Equulites absconditus Chakrabarty and Sparks

Chakrabarty, Prosanta, Chu, Jeanette, Nahar, Luthfun & Sparks, John S., 2010, Geometric morphometrics uncovers a new species of ponyfish (Teleostei: Leiognathidae: Equulites), with comments on the taxonomic status of Equula berbis Valenciennes, Zootaxa 2427, pp. 15-24 : 18-21

Equulites absconditus Chakrabarty and Sparks , new sp.

Figures 2 (Group A) and 5, Table 1 , 2

Leiognathus berbis Shen, 1984a: 57 , Fig. 318-9, Pl. 57; Shen, 1984b: 262; Shen and Lin, 1985: 135, Fig. 11; Chen and Yu, 1986: 530; Shen, 1993: 344, 705, Pl. 94.5.

Holotype. AMNH 249306, 74.0 mm SL, adult male; Taiwan: Market at Tonshi: 23° 27’ 10.1”N, 120° 08’ 19.3”E: PC-JSS-MKT-06-06: P. Chakrabarty, J.S. Sparks, Joker K.H. Chiu, P. Tai-An, 22 March 2006.

AMNH 239270, n=1, male, 75.2 mm, Taiwan, Chi Fish market at Tonshi, 23° 27’ 10”N, 120° 8’ 19”E, collected by J.S. Sparks, P. Chakrabarty, Joker H.K. Chiu, P. Tai-An, 22 March 2006; AMNH 242666, n=97, mixed sexes, 79.6–98.2 mm, Taiwan, Ko-Zi-Leow fish Market, 22° 43’ 37.9”N, 120° 15’ 18.3” E, collected by local fishermen, P.Chakrabarty, Y. Ho; 27 March 2007; LSUMZ 13236, n=1, female, 73.1 mm SL, Taiwan: Market at Tonshi: 23° 27’ 11.0”N, 120° 08’ 17.8”E: TW-08-3: P.C. Chakrabarty, H.C. Ho, 14 November 2008; LSUMZ 13339, n=21, all females, 67.2–83.6 mm SL, Taiwan: Market at Wuchi: 24° 17’ 40.6”N, 120° 31’ 17.8”E: TW-08-1: P.C. Chakrabarty, H.C. Ho, 12 November 2008; NTUM 5698, n=2; mixed sexes, 77.2–78.3 mm SL, Taiwan, Hsin-Da port, Kaohsiung, 22.87°N, 120.19°E, no collector, 16 March 1979.

Diagnosis. Equulites absconditus can be distinguished from all congeners by the combination of an expansive irregular-pentagonal, translucent flank patch in males and by a strong concavity dorsal to the orbit creating a hump-shaped rise in the dorsal profile that lends the head the appearance of being small and pointed. The new species can be further distinguished from E. elongatus and E. rivulatus by possessing a much deeper body (34–49% vs. 12.5–29.7% of SL) and from E. laterofenestra and E. klunzingeri by a translucent flank patch in males that does not reach the pectoral fin. The lack of a markedly elongate 2nd dorsal-fin spine distinguishes the new species from the other rhomboid shaped congeners, E. klunzingeri , E. laterofenestra , and E. leuciscus . The new species can be further distinguished from E. laterofenestra and E. leuciscus by a dorsal flank pigmentation pattern comprising thin transverse lines versus round semi-circles and oval shapes. The translucent flank patch in males of the new species is similar to that of E. leuciscus in shape and placement (near the midbody and not abutting the pectoral fin), and does not comprise a continuous or broken midlateral stripe as in E. antongil , E. stercorarius , and E. moretoniensis .

Description. Equulites absconditus is a medium-sized (typically adults are between 65 and 100 mm SL), elongate, and rhomboid-shaped ponyfish. The dorsal and ventral profiles are equally convex. The snout is pointed and the head is small (<31% SL and narrow). The lower jaw profile is straight. The mouth protracts strongly ventrally. The dorsal head profile is humped, owing to a rise extending from the region dorsal to the orbit to the dorsal-fin origin. (This humped profile makes the head appear smaller than in congeners.) The lips are thin and not fleshy. The posterior margin of the maxilla is exposed and reaches a vertical through the anterior part of the orbit. The teeth are small and conical, they are numerous, and aligned in several rows. The head is asquamate, whereas the remainder of the body (including the nuchal region) is scaled. In males, an expansive irregular pentagonal, translucent patch (forming more or less the shape of the “home plate” in baseball), is present on the midflank. The base of the pentagon is located slightly ventral and parallel to the body midline and the vertex is located slightly dorsal to the anal-fin origin. Both the second dorsal- and analfin spines are the most elongate, but not markedly longer than the third. There are 10 precaudal and 13 caudal vertebrae (including the ural centrum). There are eight dorsal-fin spines and 16 branched rays. The anal fin has three spines and 14 branched rays. Selected proportional measurements are presented in Table 1 (Group A).

