Pleurobrachia bachei

Pleurobrachia bachei is a member of the phylum Ctenophora and is commonly referred to as a sea gooseberry. These comb jellies are often mistaken for medusoid Cnidaria, but lack stinging cells. Traditionally, Ctenophora has been thought to represent an ancient metazoan phylum. Recent genetic data suggests that all extant Ctenophora taxa may have evolved from a relatively recent common ancestor and that this ancestral ctenophore was tentaculate and cydippid-like. Because of the virtual absence of ctenophores in the fossil record, their evolutionary history holds many more questions than answers. An individual sea gooseberry's body length can reach up to 20 mm (0.79 in) with each of the two tentacles stretching 150 mm (5.9 in). Their gelatinous globular bodies are composed of 99% water. They have eight rows of well-developed comb plates consisting of thousands of fused macrocilia controlled by an apical organ. Unlike most other ctenophores, Pleurobrachia lacks a conventional photoprotein and is therefore incapable of producing light. Their bodies are virtually transparent and the many cilia refract the light, producing rainbow-like colors that can give the false appearance of bioluminescence. The branched tentacles can be white, yellow, pink or orange. They have no nematocysts (stinging cells). Instead, the two long extensile branched tentacles are armed with colloblasts: specialized adhesive cells with which to ensnare their prey. Their mitochondrial genome consist of only 12 genes. The sea gooseberry is only alive for around 4–6 months. Pleurobrachia lack any sessile (attached) stages and are wholly planktonic in their life cycle. They are self-fertile hermaphrodites that spawn eggs and sperm freely into the sea, and develop thereafter without any parental protection with direct development. Pleurobrachia bachei is a selective carnivore and its feeding habits are analogous to other ambush 'sit and wait' predators, such as the orb-weaving spider. When searching for prey the Pleurobrachia swims with its oral pole forward to set its tentacles. To allow the two main tentacles and numerous lateral tentilla to relax and expand behind it they are often in a curved or helical pathway. Once the tentacles are set, the ctenophore drifts passively. Occasionally, it will retract its tentacles to varying degrees into the sheaths before swimming to another location where it then resets them. This behavior appears to be regulated by its hunger level and can be construed as an attempt to find an area with more prey abundance. When handling prey both tentacles contract and carry the prey to the mouth. This is achieved by several rapid rotations of the body which swipes the tentacle bearing the food across the oral region. The Pleurobrachia has its oral end opposite of where its tentacles originate.