Leach, 1814
Caprellidea are highly modified amphipods with an elongated and slender body and a reduced number of appendages. They tend to be slow moving and are found clinged to other organisms, such as filamentous algae, bryozoans, hydroids, and sponges, but also on buoys and pontoons, and may be found on the shore, in the shallow sublittoral and even at depths approaching 5000 m. Caprellids occur in the pelagic by occasion, but merely due to loss of contact with the substrate. Some caprellids are parasitic on the skin of whales.
The structure of a caprellid is less complex than that of species of the Suborder Gammaridae. The animal can be divided into a head, a thorax or pereion and an abdomen. The head and first pereion segment may be completely or partially fused and the length of segment 1 may vary appreciably. Antenna 1 is longer than antenna 2. Antenna 1 has a three-jointed peduncle and a multiarticulate flagellum. Antenna 2 has a peduncle of three or four joints and a shorter flagellum, normally of two articles. Antenna 2 may bear parallel rows of long, so-called swimming setae on the central border of the peduncle and flagellum; these setae are of taxonomic importance. The presence or absence of a mandibular palp is also important, and when present this slim palp normally projects upwards between the peduncles of antennae 2.
The pereion may be smooth or may possess dorsal and/or lateral tubercles or sharp spines. A pair of round or club-shaped gills is normally found on the ventro-lateral borders of segments 3 and 4, but may be present on segment 2 in some species.
The gnathopods are normally larger than the other pereiopods and modified into grasping claws, with a moveable finger and an opposing cutting edge. The pereiopods may be completely absent from segments 3 and 4, or may be reduced to minute appendages. Pereiopods 5, 6 and 7 are normally of approximately equal length and are used for holding on to the substratum while the animal feeds with the gnathopods. The propodus of the posterior pereiopods may bear one or two spines on its inner surface, these being termed grasping spines.
The small abdomen may be furnished with lobes and/or articulated appendages, or may be without either, differences between the sexes being usual. Although the abdomen is of taxonomic importance, its minute size makes it a difficult feature to observe.
Larval development is epimorphic, there is no postlarva. Female caprellids develop paired lamellae (oostegites) on the ventral borders of the pereion segments 3 and 4, and these lamellae enlarge to form a brood-pouch (marsupium) for the developing eggs. The presence or absence of setae on the borders of the lamellae varies between the species and is of some taxonomic value. Development of the embryos is completed within the brood-pouch and miniature caprellids eventually emerge.
Identification
The Suborder Caprellidae comprises three families. A separate text key to the families of Caprellidea can be found in Caprellidea: key to families. This key is also part of the pictorial key at Page 218: Caprellidea. Caprellid species, however, are not keyed out here, because they are essentially not planktonic and are only occasionally found with plankton sampling.
¥ Family Caprellidae (with free-living species)
¥ Family Phtisicidae (with free-living species)
¥ Family Cyamidae (ectoparasitic species on the skin of whales)
[Description after Isaac and Moyse, 1990]