Practice question

Sea spiders or pycnogonids constitute distinct marine class Pycnogonida within Chelicerata, possessing diminutive trunk where abdomen severely reduced to tiny tubercle and legs disproportionately long containing extensions of midgut diverticula and gonads, reflecting unique body organization. Anterior proboscis with terminal mouth, chelifores and palps for prey handling, ovigers for grooming and male egg-carrying. Four pairs of walking legs plus sometimes additional legs, no book gills or lungs with gas exchange via cutaneous diffusion. Despite spider-like habitus they form separate class allied to euchelicerates, justifying Pycnogonida distinct from Arachnida, Merostomata and Myriapoda.