleries they construct in rotten wood, humid earth or sandy riverbanks, and they use the moveable components of the terminal disk to trap their prey (Costa et al. 1988;Di Giulio and Vigna Taglianti 2001), seizing them with their sharp mandibles through a backward spring-like movement. Th is specialized feeding strategy allows these delicate larvae to feed on fast moving invertebrates and to occasionally feed on ants. It is likely that many non-myrmecophilous members of the subfamily Paussinae facultatively feed on ants, as has been demonstrated in the tribe Metriini (Moore and Di Giulio 2008). We hypothesize that myrmecophagy may be a preadaptation for myrmecophily.
Members of the ozaenine genus Physea Brullé are known to live inside the nests of the Neotropical leafcutting ants, Atta, and both larvae and adults have structural adaptations for this lifestyle (Eidmann 1937, Di Giulio et al. 2003. Recently adults of other ozaenine species have been found inside Atta nests including adults of Tachypeles moretianus Deuve and Serratozaena paraphysea Deuve (Moore 2008). Based on structural features of adults, myrmecophily has also been hypothesized for the Southeast Asian species Dhanya mulu Stork (Stork 1985), and the South and Central American genera Ozaena Olivier and Platycerozaena Bänninger (Ball and McCleve 1990). Larval specimens of the Malagasy species Sphaerostylus goryi (Laporte de Castelnau) were recently collected both in rotten wood with ants and in leaf litter without apparent association with ants (WM, personal observations). Th e discovery of an Eustra larva inside a Pachycondyla javana nest in Taiwan is the only report of a paussine associated with a member of the ant subfamily Ponerinae (Moore 2006). Th at Eustra larvae have been collected both inside and outside of ant nests suggests the possibility that they are at least facultatively associated with ants. In addition, a report of adults of Eustra sp. collected inside an ant nest in Taiwan was posted on the Internet (http://nc.kl.edu. tw/bbs/showthread.php?t=653&page=9). Th ese fi ndings suggest that more ozaenine taxa may be facultative or obligate myrmecophiles, even those without evident structural adaptations, and they suggest that myrmecophily has evolved multiple times during the evolution of in Paussinae (Moore 2006;Moore et al. 2010).
In this paper we: (1) present biological information about the habitats and behaviors of E. chinensis and the Eustra species from Taiwan observed in nature and in captivity; (2) describe and illustrate these larvae; (3) discuss the functional signifi cance of several unique characteristics of the genus; and (4) compare them to other described paussine larvae.

Material described
(1) Eustra chinensis Bänninger, 1949. Twenty-fi ve adults and several larvae were collected in Shanghai on February 9, 2009 and April 6, 2008. Th ey were found hibernating together in the soft, rotten wood of bristly locust (Robinia hispida Linnaeus, 1767) and weeping willow (Salix babylonica Linnaeus, 1753). Adults and larvae can be found in Shanghai throughout the year. Th ey overwinter as both adults and larvae (all larval instars), from November to April. Presumably, while these larvae are overwintering they do not feed. In captivity, a third instar larva overwintered without food for more than six months. During this time they did not close the opening of their galleries with their terminal disks, as they do to facilitate feeding during the spring and summer (as described for other ozaenine larvae, see Costa et al. 1988;Di Giulio and Vigna Taglianti 2001;Moore and Di Giulio 2006).
(2) Eustra sp. A single third instar larva was collected in northern Taiwan (Shanshya [sic]) by Gustav Tzh-wei Chen on 9.IX.2003 while excavating a nest of Pachycondyla javana Mayr (Hymenoptera, Formicidae, Ponerinae). Th e specimen was identifi ed as belonging to the genus Eustra, by a phylogenetic analysis of molecular sequence data obtained from this specimen and from sixty other members of the subfamily Paussinae, including other members of the genus Eustra.

