The anatomy of the putative pheromone pump mechanisms in the caudal region of glandulocaudines is described and discussed. Revisionary studies of the species Argopleura, Scopaeocharax and Tyttocharax are reserved for separate publications. For other examined specimens, museum numbers are given in the text, after the name of the specimens.
All tail synapomorphies are related to the putative pheromone production apparatus in males.
The dorsolateral lamellar process of the anguloarticular bone is absent in both sexes (Figure 59). In sexually mature males, the hypertrophied posterior field of the pouch scale is horizontally less elongated than in the other xenurobryconines. The horizontal length of the pouch scale of Xenurobrycon heterodon (Figure 30) is distinctly greater (depth about 72 percent of horizontal length) than X.
There is no evidence of fusion of the accessory pouch with the pouch in xenurobryconines of subgroup B. In sexually mature males and females, the cartilaginous part of the posterior process of the pelvic bone is missing (Figs. 56a,b, 37a). In sexually mature males, the anterior point of the pelvis is located in front of the first pleural rib (rib of the fifth vertebra).
In sexually mature females, the anterior tip of the pelvic bone is located well in front of the second pleural rib (the rib of the sixth vertebra) and may reach as far anteriorly as the first pleural rib (the rib of the fifth vertebra). In sexually mature females, the anterior tip of the pelvic bone lies in the area ventral to the distal ends of the anterior pleural ribs (ribs of vertebra 5). In sexually mature males, the medial two or three pelvic fin rays arch dorsally to the rest of the rays when the fin is relaxed or folded (the fin is partially spread in Figure 71).
Argopleura (apomorphy 7) has lost hooks on one to three anal fin rays in the anterior half of the fin. The monophyly of the Caudal fin hooks are absent in specimens of the examined species Argopleura and lotabrycon (Figures 8-10).
In Xenurobrycon macropus, the distal tips of the fin rays also converge in the folded fin.
Summary
Nelson referred to the fin jet mechanism as a bellows, and the pump is a type of bellows, one with a valve opening in the proximal and middle portions. The anterior portion of the opening closes as the sac is compressed and opens as the sac expands, while the smaller posterior portion of the opening remains open at all times. Therefore, we would suggest that the predominant flow of water is in the anterior portion of the orifice and out of the posterior portion of the orifice.
Direct muscle action on the fin rays as well as the general bending of the fin during tail stroke may be involved in the operation of this pump. The fin ray pump of Mimagoniates apparently evolved independently of the membrane scale pump found in other glandulocaudins. The front part of the chamber opening appears to act in an intake valve, and the rear part always remains open.
We postulate that this pump works by taking water into the anterior portion of its orifice, closing that orifice (and its connection with the posterior orifice), compressing the resulting chamber, and forcing water out of the posterior orifice. Glandular tissue is associated with the posterior opening as well as with the caudal fin rays and is particularly concentrated medially to a flap of tissue formed by modified scales just posterior to the pumping mechanism. In Appendix 3, hypotheses about the monophyly of Glandulocaudinae are reviewed, and it is concluded that there is currently insufficient information available to either support or refute a hypothesis about the monophyletic origin of the subfamily.
These are reviewed in Appendix 3, and it is again noted that there is insufficient information available to support or reject these hypotheses for all members of the subfamily. Based on habitats currently occupied by many glanders and subject to only ephemeral flooding, there appears to be little or no evidence for many species of the group to support Nelson's hypothesis.
Glandulocaudine Specimens Examined
Note: The Serrinha where Haseman gathered is or was a railroad crossing along the Rio Iguacu. The intersection is between Palmeira to the NW, Lapa to the S, and Curitiba to the NE. Note: Km 220 N of Buenos Aires is well beyond the Rio La Plata, and is in the Rio Uruguay or Rio Parana.
Colored and other specimens of the three species examined are listed in the material section of the species account in this paper.
Identification, Taxonomic, and Nomenclatural Notes on the Specimens Examined
The larger male is slightly longer than the largest specimen of Tyttocharax madeirae recorded here from the Rio Urubu. However, the posterior maxillary ramus of Tyttocharax is relatively thin and short compared to other xenobryconines and most characids. In these type specimens, a short and slender maxilla is present anterior to the first and dorsoanterior to part of the second infraorbital bone on each side.
