Hypostomus cochliodon Group

Jonathan W. Armbruster, 2003, The species of the Hypostomus cochliodon group (Siluriformes: Loricariidae)., Zootaxa 249, pp. 1-60 : 13-21

Hypostomus cochliodon Group

Diagnosis: The Hypostomus cochliodon group is diagnosed by the following characteristics, none of which is unique among loricariids: dentary angle averaging less than 80° and the preoperculo-hyomandibular ridge deflected posterior to the main body of the hyomandibula (Armbruster, in press). Wood-specializing members of the H. cochliodon group are additionally diagnosed by the following characteristics, none of which are unique among loricariids: the presence of large spoon-shaped teeth (Fig. 1C), the hyomandibula and metapterygoid sutured to their dorsal margins vs. not sutured dorsally with a notch between the two bones (Fig. 3B), the presence of a highly curved maxilla (Fig. 3B), and loss of the buccal papilla (Fig. 4B).

The Hypostomus cochliodon group can be distinguished from most other loricariids by the combination of highly angled jaws and usually less than 20 teeth per jaw ramus (occasional specimens of H. cochliodon , H. hondae , and H. hemicochliodon have been observed with counts of up to 27 teeth). Among the Hypostominae , the H. cochliodon group differs from Pterygoplichthys by having seven dorsal-fin rays (vs. nine or more); from Pogonopoma , Pseudorinelepis , and Rhinelepis by having the dorsal flap of the iris present (vs. flap absent; Armbruster 1998) and by having four anal fin rays (vs. five); from Corymbophanes , by having 0-2 median, unpaired plates posterior to the dorsal fin (vs. 3 or more); from most of the Ancistrini by not being able to evert the cheek plates any greater than 30° (vs. 75°-90°); from Spectracanthicus ( Ancistrini ) by having the dorsal fin separate from the adipose fin (vs. contacting adipose-fin spine) and by having plates on the abdomen in adults; and from Pseudancistrus ( Ancistrini ) by lacking hypertrophied odontodes on the cheek and snout margin and by having plates on the abdomen in adults.

Hypostomus microstomus Weber shares with the H. cochliodon group highly angled jaws and a low number of large teeth (Weber 1987); however, the teeth of H. microstomus are not spoon-shaped or tending towards being spoon-shaped. In addition, H. microstomus is dark gray to black with light spots versus brown with dark spots as in the H. cochliodon group.

Some Hypostomus such as H. plecostomus are variable in the angle between the dentaries. Some specimens of H. plecostomus , for example, have a dentary angle less than 80°. They differ from the H. cochliodon group by having greater than 20 teeth per ramus. Species similar to H. plecostomus also tend to have the head as wide or wider than tall while species of the H. cochliodon group tend to have the head taller than wider.

Description: Fairly large loricariids, reaching 300 mm SL. Color typically dark brown with spots generally developed over most surfaces. Most species observed have a well developed ability to alter color according to substrate.

Body shape in all except Hypostomus sculpodon deep at origin of the dorsal fin (appearing deeper than in other Hypostomus ) then narrowing posteriorly more quickly than in Hypostomus causing body to appear humped. Body of H. sculpodon not as deep. Body depth increases from snout to tip of supraoccipital at steep angle, angle of body depth increase decreases from tip of supraoccipital to dorsal-fin spinelet.

Rounded ridge present from anterodorsal corner of orbit to posterior margin of nares; ridge widest and tallest posteriorly. Rounded ridge present from posterodorsal corner of eye to end of pterotic-supracleithrum (additional, sharp ridge of bone and moderately enlarged odontodes present on pterotic-supracleithrum in H. cochliodon , H. hemicochliodon , and H. sculpodon ). Space between orbits concave such that dorsal rim of orbit raised above medial surface of head. Nares separated by flap of skin held erect in life.

