DIVISION 3. HOPLOCARIDA.
The carapace leaves at least four of the thoracic somites distinct. The eyes are pedunculate. The mandibles are without a lacinia mobilis; there are no oostegites, the eggs being carried in a chamber formed by the maxillipedes. The hepatic caeca are much ramified, the heart is greatly elongated, stretching through thorax and abdomen, with a pair of ostia in each segment. The spermatozoa are spherical, and there is a complicated and peculiar metamorphosis.
Order. Stomatopoda.
Fig. [98].—Lateral view of Squilla sp., × 1. A.1, A.2, 1st and 2nd antennae; Ab.1, 1st abdominal segment; Ab.6, 6th abdominal appendage; C, cephalothorax, consisting of the head fused with the first five thoracic segments; E, eye; M, 2nd maxillipede; T, telson. (After Gerstaecker and Ortmann.)
The Stomatopoda are rather large animals, occasionally reaching a foot in length, all of which exhibit a very similar structure; Squilla mantis and S. desmaresti are found on the south coast of England not very frequently; but they are very common in the Mediterranean, living in holes or in the sand within the littoral zone of shallow water. They differ from all the other Malacostraca by a combination of characters, and Calman proposes the term Hoplocarida for a division equivalent to the Peracarida, Eucarida, etc.
The abdomen is very broad and well developed, ending in a widely expanded telson. There is a carapace which covers the four anterior thoracic segments, leaving the four posterior segments free. The portion of the head carrying the stalked eyes constitutes an apparently separate segment articulated to the head. The antennae, mandibles, and maxillae are normal; there then follow five pairs of uniramous thoracic limbs turned forwards as maxillipedes and ending in claws; the second pair of these is modified into a huge raptorial arm, exactly resembling that of a Praying Mantis (cf. vol. v. p. 242), by means of which the Squilla seizes its prey. The last three thoracic limbs are small and biramous. The pleopods are powerful, flattened, biramous swimming organs with small hooks or “retinaculae” upon their endopodites, which link together each member of a pair in the middle, and with large branching gills upon the exopodites.
The internal anatomy exhibits several primitive features. The nervous system is not at all concentrated, there being a separate ganglion for each segment; and the heart stretches right through thorax and abdomen, with a pair of ostia in each segment. There are also ten hepatic diverticula given off segmentally from the intestine.
The female has the curious habit of carrying the developing eggs in a chamber improvised by the apposition of the maxillipedes, so that it looks rather as if she were in the act of devouring her own brood.
The metamorphosis of the larvae, despite the work of Claus[[114]] and Brooks,[[115]] is not very accurately known, especially uncertain being the identification of the different larvae with their adult forms. The chief interest consists in the fact that certain of the anterior thoracic limbs develop in their normal order and degenerate, to be reformed later, just as in the Phyllosoma larva of the Loricata (see pp. [165], 166).