Rearing conditions
Larvae of E. chinensis were reared in captivity, where ambient conditions (e.g., temperature, light and humidity) were similar to natural conditions outdoors. Five larvae of each instar were reared in 2 ml centrifuge tubes. Other larvae were reared in a plastic box (18 cm × 11 cm × 12 cm) with the fi eld-collected rotten wood. All larvae were fed springtails once a month.

Morphological analysis
Prior to preparing them for microscopy, larvae were drawn by a stereomicroscope Olympus SZX16 equipped with drawing tube. One specimen of each instar of Eustra chinensis, and the single specimen from Taiwan were rehydrated, cleared in 10% KOH, transferred in hot lactic acid, dehydrated through a series of EtOH baths of increasing concentration (10-20-50-70-90-95-100%), left overnight in a clove oil bath, and mounted on slides with Canada balsam. Th ese specimens were studied and illustrated by using a light microscope Olympus BX51 equipped with drawing tube. Another fi rst instar specimen was dehydrated through a series of EtOH baths of increasing concentration (70-80-90-95-100%), critical point dried (Bal-Tec CPD 030), mounted on a stub (by using self adhesive carbon disks), sputtered with gold (Emitech k550 sputter coater), and observed with Philips XL30 scanning electron microscope and FEI Dualbeam FIB/SEM Helios Nanolab (L.I.M.E. laboratory, University 'Roma Tre', Rome). In this paper, the general terminology of larval structures follows Lawrence (1991). Notation of primary setae and pores follows the system of Bousquet and Goulet (1984), modifi ed for Metrius contractus (Bousquet 1986). Because some of the sensilla on the abdomen and terminal disk of Eustra are homologous to those recognized in Metrius contractus (sensilla S-I to S-V) (Bousquet 1986), Pachyteles spp. (sensilla S-I to S-VII) (Di Giulio et al. 2000), and Arthropterus sp. (sensilla S-I to S-VIII) (Di Giulio and Moore 2004), we adopt here the same nomenclature used by these authors. Notation of microsculpture follows Harris (1979). An asterisk (*) following a coded seta indicates that the homology between the structure on the Eustra larvae and the corresponding code is questionable.

Eustra larval morphology
Generic diagnosis. Body length very small as compared with other Paussinae (1.75mm, fi rst instars); antenna 3-jointed (II+III fused); mandible apically bidentate, with subbasal retinaculum, ental margin of retinaculum with additional small sub-basal tooth; galea extremely long and apically sharp, distinctly longer than maxillary palp and lacinia; maxillary palpomere 3-jointed (II+III fused); claws of very diff erent size, smaller claw obsolescent; hypopleurite VI with ventrolateral, elongate digitiform protuberance, tipped by strong spine-like seta; most sternal and pleural setae of the abdomen elongate and clavate at apex; lateral plates of terminal disk thin and wing-like, pointed at apex, with dorsal margin straight and ventral margin curved; urogomphi fl attened, wider and longer than dorsal plates, composed by 7 short triangular lobes, acute at apex, separated by V-shaped incisures of diff erent depths; lobe X present between C and E2; lobe E1 divided into E1a and E1b; peculiar mushroom-like infl ated sensilla S-I of diff erent length present on surface of plates and urogomphi; sensilla S-II of two diff erent types, alternate on dorsal plates and urogomphi: (1) very long and stick-like, pointed at apex; (2) short and clavate at tip; terminal disk covered with peculiar hairy microsculpture.
