Reticulated Brittle Star
Overview
Ophionereis Reticulata, known as the Reticulated Brittle Star, is a brittle star in the family Ophionereididae. It is found in shallow parts of the western Atlantic, Caribbean Sea and Gulf of Mexico. Like other brittle stars, Ophionereis reticulata has a small flattened, pentagonal disc and five narrow, elongated arms. The disc can grow to a diameter of 15 mm (0.6 in) and the arms to a length of 120 mm (4.7 in). The aboral (upper) surface of the disc is covered with small plates and is pale grey with a network of fine reddish-brown lines, giving it its common name. The arms have a large number of short joints and are fringed on either side with short spines. They are white or pale grey and have a band of chocolate brown approximately every fourth joint. This colouration makes the brittle star inconspicuous when viewed against its typical background.
Skeletal System
Like all echinoderms, the Ophiuroidea possess a skeleton of calcium carbonate in the form of calcite. In ophiuroids, the calcite ossicles are fused to form armor plates which are known collectively as the test. The plates are covered by the epidermis, which consists of a smooth syncytium. In most species, the joints between the ossicles and superficial plates allow the arm to bend to the side, but not to bend upwards. However, in the basket stars, the arms are flexible in all directions. The ossicles are surrounded by a relatively thin ring of soft tissue, and then by four series of jointed plates, one each on the upper, lower, and lateral surfaces of the arm. The two lateral plates often have a number of elongated spines projecting outwards; these help to provide traction against the substrate while the animal is moving. The spines, in ophiuroids, compose a rigid border to the arm edges, whereas in euryalids they are transformed into downward-facing clubs or hooklets. Euryalids are similar to ophiurids, if larger, but their arms are forked and branched. Ophiuroid podia generally function as sensory organs. They are not usually used for feeding, as in Asteroidea. In the Paleozoic era, brittle stars had open ambicular grooves, but in modern forms, these are turned inward.