Shorefishes of the Eastern Pacific online information system

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Species: Microdesmus retropinnis, Double-spotted worm-goby, Rearfin wormfish

All Families:   All Genera:   All Species:

eye not tiny, not high
under eye - 2 bars
body: 2 rows oval blotches
D origin posterior
A 28-32
pectoral 10

Microdesmus retropinnis Jordan & Gilbert, 1882

Rearfin wormfish, Double-spotted worm-goby

Slender, wormlike, body height 3-9% of SL; tail (without fin) < 50% of SL; eyes not tiny, on side of head, not skin covered; snout rounded; snout and jaw with pronounced longitudinal swollen muscular ridges; mouth small, little oblique, lower jaw strongly projecting, a small fleshy knob at tip of chin; lips with a restricted free flange at sides; teeth partly in 3 rows; gill opening large (not tubular), but < base of pectoral; dorsal fin spines evenly spaced, 47-49 elements, origin ~ 2 head lengths behind head, almost midway between tip of lower jaw and anus; anal II, 28-32; pectoral 10 rays, fin short; pelvics I, 3, shorter than pectorals; tail fin rounded, as long as head; dorsal and anal fins confluent with tail fin; scales small, non-overlapping, well separated; at base of dorsal and anal fins scale rows diverge outwards and backwards; scales with 39 radiating lines.

Translucent light olive; 2 dark bars under eye; a series of irregular oval dark blotches along top of back and another series along each side; fins translucent except that blotches on top of back extend slightly onto dorsal fin; sides of head and chin irregularly spotted with brown.

Size: 12.5 cm.

Habitat: intertidal rock pools and beachrock.

Depth: 0-5 m.

Central western Gulf of California to Panama.

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  • Brackish
  • Marine
  • Inshore
  • Inshore Only
Water Column Position
  • Bottom only
  • Bottom
  • Reef only
  • Reef (rock/coral/oyster)
  • Reef associated (reef + edges-water column & soft bottom)
  • Rocks
FishBase Habitat
  • Reef Associated
Feeding Group
  • No Data
  • Carnivore
  • No Data
  • Mobile benthic crustacea (shrimps/crabs)
  • Mobile benthic worms
Egg Type
  • Pelagic larva
  • Benthic
  • No data
Global Endemism
  • Tropical Eastern Pacific (TEP) endemic
  • East Pacific endemic
  • All species
Regional Endemism
  • Continental TEP endemic
  • TEP endemic
  • Continent only
  • All species
  • 3 provinces (Cortez + Mexican + Panamic) endemic
  • Continent
  • Resident
Climate Zone
  • Northern Subtropical (Cortez Province + Sinaloan Gap)
  • Equatorial (Costa Rica to Ecuador + Galapagos, Clipperton, Cocos, Malpelo)
  • Northern Tropical (Mexican Province to Nicaragua + Revillagigedos)
IUCN Red List
  • Data deficient
  • Listed
  • Not listed
Length Max
  • 12.5
Depth Range Min
  • 0
Depth Range Max
  • 5