Hemiancistrus landoni Eigenmann, 1916




Hemiancistrus landoni, photos by K.S. Cummings

TAXA LIST

  • Hemiancistrus landoni appears to represent an undescribed genus sister to all other Ancistrini except for some from southeastern Brazil.  This relationship is particularly interesting because the species is restricted to the Gulf of Guayaquil drainage in western Ecuador.  The Gulf of Guayaquil was the former outlet of the Amazon prior to the rise of the Andes; thus, H. landoni may be a relict of a once larger early radiation of Ancistrini.  The following is from a paper I am working on.
    SPECIES

    DIAGNOSIS

    Hemiancistrus landoni is diagnosed by one unique synapomorphy: the presence of small papillae on many of the exposed surfaces of the skin (particularly the eye and the skin around the orbit). Other characteristics considered synapomorphic (based on the phylogeny of Armbruster, in press) but shared by other members of the Loricariidae are: the presence of a maxilla that is bent so that it nearly forms a right angle and the presence of a condyle on the lateral ethmoid for contact with the mesethmoid that is wide and has a shelf along its entire perimeter.


    DESCRIPTION

    Member of loricariid Subfamily Hypostominae, Tribe Ancistrini as diagnosed by Armbruster (2004). Fairly large loricariids (largest 188.5 mm SL). Body elongate, moderately dorsoventrally flattened. Body moderately convex from tip of snout to first procurrent caudal-fin spine; body deepest at origin of dorsal fin. Dorsal surface between dorsal fin and caudal-fin flattened. Ventral surface flattened. Caudal peduncle roughly oval in cross section. Head without strong ridges; orbital rim slightly higher than interorbital space; slight, rounded ridge from anterior of orbit to posterior naris; slight, rounded ridge on supraoccipital.

                Odontodes forming slight keels on lateral plates. Dorsal, supramedian, median, and inframedian plate rows complete from head to caudal fin, ventral plate row from posterior of pectoral fin to caudal fin; five rows of plates on caudal peduncle; 25-27 plates in median plate row (mode = 26). Abdomen completely plated in adults except for small regions at insertion of pelvic-fin spine, just posterior to mouth, and around anus; abdomen without platelets in juveniles. Small, circular area at tip of snout usually without plates. Nuptial males with incredibly hypertrophied odontodes on tip of pectoral-fin spine and on cheek (reaching lengths of approximately 13 mm and 19 mm respectively); keel odontodes slightly larger than in females. Opercle and preopercle with odontodes in juveniles, but few or none in adults. Cheek with 22-76 hypertrophied odontodes (juveniles with fewer, shorter odontodes than adults.

                Mouth with small, median buccal papilla and often with several folds lateral to papilla. Maxillary barbel short, reaching maximally to base of evertible cheek plates. Dorsal and ventral surfaces of eye, skin around the orbit, and occasionally skin covering the opercle with small papillae (Fig. 4). Eye with large dorsal flap of iris. Upper lip relatively thin and with large papillae. Lower lip to approximately half of distance from mouth to pectoral girdle; papillae large anteriorly, becoming smaller posteriorly.

                Dorsal fin II7; not reaching adipose fin when depressed. Pectoral fin I6; tip of spine reaching beyond pelvic-fin base when adpressed. Pelvic fin I5; tip of spine reaching middle of anal-fin base when adpressed. Anal fin I4; base of first anal-fin pterygiophore not supporting odontodes. Caudal fin I14I; straight to slightly emarginate, lower lobe slightly longer than upper; 5-6 (mode = 6) dorsal procurrent caudal-fin spines; 4-6 (mode = 5) ventral procurrent caudal-fin spines. Adipose fin with one azygous plate anteriorly and strong, triangular spine; anal-fin membrane not contacting first dorsal procurrent caudal-fin spine.

                Teeth bicuspid, median cusp long, lateral cusp short; 15-48 dentary teeth (avg. = 34); 15-43 premaxillary teeth (avg. = 30). Upper and lower jaw rami form angles slightly less than 180.

    Ground color brown in adults. Faint, large spots present on head, fading posteriorly on body. All fins with large, dark spots. Three dark saddles generally present: at posterior insertion of dorsal fin, below adipose fin, and at end of caudal peduncle. Skin of dorsal portion of upper lip with small black spots or vermiculations. Abdomen slightly lighter than sides, with large dark spots. Juveniles generally colored as adults except abdomen almost white with spots faint or absent.


    COMPARISONS

    Among the Ancistrini, Hemiancistrus landoni is most similar to Peckoltia and Hemiancistrus. Hemiancistrus landoni can be separated from Peckoltia and Hemiancistrus by the relative length of the dorsal fin (not reaching adipose fin in H. landoni and reaching in most Hemiancistrus and Peckoltia); and from Peckoltia by coloration (dark saddles present against a dark ground color in H. landoni vs. saddles absent or present, but against a much lighter ground color). Members of the Ancistrini that may be sympatric with H. landoni include Ancistrus, Cordylancistrus, Chaetostoma, Dolichancistrus, and Lasiancistrus. Hemiancistrus landoni can be separated from Ancistrus and Chaetostoma by having a completely plated snout margin (vs. a naked snout margin); from Chaetostoma, Cordylancistrus, and Dolichancistrus by having the nuchal plate and spinelet exposed (vs. covered by skin or plates), by having plates on the abdomen, and by having seven (vs. eight or more) dorsal-fin rays; and from Lasiancistrus by having the abdomen fully plated and by lacking elongate, whisker-like odontodes on the cheek and opercle.

                In addition, Hemiancistrus landoni differs from Baryancistrus, Parancistrus, and Spectracanthicus by lacking a connection between the dorsal fin and the pre-adipose plate or spine; from Panaque and Scobinancistrus by having villiform (vs. spoon-shaped or large teeth respectively); from Acanthicus, Dekeyseria, Leporacanthicus, Megalancistrus, and Pseudacanthicus by lacking well-keeled plates (keels are much shorter in H. landoni); from Exastilithoxus by lacking fimbriae along the posterior margin of the lower lip; from Exastilithoxus and Lithoxus by having plates on the abdomen; from Hopliancistrus by having more than three main cheek odontodes, none of them very stout; from Leptoancistrus by having adipose and anal fins; from Neblinichthys by lacking hypertrophied odontodes on the top of the snout of breeding males and by having plates on the abdomen; from Pseudancistrus by lacking elongate odontodes on the snout margin and by having abdominal plates; and from Pseudolithoxus by having five (vs. three) rows of plates on the caudal peduncle.


    DISTRIBUTION

    In rivers draining into the Gulf of Guayaquil and the Río Esmeraldas drainage of western Ecuador (Fig. 6).


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