Fig. 18. Spermatozoan types of the Decapoda. A: Unistellate A. TEM. x4,200. D: Unistellate spermatozoa of Penaeus setif- spermatozoan of Palaemonetes kadiakensis. SEM. X4,000. B: erus. SEM. X4,000. E: Transverse section of unistellate sper­ Ventral view of spike region of spermatozoan pictured in A; matozoan pictured in D. TEM. X4,500. F: Multistellate sper­ note that the three basic divisions (spike, cap, and cell body) of matozoa of Callinectes sapidus; note multiple arms (a) the spermatozoan can be easily recognized. SEM. X 10,000. C: extending from the cell body. SEM X4,100. s, spike; cp, cap; Transverse section through unistellate spermatozoan shown in cb, cell body; n, nucleus. 66 FELGENHAUER in many species (Koehler, 1979; Lynn and tration into the arms (Fig. 19E,F). Other spe­ Clark, 1983b; Felgenhauer and Abele, 1988). cies of reptant decapods may have a microtu- The fibrils may anastomose and extend down bular component within the radiating arms, as into the spike (Fig. 18C). An organized ac­ in the crayfish Procambarus leonensis (Fig. rosomal complex has been described for the 20A-C,E). The acrosomal reaction is essen­ dendrobranchiate shrimp Sicyonia ingentis by tially an eversion of the cell, turning the ac­ Kleve et al. (1980), but for most species, es­ rosome "inside out" with subsequent injection pecially caridean shrimp, no distinct ac- of the nucleus (Brown, 1966, Talbot and rosome has been demonstrated. Shigekawa Chanmanon, 1980; Goudeau, 1982, and oth­ and Clark (1986) provide an excellent discus­ ers; Fig. 19G). sion of what is known concerning the acroso­ The spermatozoan of astacoid reptant deca­ mal reaction. pods (e.g., crayfish) is different in its organi­ The spike may be elongate in some species zation from that described above. The promi­ (Fig. 18A-C) to quite short in others (e.g., nent acrosomal vesicle is horseshoe-shaped Crangon; see Arsenault et al., 1979; Boddeke and is not bilayered, but is crystalline in na­ et al., 1991). Two basic types of spike associ­ ture (Fig. 20A,D). The acrosomal tubule is ation with the egg surface have been de­ much reduced and distinct microtubules are scribed: either a spike-first contact with the not easily discerned (Fig. 20D,F). The radiat­ egg (Kleve et al., 1980; Barros et al., 1986) ing arms are greater in number (up to 20 or or a cap-first egg interaction (Lynn and Clark, more in some species) and are supported by 1983a,b). microtubular arrays (Fig. 20A,B,E). The cell Multistellate Spermatozoa. This spermato- membrane of this gamete is much thicker than zoan type is a multistellate cell with radiating that of most decapod spermatozoa and has arms (= spikes of some authors) extending been termed the cell capsule (Fig. 20A,E). from the cell body (Fig. 18F). These append­ Mechanics of the acrosomal "reaction" and ages are not homologous to the unistellate egg interactions have not been described. spike (Talbot and Summers, 1978; Hinsch, 1986). The most striking feature of this ga­ Female System mete is its highly structured acrosome (Fig. The ovary is located in the dorsal portion of 19A,B). The nucleus surrounds the large the cephalothorax in the same relative posi­ electron-dense acrosomal complex that is tion as the male testis (Fig. 3), e.g., lying composed of several distinct ultrastructural dorsal to the hepatopancreas (Fig. 12A). As in features. The acrosomal vesicle is bilayered the testis, the ovary is paired and its size de­ in most brachyuran crabs, consisting of an pends on the age and reproductive condition inner and outer region (Fig. 19A,B,D). The of the individual. Unlike the testis, the ovary acrosomal vesicle may be flanked by a prom­ commonly extends into the abdominal inent lamellar region (Fig. 19A,B). The ac­ somites, and in some groups, such as many of rosomal tubule is presumably supported by a the anomuran crabs, the ovary is restricted to battery of microfilaments or microtubules this position (Kaestner, 1970; McLaughlin, (Fig. 19A-D), depending on the species. The 1983). Details concerning the maturation pro­ anterior portion of the acrosomal tubule is cess and ultrastructural features of the ovary covered by a distinct electron-dense acroso­ and follicles can be found in Johnson (1980) mal cap (Fig. 19A,B). At the base of the and Talbot (1981a,b). In macrurous forms, acrosomal tubule is a thickened ring that evi­ the ova pass from the ovary down the oviducts dently aids in the support of the tubule (Fig. and exit via the gonopore on the third walking 19A). The nucleus may or may not extend legs (pereiopods). In brachyurous forms, the into the usually stellate arms. The brachyuran short oviducts lead to a saclike spermatheca crab Iliacantha sp. exemplifies nuclear pene­ within the musculature of the second walking DECAPOD INTERNAL ANATOMY 67 ot B II 1' .-•.. < - f,.<-^-\ . - - - • ... ^•^iw'^v^^ '• ••••• Q.