Head Length (% SL) 30.4

Body Depth (% SL) 43.5

Predorsal Length (% SL) 44.1

Preanal Length (% SL) 52.6

Prepelvic Length (% SL) 38.2

Head Width (% SL) 12.0

CP Length (% SL) 7.0

CP Width (% SL) 2.6

CP Depth (% SL) 5.0

Pectoral Fin Length (% SL) 21.3

Pelvic Fin Length (% SL) 12.8

Snout Length (% HL) 34.8

Orbit Diameter (% HL) 34.1

Upper Jaw Length (% HL) 45.0

Lower Jaw Length (% HL) 54.1

Interorbital Width (% HL) 35.0

Pigmentation pattern and coloration. The entire body is silvery, owing to uniform, heavy guanine deposition. Pigmentation pattern on the dorsal flank comprises dark, thin transverse lines that follow the contours of the myomeres. In addition, some small circular blotches are present throughout this region, although these blotches are concentrated along the dorsal margin of the flank if present. In life there is a yellowish tint to the posterior margin of the caudal, dorsal and anal fins as well as the midline of the flank and in the pectoral-fin axil.

Etymology. From the Latin absconditus meaning hidden or concealed. In reference to the fact that this taxon has been well represented in collections for many years, yet consistently misidentified as members of other species.

Taxonomic Status of Equula berbis Valenciennes. Valenciennes based his description of this species entirely on the very brief remarks of Forsskål and not on specimens (1775: 58; Klausewitz and Nielson, 1965). The entire description of Equula berbis (translated from the French) is as follows: “Forskal speaks about a variety of Scomber equula , named in Djidda melliet and Lohaja berbis , which has an elongate body or of lanceolate form, hardly long of a finger, the acute lobes of the tail, the side line finishing under the dorsal, and of which all the fins are bordered of yellow. It gives him for numbers: B. 4; D. 8/16; A. 3/15; C. 16; P. 16; V. 1 /5. This description is enough to prove that it is not a variety.”

No types of E. berbis are known and the original description [including the earlier comments by Forsskål (1775: 58)] does not serve to diagnose this species on the basis of unique anatomical features or distinguish it from congeners on the basis of a combination of unique attributes. Forsskål’s (1775: 58) remarks serve only to note that this taxon, which he considered to be a variety of Leiognathus (Scomber) equulus (viz., Scomber equula var minimus Forsskål ), has a more elongate body than the deep-bodied and more or less disk shaped Leiognathus equulus , a feature that is shared by a majority of ponyfishes. Forsskål also mentions a lateral stripe that terminates ventral to the dorsal fin, but he does not elaborate on whether this stripe appeared opaque or translucent. The majority of leiognathid species possess a lateral stripe of some form (e.g., reflective), although in only a few species is this stripe translucent (e.g., Equulites stercorarius , E. moretoniensis , and E. antongil ).

The description of Equula oblonga Valenciennes , in Cuvier and Valenciennes, 1835 immediately followed that of E. berbis , with the authors commenting that they would not consider E. oblonga to be different from E. berbis “if it did not have spots about which the Danish naturalist (Forsskål) does not speak”. As “First Reviser”, Günther (1860: 502) synonymized E. berbis with E. oblonga , but without any discussion as to why. Subsequently, and in violation of Article 24 of the International Code of Zoological Nomenclature (1999), Dor (1984: 136) synonymized E. oblonga under E. berbis .

Our examination of collections of leiognathids reveals that Equula berbis consistently serves as a “wastebasket species”. Much of the confusion is derived from the fact that Equula berbis was not illustrated by either Forsskål or Valenciennes. In addition, all of the features presented by Valenciennes in the original description of E. berbis are shared with other members of Leiognathidae . Because of these reasons and the fact that there have never been type specimens for comparison, the name must be considered a nomen dubium.

Despite the lack of information related to this species, it is currently considered to be one of the most widespread members of the family ( Woodland et al., 2001; Woodland in Froese and Pauly, 2009). Reports of this taxon are done without reference to original description and materials and have led to the perpetual buildup of misinformation in the literature. Revisionary systematics demands the examination of type material (if available) and a thorough consultation of the original description, otherwise leiognathid taxonomy will continue to be plagued by similar nomenclatural problems.

Figures

FIGURE 2. Specimens of Group A morphotype (A—Western Indian Ocean) and Group B morphotype (B—Eastern Indian Ocean)