Dorsal, supramedian, median, and inframedian plate rows complete from head to caudal fin, ventral plate row begins at insertion of pelvic fin and continues to caudal fin. Lateral plates usually with median keels formed from ridge of bone and enlarged odontodes; height of keels vary from absent to tall with odontodes very sharp; keels may be present or absent on any row of lateral plates; keels of first three plates of supramedian plate row angled dorsally, often confluent with keel of dorsal plate row; keels on first three plates of dorsal row forming angle from tip of supraoccipital to posterolateral corner of nuchal plate, not confluent with keel on dorsal plate row beginning on fourth plate. Base of caudal fin covered in elongate, roughly triangular plates. Entire ventral surface of head and body (including space above pectoral- and pelvic-fin rays) of adults covered in small platelets, platelets often extending onto base of pectoral- and pelvic-fin rays ventrally. Small platelets usually present in skin between dorsal fin and lateral plates of adults. Platelets on abdomen and near fins increase in number with standard length. Head covered in small plates. Frontal, nasal, sphenotic, infraorbitals, pterotic-supracleithrum, suprapreopercle, and supraoccipital supporting odontodes. Opercle supports odontodes in some species. Some odontodes present on posterior margin of preopercle. Platelets that cover anteroventral corner of opercle slightly separated from opercle allowing plates to be marginally everted (angle of eversion less than 30°).

Dorsal fin consisting of small, v-shaped spinelet, fairly strong spine, and seven rays. Caudal fin strongly forked, lower lobe longer than upper. Pectoral-fin spine strong, generally reaches posterior to pelvic-fin rays when depressed ventral to pelvic fin; cleithrum with exposed process dorsal to pectoral-fin rays that tapers posteriorly to point; pectoralfin inserted on same plane as pelvic fin such that spine, when depressed parallel with body, lies on top of and in contact with pelvic fin. Pelvic-fin spine thin, flexible, generally reaches beyond base of anal fin. Anal fin with relatively strong, unbranched first ray that supports odontodes. Adipose fin (when present) consisting of single median, unpaired preadipose plate and a stout, strong, pointed spine; adipose-fin membrane generally extending to anterior-most procurrent caudal-fin spine or just anterior to procurrent caudal-fin spines. Dorsal fin II7; pectoral fin I6; pelvic fin I5, anal fin I4, caudal fin I14I.

Jaws strongly angled, dentaries typically forming angle of less than 80°. Teeth few (5- 27, mode = 10), generally shorter and wider than most Hypostomus (Fig. 1B-C); teeth of most species spoon-shaped (Fig. 1C).

Range: From the Amazon, Aroa, Atrato, Essequibo, La Plata, Magdalena, Orinoco, Sinu, Tocuyo, Tuy, and Yaracuy river drainages and the Lake Maracaibo drainage.

Ecology: Individuals of the Hypostomus cochliodon group are most typically collected in slow-flowing, small- to medium-sized rivers, although they may also be collected in piedmont streams. They are typically associated with submerged logs in the flowing portions of the streams.

Key to the species of the Hypostomus cochliodon group

1 Adipose fin absent ........................ Hypostomus levis (Upper Río Madeira in Bolivia)

- Adipose fin present .................................................................................................... 2

2 Opercle supporting few or no odontodes (0-10; Fig. 2B) .......................................... 3

- Opercle supporting a large patch of odontodes (11+; Fig. 2A) .................................. 7

3 Body typically with wide tan dorsal stripe formed on the ventral half of the plates in dorsal row and dorsal half of plates in supramedian row, spots, if present, few, or body entirely dark brown without spots ....... Hypostomus cochliodon ( Río Paraguay)

- Body without stripes or never entirely dark brown (spots always present) ............... 4

4 Keels weak or absent .......................... Hypostomus pyrineusi (Upper Río Amazonas)

- Keels well-developed ................................................................................................. 5

5 Caudal fin bicolored with dorsal lobe light, ventral lobe dark; caudal fin without spots on ventral lobe except on caudal-fin spines. Adult males without modified odontodes on lateral plates (Fig. 2A) ............... Hypostomus taphorni (Cuyuni River)

