Compare and contrast sea squirts and lancelets.

Explanation

Sea squirts : These are included in class -Ascadiaceae of subphylum - Urochordata. These are sessile. These are solitary or colonical. Body is enclosed in a permanent test and un-segmented. All these are marine and occur from the surface water to greater depnts. Coelom in absent, pharynx is large and is perforated by numerous gill-slits. Branchial aperture in anterior and atrial aperture is dorsal. Digestive tract is .complete.. Circulations system is of open type, heart is tubular and ventral heart. These are bisexual. Development generally includes a free swimming tadpoe larva. Notochordcontinued to the tail hence the name urochordata. Ex : Ascidia.

Lancelets : Cephalochordates are also called as Lancelets. These are marine animals and are small fish without paired fins. These are typical chordrtes because they possess the notochord, tubular nerve cord and pharyngeal slits through this life. The coelom is enterocoelic respiration mostly across the external body surface. Circulatory system is of closed type, heart, blood corpuscles and respiratory pigments are absent. Excretion by protonephridia fertilization is external and development is indirect. Ex : Branchiostoma (amphioxus or Lancelet)