Name: Karl Seitz

Fish 3[1]0 Spring 2015

Alki Beach: Invertebrate Species Identification


We will be observing and identifying the diverse fauna of the Alki Beach intertidal zone. Please use care when observing and touching the invertebrates that you find. Avoid lifting up rocks since you may crush animals when you put them back down. Make sure you take the time to look in crevices and other hard-to-see places because you may find the coolest inverts there!

Identify (to the species level) 3 representatives from each of the following phyla:


1.     Mossy chiton (Mopilia muscosa)

2.     Pacific blue mussel (Mytilus trossulus)

3.     Jingle shell (Pododesmus macroschisma)


1.     Frilled dog whelk (Nucella lamellosa)

2.     Checkered periwinkle (Littorina scutulata)

3.     Ribbed or Finger Limpet (Lottia digitalis)


1.     Purple or ochre sea star (Pisaster ochraceus)

2.     N.A.

3.     N.A.


1.     Aggregating anemone (Anthopleura elegantissim)

2.     N.A.

3.     N.A.


Sketch 1 of these representatives for each phylum.


Mossy chiton (Mopalia muscosa)


Frilled dog whelk (Nucella lamellosa)


Purple or ochre sea star (Pisaster ochraceus)


Aggregating anemone (Anthopleura elegantissim)

What kind of stressors do you think these animals experience? Describe the adaptations that allow them to cope with these stressors.

Intertidal animals are subject to a wide variety of stressors throughout the day.  They are subject to extreme changes in temperature (cold when submerged, hot when exposed), mechanical stress from waves (and people stepping on them), changes in oxygen availability (oxygen will run low in pools, or they cannot breathe in air, or they cannot take in oxygen when their shells are closed), changes in salinity (tidepools will become saltier due to evaporation), fluctuations in light exposure (less light under water than when exposed), exposure to difference predators at different times (marine when submerged and terrestrial when exposed), and of course desiccation risks.  Mollusks have shells which they can use to protect themselves from many of these risks and most can also move to more favorable conditions if necessary.  Echinoderms can move so as to stay in mostly favorable conditions.  Arthropods are also able to move for the most part and those that cant (barnacles) employ similar tactics to the mollusks and close their shells when exposed.  Cnidarians can either avoid exposure to air by staying in the water when the tide goes out if they are in the medusa stage or if in the polyp stage they can cover themselves with sand or shells and reduce their surface area when exposed.  Other organisms live in the substrate so as to avoid the extreme stressors of exposure at the surface.  Organisms such as sponges will likely only survive in the intertidal zone if they settled in a favorable spot where they are not subject to the full stress of exposure.  Those that do settle in a full exposure site will likely perish quickly.

What is the coolest thing you saw today?

The coolest thing I saw was unfortunately not an invertebrate; it was a northern clingfish (Gobiesox maeandricus).  Definitely didnt expect to find any fish and especially not one as cool as this. The pelvic fin derived sucker disc is amazing; once it was stuck to you it was quite difficult to get off.


Invertebrate-wise I found this interesting worm on one of the starfish (Pisaster ochraceus), blended in quite well.  I believe it was Arctonoe fragilis, or the commensal scale worm, which is a polychaete symbiont found on echinoderms from the Gulf of Alaska down to Baja California.

Name one new thing you learned about the intertidal zone and its fauna through your careful observations.

I learned a number things today: that anemones are quite good at burying themselves, that there is way more animal life than meets the eye if you just look hard enough, that limpets can live extremely far from the low water mark, that almost every organism is habitat for another organism, and that many animals living on the hard substrate are exceedingly well adapted to stick themselves to that substrate. 

List all the invertebrates that you found today (genus, species, and common name).

(I did my best here, but I may have left out some or misidentified)


       Purple encrusting sponge (possibly Adocia gellindra or Halichondria panicea)


       Aggregating anemone (Anthopleura elegantissim)


       Mossy Chiton (Mopilia muscosa)

       Pacific Blue Mussel (Mytilus trossulus)

       Jingle Shell (Pododesmus macroschisma)

       Frilled Dog Whelk (Nucella lamellosa)

       Checkered Periwinkle (Littorina scutulata)

       Ribbed or Finger Limpet (Lottia digitalis)

       Cockle (Clinocardium nuttallii) (shell)

       Pacific Oyster (Crassostrea gigas) (shell)

       Butter Clam (Saxidomus gigantean) (shell)

       Shield Limpet (Lottia pelta)

       Plate Limpet (Tectura scutum)


       Purple shore crab (Hemigrapsus nudus)

       Green/Yellow shore crab (Hemigrapsus oregonensis)

      Slender crab (Cancer gracilis) (dead or molt)

      Acorn Barnacle (Balanus glandula)

      Dungeness Crab (Cancer magister) (dead or molt)

      Thatched Barnacle (Semibalanus cariosus)

      Giant Acorn Barnacle (Balanus nubilus)

      Crenate Barnacle (Balanus crenatus)

      Sea Flea (Protohyale spp.)

      Rockweed Isopod (Pentidotea wosnesenskii)

      Oregon Pill Bug (Gnorimosphaeroma oregonensis)

      Hairy Hermit Crab (Pagurus hirsutiusculus)


       Glassy Tube Worm (Spiochaetopterus costarum)

       Calcareous Tube Worm (Serpula vermicularis)

       Commensal Scaleworm (Arctonoe fragilis)

       Sandworm (Nephtys ferruginea)


       Northern clingfish (Gobiesox maeandricus)