The most distinctive features of the grubby, as compared with others of its tribe, are its short, simple head spines, combined with small size at maturity. It is of the typical sculpin form, though proportionately a stouter fish than either the shorthorned or the longhorned species, that is, about one-fourth as deep as it is long with smooth skin but showing the head ridges and spines typical of its genus. Most noticeable of these are a ridge with two spines running along the top of the head over each eye; a pair of spines between the nostrils; and six short spines on each side of the face between snout and gill opening. None of the cheek spines are long (p. 449). The spiny dorsal fin (9 spines), originating a little in front of the upper corner of the gill opening, is shorter (front to rear) than the second dorsal of 13 or 14 soft rays; its longest spines, measured from base to tip, are about the same length as the longest soft rays of the second dorsal; and the two fins are so close together that there is no free space between them. The anal fin (10 or 11 rays) is a little shorter than the second dorsal, under which it stands. The pectorals are of the fanlike outline characteristic of this family, while each ventral fin consists of one spine and three rays. There is no slit or pore behind the last gill arch (there is such a slit or pore in the shorthorn sculpin, at least in most specimens, p. 445).
Grubbies, like other sculpins, vary in color according to the bottoms on which they lie. All that we have seen, however (this confirms the published descriptions), have been light to dark gray or greenish-gray above, with darker shadings or irregular barrings that are most evident on the sides and on the fins. The sides of the head are usually mottled light and dark; the belly is pale gray or white. According to information supplied by Dr. A. G. Huntsman, the presence of an uninterrupted pale band of considerable length along the lower sides of the caudal peduncle is a useful field character. But we have seen some specimens intermediate in this respect between the extreme condition shown in figure 228 and the variable mottlings and cloudings of the shorthorn sculpin.
This is the smallest of our common sculpins, few growing to more than 5 or 6 inches in length, and perhaps none to more than 8 inches.[page 444]
The differences between the grubby and the shorthorn sculpin in number of anal rays, and in the presence or absence of a pore behind the last gill arch, seem sharp enough to forbid the possibility that the former may be a dwarf race of the latter. Determination, however, of these characters required such close examination, and grubbies resemble young shorthorns so closely in all other respects that it is not easy to tell the one from the other. We therefore suggest that any small sculpin that may prove difficult to name be forwarded for identification either to the laboratory of the U. S. Fish and Wildlife Service, Woods Hole, Mass.; to the Division of Fishes, U. S. National Museum, Washington, D. C.; or to the Department of Fishes, Museum of Comparative Zoology, Cambridge, Mass.
On the southern shores of New England, where the grubby is not only more nearly universal than it is to the east and north of Cape Cod, but more plentiful, it is found from tide mark down to 15 fathoms or so. But we have taken it as deep as 28 fathoms in the Gulf of Maine, and Cox has reported it in the Gulf of St. Lawrence from the stomachs of cod caught in 60 to 70 fathoms. It is found on all sorts of bottoms, most abundantly among eel grass (Zostera) during the years when this plant was more plentiful than at present. And it is the only sculpin that summer in very shoal water along southern New England (Woods Hole and up Narragansett Bay) and near New York Harbor.
In the Gulf of St. Lawrence (e. g., around the Magdalen Islands) and on the Nova Scotian coast in general, it is found in estuaries, as in the southern part of its range, as well as outside. But it seems more restricted to the open coast in the Gulf of Maine, for Huntsman found it rare as far up Passamaquoddy Bay as St. Andrews, though common at the mouth, and more plentiful in St. Mary Bay and in Annapolis Basin than it is in Minas Basin on the Scotian side of the Bay of Fundy. Neither have we seen it in salt creeks about Massachusetts Bay.
The known distribution of the grubby in summer proves that it is certainly at home in water as warm as 69° F., and perhaps a degree or two warmer; these temperatures are several degrees higher than are preferred by its larger relative, the shorthorn. On the other hand, it survives temperatures as low as 32° in winter, if not lower, both in the Gulf of St. Lawrence, on the Nova Scotian coast, and about Woods Hole. Its presence in the inner parts of Narragansett Bay on the one hand and off open coasts on the other also proves it resistant to a wide range of salinity, but it never runs up into appreciably brackish water, as far as we can learn.
Probably the grubby breeds throughout its geographic range, certainly as far north as the southern part of the Gulf of St. Lawrence. And the Bay of Fundy appears to be the site of successful reproduction, for Huntsman found grubbies of all sizes there. The spawning season lasts all winter off southern New England and until June in the Gulf of St. Lawrence, Cox having reported a ripe female on the 18th of that month, at Amherst Island (Magdalen group). The eggs, which are described as of a beautiful green color and 1 mm. in diameter, sink like those of other sculpins and stick to seaweeds or to any other objects they chance to rest upon. Young sculpins (this species among them) have been caught in tow nets at Woods Hole from January to May.
This sculpin is omnivorous like its relatives, feeding on all sorts of small animals which it finds on the bottom, such as annelid worms, shrimps, crabs, copepods, snails, nudibranch mollusks, ascidians, and on small fish, including alewives, cunners, eels, mummichogs, launce, silversides, sticklebacks, and tomcod. It also scavenges any kind of animal refuse.
North American coastal waters, from New Jersey to northern Nova Scotia and to the Gulf of St. Lawrence, both in the southern side, where it is common, and the Strait of Belle Isle.
It is probable that this little sculpin is to be found in suitable localities all around the shores of the Gulf of Maine, for it is reported as common along both shores of the Bay of Fundy (including St. Mary Bay) and at various localities in the Massachusetts Bay region, such as Cape Ann, Gloucester, Salem, Cohasset, and Provincetown, and the [page 445] Albatross II trawled 9 specimens 43-51 mm. long in 28 fathoms off the outer coast of Cape Cod abreast of Chatham, May 1, 1930. But it seems to be decidedly local in its distribution, for the only places where it has been definitely reported along the coast between Cape Ann and the Bay of Fundy is Casco Bay, nor have we caught it in any of the harbors of Maine where we have fished. In any case, it is far outnumbered in the Gulf of Maine by the two larger sculpins to be mentioned next.
Because it is so small the grubby is of no commercial value. But wherever it is common it is something of a nuisance to anglers fishing for flounders and cunners, for it bites as greedily at any bait as do its larger relatives, and it serves as a source of food, no doubt, for more important fishes.
 Placed in the genus Acanthocottus Girard, 1849, by Jordan, Evermann, and Clark, Rept. U. S. Comm. Fish (1928), Pt. 2, 1930, p 386.
 This list of fish fry eaten is from Vinal Edward's notes at Woods Hole.
 Maine has sometimes been given as its northern limit. But Doctor Huntsman writes us that in 1915 he obtained it in tide pools at Souris, Prince Edward Island; Needler (Proc. Nova Scotian Inst. Sci., vol. 20, 1940, p. 40) describes it as the common sculpin in Malpeque Bay, Prince Edward Island; Cox (Contrib. Canadian Biol. (1918-1920) 1921, p. 111) characterizes it similarly around the Magdalen Islands; Vladkykov and Tremblay (Nat. Canad., vol. 62, 1935, p. 80) report it from the estuary of the St. Lawrence, near Trois Pistoles; and Jeffers (Contrib. Canadian Biol. and Fish., N. Ser., vol. 7, No. 16, Ser. A; No. 13) (1932, p. 208) found two specimens on the beach at Raleigh, on the Newfoundland side of the Strait of Belle Isle.