Encephaloides armstrongi Wood-Mason
Creators: name: Ng, Peter K. L.
name: Patel, Heris
name: Trivedi, Jigneshkumar
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Inachidae
Encephaloides
Encephaloides armstrongi

description: Encephaloides armstrongi Wood-Mason in Wood-Mason & Alcock, 1891
(Figures 1, 2)
Encephaloides armstrongi Wood-Mason in Wood-Mason & Alcock, 1891: 259.—Wood-Mason in Alcock & Anderson 1896, p. 19, figs 2, 2a.
Encephaloides Armstrongi — Wood-Mason in Alcock 1899: 47–49.
Phalangipus somnathensis Sureandiran, Karuppasamy & Suyani, 2024: 1375, figs. 2–5.
Type material examined. Holotype of Phalangipus somnathensis Sureandiran, Karuppasamy & Suyani, 2024: male (carapace missing) (14.0 mm × 19.0 mm) (KU /COF/PS.1), Veraval fishing harbour, Gujarat, northwest coast of India, 20°50’N 70°28’E, coll. B. Sureandiran, 24 January 2023.
Other material examined. Encephaloides armstrongi Wood-Mason in Wood-Mason & Alcock, 1891: 1 male (22.3 mm × 24.8 mm), 1 female (20.6 mm × 21.0 mm) (ZRC 2014.0343), Gulf of Oman, 23º22.98’N 58º59.10’E — 23º23.23’N 58º59.87’E, ca. 350 m, coll. RRS Charles Darwin Cruise 143, 11 December 2002.
Comparative material examined. Phalangipus longipes (Linnaeus, 1758): 1 male (19.3 mm × 21.3 mm), 1 female (15.3 mm × 19.5 mm) (ZRC 2013.0181), Angsila fish port, Chonburi, Thailand, coll. S. Panhan et al., 3 December 2004.
Remarks. Careful examination of the figures in Sureandiran et al. (2024) leads us to conclude that the photograph of the specimen depicted in dorsal view (Sureandiran et al. 2024: fig. 2) is clearly not the same as that shown in the ventral view (Sureandiran et al. 2024: fig. 3). This includes the drawing of the dorsal aspects of the carapace, which was traced from the photograph by Sureandiran et al. (2024: fig. 5a). The relative lengths of the ambulatory legs in their figure 2 are much longer than those in figure 3, with the P5 almost as long as P4. Significantly, in their figure 3, the last ambulatory leg is quite short, much shorter than the fourth leg. The structure, missing and damaged leg conditions in the two figures also do not match (e.g., the size and proportions of the right P4 and P5)—it is not possible the two are the same specimen. We believe the authors somehow inadvertently assumed they were the same.
The specimen figured in the overall dorsal view by Sureandiran et al. (2024: fig. 2) clearly belong to Phalangipus but we cannot be sure of the species as the diagnostic species characters used by Griffin (1973) are not visible from the photograph or his drawing of the carapace (Sureandiran et al. 2024: fig. 5A). The prominent intestinal spine noted by Sureandiran et al. (2024) as a diagnostic character for their species is also present in P. indicus (Leach, 1815), P. australiensis Rathbun, 1918 and P. hystrix (Miers, 1886), so it is of little use in identifying the specimen. The identity of this specimen, however is irrelevant because the holotype, and the only extant specimen, is the specimen showing the ventral parts but lacking the carapace (Sureandiran et al. 2024: fig. 3). Fortunately, even without the carapace, the identity of this damaged holotype is clear.
The photograph of the ventral view of the holotype (Sureandiran et al. 2024: fig. 3) shows five characters that merit attention that were confirmed through an examination of the specimen:
(1) the thoracic sternum is partially crushed on the right side but it is clear from the drawing and the photograph of the ventral surface that although sternites 3 and 4 are fused, the two sternites are clearly separated, with sternite 3 subtriangular in shape, and separated from the subtrapezoidal sternite 4 by a wide, almost right-angled cleft, with the distal margin tranversely straight. The male sternopleonal cavity reaches to about half the length of sternite 4 (Fig. 2B) and surface of sternites 3 and 4 are almost smooth and relatively flat, without any prominences. This is also depicted in the drawing (Sureandiran et al. 2024: figs. 3, 5b; Fig. 2B).