Chaetotaxy. Frontoclypeolabrum (Figs 1a, 2a-c) without additional setae; FR 1-4,6-9 easily distinguished (Fig. 1a); medial prominence of frontoclypeolabrum with 2 minute spine-like setae on dorsal surface (Fig. 2b); FR b absent; several minute fi liform sensilla (Fig. 2b) expanded at apex present on anterior part of frontale (Figs 2e-f ). Parietale (Figs 1a,2c) with several small additional setae irregularly positioned mesodorsally, and longer additional setae placed ventrally; some setae of parietale possibly homologous to the ancestral pattern are tentatively assigned in Fig. 1a. Antennomere I (Figs 1c, 2c) with 5 dorsolateral additional setae; AN a,b absent; III with AN 1 and AN f displaced apically (Fig. 1c). Mandibles (Fig. 1d) with two large additional pores mesodorsally. Setal group gMX on stipes composed of about 10 setae (Fig. 1e); MX 6 very small, dorsal and subbasal on lacinia; galeomere II with one additional seta on ental side and a subapical, dorsal sensorial area (composed of 3 dome-like and 1 longer medial sensilla) (Fig.  3c); maxillary palpomere IV with 1 small additional seta on ental side, 2 longitudinal subapical digitiform sensilla (Fig. 3e) and apical sensorial area composed of several papillae. Prementum (Figs 1f, 3f ) with about 10 additional setae on lateral and dorsal surface, LA 3, 4, 5 not clearly identifi able; seta LA 1 close to the midline; LA a absent, LA c subapical; labial palpomere II with 2 additional setae, 1 dorsal, medially directed and 1 small ventrolateral, 2 longitudinal subapical digitiform sensilla and apical sensorial area composed of several papillae. Pro-, meso-and metanotum (Figs 4a, 5a) with about 25 setae each (identifi cation not possible). Coxa with about 20 setae; trochanter with spiniform setae present mostly on ventral side, including a long TR4; TR8 about as long as TR4 but thinner and more fl exible. Meso-and metasternum with MS4 long. Abdominal tergites I-VII ( Fig. 4c) with 4 setae on each side. Tergal side of dorsal and lateral plates of terminal disk (Figs 4c, 7b) with stiff pointed setae (sensilla S-VII) of various sizes, with cylindrical bases protruding from the plates: about 14 on each dorsal plate (epipleurite IX + tergite VIII) and about 3 on each lateral plate (epipleurite VIII); distal margin of each dorsal plate with about 12 elongated, straight and deeply corrugated sensilla S-II, of two diff erent sizes and shapes (Fig. 6a) alternately placed: type 1 extremely long (about double than type 2), stick-like, with sharp tip; type 2 thinner than 1 and distinctly clavate at apex; inner edge of each dorsal plate (Fig. 6a) with 2-3 S-II type 2 obliquely directed, increasing in size from base to apex; margin of each lateral plate with 8 sensilla S-II, 5 of type 1; caudal side of the terminal disk with numerous sensilla S-I (Figs 4d, 6a) sparsely distributed: 25-30 S-I on each dorsal plate and about 1-4 on each lateral plate. Epipleurites (Figs. 4c-d, 5c-d) of abdominal segment I without setae, II-V with one elongate sensillum S-II (type 2) each, VI-VII with several setae and S-II type 2. Sternal area of segment I with small simple setae, II-VI with elongate sensilla S-II type 2, VII with simple elongate setae (except for one, see Fig. 4d). Urogomphi (Figs 6a, 7a, c) with many S-I (about 40), mainly on dorsal surface and at margins of branches; branches A, C, X and E1b with S-II type 2 (Fig. 7a), B, E2, E1a with apical long S-II type 1 (Fig. 7a, f ). Pygidium without setae (Fig.7a).
Th orax. Tergites (Figs 4a, 5a) scarcely sclerotized, sternum not sclerotized. Pronotum wider than meso-and metanotum, transverse, about two times wider than long. Meso-and metanotum widely transverse, about two and a half times wider than long; longitudinal ecdysial line well marked on pro-and mesonotum, less evident, but present, on metanotum.
Legs. Legs well developed, 5-jointed (Fig. 4b), forelegs slightly shorter than others, mid and hind legs subequal. Coxa cylindrical, very long, about as long as trochanter and femur combined; trochanter elongate, obliquely truncate and fused apically to femur, about as long as femur and tibia combined; femur about as long as tibia and tarsus combined; tibia very short, cylindrical, slightly shorter than tarsus; tarsus more slender than tibia, conical, tapered from base to apex, with 2 sharp unequal claws (Fig. 5b): anterior claw elongate and strong, slightly longer than tarsus, apically curved; posterior claw very small and somewhat obsolescent.
