Aciculiform spines are slender and straight. They vary in size from relatively large (around 20 µm; for example, Figs 5b, 10b, 18c, 22b, 22c) to relatively small (around 5 µm, Figs 6b, 6c), and in some species these spines have a sclerotized base (Figs 3b, 21b, 23d, 23e, 24c). Two variations of the aciculiform type are the trifurcated spines (Fig. 8b) and thin setae (Fig. 2c).

Robust spines are relatively short (around 10 µm), with a simple conical shape. They are sparsely distributed (Figs 16b, 25b).

Stout spines are similar to robust spines, but larger and sometimes slightly curved; they may be arranged longitudinally (Figs 11c, 16c) or regularly alternating (Fig. 12d).

The central ridges, present in some species of Labiotermes (Figs 13c, 14c, 15c), are single structures, composed of spines with their bases fused, arranged in a helical pattern. These ridges are probably homologous to the longitudinal arrangement of stout spines in Ibitermes curupira and Mapinguaritermes (Figs 11c, 16c), since their placements are equivalent inside P1.

Small spines in rows (Figs 4c, 21c, 23c, 23f) are tiny and have a typical transverse arrangement in units of 2–6 spines.

The coverage and abundance of spines can be categorized in four types of patterns.

Proximal aciculiform pattern: composed by aciculiform spines, restricted to the proximal region (Figs 5a, 6a, 9a, 10a, 17a, 18a, 20a, 22c), and usually with three groups of small spines in the distal portion (Figs 6c, 9c, 18b, 20b), the following species can be included in this category:

Acangaobitermes krishnai: Identical to N. noiroti (see ahead).

Curvitermes odontognathus (Fig. 5): A group of aciculiform spines is located just after the mesenteric tongue (Fig. 5b), at the distal region three long branches of small spines are present.

Cyrilliotermes angulariceps (Fig. 6): The coverage is composed only by small aciculiform spines, one group located just after the mesenteric tongue (Fig. 6b), and three ovate areas are present at the distal region (Fig. 6c).

Embiratermes brevinasus: identical to E. ignotus (see ahead).

Embiratermes festivellus (Fig. 10): A triangular area of aciculiform spines is located just after the mesenteric tongue (Fig. 10b), and three oval areas, covered with small aciculiform spines, present at the distal region.

Embiratermes ignotus (Fig. 8): The only ornament is a single transversal row of trifurcate spines, placed laterally to the mesenteric tongue (Fig. 8b).

Embiratermes silvestrii (Fig. 9): An oval area of aciculiform spines is located laterally to the mesenteric tongue (Fig. 9b), and three branches of small spines, one long and two shorts, are present at the distal region (Fig. 9c).

Ibitermes tellustris: very similar to E. silvestrii (see above).

Macuxitermes triceratops: (Fig. 17): An elongated area of aciculiform spines is placed close and laterally to the mesenteric tongue (Fig. 17c), the distal portion is broadly covered by sparse small spines (Fig. 17b).

Noirotitermes noiroti (Fig. 18): A group of aciculiform spines is located laterally to the mesenteric tongue (Fig. 18c), and at the distal region three long branches of small spines are present (Fig. 18b).

Paracurvitermes manni (Fig. 20): A transversal row of aciculiform spines, placed laterally to the mesenteric tongue is located laterally to the mesenteric tongue (Fig. 20c), and three branches of small spines, one long and two shorts, are present at the distal region (Fig. 20b).

Silvestritermes euamignathus (Fig. 22): A triangular area of aciculiform spines is located just after the mesenteric tongue (Fig. 22c), the aciculiform spines form a singular palisade around the mesenteric tongue (Fig. 22b). Three branches of small spines, one long and two very short, are present at the distal region.

Central ridge pattern: characterized by the presence of a longitudinal row of stout spines (Figs 11a, 16a) or the central ridge (Figs 12a, 13a, 14a, 15a), commonly surrounded by robust spines, the following species can be included in this category:

Embiratermes robustus: very similar to M. peruanus (see ahead).

Ibitermes curupira (Fig. 11): The ornaments are concentrated laterally to the mesenteric tongue, a longitudinal row of 20–25 stout spines (Fig. 11c), and few robust spines spaced distributed around the stout spines.

