Conspectus cobitidum - Raffles Museum of Biodiversity Research

Etymology. — Named for Theriodes Kolpos (or Theriodis
Sinus in Latin, the Bay of the Beasts), a place name in Ptolemy’s
(ca. 90–168) Γεωγραφκ γφγησις (Geographikê Hyphêgêsis,
Geography). It has been identified by some as possibly
Borneo (van der Meulen, 1974, 1975). Treated as masculine.
Remarks. — Theriodes sandakanensis was originally described
as a species of Acanthophthalmus (a junior synonym
of Pangio) (Inger & Chin, 1962: 120). There was no explanation
as to why the species was placed in Pangio but the
description includes comparison only with species placed in
Pangio by earlier authors (e.g. Weber & de Beaufort, 1916;
Smith, 1945). Several of these species have a diagnostic
‘barred’ colour pattern and Inger & Chin explicitly discussed
this barred pattern. It is not appropriate to describe the colour
pattern as barred. In the species of Pangio with a barred
pattern, the bars are black, regular, with sharp edges and
contrasted on a white to yellowish background. In Theriodes,
the colour pattern is better described as dark brown
marks on a paler, yellowish brown background, made of superficial
and inner pigments; the marks are irregular and
somewhat organised in 4–5 transverse bands. Besides, species
of Pangio are more elongated, with 45–71 vertebrae (Kottelat
& Lim, 1993), while T. sandakanensis has only 35–36
(Kottelat & Lim, 1992). Roberts (1989: 103) placed T. sandakanensis
in the genus Lepidocephalichthys. It indeed
shares a number of characters with Lepidocephalichthys, e.g.,
the rounded caudal fin, the general morphology of the lower
lip, and the vertebrae counts (see Kottelat & Lim, 1992).
Theriodes is, however, missing the most obvious character
diagnosing Lepidocephalichthys, the sexually dimorphic
modified pectoral-fin rays in males. Sexual dimorphism provides
very efficient characters to identify lineages in Cobitidae
(Šlechtová et al., 2008). In many genera, males have
thickened, hardened or rigid anterior pectoral rays, often with
projections or appendages. Lepidocephalichthys is unique
in having no modification on the anterior rays but in having
the last two rays (7 and 8) fused and swollen, often with a
longitudinally elongated, often laminar, protuberance along
the dorsal surface (Kottelat & Lim, 1992: 203, fig. 1; Nalbant,
1963, 1994; Havird & Page, 2010). In Pangio, the pectoral-fin
rays of the males are longer and more rigid than in
the females, and they have a typical curled appearance (Kottelat
& Lim, 1993). In Kottelatlimia, earlier included in Lepidocephalichthys,
a number of segments of the dorsal hemitrich
of the first branched ray have a posterior laminar projection
forming a kind of blade or saw-like structure (Kottelat
& Tan, 2008: 66, fig. 3).
None of these structures is present in Theriodes. The pectoral
fin is small, with only 5 branched rays (apparently fewer
than in all other cobitid genera, 6–10). The first two rays are
thickened in the male, and the second ray (homologous to
the first branched ray in the females and juveniles) is described
as “appeared unbranched” by Inger & Chin (1962:
123). In fact it is branched but there is no membrane between
the branches. A similar situation is also observed in
Kottelatlimia and Acantopsis (Kottelat & Tan, 2008).
Kottelat: Conspectus cobitidum
138
Havird & Page (2010: 156) mentioned the sexual dimorphism
in Theriodes and Lepidocephalichthys, but in a confusing
way. The main problem is their misunderstanding of
the ‘lamina circularis’. They comment that the lamina circularis
is “formed by the first and second pectoral rays in mature
males of [T.] sandakanensis (as well as a thickening of
the first pelvic ray) vs. the seventh and eighth pectoral rays
in mature males of Lepidocephalichthys”. Elsewhere (p. 137;
also Havird et al., 2010: 13), “[t]his modification is referred
to as the lamina circularis and is formed by a fusion and
hardening of the innermost (seventh and eighth) pectoral rays.
In mature males of other cobitid genera, the lamina circularis
is formed by different pectoral rays (usually the second)
or is absent”. To refer to all types of sexually dimorphic
modification of the pectoral rays as the same structure,
under the same name, obviously is misleading as the compared
structures are not homologous. Next comes the use of
the wording ‘lamina circularis’ to refer to just any modification
of the pectoral rays. This obviously ignores that there is
a very large corpus of literature on cobitids and their sexual
dimorphism by authors in Europe, China, Japan and Korea,
spanning over about 140 years. Lamina circularis means circular
lamella. The sexual dimorphism in Cobitis was first
described (imperfectly as a swelling of the ray) by Canestrini
(1871) and it later became known as Canestrini scale. As
implied by both names, it refers to a round structure and it
would be strange to use it as a general term meaning modified
pectoral ray. The lamina circularis is a laminar, usually
but not always circular, posterior projection of the first (proximal-most)
segment of the dorsal hemitrich of the first
branched pectoral ray (see, e.g., Nalbant, 1963: 356; Kottelat
& Freyhof, 2007: 301, fig. 61). A second lamina circularis
may also be present on the second branched ray in some
species. It is not homologous with the thickened rays 1–2 of
Theriodes, with the curled rays of Pangio, with the fused
rays 7–8 of Lepidocephalichthys, or with the blade or ‘saw’
on ray 2 of Kottelatlimia. But it is apparently homologous
with the projection on the first segment of ray 2 (the proximal-most
‘tooth’ of the ‘saw’) in Kottelatlimia (Kottelat &
Tan, 2008: 66, fig. 3).
The black pattern at the base of the caudal fin is also useful
to distinguish some lineages in all families of Cobitoidea.
Theriodes has a single small black spot at mid-height of the
caudal fin, a pattern not seen in any other cobitid (but known
in other loach families). In Lepidocephalichthys and Kottelatlimia,
as in the majority of cobitids, if present, the black
spot (or one of the black spots) is in the upper third of the
caudal-fin base, usually somewhat slanted. There is no spot
in Pangio, but in some species a bar occupies most of the
caudal-fin base.
The gill opening seems smaller in Theriodes than in any other
cobitid, but this still requires confirmation. In most cobitids,
the posterior nostril is adjacent to the anterior one (or to
the base of the tube at the top of which the anterior nostril is
located), but in Theriodes there is some distance between
the tube and the posterior nostril. The diagnostic value of
this character needs to be checked in more genera.