Hydrobiologia 468: 185–192, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.
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Analysis of the morphology of Spinalona anophtalma Ciros-P´erez & El´ıas-Guti´errez, 1997 (Aloninae, Anomopoda, Cladocera) Alexey A. Kotov1,2 & Manuel El´ıas-Guti´errez1 1 El
Colegio de la Frontera Sur, km 2 Carretera Chetumal-Bacalar, Zona Industrial #2, Chetumal, Quintana Roo 77000, Mexico E-mails:
[email protected] [email protected] 2 A. N. Severtsov Institute of Ecology and Evolution, Leninsky Prospect 33, Moscow 117071, Russia E-mail:
[email protected] Received 23 July 2001; in revised form 15 October 2001; accepted 19 November 2001
Key words: Spinalona anophtalma, Chydoridae, Anomopoda, Cladocera, limb, redescription, systematics, Mexico
Abstract Morphology and variability of Spinalona anophtalma Elías-Gutiérrez & Ciros-Pérez, 1997 were re-examined using material from the original sample from type locality. As a result, some additions were given to the first description, and thoracic limbs were completely redescribed. We revealed and discussed some rare or unique traits of Spinalona, like a peculiar setulation on the labrum, distribution of aesthetascs in the antennular tip, position of the lateral seta on basal segment of endopodite of the second antenna, and the armature of swimming setae, and new structures on thoracic limbs. Although we confirmed previously reported opinion, that Spinalona is the most specific animal among Alonini, it clearly belongs to this taxon. The genus diagnosis was re-worked according to recent standards. Abbreviations: acs – accessory seta of limb I; ben – basal endite of limb III; dag – distal armature of gnathobase; den – distal endite of limb III; epp – epipodite; ext – exopodite; fpl – filter plate of limbs IIV; IDL – inner distal lobe of limb I; ODL – outer distal lobe of limb I; mxp – maxillar process on limb I; pep – pre-epipodite; sos – soft setae Introduction Recently Kotov (2000c) analysed the morphology of Aloninae Dybowski & Grochowski, 1894 emend. Frey, 1967 (Chydoridae, Anomopoda, Branchiopoda) and subdivided the subfamily into two tribes – Alonini s. str. and Indialonini Kotov, 2000. Spinalona anophtalma Ciros-Pérez & Elías-Gutiérrez, 1997 – a sole representative of the genus Spinalona – was found to be the most specific animal among Alonini. A rapid, recent progress in the systematics of the Aloninae (Chiambeng & Dumont, 1999; Dumont & SilvaBriano, 2000; Kotov, 2000a, c; Sinev, 1998, 1999; Sinev & Kotov, 2000) leads to the situation where we were able to find small defects in quite detailed previous descriptions, such as the first description of the Spinalona. In addition, different authors frequently explain in a different manner the nature of some struc-
tures, in the first place, on the thoracic limbs. As a result, Kotov (2000c, Table 1) could not find information on some important features in the description by Ciros-Pérez & Elías-Gutiérrez (1997), like the presence of accessory seta on the first limb or number of setae in the IDL of the males. The aim of this article is therefore to elucidate some fine details which we not described in Spinalona, a unique and strange genus, and to elucidate the position of this animal among Aloninae.