Abdomen. Abdominal segments I-VII (Figs 4c, d) not sclerotized, bellows-like, usually up-curved, keeping the abdominal apex in an elevated position. Abdominal sclerites barely discernable, recognised by reduction of multipointed microsculpture around setae or sensilla S-II; segments progressively wider from I to VIII. Each segment dorsally fl attened, with swollen, setiferous pleural and sternal areas. Hypopleurites setiferous, slightly protruding; hypopleurite VI with ventrolateral, elongate digitiform protuberance, tipped by strong spine-like seta. Epipleurites conical, distinctly protruding, gradually more developed from segment I to VIII; epipleurites of segment VIII (Figs 4c-d, 6a, 7d) fl attened and enlarged into two sclerotized lateral plates, smaller than the dorsal plates; lateral plates slender, triangular, about two times longer than wide at base; epipleurites of segment IX greatly enlarged and fused with tergum of segment VIII into two rectangular, sclerotized plates (dorsal plates), slightly enlarged from base to apex and widely separated in the middle by a deep V-shaped notch (Figs 4c-d, 6a); lateral plates widely separated from dorsal plates; lateral plates, dorsal plates and urogomphi forming a terminal disk articulated at base by membranes, dorsal and lateral plates move against urogomphi. Urogomphi (Figs 6a, 7a,c) wide, fl attened, each composed of 7 pointed lobes: A, B, C, X, E2, E1b, E1a (respectively from the inner to the outer); A much shorter than B; pygidium (Figs 6a, 7a) protruding, medioventrally positioned between the urogomphal insertions.

Eustra chinensis, second and third instar larvae
General morphology very similar to that described above for the fi rst instar, except for: progressive increasing of relative dimensions (see Table 1); presence of secondary setae on antennomere II (2 setae); sensorial appendage much shorter than antennomere IV; Table 1. Measurements (mm) of three instars (L 1 , L 2 , L 3 ) of Eustra chinensis and the third instar (L 3 ) of Eustra sp. Taiwan. BL = body length (from tip of mandibles to the apex of terminal disk); HW = cephalic capsule maximum width (at the base of the antennae); HL = cephalic capsule medial length (mesodorsally, from occipital foramen to anterior margin of frontoclypeolabrum); PW = prothorax maximum width; PL = prothorax medial length; TDW = terminal disk maximum width (at the level of lateral plates); DPL = dorsal plates length (from base, near articulation, to the medial apex).  retinaculum progressively longer and more falcate; stipe with wider and sharp sub-basal protuberance; labial palpomere I wider than II; tibia subequal to tarsus; pronotum about as wide as meso-and metanotum; dorsal plates of terminal disk slightly longer; lobes of urogomphi relatively longer and more slender; lobe E1a slightly longer than E1b.

Eustra sp. Taiwan, third instar larva
Unfortunately, the specimen is damaged and portions of its head and legs are missing. Only basal part of head capsule, basal half of a mandible, thorax, basal part of legs, entire abdomen and terminal disk are intact. However, there is one low-resolution image of the entire specimen, which provides only limited information of some structural details. General larval structure and most characters of the terminal disk (Fig. 6b) are very similar to those described above, especially as compared with the third instar of E. chinensis, except for the following minor diff erences: (1) lobe A of urogomphi about as long as B (A much shorter than B in E. chinensis); (2) E1a thinner and more elongate than E1b (subequal or only slightly longer to E1b in E. chinensis); (3) lobes A very close medially, almost touching (distinctly separated medially in E. chinensis).

Discussion
Eustra larvae are highly modifi ed compared with the other known larvae of Ozaenini, and have several unique structures that make their identifi cation easy. Th ese include: 1. Antennae 3-jointed (Figs 1c, 2c). Paussinae larvae generally show 4-jointed antennae, a condition typical for adephagans. Th e reduction to 3 joints in Eustra is clearly due to the fusion of antennomeres II and III.
