NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index

Can anyone tell me why postgres is creating a implicit index when
I already have a PKEY specified????

Or am I just interpreting this all wrong?

Here is the entry I am putting in:

create sequence journal_line_id_seq increment 1 start 1;

create table journal_lines (
journal_line_id int4 PRIMARY KEY DEFAULT NEXTVAL('journal_line_id_seq'),
entry_id int4,
account_id int4,
line_type int2 CHECK (line_type >= 1 AND line_type <= 2),
line_amount money,
CONSTRAINT eid FOREIGN KEY(entry_id) REFERENCES journal(entry_id),
CONSTRAINT aid FOREIGN KEY(account_id) REFERENCES accounts(account_id)
);

Here is the notice postgres spits out:
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index
'journal_lines_pkey' for table 'journal_lines'
NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY
check(s)
CREATE TABLE