Materials and methods Animals were picked from the original sample, from which the types were previously selected, placed on slides (in a drop of a glycerol-formaldehyde mixture)
186 Table 1. Complements of information on limb morphology in Spinalona anophtalma as presented by Ciros-P´erez & El´ıas-Guti´errez (1997) Limb
Feature
Ciros-P´erez & El´ıas-Guti´errez, 1997
Our data
I
Accessory seta Sensillae on endites 1–3 Maxillar process Seta on exopodite Spines on basal endite Sensillae on basal and distal endites Soft setae Exopodite setae ‘Filter plate’
Not found Not found Not described Present Not described Not found 3 3 0
Present Present Present Absent, here only a bunch of setules Described Described 5 3–4 1
II III IV V
and studied under an optical microscope in toto. Then, 10 adults were dissected for analysis of appendages. In the present article, we used a system of enumeration of setae on the limbs proposed by Kotov (2000a, b, c): all marginal setae of (1) exopodites, (2) inner limb portions (‘endopodites’), and (3) distal armature of gnathobases numbered from distalmost to basalmost elements without attempts to determine homologies between different limbs. Setae of the inner portion of limb I are marked by letters, a–h. Results Spinalona anophtalma Ciros-Pérez & Elías-Gutiérrez, 1997 Ciros-Pérez & Elías-Gutiérrez, 1997: 19–28, Figures 1–41. Type material: see Ciros-Pérez & Elías-Gutiérrez (1997). Type locality: Los Baños temporary lagoon near Atlacomulco town, the State of Mexico (19◦ 39 59" N; 99◦ 51 16" W, at 2507 m above sea level). Material examined: 16 ephippial and 4 parthenogenetic females from the type locality. Amended genus diagnosis Female. Body somewhat elongated, with regularly curved dorsal margin and distinct postero-dorsal angle, moderately compressed laterally, without dorsal keel on head or rest of body (Fig. 1). Head relatively large, head shield in plane view broad and relatively short, with posterior margin rounded, somewhat elongated, rostrum blunt. Three major head pores,
each major pore a cavity with a small pore on the bottom. Lateral pores located in a slight depression, about twice the inter-pore distance (Fig. 3). Labral keel welldeveloped, with slightly expressed or not expressed apex, and with keel margin thickened to form a special rim (Fig. 4). Body of labrum with a pair lateral projections in the middle (Fig. 2), distally on it (near labral plate) a row (more basally) and a group (more distally) of setules on each side (Fig. 5). Compound eye and ocellus absent. Valves with series of longitudinal, weak furrows (Fig. 1); ventral margin of valve depressed in the middle. Setules between marginal setae completely absent. Postabdomen (Fig. 7) relatively short and high, ventral margin straight, with three rows of long hairlike setae. Preanal margin straight or slightly convex, postanal margin short, convex, tapering from projected postanal angle toward claw, with a deep depression in distal portion, forming a peduncle for the claw. On preanal margin five-six clusters of small marginal denticles, plus 3–4 groups of setules in anal region. Lateral surface with 10–11 series of long, fine setules, plus other rows of smaller setules in proximal half of anal region. Postabdominal seta short, although exceeds preanal part of postabdomen, with distal segment slightly shorter than basal one and setulated with long, dense setules. Postabdominal claw large (Fig. 8), about half the postabdominal length, with a long (about half length of claw), stout basal spine; a bunch of about 7–8 long needle-like setules near basal spine, overlying it. A row of small denticles on ventral side of claw, distally. Bases of antennules compressed each other, although not in touch (Fig. 2). Antennules elongated in
187
Figures 1–14. Spinalona anophtalma, females from Los Baños temporary lagoon near Atlacomulco town, State of Mexico, Mexico, collected in 28.01.1994 by Ciros-P´erez & El´ıas-Guti´errez. Figure 1. Ephippial female in lateral view; Figure 2. Its head in ventral view; Figure 3. Head pores; Figure 4. Labral keel in anterior view; Figure 5. Labrum in lateral view; Figure 6. Postero-ventral portion of valve in inner view; Figures 7–8. Postabdomen and postabdominal claw in lateral view; Figures 9–10. Antennule in anterion and distal view; Figures 11–12. Second antenna and its exopod; Figures 13–14. lateral swimming seta in lateral view and crossing section. All scale bars denote 100 µm.
188
Figures 15–27. First maxilla and thoracic limbs of Spinalona anophtalma from Los Baños lagoon, Mexico. Figure 15. First maxilla; Figures 16–19. Anterior view of limb I, its IDL, setae 1 and d; Figures 20–21. Posterior view of limb II and distal armature of its gnathobase; Figures 22–23, Posterior view of limb III and its inner portion; Figures 24–25, Limb IV and its inner portion; Figures 26–27, Limb V. All scale bars denote 100 µm.