2. Mandible apically bidentate with sub-basal retinaculum (Figs 1d, 3b). A bidentate mandibular apex is also present in all known myrmecophilous Paussini larvae except Arthropterus, but in this tribe the second tooth is thought to be a subapically displaced retinaculum (Di Giulio and Moore 2004). In addition to the bidentate apex (Fig. 3b), a small subtriangular and basally directed retinaculum is present in Eustra fi rst instars, and it becomes longer and more falcate in later instars.
3. Ental margin of retinaculum with additional small sub-basal tooth (Fig. 1d). Th is margin is straight only in Physea, while it is more or less sinuate (basal half convex, distal half concave) in all other known ozaenine genera. Th e presence of a sub-basal tooth on the ental margin in Eustra may be an adaptation for piercing and holding their prey.
4. Maxillary palp 3-jointed (Fig.1e). Th e reduction of the palpomeres from 4 to 3 is a common feature of known Paussini larvae except for Platyrhopalopsis and Arthropterus. In the genus Paussus the reduction is due to the fusion of basal palpomere with the stipe. In Eustra the basal palpomere is only partially fused with stipe but still recognizable, and the actual reduction is due to the fusion of palpomeres II+III. 5. Galea extremely long and apically sharp (Figs 1e,3c). Th e galea of Eustra is twojointed as is typical of ozaenines but it is highly modifi ed: it is very strong, up-curved, and almost two times longer than the maxillary palp and almost three times longer than the lacinia. Th e apex is hook-like and unusually sharp, which would provide an eff ective tool for capturing and holding prey.
6. Strongly asymmetric tarsal claws (Figs 4b, 5b). All Metriini, Mystropomini, and Ozaenini larvae have legs with two tarsal claws of unequal size, the anterior distinctly longer than posterior, while myrmecophilous Paussini larvae have only a single claw (presumably the anterior). In Eustra the posterior tarsal claw is extremely small and almost obsolescent.
7. Hypopleurite VI with ventrolateral, elongate digitiform protuberance, tipped by strong spine-like seta (Figs 4d, 5d). Th is peculiar sensorial structure is unique to the genus Eustra. 8. Most sternal and pleural setae of the abdomen elongate and clavate at apex . Clavate sensilla have been described in the myrmecophilous genus Arthropterus (sensilla S-VIII possibly homolog to S-II, see Di Giulio and Moore 2004), which surround the terminal disk, and are also present on the thorax and cephalic capsule. In Eustra, a clavate modifi cation aff ects most abdominal mechanoreceptors as well as most sensilla of the terminal disk (see below). In particular, the terminal disk has two types of sensilla, often alternate (i.e. dorsal plates): type 1 is very long, stick-like, and pointed at the apex; type 2 is short and clavate at the tip.
9. Lateral plates of terminal disk transverse, subtriangular and pointed at apex (Figs 6a-b, 7d), with straight margins. Th e lateral plates of the Metriini, Mystropomini and other Ozaenini are wide and broadly rounded. Lateral plates of Goniotropis (Ozaenini) (Fig. 6c) are transverse and widely separated from dorsal plates similar to those of Eustra.
10. Urogomphi fl attened, wider and longer than dorsal plates, composed by 7 short triangular lobes (Figs 6a-b, 7a), acute or bidentate at apex, separated by V-shaped notches of diff erent depths, very shallow as compared to other Ozaenini. Th e fl attening and widening of the urogomphi and the reduction (Physea, Ozaenini) or absence (all Paussini, see for example Fig. 6d) of branches is a typical feature of myrmecophilous larvae (Di Giulio et al. 2003;Di Giulio and Moore 2004).
