Thoridae Kingsley, 1878

Wicksten, Mary K., 2012, Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces 3371, Zootaxa 3371, pp. 1-307 : 72-74

Family Thoridae Kingsley, 1878

The most diverse and common family of shrimps on the coasts of California and Oregon is the Thoridae . All species have a rostrum, which can vary from a single sharp tooth to an elaborately toothed blade. The eyes are large and not hidden beneath the carapace. The carapace bears two or more supraorbital teeth in Spirontocaris , one in Lebbeus , and none in other genera found in California and Oregon. Suborbital, antennal, and pterygostomian teeth are often present on the carapace, although the pterygostomian tooth may be small or absent in some species. The carapace does not have a cardiac notch. The third maxilliped is setose and bears small claws at the end of the terminal segment. It bears an exopod in adults of species of Eualus and always an additional epipod in species of Spirontocaris , Lebbeus and Eualus . Species of Heptacarpus also usually, but not always, have an epipod on the third maxilliped. Pereopod 1 is stout and chelate. Pereopod 2 is slender and chelate, and has a multi-articulate carpus with seven articles. Pereopods 3–5 are ambulatory, and end in curved and simple or stout, spinose dactyls. The pleura of the abdomen can be evenly rounded or bear sharp teeth. The telson bears dorsolateral and terminal spines.

The best-known members of this family are the coastal shrimp, Heptacarpus spp. , which can be found in tide pools, under docks, in kelp beds or on near-shore sandy bottoms. Coastal shrimps often have camouflaging or disruptive coloration, such as stripes, bands, spots, saddles and other markings of green, brown, black, tan or white. These color patterns are usually seen in adult females, while males often are translucent ( Bauer 1981).

In a morphological analysis, Bauer (1984) suggested that Heptacarpus spp. with a short, high carapace, a short rostrum, and enlarged first chelae might be considered to be relatively "primitive" compared to more slender species. He considered the number of epipods also to be important in phylogeny, with a higher number indicating a more ancestral situation, but noted that the number of epipods could vary within a species or even between the sides of a single individual. The more "primitive" species lived in tide pools rather than in deeper water. He considered the potential effects of convergent evolution, and did not attempt to designate species groups. Two of the "species" he considered now are known to be synonyms of Heptacarpu s sitchensis ( Brandt, 1851) . This work could be a good starting point for further phylogenetic analysis.

Less is known of the species of the other three genera found in the area. Species of Lebbeus range from the lowest intertidal zone to the continental slope. Species of Eualus live in kelp beds and in offshore sandy or rocky areas. Species of Spirontocaris live subtidally in kelp beds, rocky reefs, and muddy and sandy bottoms of the continental shelf.

Eualus suckleyi ( Stimpson, 1864) has been reported once from off Grays Harbor, Washington. It has a rostrum slightly longer than the scaphocerite, with teeth on the dorsal distal half. It usually lacks an epipod on the second pereopod. Butler (1980: 204) provided a diagnosis and an illustration. Word & Charwat (1976 b: 148) included Spirontocaris dalli Rathbun, 1902 in their guide to shrimps of southern California. Their range map that suggested that it had been collected off Los Angeles, California, but they gave the distribution as "from the Arctic to Sitka, Alaska.” I have not seen this specimen and know of no other reports of this species from south of Alaska.

Owen (1839) described three shrimp from Monterey, California. He did not record depth or habitat. All three later were reported by Schmitt (1921, as species of Spirontocaris ), with previous synonyms. The first of these, Hippolyte palpator Owen 1839: 89 , pl. 28, fig. 3; now Heptacarpus palpator , is recognizable from the original description and still occurs at its type locality ( Wicksten 1986). Hippolyte affinis Owen, 1839: 56 , pl. 27, fig.4; has not been reported since Owen's original description, as reported by Schmitt (1921: 56). Hippolyte layi Owen, 1839: 63 , pl. 27, fig. 3; was reported again from Vancouver I. (Bate 1866, in Schmitt 1921: 63). The type material of all three species cannot be located, nor can the specimen mentioned by Bate (1866). Rathbun (1904) transferred all three species to Spirontocaris .