^iybV><-. Fig. 19. Ultrastructural details of decapod multistellate sper­ cantha sp. x9,000. F: Cross-section through the arms of the matozoa. A-F by TEM. A: Multistellate spermatozoan of Calli- spermatozoan pictured in E; note chromatin extending into the nectes sapidus. X3,000. B: Close-up of acrosomal region of arms from the nucleus. X35,000. G: Artificially induced ac­ Callinectes sapidus. X 10,000. C: Oblique section through ac­ rosomal reaction of the multistellate spermatozoan of Eurydium rosomal tubule from the spermatozoan of Parthenope sp.; note sp. SEM. X8,500. a, arm; ac, acrosomal cap; at, acrosomal numerous microtubules (arrow). X22,000. D: Cross section tubule; av, acrosomal vesicle; cb, cell body; ir, inner region; Ir, through the acrosomal tubule of I liacantha sp. Note the microtu­ lamellar region; mt, microtubules; n, nucleus; or, outer region; bules within the tubule and the bilayered condition of the acroso­ tr, thickened ring. mal vesicle, x 80,000. E: Multistellate spermatozoan of Ilia- 68 FELGENHAUER f .•••• •' <L' f< A B '.u <'A r im™ ^^vi^^ji^ •-.. ^ •• '; 'i* "^^^%.. •• W • t ' X* ^ •••• JF • = -. mmr/y^ at *fXff* \ ''jiiiML'P^ Fig. 20. Ultrastmctural features of crayfish spermatozoa. X 36,000. E: Close-up of acrosomal vesicle; note thick cell coat TEM. A: Ultrastmctural aspects of the spermatozoan of Pro- and microtubules supporting the arms. X36,000. F: High mag­ cambarus leonensis. x3,000. B: Oblique section through ante­ nification of acrosome and presumed acrosomal tubule. rior region showing arms supported by microtubules. X 22,000. x50,000. a, arm; av, acrosomal vesicle; at, acrosomal tubule; C: Close-up of acrosomal vesicle and microtubules within the cc, cell coat; mt, microtubules; n, nucleus. arms. x40,000. D: Ultrastmctural details of acrosome. legs (pereiopods). Unlike most macrurous (Warner, 1977). The method by which deca­ decapods, internal fertilization is practiced by pods incubate their eggs varies depending this large group of crabs and spermatozoa are upon the group. Dendrobranchiate decapods stored within the spermatheca following cop­ release eggs into the water (although Lucifer ulation. The eggs are fertilized as they pass carries them briefly on the pereiopods; onto the abdominal pleopods for brooding Burkenroad, 1981), while all other decapods DECAPOD INTERNAL ANATOMY 69 for which data are available carry the eggs on in the posterior region of the cephalothorax. the pleopodal setae (Felgenhauer and Abele, The heart receives blood through a series of 1983). ostia (Figs. 3, 23). It is surrounded by a peri­ cardial sac that is penetrated by passageways THE EXCRETORY-OSMOREGULATORY where venous blood returns to the pericardial SYSTEMS chamber. The number of ostia of the heart The antennal, urinary or green glands are may vary depending on the species, but three paired excretory organs located at the base of pairs is the most commonly reported number the second antennae. The excretory pore exits (McLaughlin, 1983; Schram, 1986). The lo­ on the coxa of the antenna (Fig. 21 A, arrow) cation of the ostia varies also from paired and its location is a constant feature among arrangements in the dorsal, lateral, and ven­ decapods. Antennal glands are generally tral positions around the heart (Figs. 12A, composed of four components: the coelomo- 23). sac (= end sac), labyrinth, proximal and dis­ Figure 23 illustrates the general layout of tal tubules (= nephridial canal), and bladder the major arteries comprising the circulatory (Fig. 22). The description below is of the pattern of most decapods (Burnett, 1984). green gland of the crayfish Procambarus le- Several major arteries exit the anterior aorta onensis. (Fig. 23) servicing the rest of the body. The The mesodermally derived coelomosac is anterior aorta (= dorsal artery) may be composed of podocytes that perform an ul­ equipped with an enlargement termed the cor trafiltration function similar to that of the ver­ frontale, first described by Baumann (1917). tebrate glomerular nephron (Kummel, 1964; The basic anatomy of this modification is re­ Schmidt-Nielsen et al., 1968; Tyson, 1968; markably similar among the decapods studied Peterson and Loizzi, 1974; Johnson, 1980). by Steinacker (1978), who considered the cor The labyrinth is composed of an extensive frontale to function as an "auxiliary heart" network of coiled cuboidal cells in the inac­ (= accessory heart of Maynard, 1960). tive state and columnar cells in the active The hemocytes of decapod crustaceans are secretory condition. The labyrinth cells typi­ circulating cells (Fig. 14F,G) of the he- cally have a centrally located nucleus (Fig. molymph that perform a diversity of physio­ 2IE) with numerous mitochondria packed logical and pathological functions (see Ravin- within the extensive infoldings of the basal dranath, 1980; Bauchau, 1981; Hose et al., lamina (Fig. 21F,G) characteristic of trans­ 1987), from wound repair (Fontaine and port tissue (e.g., gills, branchiostegite; Man­ Lightner, 1973), to clotting of the he- tel and Farmer, 1983).