Speodromia Barnard, 1946

Ng, Peter K. L., 2016, The taxonomy of Speodromia platyarthrodes (Stebbing, 1905) (Crustacea: Brachyura), an unusual dromiid crab endemic to South Africa, Zootaxa 4111 (3), pp. 261-275 : 261-262

Speodromia Barnard, 1946

Speodromia Barnard 1946: 370 ; Barnard 1950: 333; McLay 1993: 182; Guinot & Tavares 2003: 74, 113; Ng et al. 2008: 35.

Type species. Dynomene platyarthrodes Stebbing, 1905 , by monotypy.

Diagnosis. Carapace transversely subovate, with anterior part produced; gastric, branchial regions swollen, other regions well demarcated; branchial regions with large, deep cavity on sub-branchial side, opening to subbranchial cavity joins shallow grooved area on remaining sub-branchial part of carapace. Front trilobate; supraorbital margin with median spine; anterolateral margin arcuate, anteriorly curving downwards towards pterygostomial region, with 6–8 low, triangular teeth. Epistome with posterior margin separated into 2 truncate lobes by deep median fissure. Antenna with article 1 subrectangular, inner margin with prominent cleft, article 2 subquadrate, distal margin with cleft. Third maxilliped relatively long, inner margin of ischium lined with prominent pectinate crista dentata. Chelipeds closely coapted to lateral sides of carapace when retracted; dorsal margin of merus with large expanded crista on distal half, that on ventral half forming C-shaped concavity; chela stout, outer surface with longitudinal rows of short setae; inner surface of fingers excavate, bracketed by strong teeth. P2 and P3 similar in form; coxa with short ledge-like projection on inner margin of posterior part which locks onto margin of pleonal somites when closed; merus with strong dorsal crista; carpus with median ridge, strong dorsal ridge, 2 low ventral ridges; propodus with median ridge, well developed dorsal ridge, 2 low ventral ridges; dactylo-propodal lock well developed. P4 prominently reduced; dorsal crista of merus distinct; flexor side of distal margin with long fixed spine which opposes strongly recurved, hook-like dactylus. P5 slender, short; merus slender, elongate; carpus, propodus elongate, unarmed; distal margin of propodus with long fixed spine on flexor side, relatively shorter spine on extensor side, dactylus hook-like. Thoracic sternite 4 semicircular; penis not calcified, long, mobile, reaching to median part of coxa of P3. P1–P5 without epipods or podobranchs. Male telson triangular, tip sharp; uropod ventral, ovate, mobile, not visible from dorsal view; no pleopods on somites 3–5. G2 without endopod. Female spermathecal groove (sternal suture 7/8) long, prominent, reaching to sternite 4; aperture to spermatheca on each side of rounded tip; coxae of P2, P3 without locking mechanism as in male; female telson semicircular, uropod relatively more longitudinally ovate compared to males.

Remarks. The morphology of Speodromia Barnard, 1946 , is quite unlike any known dromiid, with its transversely ovate carapace and anteriorly produced frontal region. In fact, in its carapace form, it superficially resembles species of Osachila Stimpson, 1871 , Sakaila Manning & Holthuis, 1981 , and Aethra Latreille in Cuvier, 1816 , genera now placed in Aethridae Dana, 1851 (see Rathbun 1916; Manning & Holthuis 1981; Ng 1999; Ng et al. 2008; Martin et al. 2009). The highly reduced last two ambulatory legs with the subcheliform dactylus and propodus (P4 and P5), however, make it clear it is a dromiid.

The characteristic form and density of the setae on the surfaces of Speodromia are not known to be present in any other dromiids and were accurately figured by Barnard (1950: fig. 64b, c). On the dorsal surface of the carapace, ventral surfaces of the thoracic sternum and pleon, and surfaces of the pereiopods, these setae are short and squamiform, forming clumps which resemble patches of granules but do not completely obscure the surface. Along the margins of the structures, however, these scale-like structures are larger and stalked to various degrees, resulting in distinct clavate setae. These clavate setae are often closely packed, making the cristae and margins higher and more prominent than they actually are.

The deep cavity in the sub-branchial region ( Fig. 5 A–D) is on the anterior half of the carapace, and forms a chamber in the branchial area which is connected to the gill chamber along the ventral margin (see Barnard 1950: pl. 64d). With regards to cavities on the carapace, Sphaeorodromia brizops McLay & Crosnier, 1991, described from one male specimen from the Seychelles, has an unusually deep and prominent orbit but the branchial and subbranchial regions are normal ( McLay & Crosnier 1991). Barnard (1946, 1950) also dissected a specimen and showed that all the pereiopods (including the chelipeds) do not possess an epipod (cf. Barnard 1950: fig. 64e).

Guinot & Tavares (2003) divided the Dromiidae into three subfamilies: Dromiinae De Haan, 1833 s. str., Hypoconchinae Guinot & Tavares, 2003, and Sphaerodromiinae Guinot & Tavares, 2003, on the basis of the structure of the carapace, penis, male pleopodal formula, structure of P4 and P5, form and position of the male and female uropods, relative length of the female thoracic sternal sutures 7/8, position of the spermathecal apertures, and presence of an endopod of the G2. Guinot & Tavares (2003) retained Speodromia in Dromiinae s. str. based on Barnard (1950). The study of the present specimens confirms this classification. While the carapace shape of Speodromia is unusual and the deep sub-branchial cavity is a unique character, all the other features used to define Dromiinae by Guinot & Tavares (2003) apply to Speodromia (see also Guinot et al. 2013; Davie et al. 2015b).

The authority of the genus is usually given as “Barnard, 1947”, but the publication was actually released in 1946 (see Ng & Kumar 2015: 2).

Figures

FIGURE 5. Speodromia platyarthrodes, male (28.1 × 22.1 mm) (SAM MB-A 000816), South Africa. A, left lateral side of cephalothorax; B, right lateral side of cephalothorax (denuded); C, left side of sub-branchial surface showing cavity; D, left side of sub-branchial cavity showing groove towards posterior carapace margin (denuded); E, F, posterior view of cephalothorax.