Chapter 10 Pelagic Tunicata Department of Oceanography References ? Bone Q, 1998. The biology of pelagic tunicates. 340p Chordata（脊索动物门） ? Urochordata（尾索动物亚门） Appendiculariae（有尾纲）＝Copelata Thaliacea（海樽纲） Ascidiacea（海鞘纲） ? Cephalochordata（头索动物亚门） ? Vertebrata（脊椎动物亚门） General characteristics Chordata Urochorda ? Expect for Larvacea, the notochord only exits in the tail of larvae. The adults process no notochord. (Urochora) ? Adult is enclosed in a sac-like tunica composed of tunicin secreted by the integument. (Tunicata) ? Without sensory organs and tubus medullaris in the adult, and with an open circulatory system. ? Usually hermaphrodites, with sexual or budding reproduction. 10.1 Appendicularia = Copelata 10.1.1 General Morphology ? do not undergo metamorphosis, the adult with a tail supported by a notochord ? gill sac simply ? endostyle short, groove-like ?♀♂hermaphrodite ? “house” 10.1.2 External features ? 1 Trunk ? 2 Tail 10.1.3 Internal features 1 Digestive system mouth→pharynx → esophagus →stomach → intestine →anus endostyle, buccal gland 2 Circulatory system 3 Reproductive system heramphrodite mouth esophagus stomach intestine anus buccal gland endostyle ovary or test 3 Nervous system ? cerebral ganglion ? caudal ganglion 5 Notochord and Muscle Bands urochord notochord cell subchord cell 10.1.4 Classification One order, Urochorda with two families, the main characteristics for classification are： ?（1）the ratio of body to tail in size and their shape ?（2）the shape of the endostyle ?（3）the position of the gill opening ?（4）the shape of the gonads Family Oikopleuridae：O. longicauda Family Fritillaridae: F. pellucida Common species ? Family Oikopleuridae Body oval Endostyle short and straight Tail several times longer than trunk Oikopleura longicauda O. dioica ? Family Fritillaridae Body long square Endostyle bent Tail short and wide with a deep groove Fritillaria pellucida 10.2 Thaliacea 10.2.1 General Morphology transparent barrel-like body covered with a solidified and thin tunica 10.2.2 External features ?circumoral lobe ?circumatrial lobe ?cadophore ?tunica ?branchial sac 10.2.3 Internal features 1 Muscle, eight hoop-like muscle bands 2 Digestive system 3 Circulatory system, heart 4 Nervous system, cerebral ganglion with two pairs of nerves Dolioloides Dolioletta DoliolumDoliolina 5 Reproductive system （1）blastozooids：♀♂protogynous hermaphrodite （2）oozooids differed from blastozooids in: ? muscle bands：oozooids 9，blastozooids 8； ? circumoral lobes：10, 12； ? circumatrial lobes: 12, 10； ? oozooids have a stolon, a cadophore and an otocyst brain branchial septumotocyst endostyle stolon digestive tract dorsal process 10.2.4 Classification 磷海樽目(火体虫 目）Pyrosomida 全肌目 Cyclornyaria 半肌目 Desmomyaria 体形群体，呈圆筒形个体，酒筒形个体，梭形 体开口数1个，在底部2个（入、出水口）2个 发光器有无无 鳃腔与排泄 管情况 分开分开不分开（联成一个 腔 环肌少，环围前后体端多，完全包围体部少数环状，多数在 腹面中断 发育直接，无幼虫期间接，有世代交替直接，无幼虫期， 有世代交替 代表种火体虫科 Pyrosomidae 火体虫属Pyrosoma 海樽科Doliolidae 海樽属Doliolum 拟海樽Dolioletta 纽鳃樽科Salpidae 纽鳃樽属Salpa Order Pyrosomatida ? Family Pyrosomatidae Pyrosoma： Order Cyclornyaria Family Doliolidae Thin test surrounded by 8 or 9 circular muscle bands. Branchial cavity spacious, larger than half of the body. The digestive tract is situated ventrally in the peribranchial cavity. ? Doliolum ? Dolioletta Dolioletta Doliolum Order Desmomyaria Family Salpidae Branchial and cloacal cavities form a continuous space in the anterior part of the body. Alimentary canal lying ventrally. Life cycle complicated with alternation of generations including sexual and asexual individuals. ? Salpa ? Thalia ? Cyclosalpa Salpa纽鳃樽 S. fusiformis Alimentary canal forms a compact “nucleus”. Thalia萨利纽鳃樽 Alimentary canal curved, with well-developed posterior processes. Test is thick and firm. Cyclosalpa Elongated alimentary canal without compact “nucleus”. 10.3 Biology and Significance 10.3.1 Distribution 1 neritic species：Oikopleuridae 2 oceanic species：Doliolum, Salpa, Pyrosoma, etc. 10.3.2 Feeding 10.3.3 Reproduction and Life history ? 1 Larvacea ?♀♂hermaphrodites (a few protogynous hermaphrodites) ?♂testis matures earlier than ovary ? external fertilization ? direct development ? 2 Thaliacea ?♀♂hermaphrodites ?♀ovray matures earlire than testis ? internal fertilization Life cycle of Oikopleura dioica Fertilization Cleavage of the egg Hatching Trunk organogenesis Tail shift and formation of the first house Growth Spawning and death Life history of Doliolum Oozooid Free larva Fertilization Budding from stolon Migration of buds Fixation and growth of buds and dorsal process Phorozooid Gonozooid Gastrozooid Degeneration of internal organs Enlargement of muscle bands m e d i a l b u d s l a t e r a l b u d s Development of free egg Disappearing of tail and growth of young oozooid Old nurse blastozooid