That’s not ratfish genitalia. That’s ratfish genitalia.

September 28, 2009 • 8:58 am

by Greg Mayer

Over at Pharyngula, PZ has linked to a story at Deep Sea News about the description of a new species of ratfish with “forehead genitals”. While it’s a great concept, the tentaculum, or cephalic claspers, of ratfish are not genitals.

Male chimaeridFig. 1. That’s not ratfish genitalia. A male ratfish (family Chimaeridae) showing the tentaculum.

The genitalia of male ratfish are the pelvic claspers, modifications of the medial side of the pelvic fins used as intromittent organs for the introduction of sperm into the female’s reproductive tract. The ratfish’s pelvic claspers are bifid and especially spectacular.

Claspers of male chimaerid.Fig. 2. That’s ratfish genitalia. A male ratfish’s (family Chimaeridae) pelvic claspers; note the bifid structure, giving the appearance distally of four claspers. The anterior of the fish is to the bottom of this photo. The medial lump anterior to the pelvic fins is the rectum, prolapsed.

For comparison, here’s a female ratfish with unmodified pelvic fins.

Female chimaeridFig. 3. A female ratfish (family Chimaeridae), showing unmodified pelvic fins.

Ratfish comprise the Holocephala, one of the two major subdivisions of the cartilaginous fishes, the Chondrichthyes, the other major subdivision being the sharks and rays (elasmobranchs). Pelvic claspers are found throughout the modern cartilaginous fishes, which therefore have internal fertilization (most bony fish have external fertilization). Although living species of sharks do not have tentacula, some fossil ones (e.g. Falcatus) did, and others had other sorts of spine encrusted bits on their front ends which may have been involved in courtship and mating.

Whether or not tentacula are genitals is a matter of the definition of genitals, of course, but the term is, to my knowledge, reserved for structures involved in the transfer and reception of gametes. If parts of the body used in courtship are considered genitals, then the throat fans of anoles and the long fingernails of turtles would have to be considered genitals, too; indeed, so would the entire human body.  Many commenters at Pharyngula  have remarked about ratfish having penises on their heads (or something to that effect), which, of course, they don’t: their genitals are in the normal place (for cartilaginous fish), alongside their pelvic fins.Female (left) and male chimaerids.

Fig. 4. A ratfish couple.

(I tried to post a short comment to this effect at Pharyngula last night, but found I wasn’t registered to do so, and then I thought, “Why talk about it, when you can show pictures”, so I waited to take some photos this morning and posted here.)

21 thoughts on “That’s not ratfish genitalia. That’s ratfish genitalia.

  1. Wait…you took these pictures this morning…where?

    Is that what you keep in your kitchen? Are you running a ratfish bordello?

    1. If only! They’re preserved specimens from our teaching collection. I took the pictures in our vertebrate zoology lab.


  2. Greg Mayer,

    So lovely to be able to say thanks and good morning. Pharyngula’s registration hates me.

    For humans, several claspers available; some are even flesh.

  3. I’ve encountered lots of these guys (Hydrolagus colliei) on trawl surveys. Don’t know about other species but H. colliei has a very large, nasty spine just anterior of the dorsal fin (I’ve received a few in the boot).

    We use the cephalic clasper as a quick sex id aid. In juvenile males it’s no more than a small whitish line down the forehead but it’s always there.

    1. I’ve always thought they were pretty rare, so it’s interesting to hear you’ve seen lots– where? Another name for some of the species is rabbitfish, after their buck teeth, and Hydrolagus means ‘water rabbit’.


      1. They’re very common here (British Columbia coast), especially in our west coast Vancouver Island and Hecate Strait surveys.

        For example, here are the total catch weight numbers of H. colliei from the latest surveys of these areas:

        2009 Hecate Strait: 8,039 kg

        2008 West coast of Vancouver Island: 3,218 kg

        They’re also common in terms of their frequency in the tows – we almost always see at least a few in every tow as long as we’re in the correct depth range.

  4. I can hear the genitalia challenged go: “Ratfishes!”.

    If parts of the body used in courtship are considered genitals,

    Why stop there then, it would make as much sense to call a Porsche genitalia.

  5. I had the same annoyance with Pharyngula last night (wanting to say comment on the error and getting thwarted by the comment registration doodads) and I am really glad that you made this post!

  6. Wow – I’ve never seen claspers like those! The shark and ray claspers are so plain in comparison.

    Now why would someone think the genitalia are at that end? Could they be thinking with the wrong head?

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