Labiotermes emersoni (Fig. 12): At the proximal region, between the mesenteric tongues, three longitudinal rows of robust spines (Fig. 12c) with the central ridge at the apex of the middle row (Fig. 12d), distal region covered with spaced small bristles (Fig. 12b).

Labiotermes labralis (Fig. 13): The internal surface is all covered with spaced robust spines (Fig. 13b), with a small central ridge (Fig. 13a).

Labiotermes leptothrix (Fig. 14): The central ridge is “S” shaped, well sclerotized with the fused spines (Fig. 14a), distal region covered with spaced robust spines.

Labiotermes orthocephalus (Fig. 15): The central ridge is composed by 10–15 slightly fused spines (Fig. 15c); distal region is covered with spaced robust spines (Fig. 15b).

Mapinguaritermes peruanus (Fig. 16): The ornaments are concentrated laterally to the mesenteric tongue, a longitudinal row of 15–20 stout spines (Fig. 16c), and robust spines spaced distributed around.

Diffuse coverage: composed of a uniform but sparse coverage of spines (Figs 2a, 7a), the following species can be included in this category:

Armitermes spininotus (Fig. 2): All surfaces are covered with spaced thin setae (Figs 2b, 2c).

Embiratermes heterotypus (Fig. 7): All surfaces are covered with a layer of aciculiform spines (Fig. 7b).

Broad coverage: characterized by a dense coverage of spines (Figs 4a, 21a, 23a, 24a), mainly aciculiform, and small spines in rows, with recurrent sclerotized spines, the following species can be included in this category:

Cahuallitermes intermedius: very similar to C. cumulans (see ahead).

Cornitermes cumulans (Fig. 4): The surface is covered by different types of spines, laterally to the large mesenteric tongue an elongated area of aciculiform spines (Fig. 4b), the distal region and the edge of the mesenteric tongues are covered with small spines in rows (Fig. 4c), the remain surfaces are covered with spaced robust spines.

Cornitermes silvestrii, Procornitermes araujoi, Procornitermes triacifer: very similar to C. cumulans (see above).

Rhynchotermes nasutissimus: very similar to R. perarmatus (see ahead).

Rhynchotermes perarmatus (Fig. 21): laterally to the mesenteric tongue there is an elongated area covered with strongly sclerotized aciculiform spines (Fig. 21b), the distal region is covered with small spines in rows (Fig. 21c).

Syntermes molestus (Fig. 23): similar to C. cumulans, the surface is covered by different types of spines, laterally to the large mesenteric tongue is an elongated area of strongly sclerotized aciculiform spines (Figs 23b, 23d, 23e), the distal region and the edge of the mesenteric tongues are covered with small spines in rows (Figs 23c, 23f) and the remain surfaces are covered with spaced robust spines.

Syntermes spinosus (Fig. 24): laterally to the mesenteric tongue, an elongated area covered with robust spines (Fig. 24b), with a small area with strongly sclerotized aciculiform spines at the middle (Fig. 24c), the edges of the mesenteric tongues are covered with small spines in rows.

The species A. armiger, A. bidentatus and U. teevani (Fig. 25) does not fit clearly in the previous proposed patterns, at the proximal region there is a irregular area covered with robust spines (Figs 25b, 25c), but without the longitudinal row of stout spines or the central ridge, and the distal region is covered with a single longitudinal and large row of spaced small spines, that can not be clearly recognize as equivalent to the broad coverage or the three branches of the proximal aciculiform pattern.

In a few of the species studied, the ornament coverage is reduced to short areas with small, sclerotized, aciculiform spines, i.e. in C. acignathus, C. bolivianus (Fig. 3) and P. lespesii (Fig. 19).

Considering the four patterns of ornamentation, the Syntermitinae can be generally classified in four distinct groups: proximal aciculiform pattern (Acangaobitermes, Curvitermes, Cyrilliotermes, some Embiratermes species, Ibitermes tellustris, Noirotitermes, Silvestritermes); central ridge pattern (Embiratermes robustus, Ibitermes curupira, Mapinguaritermes and Labiotermes); diffuse coverage (Armitermes and Embiratermes heterotypus) and broad coverage (Syntermes, Cornitermes, Rhynchotermes, Procornitermes araujoi and Procornitermes triacifer) (Table 2).