189 lateral plane, reaching tip of rostrum, and greatly compressed in transversal body plane, bases of aesthetascs not forming a circle, but distributing along elongated distal antennular surface (Figs 9 and 10). Aesthetascs projected behind tip of rostrum, two among nine aesthetascs larger than the rest. Four transversal rows of setules at lateral margin of antennule, plus row of setules in lateral portion of distal antennular surface. One–two rows of analogous setules on anterior surface too. Antennal formula: setae 0-0-3/1-1-3; spines 10-1/0-0-1. Each of two proximal exopod segments of antenna with a series of 8–12 long needle-like strong setae inserted distally. Both apical and lateral swimming setae with densely setulated basal segments, and tri-laterally armed distal segments. Basal lateral swimming seta arising not from the distal end of the endopodite segment, but from its medium portion. All epipodites of the limbs are globular, without any projections. Limb I with external accessory seta (Fig. 16, as), ODL with one very long seta, IDL with three setae of different size, no hook-like among them (Fig. 17). Two setae on both endites I and II. Anterior seta on e3 relatively large, with two sensillae at base, small elements on endites 2 and 1 also (Fig. 16). Maxillar process I with one short seta (Fig. 15). Exopodite II without setae (Fig. 20). Differences in setulation of all scrappers of limb II is minimal. Filter plate II with 5 setae, nearest to endopodite shorter than others. Exopodites III and IV small. Exopodite III with 4 setae. 5 soft setae on limb III, stout spines are expressed near stiff setae (Figs 22 and 23). Filter plate III with 3 long and 2 short setae (Fig. 22). Six soft setae on exopod of limb IV, filter plate IV with only 2 setae. Exopodite V with 3 (sometimes 4) setae. ‘Filter plate’ V with a single seta only. Limb VI absent. Ephippial female. Only part of valves modified and to form ephippium, demarcation line obscure. Dorsal portion of valve wall strongly chitinized. No outward expansion of valves in the region of ephippium, no dorsal keel. A single egg within ephippium. Valve surface of ephippial female over the egg locule finely punctuate. Pigmentation over the dorsal and ephippial region brown-yellowish (Fig. 1). Mature male. Relatively lower than parthenogenetic female. Postabdomen with slightly projected preanal and postanal angles, and gonopores open near claw bases. Marginal (postanal) denticles smaller, postabdominal claws somewhat shorter, but basal spines relatively longer, slightly curved. Antennule with twelve aesthetascs and an accessory, subterminal finger-like male seta. Limb I with all IDL setae smal-
ler than in female; long copulatory hook, attenuated distally, with two transverse ridges at the tip; large male seta, longer than IDL setae, its distal part somewhat broad and flattened, with almost parallel edges, tapering at distal fourth. Some fine details of morphology, our additions to the first description Habitus of ephippial female: Dorsal portion of valve wall chitinized (Fig. 1). Major head pores organized quite specifically (Fig. 3): each pore is a cavity with small pore on the bottom. This is visible on SEM photograph of Ciros-Pérez & Elías-Gutiérrez (1997) on Fig. 12. Labrum with well-expressed labral keel (Figures 2, 4 and 5), but its apex is not distinct in all females (Fig. 5). Keel margin thickened as special rim (Fig. 4). Body of labrum very thick in ventral view, with a pair lateral projections in the middle (Fig. 2). Distally (near labral plate) a row (more basally) and a group (more distally) of setules on each side. Valves without setules between marginal setae (Fig. 6). A row of numerous setules at some distance from posterior valve margin. These setulae of different length, which was not marked in the first description. Postabdominal seta short, although exceeds preanal part of postabdomen. Distal segment somewhat shorter than basal one and setulated with long, dense setules (Fig. 7). Postabdominal claw with setules along dorsal and ventral side reaching the same distance from the claw base (Fig. 8). Antennule elongated in lateral plane (Fig. 9), reaching tip of rostrum, and greatly compressed in transversal body plane, bases of aesthetascs not forming a circle, but distributing along elongated distal antennular surface (Fig. 10). Four transversal rows of setules at lateral margin, plus row of setules in lateral portion of distal antennular surface. One-two rows of analogous setules on anterior surface too. Bases of antennules compressed each other, although not in touch (Fig. 2). Second antenna with apical spines and spine from basal exopod segment normally longer than segments, from which those arising (Fig. 12), but in smaller part of animals all these are shorter than segments (Fig. 11). Basal lateral swimming seta arising not from the distal end of the endopodite segment, but from its medium portion. Both apical and lateral swimming setae with numerous setules on distal segments, and tri-laterally armed distal segments (Figs 13 and 14).