(2) The right third maxilliped and the anteroexternal angle of the merus is strongly expanded to form a large auriculiform structure (see also Fig. 2B).
(3) The cutting edges of the chela are lined with broad triangular teeth along entire length, without any proximal subtruncate tooth on proximal part of dactylus (Fig. 2C) (see also Fig. 1C, D).
(4) P5 is clearly the shortest pereopod and P2 the longest; P5, however, is prominently shorter than P4, with the P5 merus only about two-thirds the length of the P4 merus (Fig. 2A).
(5) The pleon is relatively broad and somites 3–6 together form a subrectangular shape, with the lateral margins of somite 6 prominently convex. This is also evident in the drawing (Sureandiran et al. 2024: fig. 5c; Fig. 1A).
In addition, the G1 is not short as figured by (Sureandiran et al. 2024: figs. 4, 5f–h), it is actually much longer (Fig. 1B).
All the characters discussed above are identical with those of Encephaloides armstrongi (Fig. 2B–E). In contrast, the ventral surface of all other species of Phalangipus is quite diagnostic: male thoracic sternite 3 is separated from sternite 4 by a shallow cleft, and with the distal margin of sternite 4 gently sloping; each lateral edge of male thoracic sternite 4 has a prominent swelling which is lined with relatively long stiff setae; the male sternopleonal cavity reaches to just before area between sternites 3 and 4 (Fig. 3C); the overall male pleon shape is triangular, with somites 3 and 4 much wider and somites 5 and 6 rectangular in shape (Fig. 3C, D) (see also Griffin 1973: fig. 6). It must be noted that while the merus of the third maxilliped of Phalangipus has the anteroexternal angle auriculiform (Fig. 3C), it is distinctly less expanded than that in Encephaloides (Fig. 2B). Most of the cutting edges of the fingers of the adult male chela are lined with distinct teeth but the proximal part of pollex is unarmed with the proximal part of dactylus possessing a distinct subtruncate tooth (Fig. 3B); this is different from the condition in Encephaloides in which the entire cutting edge has uniform cutting teeth (Figs. 1C, D, 2C). Another distinctive character of all species of Phalangipus is that while P5 is the shortest leg, it is only slightly shorter than P4, with the P5 merus only slightly shorter than the P4 merus (Fig. 3A). In Encephaloides, however, the P5 merus is markedly shorter than the P5 merus (Fig. 2A, B). In addition, all other known species of Phalangipus have a relatively slender G1, which is gently curve outwards with the distal part rounded or tapering (cf. Griffin 1973: figs. 5d, e, 8, 9a–f). Only in P. trachysternus Griffin, 1973 from Australia is the G1 proportionally much stouter, strongly setose with the distal part subtruncate (Griffin 1973: fig. 9g, h), although its general structure is like those of its congeners. None have the straight G1 with the tip bifurcated as in Encephaloides (Figs. 1B, 2D, E), which is a distinct genus character.
As such, we have no doubt that the holotype of Phalangipus somnathensis Sureandiran, Karuppasamy & Suyani, 2024 is actually Encephaloides armstrongi Wood-Mason in Wood-Mason & Alcock, 1891, and the two species are synonymised herein. Encephaloides armstrongi is a very distinctive species with a prominently swollen carapace (Fig. 2A), and we believe that if the carapace had not been detached, the species would not have been misidentified. In any case, E. armstrongi was described from the Bay of Bengal, and the species has been reported from various parts of the Arabian Sea, including Gujarat (see Wood-Mason & Alcock 1891; Alcock 1895, 1899; Alcock & Anderson 1896; Griffin 1974; Creasey et al. 1997; Kazmi 1997; Kazmi & Moazzam 2014; Dash & Koya 2017).
description: Published as part of Ng, Peter K. L., Patel, Heris & Trivedi, Jigneshkumar, 2025, Phalangipus somnathensis Sureandiran, Karuppasamy & Suyani, 2024 - a junior synonym of Encephaloides armstrongi Wood-Mason in Wood-Mason & Alcock, 1891 (Crustacea, Brachyura, Inachidae), pp. 594-600 in Zootaxa 5627 (3) on pages 595-599, DOI: 10.11646/zootaxa.5627.3.13, http://zenodo.org/record/15326163