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Crustacean Deduction

9-18-17 crustacean 049A5188Arthropods are invertebrates possessing an exoskeleton, a segmented body and paired jointed legs. Crustaceans make up one group of arthropods. Insects, spiders, ticks, mites, crabs, lobsters, woodlice, centipedes and millipedes are all crustaceans. Underneath a rotting log I recently discovered a crustacean resting right next to a clump of eggs. Not wanting to disturb the creature, I hazarded a guess as to its identity from what I could see. Its form narrowed it down to either a woodlouse (also known as sow bug, pill bug and roly-poly), centipede or millipede. Most centipedes have one pair of legs per body segment, eliminating them from the field of possibilities, for the photographed crustacean has two legs per body segment, as do millipedes and woodlice.

The next clue had to do with the eggs, which I presumed were produced by the creature right next to them. Woodlice have a “marsupium,” a chamber under the thorax which is filled with water in which their (often several hundred) eggs are brooded. Millipedes, on the other hand, lay from ten to three hundred eggs at a time, and deposit them on moist soil. In some species an adult remains to guard the eggs.

I cannot categorically say that today’s subject is a millipede and its eggs, but all signs point to it. If there is a crustacean expert among Naturally Curious readers, please confirm or correct my deduced identification!

17 responses

  1. Alice Pratt

    Interesting! Aren’t centipedes and millipedes brown-ish?

    September 18, 2017 at 8:26 am

    • Usually, Alice. This one may have molted recently.

      September 18, 2017 at 6:07 pm

  2. Mary, I agree that the creature in your photo could be a millipede. However, I think it’s worth clarifying that insects, spiders, ticks, mites, woodlice, centipedes and millipedes are not crustaceans. All of the above, plus crabs and lobsters are arthropods, but then they are split into different groups: Chelicerates (spiders and scorpions), crustaceans (hard shelled, mostly aquatic), insects (segmented with 6 legs), and myriapods (many legs – millipedes and centipedes).

    September 18, 2017 at 8:44 am

    • You are 100% right, Elise. I totally erred and appreciate your clarification. I was away and it was posted without my usual editing process!

      September 18, 2017 at 6:08 pm

  3. Nancy Condon

    This taxonomy you mention really threw me for a loop. Unless those taxonomists have only recently totally rearranged things, my understanding is that the Arthropod Phylum is made up of 4 extant subphyla: Chelicerates (spiders, etc.) Myriapods (centipedes etc.) Hexapods (insects) and Crustaceans (lobsters, etc.). I may be opening up a sticky wicket as this taxonomy stuff gets real complicated real fast, but suffice it for me to ask: Aren’t crustaceans separate from spiders, centipedes and insects?

    September 18, 2017 at 9:50 am

  4. Kathie Fiveash

    I love that you prefer making deductions to disturbing the animal.

    September 18, 2017 at 9:54 am

    • Now if I could only get my classifications down!

      September 18, 2017 at 6:09 pm

  5. Kathryn

    I so agree with the comment by Kathie – above.

    September 18, 2017 at 10:04 am

  6. Sheila Kaplow

    Unless classification of Arthropods has changed recently, I think your including insects, arachnids and myriapods as Crustaceans is mistaken . However Isopods (sow bugs etc) together with lobsters, crabs and a number of other creatures, are indeed Crustacea.

    September 18, 2017 at 10:08 am

  7. Perry Ellis

    I believe that millipedes have two pairs of legs per body segment while centipedes have only one pair per segment. The animal in your photograph has two pairs per segment, which supports your identification.

    September 18, 2017 at 11:05 am

  8. Interesting! I am wondering though if millipedes are arthropods but not crustaceans. After a mind-numbing search of Google and articles dealing with classification of arthropods, I am confused! The only terrestial crustacean seems to be the wood louse. The millipede is classified as mirapedia(sp.?), many feet. Help!

    September 18, 2017 at 3:10 pm

    • You are so right, Helen. My mistake! So sorry for the confusion. (see Cliff Fairweather’s explanation)

      September 18, 2017 at 6:10 pm

  9. Cliff Fairweather

    The animal is definitely a millipede (a diagnostic characteristic is the 2 pairs of legs per body segment) and, judging from it’s pale coloration, I’d say it had recently shed its exoskeleton. The eggs, though, look like slug eggs to me. And to weigh in on the taxonomy issue, wood lice (aka roly poly bugs, aka pill bugs) are indeed crustaceans but millipedes are diplopods.

    September 18, 2017 at 4:33 pm

    • Right on all counts! Thanks, Cliff. I, too, thought they looked like slug eggs, but the proximity of the millipede and my unfamiliarity with millipede eggs misguided me!

      September 18, 2017 at 6:05 pm

  10. Monika Grunberg

    The eggs look like slug eggs to me. Food for the critter, whatever its classification, or just co-incidence? That I don’t know. 🙂

    September 18, 2017 at 7:56 pm

  11. Jean Harrison

    Mary- I think this is the first time in many years of Naturally Curious that you have made an obvious mistake. You identification is OK, but your classification is bizarre.
    P.S. You are allowed to make mistakes, but please correct it in your next post. Do not take this message as meaning I am not an ardent admirer of you and your work, because I am.

    September 19, 2017 at 1:44 am

  12. I’ve seen similar eggs while looking for Salamanders. I always put the log carefully back after spotting our quarry. I wondered if they were slug eggs …tres kewl.

    September 26, 2017 at 9:48 am

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