The ornamentation pattern in Syntermitinae is bilaterally symmetrical or asymmetrical (in a few species). The majority of genera of Syntermitinae have a consistent pattern of ornamentation among their species; the exceptions are Ibitermes, Embiratermes and Procornitermes, particularly Embiratermes. This indicates that these genera are not monophyletic, in agreement with observations of other gut anatomical characters (Cancello and Rocha 2013, for Procornitermes; personal observation for Embiratermes and Ibitermes, manuscript in preparation).

Although these structures may have potential phylogenetic information, their relevance as characters and the congruence with the gut anatomy need to be checked in most comprehensive studies. A preliminary phylogeny of Syntermitinae was proposed in Rocha et al. 2012, but the main objective in the study is just formulate a working hypothesis to test the monophyly of Armitermes, a more specific study is necessary to make phylogenetic inferences about the evolution of the ornaments.

In studies of termite faunas, the species are commonly classified by diet. The categories are defined by a humification gradient, which ranges from whole plant matter (such as wood and dead leaves) to decomposed cellulosic compounds dispersed in the soil (see Donovan et al. 2001 for a more detailed description). Although the classification by feeding groups is widely used, more recent studies have indicated that there is a continuum among termite feeding preferences (Bourguignon et al. 2010).

No specific proposal has been made for a classification of the feeding habits of all Syntermitinae species. Based on field notes accompanying specimens deposited in the MZUSP, and inferences from worker mandibles and gut morphology, we made a compilation and a classification for their diet, and compared feeding habits and P1 patterns of ornamentation among the species examined (Table 2).

The pattern of ornamentation in Syntermitinae appears to be generally related to the feeding habit, and reflects the humification gradient. Species that feed lower in the humification gradient (litter-feeders, grass-feeders and wood-feeders) mainly display a mosaic pattern, with a wide and heterogeneous coverage of small spines (for example Syntermes, Cornitermes, Rhynchotermes). Species that feed on humidified resources (intermediate- and soil-feeders) have a more centralized pattern, with structures concentrated only in the proximal region of P1 (for example Silvestritermes, Curvitermes, Mapinguaritermes, Labiotermes) (see Table 2). This inference may be useful as an additional character to determine the species’ diet, combined with other characteristics of the gut. However, some of the species examined in this study are exceptions; for instance, P. lespesii and C. bolivianus are known as, respectively, wood-feeder and litter-feeder species, although their P1 ornamentation is much reduced.

As the P1 ornaments have never been described in detail for Termitidae species, we can only speculate as to their function. Investigating their specific function is outside the scope of this paper, but we can make some suggestions based on morphological inference and analogies with the functions of P2 suggested by Donovan et al. (2000).

These structures may function as an abrasive surface for the food mass that enters from the midgut. This hypothesis is supported by the location of the ornaments, only in the proximal part of the convex side of the mesenteric arch (see Fig. 1). However, in some cases the ridges may be irrelevant for this function, for example the isolated central ridges in Labiotermes (Figs 12–15) measure around 50–100 µm and the P1 diameter varies between 1–2 mm, and it is difficult to explain how a single structure of this size can act on the food mass.

Another possible explanation is microbial inoculation. This hypothesis is supported by the usual presence of what appears to be a bacterial film covering the spines, and some points regarding this possibility need to be considered. The pH and oxygenation conditions inside the first proctodeal segment may be very different from the third proctodeal segment, which implies that the bacterial flora will also necessarily be different. Bignell and Eggleton (1995) studied the pH conditions inside each segment of the digestive tract in various termite species, and found that P1 may be more alkaline than P3. Schmitt-Wagner et al. (2003) demonstrated for two Cubitermes species (African soil-feeder termites) that inside each hindgut compartment (P1–P5) the symbiont assemblage is composed of distinct types and proportions of microbial groups; this reinforces a microbial-inoculation hypothesis. The mean size of the ornamentation is approximately 20 µm, suggesting an association of the bacteria of the micro-oxic region, the peripheral region of the lumen, of approximately 100 µm, with oxygen availability (Brune and Friedrich 2000). To confirm this, more-detailed studies are needed to bolster this hypothesis.

In other groups of Termitidae, with the same range of feeding habits, ornamentation appears to be absent. For example, in Nasutitermitinae the species have a variety of feeding habits that cover the entire humification gradient, but we never find ornaments in their first proctodeal segment (personal observation). This suggests that in the course of termite evolution, many different strategies have emerged in response to the problems of digesting similar types of food.