It seems reasonable to assign H. affinis and H. layi to the Thoridae . The illustrated shape of the rostrum of each species is consistent with that of species of Spirontocaris or one of the other genera of thorids in the northeastern Pacific, as Rathbun (1904) reported. Holthuis (1947) re-defined the genus Spirontocaris s.s. and separated other northeastern thorids into other genera.

Holthuis (1947) discussed both H. affinis and H. layi in a section on "species incertae.” He suggested that H. affinis belongs to the genus Spirontocaris s. s. Chace & Abbott (1980) reported this species as S. affinis , presumably in the strict sense of Holthuis and not in the broad sense of Ratbhun (1904) and Schmitt (1921). The illustration clearly shows two supraorbital teeth, a feature characteristic of species of Spirontocaris . The rostrum is pictured as ventrally deep, also a character of Spirontocaris . The drawing does not show any tapering of the dorsal surface from posterior to anterior, nor does it show the conspicuous ridge that runs the length of the rostrum in species of Spirontocaris . The original description states that the "fifth segment of the abdomen" is "laterally unarmed.” Although abdominal somite 4 is unarmed in S. sica and S. holmesi Holthuis, 1947 , all of the known species of Spirontocaris in the northeastern Pacific have a small tooth on the posterolateral margin of abdominal somite 5.

It is possible that S. affinis is a senior synonym of another species of Spirontocaris in the area, but others either have a long dagger-like frontal prolongation of the rostrum, as in S. sica and S. holmesi ; a very abrupt rostrum with fewer teeth than illustrated, as in S. truncata Rathbun, 1902 ; or three supraorbital teeth, as in S. prionota ( Stimpson, 1864) . Spirontocaris snyderi Rathbun, 1902 can be colored red and occurs in Monterey Bay, but its stylocerite barely reaches the end of the first segment of the antennular peduncle. Its rostrum bears one large dorsal tooth separate from the others. If the original description and illustration are accurate, S. affinis must be regarded as a separate species.

Hippolyte layi might belong to either Heptacarpus or Eualus ( Holthuis 1947, Chace & Abbott 1980). The lack of supraorbital teeth indicates that it is not a species of Spirontocaris . The shape of the rostrum in the original illustration ( Owen 1839, pl. 27, fig. 3) suggests that it might belong to the genus Heptacarpus . The illustration shows a vague point, perhaps the stylocerite, which slightly exceeds the first segment of the antennular peduncle. This species might be a senior synonym of another species, perhaps Heptacarpus paludicola Holmes, 1900 , which has a similar rostral shape and arrangement of teeth. There is no mention of an exopod on the third maxilliped in the description of H. layi . Some species of Eualus , such as E. barbatus ( Rathbun, 1899) , have an elongate toothed rostrum but it is not curved upward, as shown by Owen in the original illustration of H. layi .

MacGinitie & MacGinitie (1968: 273) mentioned that a "new species" of Spirontocaris fed on tunicates, Ciona intestinalis (Linnaeus, 1767) . They used the generic name Spirontocaris in the broad sense of Rathbun (1904). Other than that the observation was made "at the laboratory pier", there is no information on where this "new species" was observed. These authors usually studied shallow-water and intertidal species, many of them from the vicinity of Newport Bay and Corona del Mar, California. I have been unable to locate specimens of this unknown species among the specimens that the MacGinities donated to the Allan Hancock Foundation of the University of Southern California (incorporated into the collections of the LACM) or the CAS.

There may be an additional species of Heptacarpus similar to H. palpator and H. brevirostris in southern California. Specimens from San Nicolas I. had a rostrum with 7 dorsal teeth and a shape different from that typical of H. palpator and H. brevirostris .

Many species of thorids have been described from less than 10 specimens, or without mention of diagnostic features that have been used in more recent descriptions. The degree of polymorphism in species such as Heptacarpus sitchensis ( Brandt, 1851) has created taxonomic confusion, with the species being described as three species in three genera. Similar confusion as to the correct taxonomic designation may exist in species of Eualus and other species of Heptacarpus .