292 COMPARATIVE ANATOMY CHAP. 



shell or case. Anterior antennae (adhering antennae) minute, posterior antennae 

 reduced. Oral limbs small, partly reduced. Six (less frequently 4) pairs of long 

 biramose tendril-like feet. Without heart. Hermaphrodite, occasionally with dwarf 

 males, less frequently sexes separate and dimorphic. Live in the sea. 



Family 1. Lepadidae (Pedunculata). 



Head end elongated into an attached peduncle. Lcpas (Figs. 204 and 205), 

 Conchoderma, Scalpellum, Pollicipcs, Ibla. 



Family 2. Balanidse. 



Peduncle wanting. Body surrounded by a ring of calcareous plates. Balanus 

 (Figs. 206 and 207), Tubicinclla, Coronula. 



Family 3. Alcippidae (Abdominalia). 



Body surrounded by a flask-shaped integumental mantle, with 3 or 4 pairs of feet, 

 corresponding with the last 3 or 4 pairs of other Cirrijxdcs. Live in the calcareous 

 shells of other C impedes and Molluscs. Alcippe, Cryptophyalus. 



Family 4. Proteolepadidse (Apoda). 



Body maggot-like, without tendril-like feet. Anterior (adhering) antennae ribbon- 

 shaped. Mouth a sucker. Enteric canal rudimentary. Parasitic in the mantle of 

 other Girripedes. Proteolepas. 



Family 5. Rhizocephala (Kentrogonidse), perhaps to be separated as a 

 special sub-order or order from the other Cirrij)cdcs. 



Body pouch-shaped, answers to the cephalic portion only of related Crustaceans. 

 Integument split into 2 lamellae ; between them is a brood cavity which opens out- 

 wardly by means of an aperture in the outer lamella. Enteric canal wanting. Limbs 

 wanting. Hermaphrodites, with dwarf males. Parasitic on the abdomen of Decapoda. 

 The pouch-shaped body has an adhering peduncle from which spring the branched 

 "roots" which penetrate everywhere between the viscera of the host and convey 

 nourishment into the body of the parasite. The larval stages (Nauplius- and Cijpris- 

 like larvae) are like those of other Cirripedes. Sacculina (Fig. 208), Peltogaster. 



Sub-Class II. Malacostraca. 



The body consists of 3 regions with constant number of segments. (1) The 

 head, originally formed of 5 segments ; (2) the thorax, consisting of 8 segments, of 

 which the anterior segment or segments, or all the segments, may fuse with the head 

 to form an incomplete or a complete cephalo-thorax ; (3) the abdomen, which 

 (reckoning the telson) consists of 7 segments, (in Nebalia alone, including the 

 terminal segment, of 8). All the segments of the body except the last (and in 

 Nebalia the last but one) carry limbs. The most anterior thoracic feet often 

 move into the neighbourhood of the mouth to serve as foot-jaws and to assist in 

 taking in food. The sixth pair of pleopoda (abdominal limbs) almost always differs 

 in shape from the rest, and often forms with the telson a caudal fin. A shell fold 

 springing from the posterior cephalic region is very common. A pair of compound 

 lateral eyes is always found, as is also a masticatory stomach. The female genital 

 apertures lie in the 6th thoracic segment, the male in the last. Development 

 sometimes with, sometimes without, metamorphosis. The larva hatched from the 



- is rarely a Nauplius. In many Thoracostraca the larvae pass through the Zocea 



stage. 



Legion I. Leptostraca. 



An extremely important group, which of all living Crustaceans stands the nearest 



