Victor G. Springer & Gerald R. Allen, 2004, Ecsenius caeruliventris and E. shirleyae, two new species of blenniid fishes from Indonesia, and new distribution records for other species of Ecsenius., Zootaxa 791, pp. 1-12: 1-2

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[[ Ecsenius ]]  ZBK 

Ecsenius  ZBK  now comprises 53 species, more than twice as many as the next speciose blenniid genus, Meiacanthus Norman  ZBK  .

The Prooculis  ZBK  species group is defined by a combination of characters, only one of which appears to be synapomorphic: presence on ventral surface of head of two bilateral pairs of small dark spots (Figure 1a, b; also Springer, 1988:figure 57) or single bilateral pair of elongate dark crescentic marks (Springer, 1988:figure 58) in at least some males, or two pairs of pale, round spots (Figure 2c; also Springer, 1988:figure 56; 1991:figure 8) or single pair of pale crescentic marks in some females and dark crescentic marks in some males. The central portions of the crescentic dark marks are absent in some specimens of one species ( E. prooculis  ZBK  ) that exhibits crescentic markings, thus duplicating the dark spots of other species, and it is inferred from this that the character states are homologs. The positions of the dark or pale spots on the ventral surface of the head are the same in both sexes of the same species and occupy the same relative positions in all species that have them. The anterior and posterior ends of the crescentic marks occupy the same positions as the spots. The anterior spot on each side is associated with the anteriormost sensory pore of the mandibular series. The posterior spot is in the area external to the attachments of the branchiostegals to the anterior ceratohyal, which attachments can be seen through the skin.

The presence of these markings appears to be related to size or sexual maturity of individuals, but apparently sexually mature individuals may also fail to exhibit them. Even though these markings are not exhibited by every specimen, or even most of the specimens of any of the species, their presence in some specimens of each species and not, with one exception, in any other Ecsenius  ZBK  species, suffices our hypothesis of synapomorphy. The exception is E. isos McKinney & Springer  ZBK  , one of the three species of the Trilineatus  ZBK  species group. In E. isos  ZBK  , there is a dark spot (Springer, 1988, figure 53) in the same area as the posterior spot of the Prooculis  ZBK  group species. This spot appears to be an isolation of the ventral end of a dark crescentic marking that begins dorsally on the opercle and curves ventroanteriorly, ending on the ventral surface of the head in the other two species of the group. There may be other isolated spots continuing dorsal to the ventral one in E. isos  ZBK  ; these represent positions along which the dark crescent mark lies in the other two species (Springer, 1991: figure 2).

The validity of the Prooculis  ZBK  group is supported by the distributions of its component species. Seven of the eight species are allopatrically distributed; the eighth species, E. bimaculatus Springer  ZBK  , has a partially allopatric distribution, but overlaps the distributions of two of the other species (Figure 3).

Other characters defining the group within Ecsenius  ZBK  : Small species (largest known specimen 40 mm SL, attained by only one species, E. prooculis Chapman & Schultz  ZBK  other species not exceeding 34 mm SL); dorsal-fin spines XI-XIII (strongly modally XII), segmented rays 13-15 (strongly modally 14), deeply notched between spines and segmented rays; anal fin II,15-17 (modally 16); pectoral-fin rays 12-14 (strongly modally 14); segmented caudal-fin rays 13, third from dorsalmost and third from ventralmost filamentous in adult males; vertebrae 10 + 21-23 (strongly modally 22); total dentary teeth (including anterior canines, but excluding posterior canines) 39-50, posterior canine teeth 1 on each side; lateral-line a continuous tube extending posteriorly to vertical from 8th to 11th dorsalfin spine (to 11th in only one specimen of E. bimaculatus  ZBK  ); nasal cirrus minute; no distinct dark stripes or spots on fleshy pectoral-fin base.