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The Arachnid Collaboration has been setup in the UK to develop the Cherwell sensor. This is a CMOS Monolithic Active Pixel Sensor for the detection of charged particles. The design of the Cherwell sensor came from the expertise gained from two previous designs: FORTIS and TPAC. Cherwell is 4 transistor CMOS sensor in 180 nm technology. It uses PMOS transistors requiring a deep P-well implant, a process known as INMAPS. The epitaxial layer of the sensor is 12 um thick. Cherwell consists of two arrays optimized for vertexing applications, and two arrays optimized for calorimetry applications. The two vertexing arrangements have a matrix of 96x48 pixels with a pitch of 25 um. The “reference array” is readout on a rolling shutter base with a fine resolution 12-bit, single-slope column parallel ADC. The “strixel array” has the readout and ADC circuits embedded in the space between the pixel diodes. The two sections for calorimetry are named DCAL25 and DCAL50. The former has a matrix of 96x48 pixels with 25 um pitch. The latter has a matrix of 48x24 pixels with 50 um pitch. The pixel readout for both the structures features components to provide snapshot and in-pixel correlated double sampling capabilities. At the periphery of the DCAL25, additional circuitry is added to provide charge summing of 2x2 pixels during readout. Cherwell has been characterized with different sources of radiation, and studied in test-beam at the CERN SPS. Experimental results will be presented at the conference. We have also designed a new version of the sensor (Cherwell2) as a prototype for a silicon tracker to be used in the upgrade of ALICE. The status of this sensor will also be described.