- Caudal fin with dorsal and ventral lobes similarly colored; caudal fin with spots at least on ventral lobe. Adultmales with modified odontodes on lateralplates (Fig. 2B).... .................................................................................................................................... 6

6 Color tan or gray with dark spots widely spaced (Fig. 9) ............................................ ................................................... Hypostomus ericius (Upper Río Amazonas of Peru)

- Color dark brown with dark spots closely spaced (Fig. 16) ......................................... .......... Hypostomus oculeus (Upper Río Amazonas of Peru, Colombia, and Ecuador)

7 Body typically with wide tan dorsal stripe formed on the ventral half of the plates in dorsal row and dorsal half of plates in supramedian row, spots, if present, few, or body entirely dark brown without spots. Adult males with modified odontodes on the lateral plates (Fig. 2B). Located only in the Río de La Plata drainage) ................. ...................................................................... Hypostomus cochliodon ( Río Paraguay)

- Body without stripes or never entirely dark brown, spots always present. Adult males without modified odontodes on the lateral plates (Fig. 2A). Río Amazonas drainage and drainages north of Río Amazonas ........................................................ 8

8 Buccal papilla tiny or absent (Fig. 3B). Teeth wide with short stalk and with distinctly spoon-shaped cusp (Fig. 1C). Ridge absent on pterotic-supracleithrum (Fig. 5B) ............................................................................................................................. 9

- Buccal papilla medium to large (Fig. 3A). Teeth narrow with long stalk and not with distinctly spoon-shaped cusp (Fig. 1B). Ridge present on pterotic-supracleithrum (Fig. 5A) ................................................................................................................... 12

9 Caudal fin strongly bicolored with dorsal lobe light, ventral lobe dark. Spots on abdomen very small (Fig. 22) .......................... Hypostomus taphorni (Cuyuni River)

- Caudal fin not strongly bicolored with either dorsal lobe light at the base and dark at the tip and ventral lobe dark, or entire fin light, or entire fin with spots that form vertical bands. Spots on abdomen small to large, but never as shown in figure 22 ...... 10

10 Caudal-fin spines lightly colored, generally without spots although juveniles occasionally have some faint spots. Ríos Aroa, Tucuyo, and Yaracuy ............................... .................................................. Hypostomus pagei ( ríos Aroa, Tucuyo, and Yaracuy)

- Caudal-fin spines darkly colored, almost black or with spots. Ríos Orinoco and Tuy and Lago Maracaibo drainages and west of Andes .................................................. 11

11 Relatively small number of plates in skin between dorsal-fin spine and spinelet and lateral plates (number of plates depends on SL, see Fig. 6A; Table 7) ........................ ................................................................. Hypostomus plecostomoides ( Río Orinoco)

- Tends to have relatively large number of plates in skin between dorsal-fin spine and spinelet and lateral plates (number of plates depends on SL, see Fig. 6B; Table 7; some specimens from the Rio Atrato lack this trait) .................................................... ........... Hypostomus hondae ( ríos Atrato, Magdalena, and Sinu and Lago Maracaibo)

12 Spots on body, if present, not widely-spaced, body color dark brown to black. Buccal papilla small. Dorsal-anal length to anal-fin length ratio 92.5-132.6% (average = 111.1 ± 8.4%). Interorbital width/HL ratio 44.1-55.6% (average = 49.9 ± 2.7%) ....... ........................................................................................ Hypostomus hemicochliodon ( Ríos Amazonas, Negro, Tapajos, and Xingu and upper Río Orinoco)

- Spots on body widely-spaced, body color reddish brown. Buccal papilla very large. Dorsal-anal length to anal-fin length ratio 69.6-89.7% (average = 79.2 ± 7.6%). Interorbital width/HL ratio 38.5-45.4% (average = 51.4 ± 3.1%) ............................... ............................................. Hypostomus sculpodon (upper ríos Negro and Orinoco)