Thoridae Kingsley 1879

Closeup of compound eyes of this shrimp. The specimen was brought up by a diver from 58 m depth.

Being decapods, shrimp such as Heptacarpus sitchensis have 5 pairs of pereiopods (walking legs). The 5 pairs can be easily counted in this photo. Anterior to the walking legs are 3 pairs of maxillipeds, which are legs specially modified for feeding. In this species the 3rd pair of maxillipeds is large; as long as the legs and more robust. The first pereiopod has a yellow-tipped chela. The second pereiopod is more slender and has a multiarticulatedcarpus. Pereiopods 3-5 are similar to one another but in this species their dactyl (tip) is bifid.

As with many shrimp, the 2nd pereiopod is thinner and slightly longer than the other walking legs. The carpus of the 2nd pereiopod, here draped across the dissecting pin, has a series of constrictions that divide it into seven articles. This type of structure is called a multiarticulatedcarpus.

Although Kozloff's key lists epipods at the bases of several pereiopods and the 3rd maxilliped, Wicksten et al., state that this trait is quite variable. Other references state that the epipods are often very small and hard to see. This view centers on the 2nd pereiopod (thin leg near middle). The 1st pereiopod and 3rd maxilliped are to the right of it and the 3rd and 4th pereiopods are to the left. None of the leg bases has an obvious epipod.

This view of the propodus and dactyl on pereiopod 4 clearly shows the bifid tip of the dactyl.

This dorsolateral view of the carapace shows that the species has no supraorbital spine, which would be just above the eye near the base of the rostrum. It also shows that the rostrum is slightly shorter than the postorbital carapace. The orbit is the slot in the carapace to accommodate the eyestalk and is the official 'front' of the carapace (not including the rostrum). The postorbital carapace is measured from that slot at the base of the eye straight back to the posterior margin.

Heptacarpus sitchensis has a pterygostomial spine at the anteroventral margin of the carapace, seen here just below the base of the 2nd antenna.

The ventral margin of abdominalpleuron 4 (middle-right) of this species has a spine. Abdominalpleuron 5 (middle-left) has a similar spine. The third abdominal segment (top right) of hippolytid shrimp is usually bent, leading to the family name of "broken-back shrimp".

This dorsal view of the head shows that the anterior end of the basal segment of the first antenna (antennule) has only one prominent spine near where it articulates with the second segment.

This dorsal view of a live individual shows the normally transparent or translucent tissue, the pigmented oblique lines seen on the carapace and abdomen, and illustrates how the colors can change (compare this view to those above).

Heptacarpus sitchensis, two individuals about 2 cm long. Collected intertidally from the N Oregon coast. (Photo by: Dave Cowles, April 2014)