Arcopotamonautes picus sp. nov.

(Figs. 1–4, 11)

Type material. Holotype: NMU TRW1964.03A, adult male (CW 15.6, CL 11.6, CH 5.1, FW 5.2 mm), Tanzania, Amani Area, East Usambara Mountains (-5.083333, 38.666667, 801 m ASL), coll. J. N. Raybould, 1 January 1964.

Other material examined. NMU TRW1964.03 B, 2 adult males (CWs 18.2, 17.1 mm), Tanzania, Amani Area, East Usambara Mountains (-5.083333, 38.666667, 801 m ASL), coll. J. N. Raybould, 1 January 1964 . NMU TRW1970.06, 3 subadult males (CWs 10.9–12.1 mm), 3 subadults (CWs 9.8–12.2 mm), 6 adult males (CWs 15.0– 18.4 mm), 5 adult females (CWs 18.4, 17.8, 17.3, 17.0, 16.9 mm), 4 subadult females (one damaged) (CWs 12.8– 14.2 mm), Amani Area, East Usambara Mountains (-5.083333, 38.666667, 801 m ASL), coll. J. N. Raybould, 1970 . NMU 09.03.1972, 4 adult females (CWs 15.9–18.2 mm), 7 subadult and adult males (CWs 14.7–18.6 mm), Amani Area, East Usambara Mountains (-5.083333, 38.666667, 801 m ASL), coll. J. N. Raybould, 9 March 1972 .

Diagnosis. Carapace lateral margin smooth, lacking teeth (Fig. 1A, B); S3/4 distinct, U-shaped, completely traversing sternum (Fig. 1A, B); margins of thoracic sternite S4 low (Fig. 2B, C); cheliped carpus distal tooth small, pointed (Fig. 3D); inferior margins of cheliped merus each lined by distinct small teeth, distal meral tooth small (Fig. 3C); G1TA slim, tapering to slightly upcurved tip, dorsal lobe low, with tufts of long setae proximally, otherwise smooth (Fig. 4A–E).

Description. Carapace surface smooth, widest in anterior third (CW/FW 3.0), medium height (CH /FW 1.0) (Figs. 1A, B, 2A), semi-circular, urogastric grooves deep; cardiac region weakly marked, cervical grooves short, faint; transverse branchial grooves faint (Fig. 1A, B). Front about 1/3 carapace width (FW/CW = 0.3); frontal margin straight (Figs. 1A, B, 2A); exorbital tooth small, blunt; epibranchial tooth reduced to granule; postfrontal crest sharply defined, complete, traversing entire carapace; carapace lateral margin posterior to epibranchial tooth smooth (Fig. 1A, B). Branchiostegite with two sutures, one longitudinal (epimeral), one vertical, dividing carapace sidewall into suborbital, subhepatic, pterygostomial regions, all smooth (Fig. 2A, B).

Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings at superior lateral corners; third maxilliped long exopod with flagellum; ischium with broad, deep vertical sulcus (Fig. 3E). Mandibular palp consisting of basis plus two articles; terminal article undivided, with small hardened ridge on superior margin at junction between articles (Fig. 3F). Anterior, posterior male thoracic sternum surface completely smooth; outer margins of S4 low; sternal sutures S1/2 obscure, S2/3 completely traversing sternum; S3/4 distinct, U-shaped, completely traversing sternum; thoracic episternal sulci S4/E4, S5/E5, S6/E6, S7/E7 all faint (Fig. 2B, C).

Male right (major) chela dactylus (movable finger) slightly arched, broad, cutting edge lacking teeth except for two low teeth proximally; propodus pollex (fixed finger) broad, cutting edge with three medium teeth proximally; tips of both fingers touching when chela closed, enclosing long narrow interspace; major chela propodus palm enlarged, swollen, lower margin distinctly concave (Fig. 3A). Male left (minor) chela dactylus long, slim, straight, cutting edge lacking teeth; propodus pollex cutting edge lacking teeth; tips of both fingers touching when chela closed, enclosing long narrow interspace; propodus lower margin almost straight (Fig. 3B). Cheliped merus stout; cheliped merus inferior margins lined by small teeth, distal meral tooth small (Fig. 3C, D); cheliped carpus inner margin distal tooth medium sized, pointed; proximal tooth small, pointed, followed by granule (Fig. 3D); ambulatory legs P2–5 stout, distal limb articles (merus, carpus, propodus, dactylus) not elongated; dactyli of P2–5 tapering to point, each bearing four rows of downward-pointing sharp bristles (Fig. 1A). Male pleon, telson together forming slim triangle; pleon edges slightly indented; telson triangular, apex rounded, base broadest, sides sloping outward; pleomeres PL1–6 rectangular, wider than long, PL 6 longest, more than 1/2 as long as wide; remaining pleomeres short, less than 1/3 as long as wide (Fig. 2C). G1TA about 1/3 G1SA length (G1TA/G1SA 0.3), angled outward at 45° to longitudinal axis of G1SA; G1TA slim, tapering evenly to slightly upcurved tip, dorsal lobe low, with tufts of long setae proximally, otherwise smooth (Fig. 4A–E). G1SA widest at base, narrowest at G1TA-G1SA junction; basal G1SA mesial, lateral margins smooth (Fig. 4A, B). G2TA long, flagellum-like, about 0.5 × G2SA length (G2TA/G2SA 0.5) (Fig. 5A). G2SA (Fig. 4F) long, slim, subequal to G1SA; G2SA widest at base, tapering sharply inward about one-third along length, distal 2/3rds forming long, thin, tapering, upright process (Fig. 4F).

Size. Small-bodied species, adult size range between CWs 15.6–18.6 mm.

Color. The color of living specimens is unknown, but specimens preserved in ethanol are light brown.

Type locality. Tanzania, Amani Area, East Usambara Mountains (-5.083333, 38.666667, 801 m ASL).

Etymology. The species name, “ picus ” (from the Latin for woodpecker), is a reference to the long, pointed tapering G1TA that resembles a stout woodpecker beak, together with the unusual distinctive tuft of long setae at the base of the terminal article of this species gives the G1TA a resemblance to the head of the cartoon character Woody Woodpecker, the mascot of Universal Pictures. The specific epithet is given a masculine ending and is used as a Latin noun in the genitive singular.

Distribution. Arcopotamonautes picus sp. nov. is known from a single locality in the East Usambara Mountain range in northeastern Tanzania (Fig. 11).

Habitat. See ‘Habitat’ for A. infravallatus below.

Comparisons. For comparisons see below.