In the species Microcaelurus odontocheilus, the maxilla does not reach the anterior border of the eye. We found no characters to distinguish the type specimens of Microcaelurus odontocheilus from the types or other specimens of Tyttocharax madeirae. On page 108, the male of both species of Microcaelurus odontocheilus is designated as the lectotype.
Two of these were studied by Ladiges and given to the Zoologie Staatssammlung des bayerischen Staats in Munich. Tytto-charax madeirae males have large pelvic fins, which originate ventrally to the mid-length of the pectoral fin and extend to about the fifth branchial ray of the anal fin. In Tyttocharax cochui males, the pelvic fin originates ventral to the posterior tip of the pectoral fin and extends posteriorly only to about the origin of the anal fin.
If the names refer to the same species, Tyttocharax cochui is the top synonym. In contrast, all specimens from the "lower" Amazon and Rio Madeira regions appear to be Tyttocharax madeirae.
A Critique of the Monophyly of the Glandulocaudinae
In our opinion, these six fish belong to at least two of the main groups of glandulocaudins. Nelson (1964a: 130) found one courtship behavior common to all six species, an up-and-down movement he called "zigzagging." He did not find this behavior in any of the other characids he observed and found no reports of it in the literature. Facultative oral and internal fertilization seems unlikely to us, and we agree with Nelson (personal communication) that the female's mouth of the place where the egg is to be laid is probably some kind of cleaning action.
Nelson's sample was limited to about 15 percent of known glandulocaudine species, and some of the major groups (based on similarities in gross morphology) are not represented in his sample. During the wet season, when seasonal flooding occurs and many fish spawn, including many of the glandulocaudins, the adults are dispersed in the nutrient-rich flood waters. In the coastal streams, spawning occurs seasonally associated with temperature and precipitation fluctuations, but not with prolonged flooding typical of the lowland parts of the Amazon basin, where few glandulocaudins occur.
The advantages suggested by Nelson do not apply to fishing in the short coastal streams of the lowlands or in the streams near the foot of the Andes. In our view, speculative hypotheses about ecological correlates of the evolution of morphological traits, while interesting and perhaps of scientific value, are often difficult to confirm or test. He noted that most glandulocaudines have slightly angled mouths suitable for surface feeding and suggested that glandulocaudines, like certain surface-dwelling freshwater fish, such as many species of the Poeciliidae and Hemiramphidae, have evolved internal fertilization.
Many of the glandulocaudines observed in nature (by Weitzman and Menezes) do knock insect prey from the surface of the water, as do other midwater karstic fishes with and without oblique beaks. We therefore decline to discuss in detail the question of the monophyly of the Glandulocaudinae as a whole until the groups of genera now considered Glandulocaudinae are better studied.
Addendum
Rediscovery of the Glandulocaudine Fish Pterobrycon and Hypothetical Significance of Its Spectacular Humeral Scales (Pisces: Characidae). Zoological Results of the Second Bolivian Expedition for the Academy of Natural Sciences of Philadelphia Part II: Additional New Fishes. Synopsis of the fresh-water fishes of the western portion of the island of Trinidad, W.I.
The Osteology and Relationships of the South American Characid Fishes of the Subfamily Gasteropelecinae. The 62nd Annual Meeting of the American Society of Ichthyologists and Herpetologists, Program and Abstracts (Northern Illinois University), 1 unnumbered page. Relationships of the Neon Tetras, a Group of South American Freshwater Fishes (Teleostei, Characidae) with Commentary on the Phylogeny of the New World Characters.
Relationships of the South American pygmy characoid fishes of the genus Elachocharax, with a redescription of Elachocharax junki (Teleostei: . Characidae). Synonymy in zoology should use the short form (taxon, author, first page), with the full reference at the end of the paper under Literature Cited. Extensive notes should be collected together and placed at the end of the text in a notes section.
For titles of books and articles, use sentence-style capitalization according to the rules of the language used (exception: capitalize all main words in English). Legends for illustrations should be submitted at the end of the manuscript, with as many legends typed, double-spaced, on the page as appropriate.
