Neurosecretion in Chirocephalus Diaphanus Prevost the (Anostraca)

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NEUROSECRETION IN CHIROCEPHALUS DIAPHANUS PREVOST THE (ANOSTRACA). I. ANATOMY AND CYTOLOGY OF NEUROSECRETORY SYSTEM

P. S. LAKE Department of Zoology, University of Southampton, Southampton, Great Britain 1)

A considerable body of knowledge has been accumulated about the anatomy and cytology of the neurosecretory systems of malacostracan crustaceans, especially the Decapoda (Gabe, 1966). In contrast to the wealth of data available on neurosecretion in the Malacostraca, the study of neurosecretion in the entomostracan groups has been largely neglected. Neurosecretion in the Anostraca has been studied by Lochhead & Resner (1958), Menon (1962) and Hentschel (1963, 1965 ) . In Artemia salina (L.) and Eubran- chipus sp., Lochhead & Resner (1958) reported the existence of neurosecretory cells in the brain, especially the protocerebrum, and in the suboesophageal ganglion. Menon (1962) working with a species of StreptocePhalus reported finding two types of neurosecretory cells in the brain and circumoesophageal commissures. Neurosecretory structures, "the dorsal frontal organs", and a possible neurosecretory structure, "the ventral frontal organ" were located. A neurohaemal organ, the sinus gland, was found on the dorsal side of the optic peduncle. Hentschel (1963, 1965) identified four types of neurosecretory cells in the brain of Chiro- cephalus grubei Dybowski, and three types of secretory cells in the brain of Artemia .ralina. A "sinus" gland was identified in the optic peduncle of both species. In the gnaphocephalic, thoracic and abdominal ganglia of both species, he identified three types of neurosecretory cells. The structure of the neurosecretory system of the cladocerans, Dapbnia pulex (L.), Daphnia magna Straus and Simocephalus vetulus (0. F. M311er) has been studied by Sterba (1957). Angel (1966) has reexamined Sterba's (1957) obser- vations on Daphnia magna and revealed the existence of four distinct, neurosecretory cell groups in the ventral region of the brain. He also demonstrated that removal of the ventral neurosecretory regions of the brain caused a cessation of growth at maturity and an inhibition of ovarian development, but there were no clear changes in moulting behaviour. Parker (1966) located neurosecretory material in the central nervous system of Daphnia .rcboedleri Sars and found that the quantity present was affected by photoperiodicity.

1) Present address: Department of Zoology, the University of Tasmania, Hobart, Tasmania, Australia. 274

In the copepods, Calanus finmarchicus (Gunnerus) and Calanus belgolandicus Claus, Carlisle & Pitman (1961) found two groups of neurosecretory cells in the protocerebrum. Axons from these cells lead to the frontal organs. The secretory product was abundant in summer and scarce in winter. Weygoldt (1961) investigated the neurosecretory system of two ostracods, Cy- pridei.r littorali.r Brady and Cypri.r pubera (0. F. Miiller). Four distinct types of neurosecretory cells were found in the cerebral ganglion. In an extensive study of neurosecretion in six species of Cirripeds, Barnes & Gonor (1958a, b) identified two types of neurosecretory cells in the brain. The structure of the sensory papilla X-organ in cirriped larvae has been investigated by Kauri (1966), and Tighe- Ford (1967) has suggested that neurosecretory cells in the supraoesophageal and suboesophageal ganglia of Balanus balanoide.r may be involved in the control of breeding. The present study was initiated with the intention of investigating the possible neuro-endocrine control of the rapid growth and rapid moulting rate of Chiro- cephalus diaphanus Prévost. However, since the anatomy and cytology of the neurosecretory system was not known, this was investigated first. The definition of neurosecretory cells by light microscopical techniques alone, has been shown to be a rather hazardous procedure (Bern, 1966). According to Bern's (1962) definition of neurcsecretory cells, the majority of the neurosecretory cells observed in this study may be termed "possible" neurosecretory cells, while a small number, particularly in the protocerebrum, can be termed "probable" neurosecretory cells. In the present study, due to the confusions new apparent in the nomenclature of the "X-organs", especially in the Malacostraca, the suggestions of Gabe (1966) concerning the nomenclature of the "X-organs" have been followed. Thus the Medulla terminalis or Ganglionic X-organ is called the organ of Hanstr6m and the Sensory pore or Pars distalis X-organ is called the organ of Bellonci.

MATERIALSAND METHODS

Mature specimens of C. diaphanus ( 12-25 mm long) of both sexes were used. These animals were cultured in the laboratory, and fed on algae and suspensions of the extract "Complan" (Glaxo Laboratories Ltd.). Whole specimens were fixed in either aqueous Bouin or in Masson's Bouin (Foot, 1933) for 24 hours. To allow rapid penetration of the fixative, f'xation was preceded by piercing the cuticle of the dorsal surface m many places with a fine needle. The specimens were dehydrated in ethanol, cleared in methyl benzoate plus I % celloidin and then benzene (Pantin, 1946) and embedded in paraffin wax (M.P. 56° C). Serial sections, 6-8 p thick were cut and mounted on glass slides. The staining methods used to locate neurosecretory cells and structures were: modification (1) Bargmann's (1949) of Gomori's chrome haematoxylin-phlo- xine technique (CHP).