The two species differ primarily in the tail fan, with P. rapax having a longer telson spike and lacking the bristles seen in P. parki.

Because the walking appendages are poorly preserved, it remains unclear whether Perimecturus would have been benthopelagic and swam just over the seabed like other early mantis shrimps.

Furthermore, he also studied several other specimens which he named as a subspecies, P. parki duplicicarinatus, and additional species which he assigned to the genus, including P. stocki and P.

The review found that P. parki was the only valid species of Perimecturus named by Peach, and that P. p. duplicicarinatus (which Schram misspelled as duplicarinatus), P. stocki and P. communis were all junior synonyms of it.

[5] In 1985, David Factor and Rodney Feldmann published a redescription of P. rapax, after a detailed reanalysis of the fossils which found that Schram had misinterpreted some of their features.

The large, subrectangular carapace covers the entire thorax and has a marked furrow all around its margins, as well as short keels extending from the base of the antennae.

[6] Though Schram (1978) claims P. parki has only four such ridges and P. rapax has only three, detailed reanalysis by Factor and Feldmann (1985) and Jenner et al. (1998) confirms both species actually have five.

This family was established by Ben Peach in 1908, who placed it within the now defunct order Schizopoda, believing that perimecturids were intermediate forms between Lophogastridae and Anaspididae.

[3] In 1962, the Perimecturidae family was first recognized as a group of early mantis shrimps by H. K. Brooks, reassigning it to the order Palaeostomatopoda (now delisted as a suborder and named Palaeostomatopodea).

[7] With the advent of cladistic analyses, the palaeostomatopods as traditionally construed were first recovered as a paraphyletic grouping by Jenner et al. (1998), a finding later confirmed by Schram (2007).

Archaeocaris vermiformis Archaeocaris graffhami †Bairdops elegans Perimecturus parki Perimecturus rapax †Bairdops beargulchensis †Daidal pattoni †Daidal schoellmanni †Daidal acanthocercus Gorgonophontes fraiponti Gorgonophontes peleron †Chabardella spinosa †Tyrannophontes theridion †Tyrannophontes gigantion †Triassosculda ahyongi †Tyrannosculda laurae †Pseudosculda laevis †Archaeosculda phoenicia †Sculda pennata †Sculda syriaca †Ursquilla yehoachi †Lysiosquilla nkporoensis †Nodosculda fisherorum Squilla mantis

Possessing raptorial appendages on its thorax for grabbing prey like all other mantis shrimps, Perimecturus is believed to have occupied a low trophic level as an active carnivore in its habitat.

[12] In addition, the appendages of palaeostomatopods lack the click-joint mechanism seen in unipeltatans, which is formed by a specialized joint and muscles and allows them to extend quickly and catch prey.

Therefore, they proposed that these early forms were benthopelagic predators that grabbed prey from above while swimming just over the seabed, unlike modern mantis shrimps which are bottom-dwelling.

Remains of P. parki have only been collected from the Glencartholm Volcanic Beds, a site in Scotland that dates back to the Viséan stage of the Early Carboniferous period (around 345 million years ago), making it the older of the two known Perimecturus species.

The Beds were deposited in a nearshore to fully marine environment, and P. parki is a commonly found crustacean in this locality, as are Bairdops, Anthracocaris, Belotelson and Anthracophausia.

[18] All known specimens of P. rapax originate from the Bear Gulch Limestone in Montana, which was deposited around 324 million years ago during the Serpukhovian stage of the Carboniferous period.