11. Absence of urogomphal lobe D and presence of the additional urogomphal lobe X (Figs 6a-b, 7a). Th e lobes of urogomphi were coded fi rst in Metrius by Bousquet (1986) and his notation was later slightly modifi ed for ozaenines to include the partial or total bipartition of lobes B (B 1 +B 2 ) and E (E 1 +E 2 ) (Vigna Taglianti et al. 1998). Th is notation works for all described ozaenine larvae except for Eustra, which do not have a lobe D, but rather have an additional lobe (here named "lobe X") located between lobes C and E 2 . Lobe X may be interpreted as: (1) a unique lobe (X = F); (2) D-lobe distally displaced to the margin (X = D); or (3) an additional subdivision of lobe E (X = E 3 ). Eustra larvae also have a unique subdivision of E 1 (E 1a , E 1b ).
12. Peculiar infl ated sensilla S-I (Figs 7a,c,e) of diff erent lengths present on surface of plates and urogomphi. Infl ated sensilla S-I have been described in larvae of Platyrhopalopsis (Paussini) and Physea (Ozaenini) and have been considered as an adaptation to the myrmecophilous lifestyle (Di Giulio et al. 2003). Th e sensilla S-I of Eustra are very diff erent from the homologous structures of the aforementioned taxa since these are mushroom-shaped, composed of an elongate basal stem, which emerges from a cuticular protuberance, and an apical irregular infl ation.
Like in the other ozaenine genera, larvae of Eustra live in galleries that they dig in humid soil or rotten wood and close off with their terminal disk, which they use to trap prey. However, the larvae of Eustra are so specialized and modifi ed that it is not possible to fi nd clear synapomorphies with larvae of any of the other known ozaenine genera. Some of the peculiar adaptations discussed above are similar to, but not necessary homologous to, characteristics described for the myrmecophilous larvae of Paussini and Physea (See Table 2). Since the Eustra larva from Taiwan was found inside a nest of Pachycondyla javana, it is possible that some of these traits are adaptations to a myrmecophilous lifestyle. However, we think that it is more likely that these minute larvae feed on very small invertebrates like collembolans and Drosophila, which fi rst instar ozaenine larvae consistently consume in the lab (Moore and Di Giulio, pers. obs.), than it is that they feed on Pachycondlya, which are relatively large-bodied ants. Instead, many of the unusual characters observed in these larvae could facilitate feeding on fast moving prey, including the very long radial mechanoreceptors (sensilla S-II) of the terminal disk which would sense the approach of fast collembolans, and modifi ed mouthparts including the bidentate Table 2. Characteristics of Eustra larvae that are similar to those found in mymecophilous larvae.

Eustra+Physea
galea elongate (but in a completely diff erent way: in Physea galeomere I long, II short and truncate at apex; in Eustra I short and II very long and sharp) lacinia reduced prementum elongate and tapered from base to apex labral spine wide ligula absent urogomphal lobes partially fused head short and transverse frontoclypeolabrale wide and transverse coronal suture short anterior arms of frontal sutures only slightly sinuate stemmata absent retinaculum in fi rst instar triangular, inward directed sensilla S-I infl ated Eustra+Paussini mandibles apically bidentate number of maxillary palp articles reduced (but in a completely diff erent way, see Discussion) second tarsal claw reduced (in Paussini second claw is absent) sensilla clavate or infl ated (only in Arthropterus clavate sensilla S-II, infl ated S-I in Platyrhopalopsis) urogomphal lobes short rather then strongly branched urogomphi fl at and wide antennae short and strongly directed medially stemmata absent sensorial appendage elongate head shortened and distinctly transverse mandibular apex, second tooth of retinaculum, and hook-like galea which would help the larva hold onto motile prey. Other characters, such as the fl attening and widening of the urogomphi, could be related to the miniaturization of the larval body. In the future, we hope to discover the larvae of the genus Dhanya, and compare its morphological structures with Eustra since they are hypothesized to be sister genera (Jeannel 1946;Stork 1985;Deuve 2001), as well as larvae of the species formerly classifi ed in the genus Ozaenaphenops to search for support of its synonymy with Eustra (Deuve 2001).