Rostrum with distinct upward curve, tip normally bifid; dorsal teeth not extending into distal third in adults; six or seven dorsal teeth, four or five ventral teeth; two of the dorsal teeth behind posterior edge of the orbit.
Carapace with antennal and branchiostegal spines. Antennules triramous; shorter ramus of outer flagellum about 0.85 x the length of the peduncle and fused for 0.2-0.25 of its length to longer ramus. Outer edge of stylocerite slightly convex, but may be slightly concave in very large specimens; anterior border slightly convex, apical spine long and stout.
Scaphocerite extends to half length of dactyl of pereiopod 2, or to distal tip of dactyl in juveniles; apical spine not exceeding lamellar portion. Third maxilliped extends to half length of scaphocerite or slightly less; exopod present.
Mandible with incisor and molar process, and three segmented palp. Dactyl of pereiopod 2 about 0.5 x length of propus; merus 1.25 x length of carpus.
Telson with two pairs of lateral spines.
The rostral features make this species comparatively easy to identify, but can be unreliable in specimens of 25 mm or less. Colour also varies, but pattern variations are relatively constant within a population but not between populations. P. serratus feeds on algae, small crustaceans, molluscs, polychaetes and other small benthic invertebrates.
Length up to 110 mm, usually less than 100 mm.
Variable, but normally carapace and pleon bear conspicuous bands of brownish-red pigment, oblique or horizontal on carapace but vertical on pleon. Reddish spots of pigment are dotted between these bands. Rostrum with small red pigment spots, darkest at tip. Large specimens may be an overall brownish colour with the above banding.
Down to about 40 metres .Hyperbenthic species, may swim up at night, mostly confined to the nepheloid layer. Frequent on rocky shores, in pools or amongst algae on lower shore, but also occurring in Zostera beds. May occur in same pools as Palaemon elegans but does not reach such high shore levels.
Normal breeding season extends from November to June, with some large females carrying eggs in July, August and September.
Distribution in the North Sea:
All North Sea; scarce on British northeast coasts.
Ranges from the Danish coast southwards to the Mediterranean, Black Sea and Mauritanian coast.