190 Maxilla I as a hillock with two longer and one shorter setulated setae (Fig. 15). Full redescription of thoracic limbs Limb I (Figs 16–19): epipodite small, globular. A delicate, slender accessory setae (Fig. 16: as) densely armed with fine setules on external limb face. ODL with a sole, long, bisegmented seta, its distal segment armed with short, relatively robust setules. IDL of similar size with ODL, with three robust, bisegmented setae of different size. Two of them long, their distal segments armed with fine setules. Third seta short, seems to be naked. Endite III with three thick bisegmented setae (1, a– c), seta c particularly long, all armed with short hairs. Seta 1 stout, with short setules distally, two sensillae of different size near its base (Fig. 18). Endite II with two long setae of unequal size (d–e), both setulated at their distal and basal part, but setules in the middle part are particularly robust (Fig. 19). A small element at border with endite III (Fig. 16), this is a sensillum or remainder of seta 2 of other Aloninae (Kotov, 2000a, c), here and below all these elements, probably, receptors, are marked by thick arrows. Endite I with two relatively long, thin, bisegmented setae (f–g), a small element also at border with endite II, this is a sensillum or remainder of seta 3 of other Aloninae (Kotov, 2000a, c) or other chydorid-like Anomopoda (Kotov, 2000b). Two ejector hooks of equal size anteriorly on outer portion of limb corm. Also here a series of bunches of short and long setules. Low, naked maxillar process with single, very short, unilaterally setulated seta on inner side of limb base. Limb II (Figs 20 and 21): exopodite reduced to a small lobe with rows of setules, without setae. Eight scrapers (Fig. 20: 1–8) with length regularly decreasing in inner direction, armed similarly by fine setules, only on scraper 5 these setules somewhat thicker. Minute hillocks near scrapers 1 and 5; relatively small lobes near scrapers 2–4. Gnathobase with prominent basal-ventral angle, supplied with bunch of long setules. Distal armature of gnathobase with four elements, one a bottle-shaped sensillum (Fig. 21: 1), located far from the others. Filter plate with five setae, distalmost one shorter than the others. Limb III (Figs 22 and 23): large ovoid epipodite. Exopodite flat, relatively small. Distally on it, four setae of different size (Fig. 22: 1–4), no lateral setae present. Distal endite armed with three bisegmented setae with length decreasing basad (Fig. 23: 1–3). Setae 1 & 2 stout, with short setules distally. Seta
3 with somewhat inflated basal part, distal part with long hairs. Relatively large sensillae near seta 2 and 3. Basal endite of similar size with distal endite. The anteriormost position on limb occupied by a row of 3 robust spines and one hillock, these elements regularly distributed. A row of marginal elements consists of one distalmost sensilla bottle-shaped and four setae. Each of this setae (4–7 in Fig. 23) with inflated base, and thin basal part, setulated with long hairs. Posteriorly, five soft setae of equal size, armed with rare, delicate hairs (Fig. 22). Gnathobase unclearly demarcated from basal endite, distal armature with 4 elements (Fig. 23: 1–4), one of them (1) a thick, bottle-shaped sensillum of middle size, located far from the others. Five setae in filter plate, 2 distal members short, with inflated basal part, similar to soft setae. Limb IV (Figs 24 and 25): pre-epipodite relatively large, setulated; epipodite small, ovoid. Exopodite not too large, with 4 setae distally (Fig. 24: 1–4) and 2 setae laterally (5–6). Marginally on inner limb face, a row of 4 setae (Fig. 25: 1–4). Seta 1 longest, stout, seems to be naked. Each of setae 2–4 with strongly inflated basal part, and elongated distal part, armed with fine setules. Setae 3 and 4 slightly smaller than 2. Small elements (sensillae?) near base of setae 2 and 3. Posteriorly, two groups of soft setae: 3 more distal and shorter, 2 more basal and longer. Distal armature of gnathobase with 4 elements (Fig. 25: 1–4): element 1 a truncate cone sensilla of middle size, seta 2 large, thick, bisegemented, unilaterally setulated in basal segment and bilaterally asymetrical setulated in distal segment. Element 3 similar to a hook, and 4 like a short spine. Filter plate with 2 setae of similar size. Limb V (Figs 26 and 27): Pre-epipodite small, setulated; epipodite biloobed. Exopodite small, with only 3 setae (Fig. 26: 1–3). In a single female there were 4 setae on exopodite V in both limbs (Fig. 27). Inner limb portion with protruding flap-like distal projection, fringed by long setules. Two submarginal setae on inner face of limb, distal member (1) protruding sligthly behind distal endopodite projection or not protruding at all. Gnathobase slightly expressed top, usually single. Bifurcated in the female with 4 setae in the exopodite. A single seta in ‘filter plate’.
