Holotype.—

UNNEC 1043: Laguna Brava (27°30′S 58°43′W), Capital Department, Corrientes Province, Argentina. Álvarez y Tedesco Col. 3 March 1982.

Paratypes.—

FML 10217; UNNEC 888; 1035; 1036; 1047; 6964: City of Corrientes, Capital Department, (27°28′S 58°50′W), Corrientes Province. FML 10218; UNNEC 1038; 1040; 1042: Laguna Brava (27°30′S 58°43′W), Capital Department, Corrientes Province. REB.AM 001: Reserva Ecológica “El Bagual” (26°10′58′′S 58°56′39′′W), Laishi Department, Formosa Province.

Standardized diagnosis (following Gans and Alexander, 1962).—

A small form of Amphisbaena without major fusion of head shields; with one pair of large parietals and enlarged occipitals; a blunt-tipped cylindrical tail with a faint autotomy annulus at the eighth caudal annulus; two cicatricial precloacal pores separated by a pair of nonpored medial scales (hiatus), or without pores. Specimens have 202 to 213 body annuli; 18 to 19 caudal annuli; 16 to 17 dorsal and 18 to 22 ventral segments to the midbody annulus; one or two rows of postgenials and a postmalar row. The color of preserved specimens is light brown with the ventral region crème white, similar to that of live specimens.

Description.—

This is a medium- to small-sized species of Amphisbaena. Meristic characters are summarized in Table 1. The general dorsal coloration of the living specimens is light brown, being darker in the largest specimen while the smaller ones are lighter and with a reddish ventral coloration on the first third of the body. The preserved specimens have a light brown coloration with slight ventral countershading. The pigment of each segment is concentrated as a series of stripes dorsally and as a thin band along the edge of each segment ventrally (Fig. 2). The head and the first eight annuli show denser pigmentation.

Table 1. Meristic Characters of Amphisbaena hiata (Following Gans and Alexander, 1962). For lengths, ± indicates that the specimens is partially broken, and the measurement is approximated

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The head is relatively blunt and slightly depressed (Fig. 3). The temporal muscle masses are bulky in the larger specimens, causing a sagital depression at the nape (Fig. 3). The head segmentation is typical of the genus although some proportions and shapes of scales may differ. The azygous rostral has a labial border of the same extent as the opposite mental of the lower jaw. The triangular rostral is hardly seen from dorsal view. The nasals are large and form most of the tip of the snout; the external nares are anterolaterally placed. Posteriorly, the prefrontals meet at the midline and laterally they contact the second supralabials and oculars; the prefrontals are the largest scales of the head. The frontals are semicircular and contact the oculars. The pentagonal parietals are as wide as the frontals, with their posterior border straight and parallel to the second body annulus; the parietals form part of the first body annulus. Posterior to the parietals is a pair of occipital scales, as wide as the parietals and equivalent to two segments of the second body annulus.

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Three supralabials, all of similar length, border the mouth (Fig. 3). There are three infralabials, the second being much larger than the others and the third being elongated with the angulus oris ventral to it. The ocular scale is rhomboid; it contacts ventrally with the third supralabial and dorsally with the frontals and parietals.

The mental scale (= symphysial of Vanzolini, 1991) is larger than the first infralabial (Fig. 3). The wide postmental has seven sides; its posterior tip inserts between the two postgenials. There may be a second row of three postgenials. The trapezoidal malars are wide and contact laterally with the third infralabials; anteriorly they have a point of contact with the postmental. Posterior to the malars there is a row of eight to 10 (usually 10) postmalar scales [terminology of Gans and Alexander (1962)], the lateral-most of which contact the posterior half of the third infralabials.

The first five or six body annuli are narrower than the rest, mostly in their ventral aspect, causing a flexion at the base of the neck. In this region four specimens have intercalated annuli, whereas the other eight have none. There are 202 to 213 body annuli from the one posterior to the third infralabial to the one bearing the precloacal pores. There are 16 to 17 rectangular dorsal segments per midbody annulus; these segments have similar lengths but vary in width, being wider at the anterior third part of the body (about half of length) but being very narrow at the posterior third (about one quarter of length). There are 18 to 22 ventral segments per midbody annulus; all ventral segments are quadrangular and the medial ones are larger than the lateral ones. There are no intercalated annuli along the body, although most specimens have one at the third to fifth precloacal annulus (four specimens show no precloacal intercalated annulus). The lateral sulci are marked behind the 12th to 14th body annulus. There are no ventral or dorsal sulci.

