Proceratium gibbosum

This species nests in the forest floor and the colonies are probably small. It can be found in wet evergreen and secondary tropical rainforests, nesting in the interphase of soil and leaf litter or in the debris along sheltered edges of decaying logs on floor (Image 6). Workers are solitary foragers and move at a slow pace. They feign dead when disturbed, camouflaging against the soil (Image 5D). In captivity, the workers readily accepted spider eggs as food (Image 5E) and built a nest chamber with spider silk and soil. Workers were slow in movement, looked generally uncoordinated and were averse to light. Other species that were found in the same microhabitat of Proceratium gibbosum were Tyrannomyrmex alii, Protanilla sp., Discothyrea sp., and Recurvidris sp. So far, this species is restricted to the mid-elevation tropical evergreen jungles of the Periyar Tiger Reserve, in Kerala, India.

Identification
Proceraitum gibbosum differs from the other members of the stictum species group by the following character combination: mesonotum with a small rounded dorsal hump, and petiole lacking ventral projections. Proceratium gibbosum also presents a pedunculate petiole with its dorsal margin convex in profile; all tbiae with pectinate spur, calcar of strigil with a basal spine; eyes composed of a single large convex ommatidium; propodeum unarmed but angulate, convex in profile, propodeum with a robust spine on each side, propodeal lobes broad lamellaceous expansions; head, mesosoma, petiole and postpetiole irregularly foveolate; frst gastral tergite convex in profile; antennal funicles wider than long; total length <4.8 mm; propodeum with a robust spine on each side, the propodeal lobes with broad lamellaceous expansions.

The other Proceratium species from India are Proceratium bhutanense de Andrade, 2003, described from Phuntsholing in Bhutan, Darjeeling in West Bengal, Kumaon in Uttar Pradesh (Uttarakhand), and Khasi Hills in Meghalaya (Urbani & De Andrade 2003). Bhart and Wachkoo (2014) found P. bhutanense to be conspecific with P. williamsi Tiwari, 2000 and hence is now treated as the junior synonym of the later. The species P. williamsi belongs to the itoi species group with the fourth abdominal segment sternite protruding over the third abdominal sternite (Urbani & De Andrade 2003).

According to the identification key from Urbani & De Andrade (2003), the closest known species in the stictum species group seems to be P. deelemani. However, P. deelemani lacks the distinct small rounded dorsal hump present on the new species. In addition, the petiole of the new species lacks any ventral projectons, while in P. deelemani it has a distnct ventral tooth. To P. stictum, the new species differs in the cephalic sculpture, deeply impressed on P. gibbosum and shallow on the former. Additonally, the frontal carinae of the new species diverge posteriorly, where in P. stictum they are not as divergent. Anteriorly, the frontal carinae are closer to each other in P. gibbosum, while they are farther away in P. deelemani. The frontal carinae run to a level almost midway between the anterior clypeal margin and the level of the eyes, but they extend only one third the same distance in P. deelemani (the frontal carinae are shorter in P. deelemani). The species is differentiated from P. foveolatum by the first gastral tergite being angulate on dorsum, while it is round on the curvature in P. gibbosum. The new species is diagnosed from P. shohei by the head being widest midway between the eyes and vertex, while the head is widest at the level of eyes in P. shohei. The petiolar node is relatively compressed dorsoventrally in P. shohei, while P. gibbosum has a pedunculate petiole, convex in profile.

Distribution based on Regional Taxon Lists
Oriental Region: India.

Nomenclature

 * . Proceratium gibbosum Sadasivan & Kripakaran, 2022: 21371, figs. 2A–C (w.) INDIA (Kerala).

Type Material

 * Holotype: NRC-AA-3758, 23 May 2016, Worker, Vallakadavu, Periyar Tiger Reserve, Idukki District, Kerala State, India, at 900 m, coll. by Kalesh Sadasivan, tray-sifting loose soil under a decaying log, in forest floor of a primary evergreen forest, deposited in the insect collection facility of the NCBS (National Centre for Biological Sciences), Tata Institute of Fundamental Research, GKVK, Bellary Road, Bengaluru, Karnataka 560065, India. Earlier, the holotype was with number TARG-1007, mounted for morphological study and later removed & preserved as wet specimen in absolute alcohol, deposited in the research collections facility at the Travancore Nature History Society (TNHS), Thiruvananthapuram, Kerala.
 * Paratype workers (n = 3) (Images 3–5):
 * NRC-AA-3759, 28 March 2021, Worker, Vallakadavu, Periyar Tiger Reserve, Idukky District, Kerala State, India, at 930 m, coll. Kalesh Sadasivan, tray-sifting leaflitter, in forest floor of a primary evergreen forest, deposited in the insect collection facility of the NCBS (National Centre for Biological Sciences), Tata Institute of Fundamental Research, GKVK, Bellary Road, Bengaluru, Karnataka 560065, India. Earlier, paratype number TARG-1008, preserved in absolute alcohol and currently deposited in the research collections facility at the TNHS, Trivandrum, Kerala.
 * Two other paratype workers, same data as paratype above. One paratype (TARG-1009) and (TARG-1010) both in absolute alcohol, to be deposited in the insect collection of Zoological Survey of India (ZSI), Kozhikode, Kerala.