Discussion We agree with Ciros-Pérez & Elías-Gutiérrez (1997) about the absence of the eye and the ocellus. Additionally, shape and armature of the postabdomen are
191 generic-specific traits of Spinalona. Here a series of new features were described, but some small defects were found in the first description of the thoracic limbs (Table 1). Some of these features, as well as some others, not discussed by Ciros-Pérez & Elías-Gutiérrez (1997), are rare or unique traits of Spinalona, andamong the Alonini also (the tribe Indialonini is not considered here). Rows of setules on distal portion of the labrum body were revealed in Spinalona. These were not found previously in other Aloninae (Frey, 1991; Kotov, 2000a, c), but a similar pattern of setulation was described for many species of the Ilyocryptidae (Kotov, 1999a, Kotov & Dumont, 2000). More disordered setulation of distal part of the labrum body was found in some Macrothricidae (Kotov, 1999b). Dumont & Silva-Briano (2000) pointed out the importance of labrum features for the Aloninae systematics, while in the past these features were used episodically in the taxonomy of chydorids, predominantly Leydigia (Smirnov, 1971). In many Aloninae, there are small setules between the marginal setae (Kotov, 2000a, c; Sinev & Kotov, 2000), while in Spinalona these are completely reduced. Unfortunately, this part was not described well by the majority of previous authors, and we can not affirm that this is a unique feature for this representative of the Aloninae. Presence of four transversal rows of setules at the margin of antennule seems to be common for the Aloninae (see pictures of Alonso, 1996), although we are not sure that this is a synapomorphy. In contrast, the characteristic transversal flattening of antennule leads to re-distribution of aesthetascs. As a result, they do not distribute in a circle. This kind of arrangement is not characteristic for the majority of the Anomopoda. The same transformation of the antennule was found previously in another alonine, Nicsmirnovius camerounensis Chiambeng & Dumont (1999) although one of aesthetascs in the latter is larger and located far from the others. In the bosminid Bosminopsis, the aesthetascs do not distribute in a circle also, while in Bosmina their arrangement is quite typical for anomopods (Kotov, 1997). Insertion of the lateral seta in the middle of the basal segment of the second antenna is a specific, advanced feature, not frequent in all Anomopoda, inclusive the Aloninae (see pictures of Silva-Briano, 1998). Tri-lateral armature of swimming seta in Spinalona is analogous to that in Eurycercus (Kotov, 2000b), but we are not sure about its evolutionary significance.
Ciros-Pérez & Elías-Gutiérrez (1997: 27) pointed on two main peculiarities of the Spinalona limbs: presence of only 4 setae on exopodite III and three on exopodite V. In fact, these traits are rare, but not unique for Aloninae, because there are 3–5 setae on exopodite III in Leydigia (Kotov, 2000c, Table 1), and exactly four seta in L. australis (see Sars, 1885), and three setae on exopodite V in Notoalona freyi (see Rajapaksa & Fernando, 1987). Rare for Alonini are also the 5 setae in filter plate II, and only 1 seta in ‘filter plate’ V. Really unique traits of Spinalona are associated with the inner portion of limbs III and IV. In all anomopods here, there are two rows of setae (Smirnov, 1971). According to Kotov (1998, 2000c), the row of marginal scrapers is continued in the distal armature of gnathobase, and the more medially and posteriorly located row of soft setae continued basally in the filter plate of gnathobase. The marginal row in Spinalona is organized quite typically for Alonini. But the second row is special in this genus, as compared with other alonine genera. In the majority of Alonini there are 4 (or less) soft setae here, a tendency to a reduction of this number is characteristic for limb IV. In Spinalona there are 5 soft setae both on limb III and IV. To our mind, the seta, which is the distalmost member of filter plate in the majority of Alonini, was included to the row of soft seta in Spinalona as a basalmost member. Partially, this is an explanation of small number of setae in the filter plates III–IV in Spinalona. Also, five setae in the filter plate III is a rare feature for the Alonini, and only 2 setae in the filter plate IV is unique. Numerous soft setae on limbs III-IV occur in different Macrothricidae (SilvaBriano, 1998; Dumont & Silva-Briano, 1998; Kotov, 1999b). We consider that the above described structure of limbs III–IV in Spinalona is not primitive, but results from a secondary modification. Another case of a deep secondary modification of the alonine limbs within a local clade was revealed by Kotov (2000a) for Kozhowia-Parakozhowia. Although we confirm here the previously reported opinion (Ciros-Pérez & Elías-Gutiérrez, 1997; Kotov, 2000c), that Spinalona is the most specific animal among Alonini, there is no reason to create a special supra-generic taxon for this genus, as was done for Indialona (Kotov, 2000c). It seems that all tripored alonine genera are closely related, but it should be considered that recent attempts to analyze phylogenetic relationships within chydorid-like anomopods (i.e. Olesen, 1996) are very preliminary, because of
192 a lack of data for many representatives of Aloninae. Moreover, the phylogeny of all Branchiopoda is still controversial and under discussion (i.e. Olesen, 2000; Fryer, 2001).
Acknowledgements We thank Prof. N. N. Smirnov for his valuable consultations and Prof. H. J. Dumont for criticism and linguistic corrections of earlier draft. A. A. Kotov thanks the Consejo Nacional de Ciencia y Tecnología (CONACYT) for supporting his stay in Mexico, through the Catedras Patrimoniales program.
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