On the precloacal annulus, the midventral scales do not have pores; the two scales immediately lateral have cicatricial pores, placed on the posterior half of the scale; none of the specimens has a conspicuous secretion plug, and therefore the pores are difficult to see (Fig. 4); one specimen (UNNEC 1035) does not have pores at all. There are 18 to 19 caudal annuli. The autotomic site falls behind the eighth caudal annulus. The autotomy annulus is slightly narrower than the other caudal annuli and sometimes it is difficult to see (Fig. 5). None of the specimens has a tail that is broken from natural causes, but postmortem handling partially broke the tail of two specimens behind the autotomic annulus. The tail is depressed anteriorly and slightly compressed behind the autotomy annulus. The tip of the tail is rounded and has a cap of fused scales; some of the lateral sutures of the fused scales are visible.

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Identification.—

From other two-pored species of Amphisbaena (A. dubia, A. neglecta, A. silvestrii, A. mitchelli, A. lesseri, A. miringoera, A. anemariae, A. crisare, and occasionally A. darwini and A. lumbricalis), the new species differs by having pores separated by a medial gap formed by two poreless scales. In particular, A. hiata differs from A. dubia by a lower number of body annuli (202–209 vs 213–231, respectively), a higher number of dorsal (16–17 vs 13–16, respectively) and ventral segments (18–22 vs 16–19, respectively), and the presence of a postmalar row and tail autotomy (both absent in A. dubia).

From other species having a similar number of body annuli (including the sympatric A. darwini) the new species is identified by usually having two cicatricial precloacal pores separated from each other by two annular segments (although one specimen has no visible pores), and a very faint autotomy annulus. The new species also differs from A. darwini in coloration (the pigment reaches the anterior portion of in each annular segment in A. hiata, whereas in A. darwini the pigment is usually concentrated in a central dense spot). A few specimens of A. darwini heterozonata have two pores (Gans, 1966), but these are always in contiguous segments and with a conspicuous secretion plug.

Amphisbaena hiata is readily distinguishable from all other species with neighboring distributions (A. bolivica, A. angustifrons, A. mertensii).

To allow proper identification of Argentinean Amphisbaenids the key of Montero (1996) should be modified as follows:

• 10a.

  2 poros separados por dos escamas intermedias o sin poros, pigmentación más concentrada en el borde anterior de las escamas dorsales . . . A. hiata

• 10b.

  Generalmente con 4 poros en escamas contiguas (raramente de 2 a 6), y pigmentación no como la anterior . . . 11

• 11a.

  Patrón de coloración en forma de tablero de ajedréz (con alternancia de escamas o zonas oscuras y claras) . . . A. prunicolor prunicolor

• 11b.

  Escamas con una zona central más pigmentada, a veces dando la apariencia de punteada . . . A. darwini…12

• 12a.

  Cola tuberculada, 15 a 22 anillos caudales . . . A. darwini trachura

• 12a.

  Cola no tuberculada, 13 a 17 anillos caudales . . . A. darwini heterozonata

Habitat and distribution.—

Amphisbaena hiata is found in soft sand and lime soils or in mud removed from gardens (very common in the periphery of the city of Corrientes); it is also found under logs or debris and in the air chamber of domed termite nests (Cortaritermes fulviceps).

The species is known from Formosa (El Bagual, Yanosky et al., 1993a) and Corrientes (Capital and Laguna Brava; Fig. 1). Both localities belong to the Oriental (wet) Chaco (Cabrera and Willink, 1973), seasonally flooded grasslands with “monte de espinillo” (Prosopis alba and Prosopis algarrobilla: Leguminosae), “palmares” (Copernicia sp.: Palmaceae), and “caraguatales” (Aechmea disthichanta: Bromeliaceae). Considering the distributions of this type of habitat, it is likely that A. hiata is present in the Argentinean province of Chaco and adjacent Paraguay. The new species is found in sympatry with Amphisbaena mertensii, A. darwini heterozonata, Anops kingii, and Leposternon microcephalum (Montero, 1996).

Etymology.—

The specific name comes from the Latin word hiatus, meaning gap, in reference to the gap between the precloacal pores, which is a distinctive characteristic of this species.