The Loricata include the Langouste (Palinurus) of the Mediterranean coasts, which replaces there the Lobster of the North Sea as an article of food, and the peculiarly shaped Scyllarus arctus (Fig. [111]), which is also prized in the Mediterranean as a delicacy. The bright red “Crayfishes,” Panulirus and Iasus, of the Australian coasts are also largely used as food. Besides its peculiarity in shape, S. arctus has remarkable scales on the second antennae in place of flagella. The larva hatches out as the so-called Phyllosoma, which must be regarded as a greatly flattened and modified[[139]] Mysis stage.
Fig. [113].—Phyllosoma larva of Palinurus, sp. × 5. Ab, Abdomen; Mxp, 3rd maxillipede; T, antepenultimate (6th) thoracic appendage. (After Claus.)
In the embryo of Palinurus just before hatching (Fig. [112]) we can recognise the limbs of the head and thorax normally developed in order. There are present three thoracic limbs, besides the maxillipedes. When the Phyllosoma hatches out the first maxillipedes have become quite rudimentary, and the second much reduced, while the second antennae and second maxillae are also reduced in size. The metamorphosis is completed by the re-development of the limbs and segments that have been secondarily suppressed during larval life, and by the appearance of the pleopods.
This process is again met with in the Squillidae (p. 143), but it resembles the suppression, in so many Decapodan metamorphoses, of anterior limbs and the precocious development of segments and limbs lying posteriorly. In the ordinary Decapoda, however, the suppressed limbs are merely not formed till later; while in the Loricata the limbs develop in the correct order, and subsequently degenerate. It is natural to wonder whether the condition of affairs in the Loricata represents the primitive process, and whether the precocious development of segments in the other Decapoda owes its origin to these animals having once had the direct mode of development when the segments were formed in the proper order, and to their having subsequently acquired the larval stages first of all by the degeneration, and then by the suppression of certain segments which were not of use during larval life. The complete metamorphosis, however, of the Peneidea, in which the segments and limbs appear in the right order, rather goes to show that this is the primitive mode of development in the Decapoda, and that the disarrangement in the order of appearance of the segments, both in the Squillidae and in the Loricata and other Decapods, has been independently acquired in the two cases to meet the needs of the larval existence.
Fam. 1. Palinuridae.—The cephalothorax is subcylindrical, the eyes are not enclosed in separate orbits formed by the edge of the carapace, and the second antennae possess flagella. Palinurus, with P. elephas, the European Rock Lobster or Langouste. Iasus with two species in the Antarctic littoral; Panulirus in the tropical littoral.
Fam. 2. Scyllaridae.—The cephalothorax is depressed, the eyes are enclosed in separate orbits formed by the edge of the carapace, and the second antennae have flat scales in the place of flagella. Scyllarus (Fig. [111]), with the European S. arctus; Ibacus in rather deep water with several species, chiefly found in the southern hemisphere.
Tribe 6. Thalassinidea.
This tribe is included by some authors in the Anomura, and held to be closely related to the Galatheidea, but the unreduced abdomen is carried straight and unflexed, and gives a very Macrurous appearance to the animal. The Anomurous characters are the frequent reduction or absence of the antennal scale, the fact that only the first two pairs of pereiopods are ever chelate, and the reduced series of gills. The body is symmetrical, but the first pair of chelae is always highly asymmetrical. The posterior pairs of pereiopods, although small, are not characteristically reduced as in the Anomura. The animals belonging to this Tribe attain two or three inches in length, and generally burrow in sand or mud either in the littoral zone or in deeper waters; at the same time they can swim with considerable activity by means of the pleopods.
Fam. Callianassidae.—Callianassa subterranea is common at Naples, Gebia littoralis in the North Sea.